EP0196843A1

EP0196843A1 - Dewatering nuclear wastes

Info

Publication number: EP0196843A1
Application number: EP86302115A
Authority: EP
Inventors: Charles J. Temus; Ronald E. Burnham; Gregory R. Allan
Original assignee: Nuclear Packaging Inc
Current assignee: Nuclear Packaging Inc
Priority date: 1985-03-22
Filing date: 1986-03-21
Publication date: 1986-10-08
Also published as: ES9000018A1; JPS61251798A; ES557250A0; ES8900207A1; ES553279A0

Abstract

A method of dewatering a solution or slurry that contains radioactive particles to a condition satisfactory for permanent storage. Free standing water is removed from the slurry, and then a sufficient quantity of water is removed from the particles so that at the permanent storage temperature the particles will be unsaturated with respect to adsorbed water and will act as their own desiccant during the course of the permanent storage regimen. The adsorbed waters are preferably removed by evaporation after substantially all interstitial water is removed, and most preferably by causing low humidity air to flow at sufficient velocity uniformly through the particle bed.

Description

Technical Area

The present invention relates to processing wet radioactive wastes for permanent storage and particularly to dewatering radioactive ion exchange, resins, filter media, and other particulate wastes.

Background of the Invention

The nuclear power industry generates a certain amount of wet radioactive wastes, and predominant among these radwastes are ion exchange resins and filter media that are used to scrub radioisotopes from reactor cooling waters. The resulting suspensions or slurries of radioactive ion exchange resin and in some cases filter media particles must be dewatered for safe shipping and disposal. By dewatering is meant herein the removal of water from the waste particles such that the remaining free standing water constitutes no more than 1.0% of the waste volume. ₁0 C.F.R. Part 61. By free standing water is meant the draina- ble interstitial water that freely gravity drains from a bed of particles.
Bead-type and powdered-type ion exchange resins constitute the vast majority of the waste materials that must be dewatered. Such ion exchange resins average 3800 cubic feet per year per commercial power plant and represent nearly half of the total wet wastes generated by the utilities. Lesser amounts of activated carbon and inorganic zeolite particles from radwaste treatment systems must also be dewatered prior to disposal.
Prior to 1981, when the first large-scale dewatering containers were placed into service, the aforementioned types of wet wastes were mostly solidified by, for example, admixing them with dry cement powder in disposable steel drums. However, such solidification methods have unsolved problems, including achieving structural integrity, void spaces above the solidified block in a corrodible container, waste parts that are not fully encapsulated, and pasty or unsolidfied materials. The pertinent relationships between waste media shape, size, chemical reactions, full-scale thermal effects, and waste media structure remain unsolved for the solidification of radioactive wastes in a container over the three hundred year design life of the storage regimen.
The driving factor behind the recent use of waste dewatering is economics. The availability of landfill disposal sites is clouded with political uncertainty, and the transportation costs to the few available disposal sites can be expected to increase with each new regulatory overlay. The result is the need for more waste-volume efficient methods of disposal or on-site storage, and in this regard dewatering processes are most attractive. Dewatered wastes need not undergo the volume expansion that solidificaton technologies require: instead of adding solid material to physically or chemically entrap or react with the water within the container, the water is removed from the container. Additionally, the dewatering process requires less plant floor space, capital investment, and no dusty, corrosive, or hazardous chemicals. The main mitigating circumstances against waste dewatering in the past have been changing regulations and operational uncertainty regarding the degree and amount of residual free standing water left in the container. Such free standing water is a potential vehicle for isotopic leaching, should the container fail or be punctured during transport, storage, or burial.
Prior to the free standing water criteria specified by the State of South Carolina in 1980, dewatering containers were simply thin gauge carbon steel liners with some cartridge filters unscientifically placed on the bottom. The ₁980 free standing water criteria quickly illustrated a lack of understanding of the dewatering mechanisms because the containers, dewatering tests, and procedures changed rapidly. Bead resin containers were designed with conical bottoms and low point drains or suction configurations. A diaphragm pump was typically used to remove free standing water. Powdered resin containers were designed with several levels of cartridge filters.
It is expected that the use of resin dewatering will increase due to a number of reasons. Many plants are finding it is more cost effective to not regenerate their deep bed condensate polisher resins, and instead they directly dispose of the resins after one use. A significant increase in bead resin volumes per plant results. Bead resin volumes are also increasing due to the use of portable de- mineralizers in place of evaporators. The use of powdered resins is increasing due to closer attention to power plant water chemistry. Powdered ion exchange resins are increasingly being mixed with fibrous filter aids to help alleviate resin intrusion into the reactor cooling water.
Prior testing and certification procedures have been based upon representative waste media and have not considered the range of waste forms that occur in the field, nor the permanent storage conditions. Prior dewatering methods did not lend themselves to defined endpoints: the duration of the pumping cycle was simply extended until a subjective empirical endpoint, e.g., no apparent leakage from a punctured representative container, was observed. Thermodynamic considerations, such as condensing cycles within the container during transport, storage, or burial, have not previously been addressed. Nor have chemical form effects been addressed. An understanding of dewatering mechanisms leading to the production of consistent results has not been developed or achieved. In at least one case, an extrapolation of free standing water versus drainage time has been made using specific test results. This method was mathematically unsound and unrepresentative of the actual variety of waste forms. As a result, some of the liners punctured during field tests and at burial sites have been found with unacceptable amounts of free standing water. Moreover, an understanding of the interrelations between the waste characteristics and internal container piping was not developed. As a consequence, compliance with the free standing water requirements of 10 C.F.R. Part 61 for ion exchange resins and filter media connot be assured with prior art dewatering systems.

Summary of the Invention

Pursuant to the method of the present invention a solution or slurry that contains radioactive particles is dewatered to a condition satisfactory for permanent storage. Free standing water is removed from the slurry, and then a sufficient quantity of water is removed from the particles so that at the permanent storage temperature the particles will be unsaturated with respect to adsorbed water. Briefly stated, a sufficient volume of adsorbed water is removed from the particle bed to assure the subsequent uptake of any condensed water that develops during the burial conditions. Thus, the dewatered radioactive particles will act as their own desiccant during the course of the permanent storage regimen. The adsorbed water is preferably removed by evaporation after substantially all interstitial water is removed, and most preferably by causing low humidity air to flow at sufficient velocity uniformly through the particle bed.
The dewatering method of the present invention preferably incorporates a circulating air system. Low humidity air is passed uniformly through a slurry bed of radioactive particles. The air is humidified as it passes through and removes interstitial water and adsorbed water from the particle bed. The relative humidity of the air that has passed through the particle bed is monitored in a preferred embodiment, and the air is thereafter dried and dehumidified before being circulated back through the particle bed. The air is circulated in this manner until the relative humidity of the air that has passed through the bed of waste particles falls to predetermined value. That predetermined relative humidity value is specifically selected such that at the permanent storage temperature the waste particles will be unsaturated with respect to adsorbed water, thereby precluding the formation of free standing water by condensation. In other embodiments, the process endpoint is monitored with respect to related physical parameters such as volume of moisture removed after substantially all interstitial water has been removed from the particle bed.
A disposable container with a top region and a bottom region is provided with a waste influent port for introducing the slurry into the container bottom region and with an air inlet port for introducing air into the container top region. A vapor collector manifold is selectively disposed in the container bottom region for receiving humidified air that has passed from the container top region through the slurry bed. A vapor outlet port, connected to the vapor collector manifold, is provided to remove the humidified air from the container.

Brief Description of the Drawings

FIGURE 1 is a schematic diagram showing a preferred embodiment of the dewatering system of the present invention that employs a recirculating airstream;
FIGURE 2 is a schematic vertical section through a flat-bottomed disposable container showing the disposition of a dewatering apparatus suitable for dewatering bead type ion exchange resins;
FIGURE 3 is a view similar to FIGURE 2, indicating the inflow of wet radioactive particles into the container;
FIGURE ₄ is a view similar to FIGURE 2, showing the circulation of air into the container, through the particle bed, into the vapor collector manifold, and out of the container;
FIGURE 5 is a sectional view taken along section line 5-5 in FIGURE 8;
FIGURE 6 is a detailed elevation view in partial cross section similar to FIGURE 2 showing a disposable container fitted with a vapor collector manifold suitable for dewatering bead-type ion exchange resins;
FIGURE 7 is a section taken along section line 7-7 in FIGURE 6;
FIGURE 8 is a section taken along section line 8-8 in FIGURE ₇;
FIGURE 9 is an elevation view in partial cross section of a disposable container showing the arrangement and disposition of a vapor collector assembly suitable for dewatering powdered-type ion exchange resins;
FIGURE 10 is a section taken along section lines 10-10 in FIGURE 9;
FIGURE ₁1 is a partially cutaway view taken along section Iine11-11 in FIGURE 10;
FIGURE 12 is a view similar to FIGURE 3, showing undesirable air channeling down the inner sidewalls of the container;
FIGURE 13 is a view similar to FIGURE 4, showing the nonuniform air circulation that results from insufficient pressure drop across the bed of solids and/or collector near the vapor collector manifold;
FIGURE 14 is a view similar to FIGURE 5, showing the blank areas that tend to develop above the vapor collector manifold where there is insufficient pressure drop across the bed of solids;
FIGURE 15 is a graph of friction factor versus Reynold's number for a fluid passing through a bed of solids;
FIGURE 16 is a multi-dimensional graph showing a typical operating region A-B-C-D from which a vapor collector manifold or assembly can be custom designed for specific applications;
FIGURE ₁7 is a graph similar to FIGURE 16, showing a particular test result;
FIGURE 18 presents two typical psychrometric operating curves along with numerical coordinates as discussed in the specification;
FIGURE 19 is a graph showing cation resin water vapor/vapor sorption to crosslinking curves;
FIGURE 20 presents additional water/vapour sorption curves, for different constituents of the ion exchange resin's adsorbed water; and
FIGURE 21 is a graph that presents typical processing endpoint curves of the present invention.

Detailed Description of the Preferred Embodiments

Referring to FIGURE 1, the dewatering process of the present invention preferably incorporates a circulating air system. Disposable container 10 is provided for dewatering slurry of radioactive particles to a condition for permanent storage. Air is continuously circulated in a loop from a blower 14, to and through the container 10 that houses the radioactive particles, through a water separator 16, and back to the blower 1₄.
The blower 14 supplies air at a temperature selected to facilitate drying of the radioactive particles in the container 10. The blower 14 is the source of heat input to the circulating air. The blower's transmitted heat necessarily follows from its work of pulling a suction on the container 10 and then compressing the air. The heat of compression transmitted to the air is used to benefit since the air entering the blower 14 is water saturated, having been cooled to the dewpoint in the water separator 16. The blower 14 heats the airstream and thereby dehumidifies and raises its water carrying capacity. The blower 14 is equipped with temperature instrumentation, not shown, so that the blower 14 will shut down automatically at high temperatures. This automatic shutoff is provided because the polymers that may be used in the container 10 will lose their integrity at high temperatures, e.g., above 170°F for polyethylene.
Heated, dehumidified air is discharged from the blower 14 through a conduit 18-to a filter 20 and thence through another conduit 18 into the container 10. The filter 20 includes a series of oil separators, not shown, that remove any oil that was injected into the dehumidified airstream by the blower 14. The filter 20 is provided because oil is incompatible with polyethylene and other polymers that may be used in the container 10.
The container 10 contains an apparatus, described in detail below, for causing the airstream to pass uniformly through the slurry. The air is humidified as it passes through and removes water from the slurry. The humidified air is exhausted from the container 10 and circulated via conduit 22 through a relative humidity meter 24 to the water separator 16. A water chiller 26 associated with the water separator 16 cools the humidified airstream as it passes through the water separator 16. Water 28 that condenses from the chilled air is removed from the water separator 16 via conduit 29 by a dewater pump 30. The dried air that leaves the water separator 16 is drawn through conduit 31 into the blower 14, heated and thereby dehumidified, and recirculated through the bead resin container 10. When the meter 24 indicates that the relative humidity of the airstream leaving the container 10 has fallen to a preselected value - (or another quantifiable process endpoint has been achieved as described below), the blower 14 and water chiller 26 are shut down. The container 10 is then sealed for transport and permanent disposal.
Referring now to FIGURE 2, a suitable disposable container 10 can be a disposable drum that has an outer shell 32 made of any conventional material. A waste influent port 3₄ is provided for introducing the wet radioactive particles into the container 10. A deflection plate 38 provides distribution. An air inlet port 36 is provided for introducing air from the blower 14, not shown in this view, into the top of the container 10. Uniform airflow across the top of the slurry bed can be facilitated by providing a deflection plate (not shown) at the delivery end of the air inlet port 36. A vapor collector manifold ₄0 is selectively disposed on the flat bottom 41 of the container 10. The vapor collector manifold 40 is connected by a duct 42 to a vapor outlet port 44. The waste influent port 34, air inlet port 36, and vapor outlet port 4₄ are preferably grouped together in a dewatering fill head 46 that can be reversibly inserted into the top of the container 10 temporarily seal the container, and thereby facilitate the containment of radioactive particulates, during the dewatering process. The dewatering fill head 46 is removed and the duct 42 is uncoupled after dewatering is accomplished. The container 10 is then permanently sealed.
Referring to FIGURE 3, a sufficient volume of the radioactive resin slurry 48 is introduced through the waste influent port 34, as indicated by arrow 50, to surround and cover the vapor collector manifold 40 at the bottom of the container 10. The bottom region of the container 10 can be almost completely filled with the slurry 48, leaving only an air space 54 in the top region of the container 10 sufficient for the deflector plate 38 on the air inlet port 36 to uniformly distribute pressurized air over the upper surface 56 of the slurry bed 48. The dewater pump 30 is then turned on, and the bulk of the free standing water is aspirated through the vapor collector manifold 40, duct 42, vapor outlet port 44, and thence to the dewater pump 30 as shown in FIG. 1. Thereafter the particle bed 48 is air dried in accordance with this invention.
Referring to FIGURES 4 and 5, the circulation of air through the particle bed 48 should be uniform across the entire cross section of the container ₁0. Dehumidified air from the blower 14 (see FIG. 1) is discharged through the air inlet port 36 into the air space 54. The deflection plate 38 on the delivery end of the air inlet port 36 serves to radially distribute the incoming air, indicated by arrows 58, over the upper surface 56 of the waste media bed 48. The distributed air passes from the air space 54 through the particle bed 48 along paths generally indicated by arrows 60 and thence into the vapor collector manifold 40. The percolating air 60 is humidified as the slurry 48 gives up its interstitial and adsorbed waters to the relatively dry air 60. The now humidified air, indicated by arrows 62, is collected by the vapor collector manifold 40 and discharged via duct 42 through the vapor outlet port 44. The vapor collector manifold 40, as described below, has a plurality of conduits 64 that radiate in a planar fashion from a header 66 positioned diametrically across the floor 41 of the container 10. Air 60 passes from the waste media bed 48 into the vapor collector manifold 40 through a plurality of orifices 68 spaced along the lengths of the conduits 64. Freestanding water and water vapor are drawn through the orifices 68, into the channels 70 of the conduits 64, into the header 66, through a vertical duct 42 and thence through the vapor outlet port 44. The vapor collector manifold 40 is designed, as described below, so that when the waste media bed 48 is completely free of free standing water the flow of air 60 through the bed 48 will be uniform across the entire cross section of the container 10. If the airflow 60 is not uniform, pockets of interstitial water potentially remain in any region of the resin bed 48 that is not subjected to the airflow 60. The uniform airflow 60 must also have sufficient driving force to cause migration of the interstitial water to the container floor 41.
Referring now to FIGURE 6, a flow interrupter 72 such as an annular ring is preferably mounted approximately midway down the inner sidewall 74 of container 10 in order to deflect into the media bed any airstream that preferen- taity channels down the sidewalls 74. If such an annular ring 72 is not provided the airstream will tend not to flow uniformly across the entire cross section of the resin bed 48, and a central pocket of interstitial water 96 may not be subjected to the drying airstream; (see FIG. 12).
Referring now to FIGURES 6 and 7, a suitable vapor collector manifold 40 for drying bead-type resins can have a central header 66 with a plurality of laterally offset conduits 64 disposed in planar array and resting on the floor 41 of the container 10. Suitable conduits 64 can be made of threequarter inch plastic pipe that has been through-drilled to provide suitably sized orifices 68 at appropriate intervals, as described below, along both sides of each conduit 64. The distal end of each conduit 64 that lies adjacent to the container sidewall 74 is sealed with an end cap or plug 76. The other end of each conduit 64 communicates through a cross or tee fitting 78 with the header 66, which can suitably be made of three inch plastic pipe. One end 67 of the header 66 is sealed, and the other end communicates through an elbow 80 with a duct 42, which can be flexible plastic tube, that leads to the vapor outlet port 44.
The vapor collector manifold ₄0 should be configured so that its orifices 68 are distributed in uniformly spaced array across the floor 41 of the bead resin container 10. The orifices 68 must be properly sized to achieve specific flow to pressure drop relationships with itself and the flow and -pressure drop of the fluid in the pipes. Each vapor collector manifold 40 design has unique maximum and minimum distribution characteristics corresponding to specific maximum and minimum flow rates for specific types of waste medias as described below. During the initial stages of the dewatering process the vapor collector manifold 40 acts in an analogous fashion to the sump pumps of the prior art to remove free standing water from the slurry bed 48. Thereafter, the vapor collector manifold 40 serves to draw motive air 60 uniformly across the entire cross section of the resin bed 48 to remove any remaining unadsorbed, interstitial water. In preferred embodiment the dewatering process is thereafter continued with dry air until sufficient volume of adsorbed water is removed from the waste media so that the media bed will act as a desiccant at the permanent storage temperature.
Referring now to FIGURE 8, the orifices 68 in the conduits 64 should be screened so that they will not be- comed obstructed. Concentrically disposed screening members, for example, a coarse screen member 82 surrounding a fine screen member 84 of 100-mesh screen, are preferably wrapped around the conduits 64 to prevent occlusion of the orifices 68 by resin beads and other waste particles.
Referring now to FIGURE 9, a container 10 for dewatering powdered resins filter media must be provided with a tiered series of vapor collector manifolds 40' positioned one about the other in spaced horizontal array throughout the container bottom region. As described below, the number of vertically spaced vapor collector manifolds 40' is dependent on the required fluid pulling distance through the waste media. As the bed depth over the collector manifold 40' increases the total pressure differential across the bed also increases. Pulling nearly a full vacuum is the limiting situation before another collector manifold 40' would be required. Several tiers of vapor collector manifolds 40' can be interconnected by vertical supporting members 86 to form a self-supported vapor collector assembly 88 within the container 10. The vertical supports 86 can be made of three-quarter inch or one and one-half inch plastic pipes fitted with bottom caps 90 to prevent scoring the container floor 41. The shape and outer shell 32 construction of the powdered media container 10 can be essentially as described above. A plurality of vapor outlet ports ₄₄, one for each of the several vapor collector manifolds 40', are provided in the dewatering fill head ₄6. In this embodiment four vapor collector manifolds 40' are positioned in tiered horizontal array within the container 10, one manifold 40' near the container floor 41 and the remaining three manifolds 40' at approximately equally spaced horizontal levels within the container bottom region. Each of the vapor collector manifolds 40' is an independent system of ducts that has a central header 66' with a plurality of laterally offset conduits 64'. The distal end of each conduit 64' is sealed by a plug 92 where it attaches to a vertical supporting member 86. One end of each header 66' is likewise sealed; the other end communicates with a duct 42 that leads to one of the vapor outlet ports 44. The conduits 64' and also the headers 66' have a multiplicity of spaced orifices, not shown in this view. The conduits 64' and headers 66' are wrapped with a filtering member 94 (shown in FIGURE 11) that prevents the orifices from becoming occluded by fine waste paricles. Humidified air is drawn through the filters 94 and orifices into and through conduits 64' and header 66', through a duct 42, and thence through a vapor outlet port 44.
Referring now to FIGURES 9 and 10, the alignments of the headers 66' and laterals 64' of the several vapor collector manifolds 40' are preferably offset by 90° in alternating tiers of the vapor collector assembly 88. Thus, in this embodiment the diagonal axis defined by the header 66' of each of the first, counting from top to bottom, and third vapor collector manifolds 40' is disposed perpendicularly with respect to the diagonal axes of the second and fourth vapor collector manifolds 40' in the vapor collector assembly 88. The offsetting alignments of the vapor collector manifolds 40' at successive tiers within the container bottom region facilitates uniform dewatering by minimizing cracking in the powdered media bed.
In operation, the bottom container region is filled with powdered media slurry through the waste influent port 34 so that the vapor collector assembly 88 is surrounded and covered by the slurry. A high water level is initially maintained in the container 10. As powdered media slurry is introduced into the container 10 excess water is removed via suction applied to the topmost collector manifold 40' by the dewater pump 30. When the container 10 is apparently full of solids the slurry feed is stopped. The bulk water is pumped out using the dewater pump 30 utilizing all of the vapor collector manifolds ₄0' in the container 10. As the system suction drops to a predetermined point the topmost collector 40' is shut off and suction is continued on the remaining collectors ₄0'. The next lower collector 40' is also shut off at a predetermined pressure, and so on until only the bottom collector 40' remains functioning. At the beginning of the water removal, the powdered media will tend to shrink with water removal and small amounts of slurry may be added to make up the volume. After the bulk water is removed and the suction pressure on the lowermost collector 40' drops to a predetermined level, then all collectors 40' are opened and the blower is started. More of the interstitial water is quickly removed and the drying process begins. When nearly all of the interstitial water is removed, the powdered media will begin to crack and slough away from the container sidewall 74 and vapor collector assembly 88. The air passing through these cracks removes water from the adjacent media. The entire process is stopped when the predetermined endpoint is reached.
Referring to FIGURE 11, the conduits 6₄' and also the headers 66' are preferably through-drilled at suitable intervals to produce alternating sideto-side and top-to-bottom orifices 68. The conduits 64' and header 66' are wrapped with one micron filtering members 94 to prevent powdered media particles from occluding or passing through the orifices 68.
This dewatering system will meet or exceed all established free standing water criteria for shipment and disposal of radioactive ion exchange resins. More specifically, this dewatering system has been designed and tested to consistently meet the free standing water requirements of 10 C.F.R. Part 61 for ion exchange resins and filter media. Predictable performance results are achieved using this system over the broad spectrum of waste characteristics possible with ion exchange resins and other treatment media. Other current dewatering systems do not consistently meet these requirements.
This invention provides a method and apparatus for dewatering many types of particulate waste forms, including bead type ion exchange resins from sources such as deep bed condensate systems, radwaste treatment, borated water control, reactor water cleanup, and fuel pool cleaning. Powdered ion exchange resins, e.g., "Powdex", can also be dewatered with this system, as can fitter aids such as "Celite" and "Fibra-Cel." Moreover, other liquid treatment media such as activated carbon particles, inorganic zeolites, fitter sand, anthracite particles, and odd forms of ionic exchange resins that may occur from one-time site jobs can be dewatered using this method and apparatus. Furthermore, powdered mixtures of ion exchange resins, activated carbon particles and fitter aids, e.g., "Epifloc," "Envirosorb" and "Ecodex," from condensate polishers and radwaste treatment systems can be dewatered in accordance with this disclosure, as can sludges from sump or pool bottoms decon scale, and abrasive cleanser. By sludges is meant the heterogeneous particulate mixtures that settle out in receiving tanks, sumps, and other low velocity flow regions. All of the aforementioned liquid treatment media, as well as other particles whose physical properties meet the parameters described with respect to the computational models and test data disclosed below, can be dewatered using the method and apparatus of the present invention.
Some definitions are necessary for an understanding of the present dewatering method:

Interstitial water is the water that surrounds the particles in the void space of the particle bed.

Free standing water is the interstitial water that freely gravity drains from a bed of particles.
Adsorbed water includes the water bound by weak charge interactions to the surfaces of particles such as ion exchange resins, inorganic zeolites, and other medias with chemically reactive surfaces. For the purposes of this discussion, the term adsorbed water also refers to the water held by pore diffusion with micropores in particles such as activated carbon particles.
Water vapor is the gaseous phase of water.

The method of the present invention applies a unique two-part approach to dewater particulate radwastes. Both fluid dynamic and thermodynamic analyses are applied to define operating parameters and end points of the dewatering process. The fluid dynamic methods apply to either, or both, liquid and gaseous water and air. Fluid dynamics does not apply to adsorbed water until the adsorbed water has been thermodynamically separated (evaporated) from the particles. Fluid dynamics applies to the various types of water as follows: The free standing water is simply pumped down, as it easily drains down from the particles. The interstitial water, which may be slowly draining or stuck up in the particles, is brought down by applying sufficient differential pressure of uniformly flowing air. At this point there is a two phase (gas and liquid) flow of air and water. Once the interstitial water has been substantially removed, then the adsorbed water begins to evaporate into the heated (dehumidified) airstream. The heated air is uniformly distributed through the particle bed pursuant to the fluid dynamic methodology of this invention.
Thermodynamics only applies to adsorbed water and water vapor. Proper fluid dynamics is prerequisite to effecting the appropriate result on all types of water described above. The thermodynamic applications can be considered in two parts: First, the mechanical system involving air and its capacity to transport water vapor through each part of the system must be considered with respect to fundamental mechanical heat input, heat transfer, and psychrometry. Then the chemical thermodynamics of the adsorbed water as it applies to various types of ion exchange resins and other media, and their varied chemistries, must be considered in order to determine the degree of particle drying required to meet the burial environment's free standing water criteria. In other words, finding the drying endpoint. The two parts interact where the humidity of the airstream is in equilibrium with the adsorbed water of the resin. A measurement of the air humidity flowing through a known resin type is a direct measure of that resin's water uptake capacity.
The actual physical characteristics of the waste media must be addressed in order to properly dewater waste treatment media. An overwhelming percentage of the wet wastes currently generated from nuclear reactors are bead and powdered ion exchange resins. These resin types are each relatively homogeneous when they are new. New resins have the following characteristics:
However, these resin types are subjected to forces that cause significant physical alteration during use, depending upon the system design and operation of a particular powerplant For example, the ion exchange resin from a reactor coolant cleaning system can be in a much different condition than the same type of resin from a condensate polisher. Also, one waste type can be admixed with another significantly different one, for example a combination of bead resins with powdered resins, thereby drastically changing the average effective size and shape of the waste particles to be dewatered. As another example, the transfer of waste media through high fluid shear pumps, long lengths of pipe, or tight fittings can considerably reduce the effective particle size and shape because of particle breakage. A change in the waste holdup tank, or sump or pool draw point, can also change the waste characteristics. If the draw on a waste hold tank is switched from the side to the bottom, then finer settled particles could be introduced into the dewatering apparatus, thereby significantly altering the waste's dewatering characteristics. Chemical effects on the waste media can also seriously hinder the dewatering characteristics. For example, a powdered or bead-type ion exchange resin that has been severely decrosslinked from repeated regenerations or exposure to oxidizing decontamination solutions has extemely reduced structural properties. After such decrosslinking, the strength of bead resins can deteriorate from being able to bear the weight of a person to being easily crushable with one's fingers. Any such decrease in the structural strength of the resin particles must be considered because resin crushed under the weight of a six-foot deep solids bed could effectively block the passage of free standing water into the vapor collector manifold.
Considering the potential damaging effects resulting from the aforementioned plant operations, the on-site condition of the waste media can be significantly different from the ideal values of Table 1. By combining a knowledge of the standard fines content in new resins with an estimate of the fines generation rate from normal operations and from potential abberational operations, worst case scenarios can be generated, as shown in Table 2.
The actual physical characteristics of the waste media are addressed in the appended Calculations section, wherein the waste characterization recited in Tables 1 and 2 are related to computational methods for determining appropriate vapor collector manifold or assembly configurations as well as processing parameters and endpoints in order to property dewater waste treatment media
The initial testing and design hypothesis was based on a a nearly pure fluid dynamics approach, as the fundamentals of fluid flow under a differential pressure, gravity effects and fluid distribution are as applicable to a bed of solids as they are to pipe flow. Chemical, surface phenomena, and. absorption/desorption effects were considered negligible or nonexistent at first because: (1) the surface chemical structure (mostly polystyrene) of ion exchange resin is hydrophobic, (2) ion exchange resins that are not fully oxidized are mechanically very stable, (3) the adsorbed water in the ion exchange resin is there due to chemical solution effects with fixed interior positive or negative charges that do not affect the exterior of the resin, and (4) if there were other hydration effects, they would not become obvious during the testing unless they were unmasked by the removal of all the unadsorbed, free standing and inteterstitial water. This initial hypothesis proved beneficial with regard to the aforementioned item 4. Several test and equipment modification iterations led to the result that all the free water was being removed by the fluid dynamics approach. The combination of a thermodynamic and resin water/water vapor sorption phenomena was then unmasked. At 'that point, the engineering methods shifted to a material drying approach on the premise that dewatered ion exchange resins contain adsorbed water and can behave like desiccants once that adsorbed water is removed.
With regard to fluid dynamics, using a purely fluid dynamics approach leads to two phase (liquid and gas) flow in the resin and the necessity of pulling out pockets of free standing and iterstitial water. Under a fluid dynamics hypothesis, all of the free standing water is pulled out when subjected to sufficient uniform differential pressure across the resin. This is basically the mechanical portion of the process. Given the hydrophobic nature of the resin surface and the chemical solution effects of the adsorbed water, there should be a definite conclusion to the mechanical dewatering portion of the dewatering process. Any further dewatering would have to be a nonmechanical method such as evaporation, chemical enhancement, or solvent extraction; see the Thermodynamics discussion below.
Carrying the fluid dynamics hypothesis of dewatering to its conclusion leads to the design being based on two phase flow. Unfortunately, two phase flow in a bed of solids, particularly in the size range of the subject media treatment particles, is not empirically well founded. Hence, the need for confirming test data. In fact, most single phase flow is empirically more well founded with larger sized solids and higher flow rates. The prior art has not used any engineering hypothesis and has instead relied on single point testing for conclusions to be applied to all field conditions. This approach has not worked well. On the other hand, testing all possible waste types and forms is unrealistic. Hence, the all encompassing analytical model set forth in the appended Calculations section was developed and proved by single point testing.
The flow of fluid through a bed of solids and then the residual free standing water is based on an interplay of the following resin characteristics: resin effective diameter; the shape of the resin; the packing or effective void volume of the resin; and the depth of the resin bed. The relative importance of each of these factors is discussed in the Calculations section. The different characteristics of the resin cannot be encompassed unless there is a good understanding of the hydraulic performance of the collector manifold and pumping system. The hydraulic factors to be considered are the following: a uniform minimum velocity through the bed of solids; the vapor collector manifold has design limits for achieving the uniform velocity via uniform collection; the losses in the pump and piping system external to the container, performance curve of the blower; and container design effect on flow paths. The factors cited above for both resin characteristics and hydraulic factors must also be combined with the state of the motive fluid that is applying the differential pressure to the free standing and interstitial water. Therefore, the following must also be considered: the temperature of the fluid moving through the bed of solids; the viscosity of the fluid; the molecular weight of the fluid; and the compressibility of the fluid.
Thus, there are a total of thirteen major factors affecting the fluid dynamics hypothesis, and the relationships between all of these factors are defined in the appended Calculations sections as they apply to field conditions. Full scale test data has been used to verify the model. The fluids dynamics hypothesis has proven to be substantially correct under field testing conditions.
With regard to thermodynamics, ion exchange resins contain a considerable amount of adsorbed water, on the order of 35 to 65 weight percent, even when they have no interstitial water. The adsorbed wafer has unique chemical solution characteristics since only one of the plus or minus charged ions in the solution is free to move while the other charged ion is fixed to the plastic bead. The plastic resin itself is hydrophobic and the adsorbed water is there due to chemical solution effect. Therefore the adsorbed water has evaporation properties unique to the chemical form of the waste's adsorbed water. Since the waste can be expected to undergo substantial temperature changes during processing, transport, and storage, the ability of the adsorbed water to leave the resin must be addressed.
The thermodynamics and the flow of air/water vapor mixtures is known. The water uptake capabilities, or desiccant effects, of ion exchange resins are also known. The thermodynamic hypothesis has several points: Thermal and fluid dynamics are related only with respect to even distribution of the drying air for the purpose of removing some of the adsorbed water. It is more efficient to remove free standing water by mechanical means (fluid flow) than by evaporation (thermodynamics). There is an air/water vapor to resin retained water equilibrium point that signals the desired drying endpoint. The dryness of the resin should correspond to not generating free water in the burial environmental conditions.
The predictable drying of a material depends on the state of the drying fluid and the state of the fluid to be dried. Compared to the state of the solutions in the waste media slurry, the state of the drying air is very straightforward. Psychrometric charts and fundamental heat transfer relations can be applied to forecast the expected generation of free water from air and the drying capacity of the air flowing through the waste media. Specialty data must be applied to the removal of adsorbed water from ion exchange resins. From that data the following factors have been found to effect the drying of various resins: moisture content of the resins; chemistry of the retained water; capacity or number of functional exchange sites remaining on the resin; and degree of crosslinking of the resin's polymer structure. There are an infinite number of combinations of the factors listed above. It was recognized early in the testing that the thermodynamic aspects of the dewatering system would have to be oriented to the worst case scenario, as complicated resin analysis at a power plant is not feasible.

Testing

Extensive testing has been conducted in order to qualify the dewatering system of this invention to the free standing water requirements of 10 C.F.R. 61 for both bead and powdered media. The regulatory limit for free standing water in a high integrity container has been established at 1.0% of the waste volume by 10 C.F.R. 61, which also establishes that the test methods contained in ANSI 55.1 are to be used to detect the presence of free water. The method and apparatus of this invention have performed well within these limits, particularly with regard to the absence of free water over the expected chemical and physical range of the waste process. This range in properties of the resins has been considered in the testing program, the equipment design, and the operating parameters for this system.
The bead resins used in the test progam were selected to be within the resin properties that are expected to be encountered in the field. The equipment design and the operating parameters which have been established for this equipment were selected to preclude the presence of free water for normal waste materials and to detect abnormal, or worst-case, materials prior to dewatering. In addition in order to assure compliance with the regulatory limits with the waste stream variations which will be encountered in the field, an initial acceptance criteria of 0.1% free water was imposed for the qualification tests. As the testing progressed the solving of various fluids and thermodynamic phenomena led to the practical result of zero free water at the relatively cool burial temperature.
The bead resins used in the testing program were of two types, spent anion resins and new, off-specification cation resins. The anion resins were representative of bead resins which have been regenerated many times and fouled with large organic molecules. They tend to be oxidized with less crosslinking and are of a smaller average particle size. The cation resins on the other hand are representative of bead resins which have not been regenerated, are very spherical and are on the upper end of the scale as far as size and shape. The cation resins are thus more representative of the bead resins which will be encountered in the field. With the possible exception of deep bed condensate polishers, most resins are not regenerated at nuclear power plants. For this reason, the cation resins were used extensively to establish system design and operating parameters, and because their physical and chemical characteristics were better known. The anion resins were subsequently solved on a worst case basis.
The powdered resins used- in the testing program were spent and of the "Ecodex" or "Epifloc" type. The fitter aid present in these materials tends to hold water more readily than the resin, making them the most difficult of the powdered resins to dewater. Powdered media, such as "Powdex", "Ecodex" and "Epifioc", have granule diameters averaging 0.00₁5 inches as compared to about 0.02 inches for bead type resins. Flow through a bed of powdered media is affected by the presence of fibrous material. The fiber is intended to enhance filterability of the precoat. The consequence in dewatering is a change from a rigid bed of solids to a spongy and compressible one. With regard to powdered media, the approach has been to do the best possible job removing the interstitial water, recognizing that shrinkage during dewatering will cause sloughing and random cracking. To compensate for the randomness of the media sloughing, water removal has been enhanced through the use of air drying techniques. The result of this approach has been shorter and more thorough dewatering than previously available.
The physical measurements which have been taken over the course of the testing program show good correlation to the analytical methods as presented in the Calculations section. Powedered resins have been succesfully dewatered in the qualificational testing program. Bead resins have also been successfully dewatered. Cation resins were dewatered, producing no drainage of free water following an eight hour dewatering cycle. Regenerated anion bead resin beads took no more than ₁6 hours to dewater.

CALCULATIONS

Introduction

The method of the present invention employs a two-part approach to dewater radioactive particles to a condition satisfactory for permanent storage. Both fluid dynamic and thermodynamic engineering analyses must be considered in order to define the operating requirements of such a dewatering system. Fluid dynamic analyses are used to effect the complete removal of unadsorbed, free standing and interstitial water from the bed of radioactive particles and to uniformly air-dry the particles thereafter. Thermodynamic analyses are used to insure that free standing water does not thereafter develop as a result of condensation cycles that result from temperature fluctuations during transport, storage, and disposal.

FLUID DYNAMICS

Solving the fluid dynamics problem involves three principal analyses: (1) the performance through the resins (2) the performance of the vapor collector manifold, and (3) the performance of the mechanical equipment

Flow Through a Bed of Solids

Standard fluid flow relationships have been developed for single phase (gas or liquid) flow in pipes, ducts, and beds of solids. Unfortunately, the same relationships have not been developed for two phase (gas and liquid) flow in a bed of solids. Nevertheless, there are fundamental principles which can be drawn upon and verified through testing. The primary goal is to achieve plug flow through all of the particle bed at a sufficient rate to pull the interstitial water out. Therefore, two items must be established: (1) the criteria for even flow, and (2) the minimum flow required to move the interstitial water. All forms of liquid treatment media particles must be considered.
The flow of a fluid in a bed of solids depends on the characteristics of the solids. The pressure drop of a compressible fluid flowing through a bed of solids can be exoressed as shown in Eauation 1.
Equation 1:
wherein:

p = the inlet and outlet pressures
z = compressibility factor
R = gas constant
G = gas velocity
T = temperature
g_c = gravitational constant
M = molecular weight
f_m = modified friction factor
L = depth of solids
e = interstitial void fraction
s = solid shape factor
Dp = equivalent diameter of the solids, average. R.H. Perry & C.H. Chilton, Chemical Enoineers' Handbook, 5th Ed., McGraw-Hill Book Co., pp. 5-52 to 5-54 (1973).

Equation 1 has been found to be very accurate for beds of solids similar to ion exchange media, zeolites, and activated carbon particles. Testing has shown good correlation to Equation 1, with an error of less than 1 percent. It is important to note the significance of the media's physical characteristics in Equation 1. A change in the shape of the particles will affect the terms of sphericity, void fraction, effective diameter, and the modifed friction factor. A small difference in one of these terms can lead to a rate of change in the pressure drop exceeding a square function.
It has been determined that the modified friction factor, f_m, is in the laminar flow region for all of the expected waste media forms. As in the case of fluid flow in a pipe, the modified friction factor is a function of the Reynolds number except that it must be modified for the flow in a bed of solids. The modified Reynolds number can be calculated using Equation 2.
Equation 2:
wherein:

N' _Re = Modified Reynolds Number
u = viscostiy. R.H. Perry & C.H. Chilton, Chemical Enaineers' Handbook, 5th E., McGrawHill Book Co., pp. 5-52 (1973).

In the turbulent flow range, the friction factor is constant for a given material. Therefore, the pressure drop is proportional to the flow rate of the air through the bed of solids. In the laminar flow range, the friction factor is inversely proportional to a logarithmic relation to the Reynolds number. Therefore, in this case the solids pressure drop is more highly dependent on the gas flow rate and the gas viscosity. Since the gas viscosity is dependent on the temperature, the ambient air temperature in a field case must be considered. The modified friction factor f_m is read off an experimentally determined plot of N'_Re versus f_m as shown in FIGURE 15. R.H. Perry & C.H. Chilton, Chemical En(3ineers' Handbook 5th Ed., McGraw-Hill Book Co., pp. 5-52 (1973).
The parameters for the physical characteristics of the solids are well founded. The void fraction and shape factor are tabulated or graphed for shapes varying from nearly perfect spheres to flakes and odd plastic shapes.

Flow Through Perforated Pipe Distributors

Perforated pipe distributors are used in water treatment and chemical manufacturing equipment. Experience has shown the empirical design methods available to be very accurate. Pressure readings taken during full scale testing have confirmed the accuracy of these methods. There is an economic trade-off between the capital equipment required to achieve a minimum velocity through the bed of solids and the extent of the disposable distributor required in the container.
The design of the distributors has involved standard orifice and pipe flow calculations. The key, however, is to determine the criteria for even distribution so as to avoid potential maldistribution problems that can occur in a bed of solids and around the pipe distributors. It should be noted that a bed of solids can itself be a means of distributing a fluid. Therefore, the bed of solids and the distributor are interrelated. Containers which have been used in the past have had maldistribution problems. It can take days for the free standing water to migrate to the bottom of a container of the prior art.
The vapor collector manifold used in the dewatering containers of the present invention is commonly referred to as a header and lateral type, with drilled and screened laterals. The header is the central backbone and the lateral conduits come out from it The lateral conduits are designed such that the screen does not blank off or constrict the orifices when the resin is loaded on top and the fluid is flowing into them.
The calculated flow through a bed of solids can be incorporated with the distributor design calculations since the inlet pressure of the distributor is the bottom pressure of the bed of solids. The orifice equation is summarized in Equation 3.
Equation 3:
wherein:

w = flow rate
C = coefficient of discharge
Y = expansion factor
A₂ = orifice cross section area
g = gravitational constant
P = upstream and downstream pressures
p ₁ = upstream density
B = orifice to pipe diameter ratio.

R.H. Perry & C.H. Chilton, Chemical Enaineers' Handbook, 5th Ed., McGraw-Hill Book Co., pp. 5-11 (1973).
The coefficient of discharge, C, is dependent on the orifice Reynolds number and the ratio of the orifice to pipe diameter. The discharge coefficient is essentially constant below certain diameter ratios and above certain Reynolds numbers. The expansion factor, Y, is a function of the ratio of upstream and downstream pressures and the specific heat ratio of air. In the expected operating conditions, Y is equal to one.
The criteria for the evenness of flow across any one square foot covered by the distributor was arbitrarily set, by experience, at 5% maldistribution. The degree of distribution can be determined from the ratios of the air kinetic energy and friction loss in the lateral (due to air flow) to the orifice pressure drop. The actual percentage of maldistribution can be calculated by Equation 6. The applicable equations are:
Equation 4:
(V² _i/2g_c)
wherein:

K.E. = Kinetic Energy
V_I = velocity at the lateral inlet
a = average velocity correction factor
hp = pressure loss across the lateral
f = friction factor of the pipe lateral
D = lateral diameter
h_ol = pressure loss across the first orifice.
R.H. Perry & C.H. Chilton, Chemical Enoineers' Handbook , 5th Ed., McGraw-Hill Book Co., pp. 5-47 to 5-48 (1973).

The average velocity correction factor, a, is equal to ₁.₁ for long, straight pipes. The friction factor, f, is the standard value used for PVC pipe. Equation 6 is valid only when the orifice coefficient of discharge, C, is constant, as it is within the constraints stated above.
The distance between lateral conduits and the distance between orifices has been established based on economic considerations. There is a limiting return on the addition of more orifices and laterals. An increase in pressure drop due to air flow becomes more cost effective. The geometry determination is mostly qualitative based on experience. The actual distribution effects are a combination of the orifice locations and the distribution effect of the bed of solids. This problem is addressed below.

Distribution Criteria

There are maximum and minimum effective flow rate for a given distributor design. If the flow is too low, the fluid will enter the distributor at the point of least resistance, the center collection. point at the header and the vertical riser pipe. If the flow is too high, the air velocity in the lateral at the entrance to the header will be too great to allow flow in the center of the laterals, the flow would prefer to enter the outer perimeter of the laterals.
Most of the dewatering procedure occurs under the effect of two phase, gas and liquid, flow. The distribution criteria for the combination of the distributor and the solids can be achieved with single phase flow correlations since the end of the dewatering procedure is completely gas phase. Initially, the vapor collector manifold geometry was determined for gas flow through the largest sized bead ion exchange resin. Two phase flow distribution problems occurred directly above the distributor laterals. However, the solution was found to be simply to increase the minimum required pressure drop across the resin by increasing the air flow rate. That approach has been successful. Prior art has been based on waterflow.
FIGURES ₄ and 5 illustrate the desirable uniform, plug flow of drying air across the entire cross section of the container. By way of contrast, FIGURES 13 and 14 illustrate the effect of insufficient distribution, or pressure drop, across the bed of solids near the distrubutor. Blank areas 98 occur above the lateral conduits 64 when there is insufficient pressure drop. The interstitial water in such blank regions 98 tends to increase the effective solid diameter, lower the effective void fraction, and alter the shape factor. When all of these values change in relation to each other it can be seen from Equation that the pressure drop across the bed of solids goes up dramatically. The airstream 60 can preferentially flow around the blank areas 98 above the distributor 40 such that there is an equilibrium between the resistance to air flow 60 in the solids ₄8 and the resistance to flow due to the interstitial water in the blank pocket 98 above the lateral 64. This phenomena was observed during testing.
The only way to find the minimum pressure drop required to eliminate the two phase pockets 98 above the lateral 64 is experimentally. The minimum pressure drop experimentally measured from a successful test can be empirically extended to other solid diameters by the velocity head concept. A velocity head is defined in Equation 7. Equation 7:
wherein:

V = media fluid velocity
g_c = gravitational constant.
R.H. Perry & C.H. Chilton, Chemical Enaineers' Handbook , 5th Ed., McGraw-Hill Book Co., pp. 5-22 and 5-49 (1973).

It has been found in similar applications that it takes at least 10 velocity heads to achieve even distribution across a bed of solids with a single fluid phase. It has also been found that greater than 10 velocity heads is required to overcome the two phase pockets above the lateral conduits. The number of velocity heads had been extended to different solid sizes and characteristics. The minimum operating parameter for velocity heads, as applied to granular types of media, is conservatively fixed at 26 as the result of testing.

Powdered Media

The dewatering container internals for powdered media are based on water flow. The calculations for water flow in powdered media are similar to those used in Equation for air flow through granular media. Equation 8 is the formula used for flow of an incompressible fluid through a bed of solids.
Equation 8:
wherein:

p = density
and the other parameters are as in Equation 1.
R.H. Perry & C.H. Chilton, Chemical Enaineers' Handbook, ₅th Ed., McGraw-Hill Book Co., pp. 5-52 to 5-53 (1973). The factors representing the properties of a gas have been dropped out The temperature term has also been dropped, but still plays an important role incorrecting the viscosity term used in establishing the Reynolds number and the corresponding friction factor, f_m. The same friction factor plot as shown in FIGURE 15 is used for liquids. The pressure drop of water flowing through ion exchange resins is well founded, and Equation 8 correlates to that data with less than a ₁ percent error.

The shape factors and void fraction for powdered media are considerably different than for bead-type resins. Powdered media has more of a sliver shape. Therefore, the shape factor will go down, simulating crushed glass or certain types of sand. The void fraction will go up since the packing efficiency will not be as good as for spheres.
The use of Equation 8 to establish the elevation of the filter banks and the spacing between filters represents a significant advance in water removal efficiency. The maximum distance that water can move to the filter can be determined based on pressure drop, with a perfect vacuum being the ideal upper limit. If the pressure drop is dissipated at a distance less than the distance between the filters, then the possibility of a water pocket exists. This concept combined with properly designed distributors provides an improvement over the prior art.
The powdered media dewatering relies on air drying to remove the tail of the free water that mostly occurs from thermal effects. Since the same dewatering system is used on granular media, it also receives the benefit of the air drying. The evaporation effects are calculated in the Thermodynamics discussion below.

Summary of Fluids Calculations

The foregoing fluids calculations can be integrated in a single software package. The logical calculation sequence follows the same path as the fluid flow through the actual system and as the calculations are ordered above.
The calculations for determining the operating range of the dewatering system can be used to devise an operating region that is bounded by four curves: (1) the blower operating curve (2) the maximum possible flow out of the distributor (3) the minimum flow curve determined by the velocity head concept, and (4) the lower distributor performance curve determined by the distribution criteria Such an operating region assumes that all other factors are held constant Realistically, some of the factors will change in relation to each other. However, the most important tie is between the voidage and the shape factor; as one changes, the other tends to compensate for it
The unique result is a region defining the operating parameters of the container and process system fluid flow as it directly relates to the waste characteristics. This operating region as predicted by the aforementioned calculations is summarized on FIGURE 16 for the current production system. This operating region is bounded by the collector distribution criteria curves 102, 104, the blower operating curve 106, and the minimum velocity head flow rate curve 108, all as derived from the calculations above, that intersect at points A, B, C, and D on FIGURE 16. Average particle diameter curves 110 on FIGURE 16 are derived from Equations 1 and 2. The only curve not derived using the above-stated calculations is the blower performance curve 106. The blower curve 106 can be selected from equipment supplier data to overlay the other curves such that both powdered and bead resins are optimally processed by the same mechanical system.
This same set of curves can be expressed in other formats. For example, the curves could be normalized to flowrate versus pressure drop per foot of bed depth. The applications would be the same. It is important to note from the following summary the many concepts that have been assembled to determine the operating region (defined by points A-B-C-D of FIGURE 16) necessary to property meet the free standing water regulations on commercially available waste media.
The distributor operating curve 112 shown on FIGURE 16 is a horizontally oriented parabola as expected by the combination of the distributor and particle calculations of Equations 1 and 3. The calculation combination results from the fact that the pressure at the bottom of the bed of particles is the inlet pressure to the collector. The distributor operating curve 112 represents a relationship of the flow to the collector's interior pressure. The upper half of the curve 112 represents the growing size of the particles up to the point where the particle bed has no effect on the reduction of the collector inlet pressure. The maximum flow capability is reached due to the orifice pressure drop resulting in a full vacuum inside the collector. The bottom half of the parabola ₁12 represents a diminishing particle size as the resulting pressure at the bottom of the particle bed, or the collector inlet, goes to a vacuum.
There are three curves on FIGURE 16 that define the flow limits required to maintain proper fluid distribution. Two collector distribution criteria curves 102, 104 (shown as dashed lines in FIG. ₁6 as derived from Equations 4, 5, and 6) are only associated with the flow distribution attributed to the collector. The minimum flow rate curve ₁08 is only associated with the eveness of flow and minimum velocity across the bed of particles required for overcoming two phase flow restrictions. The uppermost collector distribution criteria curve 102 indicates the maximum collector flow allowed before the distribution criteria is exceeded. The momentum and friction of the fluid is too high in the center parts of the collector to allow even fluid entry into the orifices. The lowermost collector distribution criteria curve 104 represents the minimum collector flow required to meet the collector distribution criteria. If the flow is too low, the orifice pressure drop will be too low in relation to the lateral friction losses. The fluid will preferentially enter the orifices towards the container center. The minimum flow rate curve 108 is experimentally set to provide a minimum pressure drop to overcome maldistribution due to two phase pockets. The use of the velocity head concept as discussed with reference to Equation 7 is substantiated by test results and the fact that flow correlations are directly related to the square of the fluid velocity.
All of the curves on FIGURE 16 were verified by actual test data and found to be accurate with less than 1% error. A representative test point 114 is shown on FIGURE 17 and the relevant test data is disclosed thereon and discussed below with reference to Example 1. The unique capabilities of this method are supported by an actual power plant application. Many plants currently solidify their mixtures of ion exchange resins because they cannot be properly separated before dewatering by prior art systems. The calculation methods of the present invention allow for determining if the characteristics of the resin mixture will fall within the prescribed operating region. The appropriate fluid collector design and number of collector levels can be designed to fit with the existing mechanical equipment and still maintain certainty of meeting the regulatory limits on free standing water. Hence, the existing liquid treatment medias mixtures found in actual applications can benefit from the economics of volume reduction and the simplicity of this invention.
While FIGURE ₁6 represents the operating region of a specific existing system, the operating region can be attered to fit unique economic or operating requirements. The same basic analytical methodology could be used to move, shrink, or expand the operating region. A realistic example would involve an application where only small containers, say 50 cubic feet instead of 200 cubic feet, are to be used and/or short processing times are not required. A smaller mechanical processing system could be utilized in proportion to the waste volume size and the time necessary to process the waste. Then the operating region could represent a lower flow rate area for smaller containers or it could be shifted down and to the left using more collector levels than otherwise required in the container. The ability to uniformly flow the fluids through the container by the analytical methods and the specific mechanical equipment design allow for such collector flexibility in meeting field conditions.
The fluids calculations can also accurately perform a parametric study on the waste form, as shown for example by FIG.17, to determine the effect of other waste variables such as particle depth, fluid temperature, particle shape, and particle bed void volume. This unique capability allows for custom designing the container internals. The custom designed container internals in effect match the waste form to the mechanical processing equipment For example, the same basic design techniques are used on the layered powered material internals as in the bead materials but the result is a "four containers in series" design (the tiered levels) for the powdered material because of the limiting effect of pulling a vacuum through the finer media. If such a mixture were processed in an unheated building in a cold climate, then the fluid temperature would be of concern since the location in the operating region can be aftered by up to 30% by the change in the fluid viscosity with temperature.

THERMODYNAMICS

Approach

The dewatering system of the present invention uses convective evaporation with air for two purposes: (1) to enhance the removal of any residual free standing water, and (2) to slightly dry the resin such that it provides a desiccant-like effect with respect-to condensate generation. The difference between the granular and powdered media, as far as evaporative effect, is the difference in the composite structure of the entire media bed towards the end of free water removal. The granular media maintains a rigid structure that is very conducive to fundamental dynamics and subsequent drying. The powdered media exhibits a somewhat random creviced structure when the unadsorbed water is nearly all drawn out of the media. Evaporative water removal compensates for the randomness of the crevices by drying the exposed faces of the cracked powdered media. The dried media absorbs excess moisture from the interior of the bed as described below.

Mechanical Equipment Thermodynamics

Psychrometric operating curves can be developed that represent the heat, dewpoint, and water vapor operating curves of the dewatering system after free water removal but prior to the complete drying of the resin. The curves can be drawn on the applicable portion of a standard psychrometric chart wherein water content, dry bulb temperature, and constant enthalpy form the axes. R.H. Perry & C.H. Chilton, Chemical Enaineers' Handbook, 5th Ed., McGraw-Hill Book Co., pp. 12-4 and 12-5 (1973).
FIGURE 18 represents the heat, water, and water vapor operating curves of the dewatering system after free water removal but prior to the complete drying of the resin. The curves are drawn on the applicable portion of a standard psychrometric chart. Points 1, 2, and 3 on FIGURE ₁8 represent the input to the blower (or exit from the water separator), heat rise seen at the exit of the blower, and the saturated condition at the exit of the container, respectively. Moving along the dew point line from point 3 back to point 1 represents the condensation of water in the water separator. Extension of the horizontal line to point 4 on FIG. 18 is due to adding heat via an outside source or heater. The fixed temperature in the water separator represents a constant saturated air reference point from which to work from. The prototype testing used a conservative 60°F air exiting the water separator. The production system utilizes a water chiller that can maintain a lower air temperature.
The amount of water removed from the system is determined from the right-hand side of the psychrometric chart. The distributor limiting flow rate of 260 standard cubic feet per minute is used, and the minimum and maximum water removals as determined by the two charts on FIG. 18 are 26 and 50 gallons, respectively, over an 8-hour cycle. This illustrates that a further advantage can be attained by adding an auxiliary heater to superdehumidify the airstream 18 after it leaves the blower. It is interesting to note that testing and previous experience indicates drained residual free water, without evaporative drying assistance, has been in the range of 10 to 25 gallons. However, that testing did not allow for the entire waste contents to reach the burial condition temperature of approximately 55°F. At the burial conditions up to 60 gallons of water could be produced from condensation alone in prior art systems in which the media is not dried.
Since the dewatering system preferably operates in a recycle mode, it is essentially closed with respect to the atmosphere. Therefore, on FIGURE 18, the water content when going from point 1 to points 2 and 4 is constant and the change is due only to heat input as the air passes through the blower (and heater, if applicable). The line from point 2 to 4 represents the heat added by the heater. When the air is passing through the container there is no appreciable change in the heat content of the air and water vapor mixture. Therefore, the line from point 2 or 4 follows the constant enthalpy line up to the saturated air line at point 3, gaining moisture along the way. From point 3 to 1, the water separator drops the air temperature and much of the water content as it moves down the saturated air line.
The detailed design has taken into account heat losses out of the container walls and in the filter and piping. The effect of heat losses on the curves shown in FIGURE 18 is that they slightly deviate from the constant value lines. When the resins are dried below their saturation point, point 3 will begin to move down line 2 -3 and shown a lower refative humidity at the container exit. The other operating lines will remain the same.
The accuracy of using psychrometric charts to characterize the operating parameters of the dewatering system were verified with temperature, humidity, and water removal measurements. Even when pressure and heat loss deviations are ignored, the results are within good design practices.

Ion Exchange Resins

Ion exchange resins represent the worst thermodynamic case because they contain 35 to 65 percent bound water after all of the free water has been removed. The bound water remains available, to varying degrees, for vaporization within the resin bed and subsequent condensation around the container wall when the container is exposed to a lower temperature at burial conditions relative to the temperature of the waste during the dewater processing. Bead-type resins represent a worst case for condensation because of their much greater ability to move air and water vapor within the resin bed. Prior art dewatering systems have not addressed the operating condensation problem.
The approach of the present invention to the condensation problem follows these steps: (1) determine the credible worst volume of water that may be present due to condensation in the buried condition; (2) find the degree of resin dryness that must be achieved to allow for reabsorption of any condensation that. may be generated in the burial condition; and (3) determine a finite end point for the dewatering process. Two parameters unique to ion exchange resins are critical to solving the aforementioned three steps. First, the heat capacity of the polystyrene, water, and chemicals that make up the resin must be determined. Second, a resin drying relationship must be found.
The heat capacity values for various chemical forms of ion exchange resins are not well tabulated. However, a relation to the material properties was found that closely matches experimental results. Equation 9 is the method used to determine the heat capacity values for various resin forms.
Equation 9:

wherein:

Cp = Heat capacity of the resin, water, pure liquid chemical and polystyrene, respectively, Btu/tb.-°F.
X = Molar fraction of water, pure liquid chemical and polystyrene, respectively.
J.M. Smith & H.C. Van Ness, Introduction to Chemical Engineering Thermodvnamics, 2nd Ed., 1959, McGraw-Hill Book Company, pp. 128-₁30. The reference indicates that Equation 9 should only be used when no other methods are available. Heat capacity values for pure components were derived from standard chemical thermodynamic tables. The results of Equation 9 were checked against Values derived form actual testing temperature data and an equation analogous to Equation 10, below. The deviation between cai- culated and test values has been less than 0.1 Btu/Ib.-°F.

Since the heat capacity is dependent on the type or resin and its chemical form, Equation 9 allows for finding the worst case, largest heat capacity value that may be encountered in field conditions. Actual Calculations on a range of chemical compositions shown the water content to be the overriding factor since its heat capacity is several times greater than the other components and has a significant molar fraction. Therefore, the range of possible heat capacity values is not great in absolute value, but has a significant impact on large volumes of resin. Heat capacity data for the pure chemical solutions in the resin were derived from sulfate salts for the cation and sodium salts for the anion.
The highest temperature the waste media is expected to be is 110°F. The burial condition is 55°F. A conservative assumption is that all of the heat content of the waste media spanning 55° to 110°F is capable of vaporizing water adsorbed in the resin and then condensing at the container wall. The total heat available to produce condensate is given by Equation 10.
Equation 10:
wherein:

Q^R = total heat content of the resin, Btu
V_R = volume of the resin, ff
p_R = density of the resin, Ibs./ft³
Cp_R = heat capacity of the resin, Btu/Ib-°F
T_R = temperature of the waste, °F
T_∞ = ambient temperature of the container, °F.
J.M. Smith & H.C. Van Ness, Introduction to Chemical Engineering Thermodynamics 2nd Ed., 1959, McGraw-Hill Book Company, pp. 56-57.

For design purposes, the maximum heat capacity, volume, and density values can be used to size equipment Equations 9 and 10 were used to help distinguish if there were significant differences between various types of resins. At this point there are not large differences between resins but there are when it comes to adding sensible heat to the resin to achieve the desired dryness endpoint, as explained below.
Once the total heat content is derived from Equation 10, the maximum water volume that can be derived from condensation is determined from the psychrometric chart. Assuming the temperatures, 55° to 110°F, the enthalpy change and the change in water content can be read from the chart. The total heat content divided by the enthalpy change per pound of air gives the total pounds of air required to cool the resin. The total pounds of air times the water content of the air gives the maximum total poundage of water expected to condense from the resin. This calculation can be eliminated by maintaining the media slurry at the expected storage temperature of, e.g., 55°F during the course of the dewatering treatment, as described below, as T_R would then approach T_∞.
In this system, condensation never forms in the burial condition because the dried resin readsorbs the water before it can form. At the worst case, the dewatered and dried resin in these containers has a saturated water/water vapor equilibrium equivalent to 55°F, or the burial condition. When the temperature drops from the maximum waste temperature of 110°F to 55°F, the dried resin acts as a very efficient desiccant to adsorb the additional moisture in the air.
Once the maximum volume of water for resin readsorp- tion is determined, the next step requires data outlining the water uptake performance of various resins. The water uptake performance of ion exchange resin is complicated by three main characteristics of the resin: (1) the capacity of the resin, (2) the degree of crosslinking, and (3) the nature of the chemical solution in the resin. Items 1 and 2 can be conservatively quantified at the maximum published capacity for any strong cation or anion (2.1 and 1.4, eq./1., respectively) and at maximum of 10% (divinylbenzene, DVB) crosslinking for each resin type, respectively. FIGURE 19 illustrates the effect of resin crosslinking on the ability of the resin to hold water. F. Helferich, Ion Exchange, McGraw- Hill, 1962, p. ₁07. Oxidation and repeated regeneration can affect the crosslinking.
The nature of the resin's aqueous phase is analogous to vapor pressure equilibriums of aqueous solution thermodynamics. As the concentration of the solution increases, the liquid vapor pressure decreases. At some point, there is an equilibrium with the surrounding gas. Equilibrium water/vapor sorption curves can therefore be prepared for the worst expected case cation and anion resins. F. Helfferich, Ion Exchange, McGraw-Hill, 1962, pp. 100-109, herein incorporated by reference. FIGURE 20 presents the equilibrium curves for the expected case cation and anion resins. Note the dependence on the chemical form of the resin. If the resin is severely fouled, or the ion in the slurry water is a large molecule like that found in decontamination solutions, the curve tends to be nearly flat and lower on the vertical scale. Such a curve would be the worst expected case since it indicates the relative humidity endpoint must be much lower.
The weight of the maximum expected water to be generated, as explained above, can be divided by the weight of the resin. The result can be applied to the curves of FIGURE 20 and the corresponding relative humidity becomes the process endpoint Then as the temperature of the resin drops from the process ambient to the burial condition, the humidity in the container increases and the resin will take up the moisture in the air. As the moisture content increases and/or the relative humidity endpoint decreases, more resin sensible heat is required to achieve the endpoint
From the rationale described above, a worst case dewatering endpoint curve can be developed, and the ordinates of the curve that is best suited to field operations can be determined. For example, the waste beginning temperature is one ordinate but the other may be humidity, processing time, dry and wet bulb temperature, or volume of water removal from the container after the beginning of the drying cycle. Possibly several waste specific endpoint curves may be required. The worst case would be one each for cation and anion resins in the once used or regenerated state. Such an approach would encompass the major field differences in moisture retention, chemistry, capacity, and crosslinking. The ability to determine the effectiveness of the dewatering system across the full spectrum of waste forms has very good promise since the analytic projections have shown excellent correlation to the single point derived from field tests.

Process Endpoint Derivation

The purpose of the endpoint method or methods used with this invention is to come to a definite point where the process may be stopped and still assure that enough adsorbed water has been removed to preclude the generation of free standing water by the condensing cycle described above. Many endpoint methods can be developed out of the aforementioned thermodynamic calculations. However, the methods apply to either the properties of the air or the amount of adsorbed water removed from the waste. Either method stems from the chemical or physical characteristics of the adsorbed water and waste media, respectively, as described in the calculations section on thermodynamics. With respect to the properties of the drying air, the endpoint methods can include, but not be limited to, the humidity, wet bulb and dry bulb temperature, flow rate to wet bulb temperature relations that relate to the adsorbed water removed, etc. With respect to the adsorbed water removed, it could be simply measuring the amount of water coming out of the water separator, a time versus water removal rate relationship, container weight loss, etc.
Our field tests have proven many new concepts in radwaste dewatering technology. The invention's analytical and testing results represent the first time the free standing water question has been practically addressed and solved with respect to the container's burial condition. It is also the first time full scale testing has been used to confirm single data points within a predetermined operating region. The prior art relies on measurement of the pumped or drained free standing water to determine the processing endpoint This type of endpoint can at best be treated statistically and not in direct relation to any of the waste's properties or with respect to the generation of free standing water in the burial condition. The invention uniquely utilizes a process endpoint that (a) is directly related to the waste's free standing water generation characteristics and (b) is oriented towards meeting the free standing water regulations in the burial con- ' dition.
The significance of the waste media's pre-dewatering temperature was outlined with reference to the foregoing thermodynamic calculations. Simply stated the waste media's heat content can provide the energy for evaporating water from the waste. The water vapor subsequently condenses due to the lower temperature at the container wall during burial conditions.
The waste media, when in the radwaste hold up tank, is typically in the 80 to 90 degree Farenheit range. Temperatures in the nineties are not uncommon and occasionally occur up to 110°F. After the waste leaves its hold up tank, other factors usually act to lower its bulk temperature. The sluice water is often at a temperature less than the waste. Also, the locations used for dewatering are typically very similar to a warehouse's transportation area, having cold concrete slabs, high ceilings and large, uninsulated transportation doors.
Other than a waste temperature change due to the sluice water, the only other way to affect the waste temperature is by ambient conditions. The waste media, as it sits in the container, has very good self-insulating qualities. Therefore, the ambient conditions can lower the waste temperature only when (a) they differ significantly from the sluiced waste temperature and (b) the waste sluicing flowrate is low/or in long pipe runs. The ambient conditions obviously can be extreme. Radwaste areas in U.S. nuclear plants in the upper midwest can fall below freezing while in the southeast and southwest temperatures can be above 110°F. The burial temperature is a constant temperature, typically 55°F.
Two entirely different types of bead resins were selected for the qualification test program and processing endpoint determination: a new, unused cation resin of known chemical form that is very commonly used in the industry, and a used anion resin in a fouled and regenerated state. See the following Examples 1 and 2. The new cation resin provided as base data point since all of the chemical and physical characteristics of the new resin were known. The used anion resin represented a worst thermodynamic case. It was fouled with organics and had been subjected to repeated chemical regenerations. The use of the two types of resins provided the following testing/verification advantages: (1) the analytical methods could be verified on a media of known physical and chemical characteristics, and (2) the analytical predictions and process equipment could be proven on an unknown waste form.
The method of this invention preferably utilized the humidity of container exhaust air and the waste's temperature prior to dewatering as the endpoint parameters. The impact of the waste temperature has been described above in conjunction with Equation 10, and that of the exhaust air humidity in the discussion of vapor equilibriums following thereafter. The system operators will preferably use a direct reading humidity meter 24 to determine the endpoint of processing. Other methods for determining the humidity could also be used. An example would be wet and dry bulb temperature measurements.
The exhaust air humidity versus waste temperature curves for the processing endpoints depend on the specific chemical nature of the resin's adsorbed water solution and the chemical form of the resin itself. This fundamental discovery is a significant advance in the art FIGURE 20 illustrates this interdependence. These curves explain the observed difference in time required to reach the same effective dewatered state in resins that otherwise have the same physical structure. For example, in the testing program it took up to 16 hours to dewater organically fouled anion resins but less than eight hours to dewater hydrogen form cation resin. Similar curves can also be developed for non-ion exchange waste medias as described above.
However, it is not practical to have an endpoint curve for every possible resin chemical form. The expected resin chemical forms can be conservatively simplified into broad categories as suggested by the water uptake curves of FIGURE 20 and the above-incorporated Helfferich reference. From that reference, for monoelemental ions the curve shapes are nearly identical within the range of humidity values of concern (90-100%). When mulfielemental ions are considered, the curves are much flatter, and consequently a much lower humidity must be achieved in order to remove the same amount of water. The worst case multi-elemental curve can be selected.
Therefore, the general classifications of bead resins are the following:

Group 1. Non-regenerated, or once used, cation or anion resins loaded with or having been treating waters with over 90% of the total water analysis as monoelemental or simple oxide ions. Examples of such ions are the cations Na, CA, H, Ba, Cu, Mg, Cs, Fe, and the anions Cl, OH, Br, F, I, NO,, S04. HC0₃.
Group 2. Cation resins that have either been repeatedly regenerated or having been treating water with over 10% of the total water analysis as multi-elemental ions, especially detergents and decontamination solutions.
Group 3. Anion resins that have either been repeatedly regenerated or having been treating water with over 10% of the total water analysis as multi-elemental ions (except simple oxides as listed under Group 1, above), especially detergents and decontamination solutions.

FIGURE 21 presents process endpoint curves that have been derived for the groupings described above, and specifically for those resins that are normally encountered in field conditions: cation capacity less than 2.1 eq./1., anion capacity less than 1.4 eq./1., and all having less than 10% DVB crosslinking. On FIGURE 21, the dewatering endpoint curve 118 is applicable to the abovestated Group 1 resins; curve 120 to the Group 2 resins; and curve 122 to the Group 3 resins. It has been conservatively assumed that regenerate resins will accumulate large molecules over their processing time because of the tendency for incomplete regeneration effects and long term organic fouling. The processing endpoints for groups 1,2, and 3 resins are stated as functions of beginning waste temperature versus relative humidity of the exhaust air from the container. Knowing the general resin type and the beginning waste temperature one can simply read the relative humidity endpoint from the appropriate curve.
The application of the resin groupings to specific plant processes will be primarily by experience. The nuclear utilities do not have the analytical equipment for determining the full water or resin chemical analysis. Usually the chemi- cat composition of the resin must be determined by the normal operating parameters of the specific process or from a knowledge of the chemicals put into the batch to be treated by the liquid treatment media. When there is uncertainty, then the worst case endpoint curve can be used with certainty. FIGURE 21 thus serves as an example of the means to group the waste media's possible characteristics within the limited capabilities of the power plant
The foregoing discussion on direct humidity endpoints is directly applicable to any fixed bed or rigid solids. In the case of powdered media, the particles are currently not necessarily a fixed and rigid bed, though advances in the art may lead to that condition. For powdered media the humidity readings are used to indicate the end of the saturation point of the media. This is realistic since the interstitial water is removed prior to the media's cracking and sloughing. After that point is reached, the amount of water removed from the media can be measured as it comes out of the water separator. From a knowledge of the proportion of ion exchange resin and the pore diffusion capabilities of the waste structure and the waste particles themselves, the water uptake capabilities of the powdered media can be determined as described above and that water volume then set as the post-drying water separator effluent endpoint.

Conclusion

Thermodynamically, the typical operating region for the dewatering system will easily allow for overdrying most of the expected resins. Tracing the origins and specifications of the plant resins will assure operations within the system's thermal capabilities. The method of the present invention has addressed "atmospheric" conditions within the waste media bed because it has been found to definitely contribute to free standing water. Prior art test programs have incorrectly concluded that atmospheric factors are not significant The effect can be easily masked by fluid dynamic problems and the very low thermal conductivity of the resin and air.
Powdered media follows the same principles of fluid dynamics and thermodynamics as granular media. However, the dewatering design purpose is different since powdered media structurally differs form granular media but does not significantly differ within the specific waste type like granular media. For example, "Ecodex" does not get as beat up as condensate polisher bead resins and there are relatively not as many different types of powdered treatment media. An initial water flow design is used prior to an evaporative drying step. The consistency of the waste form is counterbalanced by the randomness of the cracking of the resin after free water removal. The residual free water which may be present after the initial flow removal, or generated by condensation, is successfully evaporated or reabsorbed by the same mechanism as in bead resins.
The design and testing was based on ion exchange resins since they are the primary market For example, the respresentative endpoint curves in FIG. 21 were derived for ion exchange resins as stated above. However, the calculations and methodology described herein also apply to other treatment media such as activated carbon and inorganic zeolites. The fluid dynamic factors used for ion exchange resins, including flow, voidage, solids, size and shape are also applicable to other treatment media. The thermal methodology and endpoint determination process described above are also directly applicable to other forms of treatment media. The test techniques used on the ion exchange resins can be duplicated on other media such as carbon, zeolites, and sludges.
It should also be emphasized that the aforementioned liquid treatment media can be successfully dewatered by cooling the waste slurry to the expected burial temperature prior to applying the above-stated fluid dynamic principles and methodology. For example, the media could be contacted with chilled water or with refrigerant coils prior to mechanical dewatering as described above. In this way, the wastes can be preconditioned so that the condensing cycle--as defined and quantified for the first time herein--will be inhibited down to the burial temperature.
In summary, the method and apparatus of this invention are based upon a multiplicity of innovations that significantly advance the arL These innovations include the following:

1. The application of fluid flow calculations through a bed of solids. The physical characteristics of the solids are taken into account
2. The use of item 1 to detemine the number and arrangement of collectors in the container.
3. The use of item 1 to define the inlet conditions of the collectors.
4. The determination of the minimum fluid flow through a bed of solids to effect full removal of interstitial water.
5. The design of the collectors to effect uniform flow through the cross section of the particle bed. The precise size and pressure drop of the orifices and the flow in the
conduits are balanced together.
6. The use of a flow interrupter at the container wall to preclude preferential channeling of the drying airstream down the container walls.
7. The waste media is dried below its water saturation point such that it will readsorb any generated free water.
8. Item 7 is precisely achieved to correspond to the waste media's long term burial conditions.
9. The processing endpoint for items 7 and 8 can be determined from direct readings of the container exhaust air humidity. Alternatively, the volume of water removed from the media after the drying cycle begins can be used to precisely define the processing endpoint.
10. The processing system is a closed loop. The water separator simultaneously keeps the air below temperature limits, condenses water from the air, and removes the entrained water form the airstream.
11. The blower circulates and heats (dehumidifies) the air. The dehumidified air dries the waste particles. While airflow from the container top region through the container bottom region has been described herein, the drying airstream can alternatively be passed through the manifold into the slurry, and the humidified air that has passed through the slurry can be exhausted from the container top region.

The following examples are presented to illustrate the dewatering method and apparatus of the present invention and to assist one of ordinary skill in making and using the same. The following examples are not intended in any way to otherwise limit the scope of this disclosure or the protection granted by Letters Patent hereon.

EXAMPLES

Numerous small scale tests were conducted in order to determine the initial full scale design and operating parameters. Such tests were made to determine maximum conduit spacing, particle size distribution, drying effects, and column tests. Many full scale tests were conducted using prototype equipment in order to establish the design and operating parameters that have been described above.
There are several procedural steps prior to the processing of waste or testing materials. The first step is to conduct a preliminary waste characterization. Most often this is conducted prior to the equipment arriving at a power plant and it consists of a questionnaire. The questionnaire insures that the waste to be processed is within the operating bounds of the container piping and the processing equipment. If it is not within bounds, then the system is modified as described in the Calculations section to accommodate the abnormal waste conditions. Once the equipment is at a power plant, it is thoroughly inspected for damage, especially the container's internal dewatering apparatus.
Shortly after the equipment has been set up, it is function- any tested without waste for the purpose of discovering any operating problems. The last preprocessing step is to confirm the nature of the waste, the expected radioactive fields, coordinate the waste transfer methods, and confirm all mechanical and personnel safety features and valve settings.

EXAMPLE1

In this example unregenerated cation ion exchange resins with monoelemental chemistry were processed. The resin was known to be of relatively undamaged and, therefore, nearly uniform spheres of 0.0256 inches average size, in the sodium form, with 8% crosslinking, and 45% water content
A 200 cubic foot capacity container with a six-foot particle bed depth was used. An air space of approximately six inches was left above the top of the slurry bed. Structural steel skids containing the water separator, blower with filter, and control valves were situated near the waste container. Four-inch diameter hoses were used to interconnect the container, water separator, and blower. One hose was connected from the container vapor outlet port to carry the container water and exhaust air to the inlet on the water separator. Another hose was connected from the water separator outlet to carry the dried air to the inlet of the blower. A third hose run from the blower outlet filters to the container air inlet port.
The water separator was a two-foot diameter by five- foot high stainless steel vessel with a flanged top. The water separator contained a heat exchanger evaporating a compressed refrigerant for cooling the air. The coil 98 was located under the water level at the separator bottom. The exhaust air from the waste container entered underneath the chilled water level. The cooled air rose to the top of the separator after passing through a demister pad 100. The demister pad 100 is stainless steel wool that drops the entrained water out of the air by impingement A two-inch hose drained surplus water from the water separator, under suction from a three-inch diaphragm dewater pump, to a nearby floor drain.
A stand alone, five ton refrigeration unit on the order of 30,000 B.T.U. was located next to the water separator. Inlet and outlet refrigerant lines recirculated the refrigerant from the refrigeration unit through the water separator.
The blower was a 30 horsepower rotary vane blower - (average 250 SCFM).
The hose connections at the waste container were on a fillhead that rested on the container opening. The fillhead was fabricated from stainless steel plate and sheetmetal and contained all of the connections between the exterior and the interior of the container. The fillhead also contained waste shut off valves, a TV camera, radiation sensors, and container waste level instrumentation connections, all conventional.
The flat-bottomed container used to dewater these bead resins had a single level vapor collector manifold at the container bottom, as shown in FIGURES 6 and 7. The header was a three-inch plastic pipe, and the lateral conduits were three-quarter inch plastic pipe that had been through-drilled to provide one-quarter inch orifices at approximately four-inch intervals along both sides of each lateral conduit. The orifices were screened with a coarse screen (Naltex Flex Guard III) surrounding a 100-mesh screen (McMaster-Carr). The lengths of the conduits on each side of the header, listed moving away from the open end of the header were: 17.75, 23.75, 27.75, 30.00, 31.50, 32.00, 31.50, 30.00, 27.75, 23.75, and 16.00 inches, with the conduits spaced 5.62 inches apart. This container also had an annular ring, in this case made of one and one-half inch pipe, affixed approximately midway down the inner sidewall.
Power, air, water and instrumentation connections were made prior to receiving waste into the container. These connections included water high level switch in the water separator, temperature sensor at the blower, camera cables, waste level sensor lines, and blower and refrigeration unit power cables, and dewater pump air line.
The cables with control or monitoring functions led to a free standing control panel. It is advantageous to have the control panel free standing such that it can be located outside of high radiation zones thereby reducing the operator's exposure. The panel contains ON/OFF switches with or without an AUTO function for the blower and refrigeration units. The panel also includes blower exit and container inlet temperature indicators with high limit switches, emergency shut off switch, radiation monitor, status lights, and the television monitor. After all of the preliminary check offs, the system is ready to receive the waste.
Once the operator received the go ahead to prepare to receive the ion exchange resins the fillhead TV, radiation monitor, level switch circuitry, and the dewater pump were turned on and their performance double checked. Plant personnel were notified that waste transfer is going to begin. The operator remotely opened the waste influent port in the fillhead. The waste entering the container was observed on the TV monitor. The waste was a slurry of water and ion exchange resin of the above-stated composition. This slurry was at 80°F as it entered the container. The dewater pump removed the slurry water through the bottom vapor collector manifold at a rate faster than it entered. The pile of resin easily flattened out across the container bottom. As the resin level rose toward the top of the container, a high level switch indicated a warning at the panel. The operator could also notice the level via the TV monitor. At this point a waste inlet valve in the waste influent port was open and shut, in coordination with the plant personnel, to allow the last increments of waste into the container bottom region. The operator had the option of turning down the dewater pump to allow water to rise to the top of the resin in the container to aid in letting the resin bed flatten out under the container top region. When the container was as full as possible, leaving only an airspace of approximately six inches in the container top region, the waste influent port was secured shut after draining the line.
The dewater pump continued to operate after waste transfer was completed. The dewater pump then removed the bulk of the interstitial water in less than 25 minutes. Thereafter the water eminating out of the dewater pump hose tapered off to a small trickle. The refrigeration unit was turned on and the blower shortly thereafter. As soon as the blower was turned on the dewater pump discharge hose was flooded with water. (The sudden draw on the residual interstitial water is occasionally so sudden that the high level switch in the water separator kicks off the blower.) In five to ten minutes the dewater pump discharge hose effluent tapered off to a trickle. At this point less than 35 minutes had elapsed, and the waste was already at the equivalent dewatered point of several days processing with prior art systems.
After about ₄₅ minutes elapsed time the differential pressure across the resin bed had tapered off to a steady state value (within a few hundredths of a PSI predicted by the analytical methods summarized above with reference to the curves on FIG. 16 and the test point 114 on FIG. 17) corresponding to all air flow through the resin. This point corresponds to the prior art's ideal capabilities. Actual drying (removal of adsorbed water) of the resin had begun. The trickle of water leaving the dewater pump discharge hose thereafter was condensed water originating from the resin. Within one hour from the beginning it was noticed on the TV monitor that the ion exchange beads on the top of the resin bed were significantly smaller, lighter, and tending to swirl around the inside top of the container. From the testing program it is known that the light resin at the top is a result of contact with less than 10% relative humidity air. The resin only an inch below the light resin was still nearly saturated with water at this beginning of the drying cycle.
The operating conditions were maintained nearly constant from the one hour point to the five to six hour point The trickle of water out of the dewater pump discharge hose and the air's differential pressure across the resin were observed to be nearly constant. Wet and dry bulb measurements or direct humidity readings showed 100% relative humidity in the exhaust air from the container. Near the six hour mark the relative humidity readings started to gradually drop below ₁00%. The appropriate process endpoint curve 118 on FIGURE 2₁ indicated, as explained above, that the humidity should read below 99% for such unregenerated cation resins containing more than 90% monoelemental ions and at 80°F. This endpoint was reached during the seventh hour and the system was shut down at the end of the eighth hour.
An overhead crane removed the fill head from the container. A permanent lid was immediately installed on the container opening to prevent the possibility of air at greater than the endpoint relative humidity from re saturating the resin. Once the permanent lid was affixed, the container was ready for shipment to an approved landfill for permanent storage.
As a test, the dewatered resin in this Example was allowed to cool until its core temperature was less than the normal burial temperature of 55°F. To effect a core temperature of less than 55°F, the outside of the container was necessarily less than 55°F. No free standing water generated from the container until a core temperature of less than ₄5°F was attained. The fact that the threshold temperature was 10°F less than predicted is due to the conservative nature of the Calculations and equalization with the super dry resin at the top of the resin bed.

EXAMPLE 2

Anion ion exchange resins were dewatered in this Example. These resins had been regenerated, with slight degree of resin breakage and had an average diameter of 0.02463 inches, about 55% adsorbed water, plus a high visible degree of large organic molecule fouling its adsorbed water. This resin represents the worst type of resin to be encountered.
The waste prescreening, equipment set up, equipment check out, functional testing, preoperational coordination with power plant personnel, and start up were as described in Example 1. This anion resin was processed identically as the cation resin in Example 1. As with the cation resin, the pressure drop through the resin was predicted by the analytically derived performance curves to within a few hundredths of a PSI. The resin was dewatered at 80°F. The relative humidity endpoint predicted by the appropriate processing endpoint curve ₁22 on FIGURE 21 was about 92%. It took about 15 hours of drying to reach the endpoint for this anion resin. After the humidity endpoint had been achieved, the generation of free standing water was similar in nature to the cation resin cited above. Here again, the regulatory limits set by 10 C.F.R. Part 61 were met.

EXAMPLE 3

Powdered media was dewatered. This media was a mixture of combined cation and anion powdered ion exchange resins with a cellulose-based filter aid. The effective size of the media was 0.002 inches. All powdered media is unregenerated, typically monoelemental ions in the adsorbed water and of consistent, uniform size. The narrow and consistent physical characteristics of powdered media simplify the application, but 1he nonuniform structural nature of the media bed in the container complicate the application with respect to its cracking after interstitial water is removed.
The waste prescreening, equipment check out, func- tonal testing, preoperational coordination with power plant personnel, and start up were the same as described in Examples 1 and 2. The only difference in the equipment set-up was that a tiered series of vapor collector manifolds as shown in FIGURE 9 was provided in the container bottom region. The four vapor collector manifolds were positioned 6.0 23.25, 40.5, and 57.75 inches, listed lowermost to uppermost, above the container floor. Also, an annular ring was not provided. The conduits and headers were through-drilled at two-inch intervals to produce al- temating side-to-side and top-to-bottom orifices. The orifices were screened with one micron filters (Hytrex). Four one and one-half inch hoses interconnected the vapor collector manifolds and the water separator.
As the waste media was sluiced into the container the dewater pump removed the excess water through the uppermost vapor collector manifold. This method allowed for maximum compaction of the waste into the bottom of the container. After the media bed reached the top collector, additional waste was introduced in an intermittent fashion until the container was apparently completely filled. The waste influent port was then secured shut
Valves to the vapor collector manifolds were opened sequentially, from the uppermost to the lowermost, as the vacuum at each manifold reached approximately 25 inches of mercury. This point was selected as a reasonable maxi- . mum vacuum capability of the dewater pump. The valves to the manifolds were then closed sequentially from uppermost to lowermost as the vacuum at each manifold fell to approximately five inches of mercury, at which point the vacuum drop off was observed to plateau. During this process most of the interstitial water was removed. Observation of the TV monitor showed that the surface of the particle bed had begun to crack. At this point approximately 40 minutes had elapsed since the dewatering process was initiated.
Then the blower was turned on. A momentary rush of water entered the water separator and thence exited from the dewater pump discharge hose. Within 30 minutes, the vacuum level at the water separator stabilized at approximately 11 inches of mercury. Over the course of the eight- hour test the vacuum level at the water-separator gradually dropped to ten inches of mercury.
System operating parameters were monitored over the full course of the test. After eight hours of continuous operation the system was shut down.
The container was sealed, a low point drain valve opened, and the container was allowed to cool. The container was monitored for drainage of free standing water over the period of the next ten days as it was allowed to cool to burial condition or below.
No free standing water developed.

EXAMPLE 4

A comparative test with the best prior art system and procedures was conducted using the cation resin of Example 1. The container was of the same type and configuration as used in Example 1, except that it was fitted with a conical bottom and a hub and lateral type water collection system, similar in all aspects to prior art systems.
The resin bed was heated to a temperature of approximately 95°F in order to duplicate typical power plant conditions. Temperature sensors were placed at the center of the resin bed and along the resin perimeter.
Following the standard operating procedures for prior art systems, suction was maintained on the container water collection system eight hours a day for a period of three days until the volume of water pumped from the container over the course of eight hours was less than five gallons. The container was then allowed to cool to a core temperature of less than 55°F in order to duplicate burial conditions. A total of approximately 40,000 ml (10.5 gallons) of free water drained from the container. This volume of water represents approximately 0.75% of the total container contents, exceeding the one-gallon criteria for disposal at the Handford disposal site, the 0.5% by volume free standing water requirements for carbon steel containers at the Bam- well disposal site, and nearly exceeding the 1.0% criteria for high integrity containers at the Barnwell facility.
It should be noted that the comparison test was conducted using resins which were easiest to dewater. Had the tests been conducted using spent, regenerated resins the 1.0% criteria would probably have been exceeded as well.
While the preset invention has been described in con- juction with preferred embodiments, one of ordinary skill after reading the foregoing specification will be able to effect various changes, substitutions of equivalents, and other alterations to the methods, devices, and compositions set forth herein. It is therefore intended that the protection granted by Letters Patent be limited only by the definition contained in the appended claims and equivalents thereof.

Claims

1. A method of dewatering a slurry containing radioactive particles to a condition for permanent storage, comprising the steps of:

(a) removing substantially all interstitial water from the slurry; and

(b) thereafter removing a volume of adsorbed water from the resulting particle bed such that at the permanent storage temperature the particles will be unsaturated with respect to adsorbed water.

2. The method of Claim ₁, wherein the adsorbed water is removed by causing low humidity air to flow through the particle bed.

3. A method of dewatering a slurry containing radioactive particles, comprising the steps of:

(a) removing substantially all free standing water from the slurry;

(b) thereafter causing air to pass uniformly through the resulting particle bed;

(c) thereafter separating water from the air; and

(d) dehumidifying the air from the step (c) and circulating the dehumidified air through the particle bed in accordance with steps (b) and (c) until a volume of adsorbed water is removed from the particle bed such that at the permanent storage temperature the particles will be unsaturated with respect to adsorbed water.

4. The method of Claim 3, wherein the volume of adsorbed water removed from the particle bed is monitored by measuring the separated water of step (c).

5. The method of Claim 3, wherein the volume of adsorbed water removed from the particle bed is monitored by measuring the relative humidity of the air between steps (b) and (c).

6. A method of dewatering a slurry containing radioactive particles, comprising the steps of:

(a) providing a disposable container with a top region and a bottom region, the container including a vapor collector means selectively disposed within the container bottom region;

(b) adding to the container a volume of the slurry sufficient to overlie the vapor collector means;

(c) passing air through the slurry, the air entering the container top region and passing through the slurry and into the vapor collector means before being exhausted from the container; and

(d) continuing to pass air through the slurry until a volume of adsorbed water is removed from the particles such that at the permanent storage temperature the particles will be unsaturated with respect to adsorbed water.

7. The method of Claim 6, wherein the endpoint in step (d) correlates with a dewatering endpoint curve of FIGURE 2₁.

8. The method of Claim 1, 3 or 6, wherein the radioactive particles comprise liquid treatment media.

9. The method of Claim 1, 3 or 6, wherein the slurry containing radioactive particles comprises bead type ion exchange resins, powdered type ion exchange resins, or combinations thereof.

10. The method of Claim 1, 3 or 6, wherein the slurry containing radioactive particles comprises one or more of the following: filter aid materials, carbon particles, inorganic zeolites, filter sand, anthracite particles, and sludges.

11. An apparatus for dewatering a slurry containg radioactive particles, comprising:

means for causing air to pass uniformly through the slurry; means for thereafter separating water from the humidified air; and

means for thereafter dehumidifying the air and circulating the dehumidified air through the slurry.

12. The apparatus of Claim 11, further comprising means for monitoring the relative humidity of the air that has passed through the slurry.

13. An apparatus for dewatering a slurry containing radioactive particles, comprising:

a disposable container with a top region and a bottom region;

an influent port means for introducing the slurry into the container bottom region;

an air inlet means for introducing air into the container top region;

a vapor collector means selectively disposed in the container bottom region, for receiving interstial water and also humidifed air that has passed from the container top region through the slurry; and

a vapor outlet means, connected to the vapor collector means, for removing the water and the humidified air from the container.

14. The apparatus of Claim 13, wherein the vapor collector means comprises at least one manifold disposed in planar array, the manifold being provided with orifices in spaced array, and the orifices being covered by filter means to prevent entry of particles into the manifold.

15. The apparatus of Claim 13, wherein one manifold is disposed on the floor of the disposable container.

16. The apparatus of Claim 15, wherein the floor is flat

17. The apparatus of Claim ₁₄, wherein the disposable container is provided with a flow interrupter.

₁8. The apparatus of Claim 1₄, wherein a plurality of manifolds are disposed in spaced horizontal tiers above the floor of the container.

19. The apparatus of Claim 13, wherein the vapor collector means performs within the operating region bounded by the coordinates A-B-C-D in FIGURE ₁6.

20. A method of dewatering a slurry containing radioactive particles, comprising the steps of:

(a) bringing the slurry to the permanent storage temperatures or below; and

(b) thereafter removing substantially all interstitial water from the slurry.