JPH01292295A - Method and apparatus for reducing diffusion of gas through construction - Google Patents

Abstract

PURPOSE: To suppress dispersion of radon gas by applying a coating to the surface of a structure and forming a continuous shell of a coating. CONSTITUTION: A concrete floor 12 and a concrete wall 14 form the surface of a chamber 10. Frame members 16, 18 are bonded to the floor and wall and then a coating 20 is applied to the members 16, 18. A wood panel or a plaster board, generally referred to a dry wall, is employed as the coating 20. A shell 22 covers the, concrete floor 12 and coating 20 entirely. The shell 22 is formed by spraying the coating 20 onto the surface. Preferably, the coating 20 is rigid polyurethane having rigid independent bubble structure. This structure holds radon gas entirely and suppresses dispersion thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method and apparatus for reducing the diffusion of radon gas and radioactive decay products through structures, and more particularly to This invention relates to a technique for preventing the diffusion of radon gas and radioactive decay products by applying foam to the surface of objects to form a continuous shell.

BACKGROUND OF THE INVENTION For environmental, health, and safety reasons, it is desirable to prevent the diffusion of gases through structures.

Radon gas, widely discussed and studied, is found in the soil surrounding the foundations of houses and in residue storage silos or disposal pits of uranium processing facilities.

Storage silos are man-made units, which will be discussed in more detail later. A waste bit is usually an opening in the ground, often in the form of tailings from which uranium ore has been extracted. The waste is pumped back to the tailings and a clay or concrete cap approximately 1.64 m (5 ft) thick is placed over the top of the opening.

From a health and safety standpoint, it is important to prevent radon from spreading into homes.

Those skilled in the art recognize that exposure to radon above a certain level puts a person at risk for lung cancer.

In industrial facilities, it is important to reduce the diffusion of radon into the atmosphere from residual storage silos or waste bits. Radon in the air spreads out and decays within several kilometers around the silo or bit. Because radon is diffused in this way, radon above background or natural radon levels cannot be detected. It is not possible to determine whether the measured radon levels are due to storage facility residue or natural radon. There are environmental, health and safety concerns as people living within several kilometers of a silo or pit may be exposed to high levels of radon.

BACKGROUND OF THE INVENTION The traditional method of preventing the diffusion of radon from storage silos into the atmosphere has been to shield the silos with clay or similar materials or concrete. However, the thickness of the clay or concrete layer required to prevent radon diffusion is often greater than about 1.5 meters (several feet), which is not economically viable. Furthermore,
The use of clay or concrete requires that the silo structure be made smaller than desired from a structural point of view in forming the clay or concrete layer. If a larger silo is desired, a support structure is required to prevent the silo from collapsing under the weight of the additional clay or concrete layer. Due to the thickness of the clay or concrete layer, which reduces the diffusion of radon gas, it is not possible to form a continuous clay or concrete shell on the surface of the silo. Cracks or voids in the clay or concrete layer reduce the effectiveness of reducing radon gas diffusion.

If it is desired to prevent radon gas from entering the foundations of a house or similar structure, it is not practicable or economically preferable to cover the walls and floor areas with a further layer of concrete or clay. do not have. The use of clay or concrete for the walls and floors of the foundation significantly reduces the available living space. It is not economically possible to excavate around the foundation of a house or building to provide a thick layer of concrete or clay between the ground and the foundation. Also, it is not possible to pour concrete or clay below the supporting concrete slab of the foundation without causing structural damage to the concrete slab or the structure.

Problems to be Solved by the Invention Accordingly, it is an object of the present invention to coat the surfaces of silos or structures to prevent the diffusion of radon gas through these structures. Another object of the invention is that the resulting shell is cost-effective, fills all voids and cracks on the surface, and provides a continuous shell that covers the surface of the building. The object is to provide an outer shell that can be easily formed on the surface.

SUMMARY OF THE INVENTION The present invention provides a method and apparatus for reducing the spread of radon gas and radioactive decay products through a building. A coating is applied to the surface of the building, forming a continuous shell of coating on the surface. This shell retains almost all the gas within the shell, reducing the diffusion of gas through the structure. Preferably, the shell is comprised of a rigid polyurethane foam with closed cells.

Effects The present invention has the advantage that the coating is easy to form, fills all cracks and voids in the surface to form a continuous shell, and is cost effective.

DESCRIPTION OF THE PREFERRED EMBODIMENTS It is believed that the present invention will be readily understood from the following description of preferred embodiments, shown by way of example in the accompanying drawings.

FIG. 1 shows a cross section of a portion of chamber 10. As shown in FIG.

A concrete floor 12 and concrete walls 14 form the surfaces of the chamber 10. As will be apparent to those skilled in the art, concrete floor 12 and concrete walls 14 may be constructed from brick and mortar or similar structural materials. Frame members 16 and 18, typically made of wood or metal, are secured to concrete wall 14 and concrete floor 18, respectively, using various fasteners such as nails, screws, bolts, etc. After the framework members are secured to the floor and walls, the coating 20 is applied to the framework members 16 and 18.
It can be attached to. The covering 20 can be a wooden panel or gypsum board, commonly referred to as drywall.

Drywall can also be painted or wallpapered to create a more livable atmosphere. As will be clear to those skilled in the art, the foundation of the house can be a so-called unfinished basement, consisting only of concrete walls 14 and a concrete floor 12. A shell 22 covers the entire concrete floor 12 and sheathing 20. It will be appreciated that in the absence of framework members 16 and 18 and sheathing 20, shell 22 may cover concrete walls 14 and concrete floor 12.

To form the shell, a coating forming i22 is sprayed onto the surface. Preferably, the coating is a rigid polyurethane foam with a rigid closed cell structure. Foamed materials are self-adhesive and have excellent insulating properties. Cracks and voids on the surface are filled by spraying the foam material.

Prior to forming the shell 22, the surface to be coated may be cleaned to remove dust and loose particles. If dust and loose particles are not removed, imperfections will remain in the formed shell 22 and the continuity of the shell will be compromised. Such imperfections prevent continuous shell formation, requiring either cutting and repair of the imperfections or stripping the shell and recoating the surface.

As those skilled in the art know, polyurethane foams are two-component coatings. As will be apparent to those skilled in the art, the equipment necessary to apply two-component coatings is commercially available from several manufacturers. One such manufacturer is Foam Enterprises Research of Minneapolis, Minnesota.
e5arch).

The two components that make up the coating typically consist of a polyol and a diisocyanate, which are pumped from their respective containers through flexible hoses to a spray gun. Both components are mixed in a spray gun and sprayed using an agent onto the surface to be coated. A preferred spraying agent is a fluorocarbon such as trichloromonofluoromethane. The operator applying the coating can control the thickness of the coating by adjusting the flow rate of the components and the distance between the spray gun and the surface to be coated. Both components begin to react when mixed, but the coating reaches the surface before foam formation. The foam formed is rigid and structurally stable. A continuous shell can be formed by spraying both components.

A shell can also be formed by injecting both components onto the surface to be coated. First, both components are mixed together with a spraying agent and then poured onto the surface to be coated, thereby forming a continuous shell.

As shown in FIG. 1, the shell 22 is continuous and the covering 20
There is also no joint in the contact area between the floor 12 and the floor 12. The density of the foam is preferably 40 to 56 kg/cm' (2.5 to 3.5 bonds/cubic foot) by adjusting the flow rate of the zero component and spraying by adjusting the pressure of the agent. The density of the foam can be controlled.

If it is not desirable to cover the sheathing 20 with foam for aesthetic reasons, foam may be applied to the space between the wall 14 and the sheathing 20, which are joined by the framework members 16 and 18. can. The operator creates a hole through the coating 20, being careful not to make a hole in the framework member 16 or 18. The above-mentioned spraying method is used,
The nozzle of the spray gun is inserted into the hole to spray the coating onto the inner surface of the wall 14. Although most of the inner surface of the wall 14 is covered, the areas of the wall 14 where the framework members 16 and 18 abut are not covered with foam. The floor 12 is applied separately from the inner surface of the wall 14. The coating can also be applied by first mixing the image components and injecting the coating-forming substance through the holes. When the coating reacts to form a foam, the foam expands to fill the space. Blowing through the holes or injection does not form a continuous shell, and as a result, the reduction in radon gas is reduced when compared to a continuous shell applied directly to the coating 20 and floor 12, i.e. shell 22. It will be somewhat incomplete.

A preferred polyurethane foam is sold by Form Enterprises Research, Minneapolis, Minn., under the trade designation MG2-B. MG2-B
isocyanate polyester and polyester
It is a triol-based material. The resulting polyurethane foam has a rigid, closed cell structure. The advantages of using foam with closed cells are compression resistance, good adhesion and thermal insulation (low heat transfer coefficient). Because closed-cell foam is resistant to compression, it is possible to walk directly over the foam floor without damaging the foam. If desired, a floor covering, such as tile or carpet, can be applied over the exposed foam surface to provide an aesthetically pleasing walking surface. Additionally, wall coverings such as wallpaper or panels can be applied directly onto the foam covering the wall. When a painted surface is desired, it is necessary to provide a base coat with a smooth surface on top of the foam surface to obtain a smooth surface suitable for painting.

The closed cell structure works to reduce the diffusion of radon gas. Radon diffuses through walls, floors and other parts of the structure. When it comes into contact with the foam, the radon diffuses into the closed cells of the foam. It enters the foam, further diffuses □, and enters and exits the closed cells of the foam. As described below, the bulk diffusion rate coefficient of the foam
oefficient) is small, it takes a long time for gas to diffuse from one bubble to another. Because of the long diffusion time, radon decays to harmless products before it can enter or exit a particular structure through the foam barrier. Radon, which has a half-life of about 3.82 days, decays into solid particles of PB210,
pb210 further decays to lead element (pb).

The mechanism of decay of radon to elemental lead will be obvious to those skilled in the art. The size of the solid particles is at the molecular level and will not clog the cells of the foam.

Although the above discussion refers to reducing the diffusion of radon through the floors and walls of the foundation of a house, the same applies to storage silos or waste pits that house residues from uranium ore processing facilities. I can say it. It is clear to those skilled in the art that the foam thickness required in a storage silo or waste pit is greater because the level of radon is much higher in the storage silo or waste pit than in the ground surrounding the house. It's obvious.

As mentioned above, silos or waste pits can be used to store waste residues. Storage silos are generally cylindrical in shape and made of steel-reinforced concrete.
It also has a dome-shaped cover of concrete family reinforced with steel. A typical example of a silo is 24.4m in diameter.
(80 feet) and approximately 8.3 meters (27 feet) high. The cylindrical part of the silo is usually surrounded by an earthen embankment, with a concrete dome exposed above the ground. Generally, silos are designed to be filled with metal oxide slurry containing radioactive residues.

The residue settles to the bottom of the silo and the water is drained off as supernatant and reused for the preparation of the next slurry.

Because the silo's dome is above the earth's surface, the dome is weathered by the sun, wind, rain, and other weather phenomena.

Concrete domes are susceptible to weathering, cracking, and other damage. If the dome were to crack or become damaged, large amounts of radioactive gas could be released into the atmosphere.

Therefore, the use of foam sprayed onto the inner surface of the dome has the effect of reducing gas diffusion even if the dome cracks. Even if the dome is completely destroyed, the foam is strong enough to maintain the integrity of the silo until emergency response crews arrive to seal and contain the radioactive residue and repair the silo in a timely manner. let

The foam coating of the inner surface of the dome is carried out in a manner similar to that described above for the coating of the floor and walls of the base. The foam component is conveyed from the loading tanker via a split feeder to the distribution vehicle.

The distribution vehicle has equipment used to control the flow of the same components. A flexible Φ hose is connected to the distribution car and conveys the foam component from the distribution car to the portable spray gun. The dome of the silo can be inserted into the overflow manhole to access the inner surface of the dome. The foam components are mixed with a spray gun and a spraying agent is used to spray the foam into the interior of the silo. The spray gun allows the operator to control the direction of foam flow.

Theoretical calculations were performed as to whether the use of foam could reduce the diffusion of radon through the dome of a silo. Those skilled in the art will understand that similar calculations apply to the walls and floors of the house described above. Calculations were performed for a silo without a coating and for a silo with a foam coating.

The following equation was used to calculate the radon flux from a bare ore waste source (for unclad silos).

J0 = 1 x 10'[Ra]pE(tDo/P
a)'' (1) Equation (1) is based on the U.S. Nuclear Regulatory Commission (υn1ted 5tates Nuclear Re
“ by gulatory (:ommission)
Final Generic Environment
al Impact Statement
NIJREG-070 of “nium Milling”
6, Volume 1II, Appendix D (September 1980) Formula (1
6) applies.

In formula (1), [Ra1=concentration of radium-226 in the ore waste solid (, C
+/g) P = Density of ore waste solid (g/cm') E = Energy emitted from mineral waste (dimensionless) D, = Effective bulk diffusion coefficient of radon in mineral layer (cm'
/5ec) p0 = Porosity or porosity in mineral waste solid (dimensionless) t = Radon 222 (7) decay constant (sec-') Formula (1
) Before finding the inner diameter, /P, and t, the diffusion distance of the mineral layer must be known. Diffusion distance is defined by the following equation.

t, -[Do/Pot 10. s
(2) Equation (2) is expressed by T. H. Borac (T, H.

The formula is taken from the report "Calculation of Radon Emission, Diffusion, and Dosimetry from 165 Storage Tanks in Feed Materials Manufacturing Centers" by David Borak (Fernald, Ohio, October 1985). . Also, from Bolak's report, [Ral, p.
, E'2, and the following values were taken.

[Ra] = 2'x 10' pci/gP = L
, S g/cm' E = 0.2 L = 150 cm The decay constant t of Radon-222 can be known from several documents well known to those skilled in the art, and its value is 2.1 x 10-'
(sec-”).

If t is known, Do/Pa and furthermore Jo can be determined by the following formula.

L = [D, /Pot]'・8(2)D, /P0=
L't (31=4.7
If 3x 1 0-2 cm'/5ecO0/P is known, Jo can be calculated from equation (1).

Jox2. Ox 10 'pci/m'sec Since the radon flux Jo of the bare mineral debris source has been calculated and is now a known quantity, the radon flux J from the surface after being reduced by the foam coating can be calculated using equation (4). It can be found using

' J, +JofExp(-b'zI)
(4) Equation (4) is defined in NUREG-0706 as follows.

f=2/[(1+z)+(1-z)Exp(-2b+x
+)) (5)z = po/p+ [(Do/Po
)/ (D+/P+)]” ' (6) bI= (t
P+/D+)'・5(7)×1-thickness of coating material (cm
) P, = porosity of the coating material (dimensionless) DI = effective bulk diffusion coefficient of radon in the foam (
m''/5ec) From various documents known to those skilled in the art, Pl and Dl are given by the following equations.

P, = 0.95 D, = I x 10-7 cm''/secχ1 is 300 cm from Borak's paper.

P, , D, and t (as described above) are expressed by equations (5) to (7)
By substituting into , bl and f can be calculated as follows.

b+=1.42cm-' f=0.029 Once b, , f and χ are determined, Jl can be calculated from equation (4).

J1=0 Therefore, based on the above assumptions, no diffusion of radon through the foam will occur.

The overall structure of the dome makes it possible to keep the height of the foam to 61 cm. If J in a certain area on the dome is calculated as χ+=61 cm, it will be as follows.

b+ = 1.42cm-' Exp(-b, x,)! 2.68x 1 0-”E
Since xp(-b+x+) is approximately zero, the thickness is 61
cm of foam essentially reduces the diffusion of radon gas from the silo.

The above statement is a theoretical way to know if foam reduces the diffusion of radon through a silo. To confirm the above theoretical calculations, a laboratory-scale experiment was conducted to find out the effect of polyurethane foam on reducing radon gas diffusion. Varying amounts of radium-containing residue were added and then the charcoal container was placed on top of the foam-filled container.

The effectiveness of the foam in reducing radon gas diffusion was determined by comparing the activity of a charcoal container exposed to a radium-containing residue with and without the foam between the residue and the charcoal container. . Two experimental tests were conducted.

In the first test, 26g of each radium residue was
, 36 g, 40 g and 45 g were used in 150 mft plastic containers. Radium residue, Department of E, Fernald, Ohio
energy's feed materials
Taken from an actual silo sample from the early 1970's at Production Center. The foam material used in the experiment was similar to the closed cell polyurethane proposed in the present invention and was obtained from a hardware store. A charcoal container was taped to the open end of each sample container to determine a baseline of expected activity of radon daughter nuclides absorbed in the charcoal container. The charcoal container used was approximately 7cm in diameter.
It is a container with a height of 2.54 cm.

The charcoal container was secured to the residue container with tape, with the opening of the charcoal container facing toward the residue. Approximately 3.
A gap of 81 cm was left. After 24 hours of exposure to the residue, the charcoal container was removed and a Ludrem rate meter (
Beta/gamma activity was counted using a Ludlem rate meter and a pancake probe. In addition, a control container was kept exposed to the laboratory atmosphere to determine whether radon was present in its natural state. The sample container was then injected with polyurethane foam material and a new charcoal container was taped to the sample container before the foam cured. The exposure time to the residue was varied, and the charcoal container exposed for a predetermined time was removed and the beta/gamma activity was counted. Six sample numbers 1 to 4 whose test results are shown in Table 1 below correspond to residue weights of 26 g, 36 g, 40 g, and 45 g, respectively. In the foam column, r'jesJ indicates that a foam is present in the sample container, and "nO" indicates that only air exists between the charcoal container and the charcoal container. The exposure time (hours) of the charcoal container is noted for each test. The last column of Table 1 shows the counts per minute (CPM) of beta/gamma emissions above the background value measured immediately after removing the charcoal container from the sample container. The charcoal container was a fraction of the initial count, indicating that the activity was due to radon daughter nuclides and not contaminants from long-lived lingering.

(Left below) Table 1 Two 1400m1 containers each containing 100g of residual pickle.
A second test was conducted using a glass container with 300 ml of water. Following the same procedure as above, we first counted the radon gas absorption of the charcoal containers without the foam. However, there are some differences between the first and second tests. After the charcoal container was first exposed to 100 g of sample residue, the sample was injected with foam and the foam was allowed to cure before attaching a new charcoal container to the sample container. The reason for curing the foam before placing the charcoal container over the sample container is that activated carbon has a particular affinity for the organic vapors released from the foam during curing, and prior to the absorption of radon gas at the beginning of the first test. The problem is that the foam becomes almost saturated. Additionally, an air space remains between the top of the foam and the charcoal container.

The results of the second test are shown in Table 2. Both sample numbers 5 and 6 were placed in a 1400 m J2 capacity glass container.
00 grams of residue.

The first test with no foam present in the container is indicated by a "NO" in the foam column of Table 2. The exposure times for Sample Nos. 5 and 6 are the same for each case with and without foam. The last column is the counts per minute (CPM) as in Table 1.

(Left below) People - Once we have the data shown in Tables 1 and 2, in any case,
It can be seen that adding foam between the residue and the charcoal container reduces the diffusion of radon gas into the charcoal container. Samples 1.2 and 4 of Table 1 demonstrate the adsorption of radon gas on charcoal in the presence of foam. However, it was concluded that the activity in these samples was due to leakage of radon gas around the foam or through the cracks and not to diffusion through the foam. The reason for this conclusion is that the thickness of the foam present on top of the residue in the test ranged from 2.5 cm to 3.8 cm, which was the minimum thickness for a seal for a 150 mA container. Therefore, it is presumed that a reliable seal could not be obtained with Samples 1.2 and 4.

In the second test, the dimensions of the container were increased and the thickness of the foam was increased. The weight of the residue also increased, increasing the radon flux from the residue. According to the results of the second test,
No diffusion of radon gas was observed through the foam's average thickness of 5.6 cm. In the second test, a glass container was used to visually observe the condition of the foam seal; It was in good condition.

Experimental results show that properly sealed closed cell polyurethane foam completely reduces radon gas diffusion. The critical factor the data indicates appears to be the integrity of the foam seal over the radon production residue. However, good reductions are also observed when no global hermetic sealing is performed.

Radon diffusion coefficients were measured for four types of polyurethane materials by Rogers and Associates Engineering Corporation, Salt Lake City, Utah.
Engineering Corporation;
The reduction ability of each of the foams manufactured by RAE (hereinafter abbreviated as RAE) was independently confirmed.

Foam Enterprises Re5ea, Hyuston, Texas, using sample holders supplied by RAE.
Samples were prepared in the R.C.R.C. facility and returned to the RAE. The sample holder has a length of approximately 15-20 cm and a diameter of 2.5 cm.
cm polyvinyl chloride (PVC) tube.

A stopper made of the foam to be tested and having a thickness of 10 cm was placed in the center of the tube, dividing the tube into two sections with the stopper separating each section. The tube was placed in a radon diffusion chamber. A radon source was placed in one section of the tube and a radon detection device was placed in the opposite section. tlrani, which counts radioactivity over time and was issued by the U.S. Energy Administration in May 1986.
um Mill Tailing Remedial A
ction Project DOE/UMTRA-0
50425 “Technical Approach
Diffusion coefficients were measured according to the procedure described in the ``Document''. The above RAE was determined according to Federal Regulation No.
0, Part 1 et seq.
tion agency laboratory). The diffusion coefficient measurement results are shown in Table 3 below.

The foams listed in Table 3 above are available from Foam Enterprises Research under the trade designations listed in the table.

Using the measured diffusion coefficients, residual control values, and coating composition and thickness, V.C. Rogers, K.K. "7-, IL
“Kalkwarf (V, C, Rogers, Ni, Ni, N1
RAECO is a computer program outlined in "Radon Reduction Handbook in Uranium Mine Residual Coating Design J" by D. Elson and D. R. Kalkwarf, NtlREG/CR-3533.
Radon reduction and surface flux were calculated using M. The source data used is listed below.

The composition of the coating and the surface flux calculated by RAECOM are shown in Table 4 below.

The use of foam (void filling) to reduce the diffusion of radon gas is believed to be a viable alternative over water absorption, solid medium absorption and temperature control. The following assumptions were adopted to develop the alternative method described above.

*Annual amount of radon-222 diffused through the dome *Annual release of radon-222 due to expansion of the gas inside the dome *The impossibility of holding the dome at a pressure significantly higher or significantly lower than atmospheric pressure* Similar to atmospheric temperature fluctuations, the temperature of the silo gas phase will also fluctuate; the need for an interim (3-5 year) solution to control radon emissions until a final proposal is developed and implemented; The dome is structurally weakened by environmental factors and has limited ability to support additional loads. *Methods employed to reduce radon emissions must be removed when the final proposal is directed. What not to do Many applications employ water column absorption to control the release of gaseous pollutants, where the effluent gases come into contact with water and are absorbed by the water. Successful water column absorption depends on the solubility of radon gas in water compared to other gases present. In fact, it is estimated that the solubility of radon gas in water is high enough to allow controlled release from silos. Water column systems have relief lines that lead into a constantly moving water column. Replenishment of the water column is necessary to prevent the water from becoming saturated with gases.

The radon must then be kept in the tank until its activity has decayed to an acceptable level. next,
The degassed water is returned to the water column to absorb the corn gases from the silo. Critical factors for the design of this system are the efficiency of radon gas absorption in the water, the amount of water required, the flow rate, the need for shielding, and the need for wastewater treatment. The use and construction of the equipment necessary for water column absorption is well known to those skilled in the art.

Solid media absorption has been used as an effective separation method to preferentially remove gaseous components from flowing streams. The system has a filter and blower unit that draws gas from the silo manhole through a relief line, the gas is refluxed through activated carbon, and the radon gas is adsorbed on the activated carbon.

The remaining gases are returned to the other side of the silo dome,
A closed system is completed. If another activated carbon bed is installed in parallel and the activated carbon bed is found to be saturated after sampling and measuring the downstream gas, a valve is actuated to separate the saturated activated carbon bed and replace it with a new activated carbon bed. Reflux the gas. Important factors to consider in the design of this type of system are the absorption efficiency of the activated carbon bed, the total absorption capacity of a given activated carbon bed until saturation, the required flow rate, and the required shielding. The use and construction of the equipment necessary for solid medium absorption is well known to those skilled in the art.

The method of coating the inner surface of the dome with foam has been described in detail above. Filling the void above the residue in the silo with a rigid polyurethane foam material helps remove radon gas from existing storage vessels where radon gas has accumulated above the residue. Additionally, the foam material acts as a barrier to diffusion, trapping radon gas from the residue, holding it until it collapses into corresponding particulate daughter species, and preventing radon gas from escaping into the surrounding environment. has. To fill the voids in the silo, foam material can be pumped into the silo through four manholes located on the silo dome. The process of replacing the radon gas present before the process with a void filling system may - in some cases, utilize a water column absorption system or a solid media absorption system.

The most critical design issues with void-filling systems are the structural impact of the foam, the compatibility of the foam with residue, and the sealing effectiveness of the foam material.

A temperature control system installed in the silo maintains the gas within the silo at a constant temperature and controls the escape of radon gas due to temperature rise and expansion of the gas due to temperature rise. The system may also include a filter and blower unit that sucks the gas through one of the silo's manholes and circulates the gas through a cooling unit that cools the silo and holds the silo at a near constant temperature before returning the gas to the silo. good. Thermostatic control of the cooling unit may also be tailored to seasonal variations in temperature to avoid excessive cooling. The most critical design requirements for this system are flow rate and cooling unit capacity. The use and construction of the equipment necessary for temperature control is well known to those skilled in the art. The above four types of radon release control methods were evaluated in light of the following criteria:
They were ranked numerically from 1 (lowest level of satisfaction) to 5 (highest level of satisfaction).

(Hereafter, extra white) The ranking results are shown in Table 5 below.

Alternative method EA R10ET $ Total The criteria for each ranking and the validity of the ranking will be explained below.

The environmental acceptability of the alternative method was determined by evaluating its ability to reduce radon emissions with minimal impact on the surrounding environment. Factors such as expected treatment efficiency and waste generation from the treatment system were taken into account. The ultimate goal of operating a radon emission control system is dissipation modeling (dispersion modeling).
The goal is to reduce the radiation exposure of residents closest to the treatment plant to 25 millirem or less (whole body) and 75 millirem or less (vital organs), as measured by ion modeling. The above exposure limits are set forth in Title 40 of the Code of Federal Regulations (CFR) Bart 191 (40 CFR 191). Although the releases do not meet the definition of transuranium or high-level waste as set forth in 40 CFR 191, the goal is to keep the releases within the exposure standards described above.

Referring to Figure 5, it can be generally said that alternative method 1.2
and 3 are equivalent in terms of environmental acceptability. Because Alternatives 1.2 and 3 reduce radon diffusion and thermal release, these alternatives are believed to have the effect of reducing radon emissions to less than 25/75 mRem. Temperature control systems are given a lower rating than other alternatives because temperature control systems do not reduce the concentration of radon gas inside the silo dome and therefore do not reduce radon emissions by diffusion. Although the void filling method may increase the volume of waste that must be disposed of in the future, it is more environmentally acceptable due to the additional benefit of structural reinforcement of the dome.

Alternative reliability/workability was evaluated by estimating how well the system would perform given a three to five year period and estimating maintenance and operational requirements. The selection of a three to five year period takes into account the time required before the final remediation process is designed and implemented. The most reliable/workable alternative was determined to be a void fill system. Although temporary radon treatment is required before performing void filling, over a 3- to 5-year period, this passive alternative is more reliable and workable than other 3 fl alternatives. It was concluded that the quality was substantially high.

The other three alternatives were ranked similarly lower than the void fill system, and each of these three alternatives is expected to require significant maintenance to remain reliable. Ta. Implementation time was evaluated by estimating the time required to design, construct, and operate each alternative system as a radon emission control system. Alternatives 2.3 and 4 are equivalent rankings in terms of fulfillment time, are relatively simple, and considering the technology available for these three types of systems,
It was estimated to be June 1st. The water column absorption method has a long estimated design time (1
2), so it is ranked lower than the other three alternative methods.

The price of the alternative method is evaluated by estimating how many times the estimated total cost of the alternative method is compared to the method of the present invention.

In terms of total cost, all alternatives are considered approximately equivalent. The void filling method is different from the other 3f! due to the cost of the filler material and the cost that would be required to remove the filler material.
It is estimated that the cost is higher than that of alternative method 1.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a shell attached to the wall and floor of a building in accordance with one embodiment of the invention. 10...Room 12...Concrete floor 14...Concrete wall 16.18...Frame member 20...Coating 22...Shell (polyurethane foam) FI01

Claims (8)

[Claims] (1) A method for reducing the diffusion of radon gas and radioactive decay products through a structure, the method comprising: applying a coating to the surface of the structure to form a continuous shell of the coating on the surface; A method wherein the shell reduces diffusion of radon gas through the structure by retaining substantially all of the radon gas. 2. The method of claim 1, wherein said continuous shell is formed from a rigid polyurethane foam, said foam having a closed cell structure. 3. A method according to claim 2, characterized in that the continuous shell formed from polyurethane foam has a density of 40 to 50 kg/m^3. (4) The bulk diffusion rate coefficient of the foam is 1×10^-
The method according to claim 2, characterized in that the rate is ^4 to 1 x 10^-^7 cm^2/sec. (5) A device for reducing the diffusion of radon gas and radioactive decay products through a structure, the device having a shell formed by applying a continuous coating to the surface of the structure, wherein substantially all of the radon gas is absorbed by the shell. A device characterized in that it is configured to be held inside. 6. The device of claim 5, wherein said covering is comprised of a rigid polyurethane foam, said foam having a closed cell structure. (7) The density of the polyurethane foam is 40 to 50K.
6. The device according to claim 6, characterized in that the g/m^3. (8) The bulk diffusion rate coefficient of the foam is 1×10^-
6. The device according to claim 6, characterized in that the rate is ^4 to 1 x 10^-^7 cm^2/sec.