DE1220048B - Process for transferring radioactive substances into a permanent form that can be stored and transported - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Int. CL:

G21f

German class: 21g-21/33

Number: 1220 048

File number: L 37326 VIII c / 21 g

Filing date: October 21, 1960

Opening day: June 30, 1966

The invention relates to a method for transferring radioactive substances which are in a solution contained as components that can be separated out by filters or converted into a filterable form in a storable and transportable permanent form. The procedure is primarily used for treatment of radioactive waste. It will also use this method in concentration suggested by radioactive isotopes. In a further embodiment of the invention, a indicated advantageous device for performing this method.

Various nuclear chemistry processes result in radioactive waste precipitated in solutions, which are removed from these liquids and put into the most compact possible transport or storage form should be transferred. Concentrating and filtering out the radioactive components offers in in practice considerable difficulties.

The disposal of radioactive waste is one of the most urgent tasks and they are different Suggestions for their solution have been made. For example, there is a procedure in German Auslegeschrift 1 053 686 has been described for rendering radioactive isotope waste harmless, which is caused by the Use of powdered substances with high radiation absorption capacity as recording material for the finely divided isotope substances is marked. These powdered substances are said to be the radioactive liquids or they are intended to be used to filter liquids. However, it is in the Within the scope of this invention, no way is shown how the liquid in which the radioactive substances are dissolved can be removed from the substances used for suction from the filter residue. Since the Radioactive waste disposal particularly depends on the weight and / or volume of the To reduce waste, it is a serious disadvantage if the liquid in which the radioactive substances are present suspended cannot be completely eliminated.

A method is also known (German Auslegeschrift 1088 624) for converting radioactive waste, which is contained in a solution as components that can be separated by filters, into a permanent form that can be stored and transported (column 4, lines 10 to 18). In this process, the medium containing the waste is passed through filter elements in which the waste is retained and brought into a dry form by drying at temperatures above freezing point (column 3, lines 55, method for transferring radioactive substances
Materials in a storable and transportable
Permanent form

Applicant:

Leybold high vacuum systems G. m. B. H.,

Cologne-Bayenthal, Bonner Str. 504

Named as inventor:

Dr. rer. nat. Georg-Wilhelm Oetjen,

Cologne-Marienburg;

Dipl.-Ing. Wilhelm Nerge, Rodenkirchen;

Hanns Eilenberg, Rösrath;

Friedrich Fauser, Cologne-Mülheim;

Dr. med. Karl-Heinz Neumann, Wilhelmshaven

to 56) and, if necessary mixed with non-readioactive additives, in the transport and storage containers can be introduced (column 4, lines 10 to 18). It is essential that at this method involves drying by heating (column 3, line 15) in conjunction with a vacuum is carried out. The main disadvantage of this process is that due to the effect of temperature highly radioactive and toxic substances escape in vapor or gas form. This will the real purpose of the treatment, namely the complete transfer of all radioactive substances Shares in a storable permanent form, not reached. Some of the radioactive contaminants remain in the solution thickened by evaporation and finally changes into the solid dry form. A The second part of volatile substances is expelled during the evaporation process and can can only be separated completely with difficulty even by downstream filters. This evaporating Share can consist of radioactive substances, which far exceed the permissible level of activity in the atmosphere let get.

In contrast, the use of the freeze-drying process takes a completely new approach. The technical progress lies above all in one compared to the evaporation process cheaper decontamination factor, d. This means that most of the radioactive substances remain in the Dry substance and are not as in the evaporation process in vapor form or as a gas from the

609 587/343

expelled liquid phase. During the process of freeze-drying, which consists of various Publications is known (Neumann, "Plan of Freeze Drying", 1952, and the magazines "Vacuum Technology", January 1955, p. 109, 115, 123, 130; »Chemistry-Engineer-Technology«, 1955, p. 5, and 1957, p. 267), so far mainly for the production of high quality products on the pharmaceutical Area as well as for certain foods, transfers this here claimed the application of freeze drying to a completely new field.

The invention shows a way, after the radioactive waste, which in a solution as by Filters separable components are contained, converted into a storable and transportable permanent form can be, wherein a liquid containing the radioactive substances is passed through filter elements in which these substances are retained. It must be seen as insignificant whether these components which can be separated off from the solution were produced by a chemical precipitation process, largely insoluble substances or possibly by lowering the temperature or in some other way achieved crystalline deposits in a solution of less radioactivity than these separable Components are. The characteristic of the invention is seen in the fact that the filter residue subjected to a freeze-drying process known per se, thereby producing a dry product which, possibly mixed with non-radioactive additives, into the transport or Storage container is introduced. The filter residue is thus used in a freeze drying process subject, which is usually shut off under a high vacuum in a correspondingly airtight and gas-tight Drying chamber can be carried out. Freeze-drying creates a mostly powdery one Dry product as a direct process product, so that a subsequent comminution, as in Melting or sintering processes generally do not appear to be necessary.

The freeze-drying product is easy to mix with non-radioactive additives and can for example be enclosed in a solid body by adding concrete.

According to a further development of the invention, the freeze-dried radioactive waste is mixed with an additive and subjects this, preferably after a pressing process, to form a Moldings a known melting or sintering process, whereby solids can be produced. Although the melting down or sintering of radioactive waste is to be regarded as known, it has been achieved the use of freeze-dried waste as the starting material is particularly advantageous Results.

Because the freeze-dried waste after completion of the freeze-drying process as a loose topping the filter elements are present and their removal as possible without transporting these filter elements or wants to carry out work processes that are difficult to control remotely, can be a further improvement can be achieved by removing the radioactive substances on the filter elements is replaced by a correspondingly directed gas and / or vapor flow, such a flow being preferred can be generated by venting the vacuum filter chamber. Man can also use the atmospheric pressure to be subjected to the filtering process Press the solution into the filter chamber.

5 Although the process details described are initially for the separation of radioactive waste have been given from solutions, it seems advantageous to follow this rule as well Carry out a concentration of radioactive isotopes, these substances first being in the form a filterable solution must be brought, in which the components remaining in the filter generally represents an enrichment of these isotopes. Here, too, are those on the filter elements deposited radioactive substances then a known freeze-drying process subjected and thereby brought into a dry form, which is a concentrate.

It may also be useful to remove the filter elements during the freeze drying process to use as insert vessels for the radioactive substances, the filter chamber through a connection pumping devices known per se for separating vaporous constituents, in particular of water vapor, can be designed directly as a freeze-drying chamber. the Pump devices can, for example, consist of a deep-freeze condenser with a connected one or multi-stage mechanical pump, optionally using Roots pumps be. Since the occurrence of radioactive gas and suspended matter must be expected, the Pumps do not release the extracted gases or vapors directly into the surrounding atmosphere, Rather, it is necessary to connect an absolute filter upstream.

An advantageous device for performing the method steps described can be designed in this way be that a plurality of filter elements are arranged in a filter chamber and that these filter elements can optionally come into contact with heating and / or cooling devices. Such Filter elements are designed, for example, as filter bags, which are placed side by side in pairs Heating and cooling grids are stretched. The heating is especially significant because it is there a rapid completion of the freeze-drying process is ensured. It has been found to be particularly beneficial proved to use a so-called "vacuum steam heating" in the heating device, which in a system shut off from the outside air, a vaporous heating medium, preferably Contains water vapor at a correspondingly low air partial pressure, so that the vapor temperature is about 50 to 80 ° C.

A major advantage of the new process when it is used to separate radioactive waste lies in the high decontamination factor that can be achieved. This can, however, improve this that one adds colloids or gels to the solution to be separated before the filtering process to which the substances to be separated preferentially accumulate. Such an addition also appears in the Isotope concentration advantageous.

The drawing shows the layout of a complete system with the features of Invention shown.

One recognizes a vacuum-tight lockable filter chamber 1 in which two filter bags 2 are each perforated Pipelines 3 are unclamped. These perforated pipes 3 are via a collecting line 23 connected to a storage container 12 for the filtered solution, in which with the help of a Vacuum pump 21 a corresponding negative pressure, which is used to carry out the vacuum filter process sufficient can be generated. The output of the vacuum pump 21 goes through an absolute filter 22 into the surrounding atmosphere. Inside the filter bags 2 there are also tubular heating and cooling tubes 4, S. So that the vacuum-tight lockable filter chamber 1 according to the features of the invention used as a freeze-drying chamber for carrying out a known freeze-drying process can be, are fed to this by a compression refrigeration unit 24 deep-freeze condenser 6 and a multi-stage mechanical vacuum pump 7 connected. The with the help of these aggregates extracted gases and vapors are in the deep-freeze condenser 6 of their vaporous components largely freed, with the condensate of the deep-freeze condenser 6 under corresponding Precautions must be collected in a lockable collection container, not shown. The from the multistage vacuum pump 7 pumped out gas portions pass before their outlet into the ambient atmosphere another absolute filter 8.

A ventilation valve 9 is also provided in the collecting line 23, with the aid of which the interior space the filter bags 2 can be ventilated. To avoid unwanted agglomeration of the powdery product collected in a funnel-shaped collecting space 10 of the filter chamber 1 mechanical or electromagnetic vibrating devices known per se can be provided, which at the same time a proper functioning of the closure member of a lockable removal opening 11 guarantee.

With a storage container 12 is designated, in which the resulting solution in the filter process through the vacuum generated by the mechanical vacuum pump 21 can be withdrawn. The feed the unfiltered solution takes place from a storage vessel 13 in the region of the lowest point of the filter chamber 1, in which a corresponding liquid level is established. That in the storage container 12 collected filtrate can optionally be returned to the storage vessel 13, so that a multiple filtering process can be carried out.

The heating tubes 4 are expediently designed as hollow condensation elements, those of a vacuum steam generator 14 steam can be supplied. This type of heating enables a Particularly even temperature distribution, as any temperature deviation along the heating pipes is immediate to an intensification or to the cessation of the condensation of the vacuum vapor and thus gives cause for the exchange of corresponding amounts of heat. The cooling tubes 5 are an evaporator Compression refrigeration unit 15 switched, an advantageous arrangement under certain circumstances so It can be constructed that this compression refrigeration unit 15 also includes the deep-freeze condenser 6 feeds.

With 16 a mechanical device is referred to, which from a further storage container 17 a Additive is supplied. A hydraulic press then follows in the course of the machining process

18, in which the mixture is compressed to form a corresponding compression molding. This molding goes into a melting or sintering furnace

19, in which it fused to form a homogeneous solid with preferably glass-like properties or is sintered together. The product of the melting or sintering process can be

ίο then in biologically shielded, lockable Use transport container 20 and can be transported in this form.

When carrying out the process, the starting solution to be filtered is first filled from the Storage vessel 13 in the filter chamber 1, so that a corresponding liquid level is reached, the can be maintained during the filtering process by refilling if necessary. The too separating solution washes the outer surfaces

ao of the filter bags 2 and is thereby pressed towards the interior of the filter, since one in the collecting line 23 a corresponding negative pressure is generated, the filter process being carried out as a conventional vacuum filtering can be. The filtrate enters the storage container 12, while the filtered substances precipitate as a surface layer on the outer surfaces of the filter bags 2. the Filter bags can advantageously consist of a plastic, for example vinyl.

After the filter process has been carried out until the outside of the filter bags 2 a sufficient layer thickness of the filtered substances was created, the filter chamber 1 is of the any unfiltered solution that was still present was emptied and returned to the storage vessel 13. Of the Pasty filter residue is now in the filter chamber 1 in a freeze-drying process to subjugate, and for this purpose the deep-freeze condenser 6 together with the multi-stage mechanisehen Vacuum pump 7 put into operation. There is a sublimation of the water in ice form, which is reflected in the freezer condenser 6. This results in a particularly favorable decontamination factor, because there is no temperature increase that drives out the volatile substances, such as in the evaporation process. During the freezing process, the heating and cooling tubes 4, 5 a corresponding influencing of the temperature of the goods to be dried, so that with optimal drying conditions, d. H. with the shortest drying time, can be worked.

After completion of the freezing process, the dry product is located as a loose surface layer on the outer surfaces of the filter bags 2 and is removed from them by venting the interior of the filter blown off with the aid of the ventilation valve 9 and falls into the funnel-shaped collecting space 10 of the Filter chamber 1. From there, the dry product is removed through the lockable removal opening 11, fed to the mixer 16 and mixed there with a non-active additive. It takes place the Forming a preform in the hydraulic press 18, which is then in the melting or sintering furnace 19 to a solid with z. B. Slas-like properties can be melted or sintered together.

If the working method is modified, the melting or sintering process is omitted and one uses

another, non-radioactive additive from the further storage container 17, the mixture can be brought into appropriate forms.

The system shown schematically in the drawing requires a practical implementation whole number of shut-off valves, with the help of which individual components for cleaning or repair purposes can be released from the overall system. These shut-off elements, which appropriate apart from the biological shielding, they are not shown in the drawing Disregarded for reasons of clarity. In general, two filter bags are used instead of the ones shown 2 use a larger number of such filter elements and possibly also a multi-stage one Select filter process.

The particular advantage of the new method in the concentration of isotopes is that any exposure to heat that could cause an impermissible increase in temperature is excluded can be. The use of heated grids does not conflict with this point of view, because the heat supplied to the filter material with their help is only that in the freeze-drying process Any evaporation cooling that occurs is compensated and thereby an undesirable temperature drop of the product to be dried, which would significantly increase the drying time. Man in such a concentration process, for example, a pre-concentrated solution can be assumed, in which by chemical or physical means the occurrence of nitridable components with higher radioactivity than the surrounding solution is made possible. The filtering process already described then follows, generally after reaching a certain layer thickness, ζ. B. 1.5 to 2 cm, the The filter process is canceled and the remaining contents of the filter elements are returned to the storage container. This is followed by a freeze-drying process of a known type, and the dry product can then be processed further as a concentrate of the corresponding isotope.

The new process is not limited exclusively to the use of aqueous solutions. It can rather, they are also used with other, in particular organic, starting solutions.

Claims (8)

Patent claims: 1. Process for the transfer of radioactive materials, preferably waste materials, which are in a solution as constituents which can be separated off by filters are present or can be precipitated into a storable and transportable permanent form in which the concentration of radioactive substances is compared the liquid is significantly increased, with a liquid containing the radioactive substances is passed through filter elements on which these substances are retained, thereby characterized in that the filter residue is a freeze-drying process known per se subject and thereby a Dry product is produced which, if necessary mixed with non-radioactive additives, is placed in transport or storage containers. 2. The method according to claim 1, characterized in that the mixed with an additive, radioactive waste obtained by freeze-drying, preferably after a pressing process, in a known manner by melting or Sintering processes can be brought into the form of a solid. 3. The method according to claim 1, characterized in that the after the freeze-drying process radioactive substances on the filter elements by a gas or vapor stream, preferably by venting the vacuum filter chamber, removed and taken to a collecting vessel. 4. The method according to claim 1, characterized in that the filter elements during of the freeze-drying process serve as insert vessels for the radioactive substances and that the Filter chamber through the connection of known pump devices for separation vaporous constituents, in particular water vapor, is operated directly as a freeze-drying chamber. 5. Device for performing the method according to one of claims 1, 3 or 4, characterized characterized in that several, preferably sack-shaped filter elements in a filter chamber are arranged to receive the filtered out radioactive substances and that these Filter bags are optionally connected to heating and / or cooling devices. 6. Apparatus according to claim 5, characterized in that the heating and / or cooling devices Are tubular and together with likewise tubular evacuation lines Form a grate on which the filter bags can be stretched. 7. Apparatus according to claim 5, characterized in that the heating device is a steam heater, wherein the steam pressure is so much below atmospheric pressure that the vapor temperature is about 50 to 80 ⁰ C. 8. Apparatus according to claim 5, characterized in that that the interior of the filter bags lying in the liquid level of the filter chamber is connected to an evacuation device for generating a negative pressure, so that the radioactive substances are deposited on the outside of the filter bags. Considered publications:
German Auslegeschrift No. 1 053 686,
088 624; Neumann, "Outline of Freeze Drying", 1952; Journal: "Vakuumtechnik", January 1965, pp. 109, 115, 123, 130; Journal: »Chemie — Ingenieur — Technik«, 1955, P. 5, and 1957, p. 267. 1 sheet of drawings