GB1565822A

GB1565822A - Method of cleaning components contaminated with radioactive sodium and plant when used for carrying out the method

Info

Publication number: GB1565822A
Application number: GB41443/76A
Authority: GB
Original assignee: Kernforschungszentrum Karlsruhe GmbH
Current assignee: Forschungszentrum Karlsruhe GmbH
Priority date: 1975-10-08
Filing date: 1976-10-06
Publication date: 1980-04-23
Also published as: JPS5246298A; DE2545031C2; DE2545031A1; FR2327611A1; FR2327611B1

Description

(54) METHOD OF CLEANING COMPONENTS CONTAMINATED WITH RADIOACTIVE SODIUM AND PLANT WHEN USED FOR CARRYING OUT THE METHOD (71) We, KERNFORSCHUNGSZEN TRUM KARLSRUHE GESELLSCHAFT MIT BESCHRAENKTER HAFTUNG, formerly GESELLSCHAFT FUER KERN FORSCHUNG m.b.H., of 5 Weberstrasse, 75 Karlsruhe 1, Germany (Fed.Rep.); a German body corporate, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the follow mg statement: The present invention relates to a method of cleaning components of nuclear technical plants contaminated by radioactive sodium m a container by successive spraying of the components under a protective gas with steam and water and a plant for carrying out this method, comprising a sealable washing container to receive the components or the articles contaminated with radioative sodium, which container in its interior has a plurality of spray nozzles for the steam or the washing liquor, and supply and discharge conduits with associated pump and washing liquor containers.

It is known to clean components contaminated with sodium under an inert atmosphere with steam and water and for the accruing effluent to be conducted directly to the decontamination or the processing station. With larger quantities of articles to be cleaned (e.g. when changing fuel elements unnecessarily large quantities of liquid accrue. Though these are partly used for neutralising acids, it is necessary in any case for the water, before the final deposit to be evaporated. this, however, is connected with an accordingly high energy consumption. Proceeding from this prior art, the present invention proposes a method and plant for reducing the liquid accruing during cleaning of plant components contaminated with radioactive sodium, since the removal of these effluents by evaporation is connected with a high energy consumption.Moreover, the large storage capacity required for such liquids is reduced, whereby saving of plant costs is made possible.

According to the present invention there is provided a method of cleaning components of nuclear plants contaminated with radioactive sodium in a container by successive spraying of the components with steam and aqueous liquid under an inert gas, in which the resulting washing liquor is repe atedly recycled after the first washing operation for renewed spraying.

Preferably, the returning of the washing liquor is effected in stages dependent upon the concentration of the liquor, whereby the liquor is not recycled until a predetermined maximum concentration of waste removal has been attained. A particularly preferable embodiment of the method consists in that the washing liquor is transferred, preferably in two concentration stages in two intermediate storage containers and from there independently of the degree of cleanliness of the components, first the strong and then the weak washing liquor and subsequently clean water is sprayed into the cleaning container, whereby after each spraying operation the washing liquor dependent upon its concentration is again conducted into the given intermediate container.

Further in accordance with the invention, there is provided a plant when used for carrying out the above identified method comprising a sealable washing container to receive the components or articles for washing contaminated with radioactive sodium, which container in its interior is provided with a plurality of spraying nozzles for the steam or washing liquor and supply and discharge conduits with associated pump and washing liquor containers in which the discharge conduit of the container is conducted into at least one intermediate storage container which by means of a conduit adapted to be shut down with a shutoff member is connected to the supply conduit for the spraying nozzles and which is provided with a further discharge conduit adapted to be shut off for the concentrated washing liquor.

A particularly favourable feature thus is that the discharge conduit is divided into two branches which are adapted to be shut off by means of regulating members, and which lead to two intermediate storage containers, which in turn are connected by two conduits adapted to be shut off, leading to the spraying nozzles, and that from the intermediate container for washing liquor of higher concentration a discharge conduit also adapted to shut off leads to the waste water removal. Finally it is also preferable for a steam inlet, a protective gas inlet, a water inlet and an inlet for recycled or returned washing liquor to each be individually closable and to be connected together to the supply conduit to the spraying nozzles.

The present invention will be further illustrated, by way of example, with reference to the accompanying drawing, in which the single Figure schematically shows the structure of a washing plant in accordance with the invention.

The main component of the plant is the washing container 1 in which the material to be washed la is located, which material may be charged into the container 1 after removing the tightly sealable closable cover 23. A heating system 17 is located around the container 1 which serves for drying of a cleaned material la. Moreover, the heating provides a crude preliminary cleaning by melting off large quantities of Na at temperatures of about 1200C. By material 1a to be cleaned in the container 1, there are normally understood components of sodium-cooled nuclear reactors which are removed from the reactor core and which are contaminated with radioactive sodium from the cooling circuit. It is, however, also possible to treat any other components contaminated with sodium.A spray conduit 24 is connected to the washing container 1 which leads to the different spraying nozzle groups 20, 25 and 26 in the container 1. By means of the nozzles 20, the articles being washed are sprayed from above and by means of a plurality of nozzles 25 and 26 spread over the circumference are sprayed from the side. The spraying conduit 24 is provided with three supply conduits 19, 27, 28 which are adapted to be shut off by means of the valves 29, 3 and 4. Steam is supplied through the conduit 19 and nitrogen as inert gas through the conduit 27.

The washing liquor (NaOH + H2O) produced in the container 1 by the washing operation is returned through the conduit 28 for renewed spraying via the nozzles 20, 25 and 26 into the container 1. The necessary spraying pressure is produced by means of the pump 47 incorporated into the conduit 28.

Likewise via the conduit 28, clean water may be supplied from the water connection 30 via the valve 5 and the storage container 31. The supply conduit 28 is divided at the side of the water connection into two further branches 34 and 35. The conduits 32 and 33 are adapted to be shut off by means of the valves 6 and 7. Supply conduits 36 and 37 with the stop or control valves 10 and 11 are led together from the containers 34 and 35 via the pump 9 to the container discharge conduit 21. Control is effected by means of the control circuit 22, which after measuring the concentration by means of the feeler 22a, distributes the washing liquor dependent upon its concentration via the valves 10 and 11 to the conduits 36 and 37. The pump 9 thus serves the conveying of the washing liquor.

The container 35 with conduit 37 and the valve 11 serves to receive the washing liquor of higher concentration, the container 34 with the conduit 36 and the valve 10 to receive the liquor of lower concentration. A discharge conduit 38 is connected to the container 35 via a stop valve 8, which leads to a precipitation container 12 in which the sodium is precipitated. A branch 39 of the conduit 38 leads directly to the decontamination plant. The reactants for the precipitation in the container 12 are supplied via the conduit 40, and the conduit 41 leads via a valve 13 to the filter 14, in which the radioactive sodium is precipitated as filter cake. From the filter 14, the precipitated sodium is precipitated as filter cake.From the filter 14, the precipitated filter cake returns with the radioactive sodium to the decontamination region via the conduit 42 and the residual water, e.g. dependent upon the pH value, via the conduit 43 into the storage container 34 or 35.

A vacuum pump 18 is connected to the container 1 for the drying operation, and a return condenser 16 for the extracted moisture. The returning of the condensate is effected via the conduit 44 and the valve 45.

A recombinator 18 with platinum catalysts is provided to recombine hydrogen and oxygen as water (2H2 + O2 ~ 2H2O). The washing process is controlled by means of the measuring devices 2 for pressure (hydrogen and oxygen) concentration in the container 1. The supply of steam, water, nitrogen or recycled washing liquor occurs in accordance with the predetermined nominal values therefrom, via the control circuit 46.

The container 1 is first filled with protec tive gas (nitrogen) via the valve 3. Then via the steam inlet 19 and the valve 29, with the valves 3 and 4 closed, steam is injected into the container. Due to this, the sodium on the plant components to be cleaned is converted into sodium oxide. Subsequently, with closed valves 29, 3, 6, 5 and opened valves 4, 7 slowly and continuously liquid i.e. sodium lye of higher concentration is conducted from the container 35 into the container 1. This liquid may also be admixed to a greater or lesser extent with the valves 5 and 29 open. The injection into the container itself occurs via the injection valves 20. This operation is continued until the lye concentration in the container 35 is so strong or until the proportion of water therein is so low that no washing reaction any longer occurs in the container 1.During the process, the liquid after cleaning is constantly extracted via the conduit 21 from the container and returned via the control circuit 22 and the valve 11 and the conduit 37 into the container 35. The control system 21 now conducts the extracted liquid depending upon the concentration either via the valve 10 or 11 into the intermediate storage tanks 34 or 35. If no more reaction occurs in the container 1 with the liquid from container 35, then the washing liquor with the higher proportion of water is conducted from the container 34 via injection nozzles 20 and returned via valve 10 and the conduit 36 into the container 34, until no reaction occurs any longer in container 1. If the washing process in the container 1 continues constantly in this manner, only a little sodium residue is finally left, so that the reaction becomes increasingly less.Finally, the operation is carried out with constantly higher water contents to accelerate the reaction, until finally only some perfectly clean water is injected from the container 31 via the valve 5 into the container. By means of the valves 6 and 7 a mixed setting may also be operated. When the washing operation has ended, (the control occurs via the pressure, the partial hydrogen and oxygen pressure in the container), spraying is again carried out with clean water via the valve 5 in order finally to remove the liquor adhering to the washed articles. The waste water from this cleansing operation is then returned into the tank 34 and is used as a weak solution for the next cleansing operation.Highly concentrated washing liquor from the container 35 is discharged via the conduit 38 and depending upon the degree of contamination either conducted to the decontamination plant or precipitated in the precipitation container 12. Here the sodium is precipitated, passes through the filter plant 14 and is discharged.

For drying, the container 1 is evacuated by means of the pump 18 and heated by the heating system 17. The recombinator 15 should convert the accruing hydrogen into water to save large residual gas quantities accruing. The change-over between the tanks 34 and 35 occurs in dependence upon the reaction in the container 1. It is influenced by the time factor which would excessively extend the washing operation.

By the repeated use of the lye or liquor for the cleaning process and by the possibility of chemically precipitating the accruing NaOH and filtering it, in a plant as shown in the figure, the waste liquor accrument is considerably reduced. The repeated use of the same liquid supply and the possibility of producing solid wastes are a considerable advantage which leads to a considerable reduction of the energy requirement in the decontamination region. A reduction of the required storage capacity is also connected with a considerable saving of costs.

WHAT WE CLAIM IS; 1. A method of cleaning components of nuclear plants contaminated with radioactive sodium in a container by successive spraying of the components with steam and aqueous liquid under an inert gas, in which the resulting washing liquor is repeatedly recycled after the first washing operation for renewed spraying.

2. A method as claimed in claim 1, in which the recycling occurs in stages dependent upon the concentration of the liquor and that the liquor is not recycled until reaching a predetermined maximum concentration of waste removal.

3. A method as claimed in claim 1 or 2, in which the washing liquor is transferred, preferably in two concentration stages in two intermediate storage containers and from there independently of the degree of cleanliness of the components, first the strong and then the weak washing liquor and subsequently clean water is sprayed into the cleaning container, whereby after each rinsing operation the washing liquor dependent upon its concentration is again conducted into the given intermediate containers.

4. A method of cleaning components of nuclear plants contaminated with radioactive sodium, as claimed in any preceding claim, substantially as hereinbefore described.

5. Plant when used for carrying out the method according to any one of claims 1 to 4 comprising a sealable washing container to receive the components or articles for washing contaminated with radioactive sodium, which container in its interior is provided with a plurality of spraying nozzles for the steam or washing liquor and supply and discharge conduits with associated pump and washing liquor containers in

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. tive gas (nitrogen) via the valve 3. Then via the steam inlet 19 and the valve 29, with the valves 3 and 4 closed, steam is injected into the container. Due to this, the sodium on the plant components to be cleaned is converted into sodium oxide. Subsequently, with closed valves 29, 3, 6, 5 and opened valves 4, 7 slowly and continuously liquid i.e. sodium lye of higher concentration is conducted from the container 35 into the container 1. This liquid may also be admixed to a greater or lesser extent with the valves 5 and 29 open. The injection into the container itself occurs via the injection valves 20. This operation is continued until the lye concentration in the container 35 is so strong or until the proportion of water therein is so low that no washing reaction any longer occurs in the container 1.During the process, the liquid after cleaning is constantly extracted via the conduit 21 from the container and returned via the control circuit 22 and the valve 11 and the conduit 37 into the container 35. The control system 21 now conducts the extracted liquid depending upon the concentration either via the valve 10 or 11 into the intermediate storage tanks 34 or 35. If no more reaction occurs in the container 1 with the liquid from container 35, then the washing liquor with the higher proportion of water is conducted from the container 34 via injection nozzles 20 and returned via valve 10 and the conduit 36 into the container 34, until no reaction occurs any longer in container 1. If the washing process in the container 1 continues constantly in this manner, only a little sodium residue is finally left, so that the reaction becomes increasingly less.Finally, the operation is carried out with constantly higher water contents to accelerate the reaction, until finally only some perfectly clean water is injected from the container 31 via the valve 5 into the container. By means of the valves 6 and 7 a mixed setting may also be operated. When the washing operation has ended, (the control occurs via the pressure, the partial hydrogen and oxygen pressure in the container), spraying is again carried out with clean water via the valve 5 in order finally to remove the liquor adhering to the washed articles. The waste water from this cleansing operation is then returned into the tank 34 and is used as a weak solution for the next cleansing operation.Highly concentrated washing liquor from the container 35 is discharged via the conduit 38 and depending upon the degree of contamination either conducted to the decontamination plant or precipitated in the precipitation container 12. Here the sodium is precipitated, passes through the filter plant 14 and is discharged. For drying, the container 1 is evacuated by means of the pump 18 and heated by the heating system 17. The recombinator 15 should convert the accruing hydrogen into water to save large residual gas quantities accruing. The change-over between the tanks 34 and 35 occurs in dependence upon the reaction in the container 1. It is influenced by the time factor which would excessively extend the washing operation. By the repeated use of the lye or liquor for the cleaning process and by the possibility of chemically precipitating the accruing NaOH and filtering it, in a plant as shown in the figure, the waste liquor accrument is considerably reduced. The repeated use of the same liquid supply and the possibility of producing solid wastes are a considerable advantage which leads to a considerable reduction of the energy requirement in the decontamination region. A reduction of the required storage capacity is also connected with a considerable saving of costs. WHAT WE CLAIM IS;

1. A method of cleaning components of nuclear plants contaminated with radioactive sodium in a container by successive spraying of the components with steam and aqueous liquid under an inert gas, in which the resulting washing liquor is repeatedly recycled after the first washing operation for renewed spraying.

which the discharge conduit of the container is conducted into at least one intermediate storage container which by means of a conduit adapted to be shut down with a shut-off member is connected to the supply conduit for the spraying nozzles and which is provided with a further discharge conduit adapted to be shut off for the concentrated washing liquor.

6. Plant as claimed in claim 5, in which the discharge conduit is divided by means of control members into two branches adapted to be shut off which lead to two intermediate storage containers, which in turn are again connected with two conduits adapted to be shut off to the conduit leading to the spraying nozzles and that from the interme dilate storage container for washing liquid of higher concentration a discharge conduit also adapted to be shut off leads to the waste water removale.

7. Plant as claimed in claim 5 or 6, in which a steam inlet adapted to be shut off a protection gas inlet a water inlet and inlets for the recycled washing liquor are connected together and to the supply conduit to the spraying nozzles.

8. Plant for cleaning components, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.