GB2285534A

GB2285534A - Method for processing radioactive waste solution

Info

Publication number: GB2285534A
Application number: GB9500279A
Authority: GB
Inventors: Masafusa Ohuchi; Tsuneo Watanabe; Toshiyuki Kai
Original assignee: Mitsubishi Nuclear Fuel Co Ltd
Current assignee: Mitsubishi Nuclear Fuel Co Ltd
Priority date: 1994-01-07
Filing date: 1995-01-06
Publication date: 1995-07-12
Anticipated expiration: 2015-01-06
Also published as: FR2714995A1; GB9500279D0; JPH07198894A; GB2285534B; FR2714995B1

Abstract

A calcium compound and iron chloride are added to an alkaline radioactive waste solution containing uranium, UD, FP and TRU, and fluorine, and then the mixture is stirred and the precipitates agglomerated by stirring are removed in a first filtration step (14) from the stirred solution. In a first pH adjusting step (15), nitric acid is added to the filtrate to adjust the pH to 3 or less, and (16) one or more of a lanthanide compound, a titanium compound, a zirconium compound and a hafnium compound is added to the pH adjusted solution. An alkaline aqueous solution is added to adjust the pH to 9 or more, and then the precipitates agglomerated by the pH adjustment (7) are removed by filtration from the pH adjusted solution (19). <IMAGE>

Description

METHOD FOR PROCESSING RADIOACTIVE WASTE SOLUTION BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a processing method for reducing contents of uranium, uranium radioactive decay nuclide (hereinafter referred to as "UD"), nuclear fission product (hereinafter referred to as "FP"), transuranium elements (hereinafter referred to as "TRU") and fluorine in an alkaline radioactive waste solution containing uranium which is an a and/or ss decay nuclide. UD. FP and TRU as well as fluorine by removing uranium. UD. FP and TRU as well as fluorine from the waste solution.

2. Description of the Related Art A cylinder containing uranium hexafluoride which had been used for producing UO2 pellets is washed after use and before filling with fresh uranium hexafluoride. The washing solution contains fluorine and uranium, as well as a ss decay nuclide such as thorium which is a daughter nuclide of uranium. There involves problems in the point of environmental safeguard to discharge the washing solution from a plant as a waste solution as such Thus. by providing drain control criterion's for respective elements to be contained in the waste solution, the radioactive waste solution which is a washing solution is processed so as to be lower than the respective drain control criterion's and then discharged from the plant.

As shown in Fig. 3. to a solution containing uranium which is a cylinder washing solution has heretofore been added an alkaline compound aqueous solution such as NaOH, etc., and the mixture is then processed under stirring to agglomerate uranium precipitates and the precipitates are removed by filtration. A radioactive waste solution obtained by the above stirring step 1 and the previous filtration step 2 has been processed by the following method.That is. the processing method comprises a step 3 of adding slaked lime and iron chloride to the radioactive waste solution which is a filtrate of the filtration step 2 and stirring the mixture: a filtration step 4 of filtrating the stirred mixture to remove the agglomerated fluorides of calcium and iron generated by stirring: and an ion-exchange step 5 of passing the filtrate into an ion-exchange column to effect ion-exchange, thereby removing the remaining uranium and ss decay nuclide such as thorium, etc.. which is a daughter nuclide of uranium.

This conventional agglomeration-precipitation processing method involves problems of not only requiring an expensive ion-exchange resin but also newly generating a solid waste material containing used ion-exchange resin processing of which is extremely difficult.

Also. the processing method is effective as a processing method for a waste solution from a washing solution of natural type enriched uranium. but cannot be applied to a waste solution in the case of a recovered-uranium type enriched uranium which contains a minute amount of FP and TRU. That is, the method can process fluorine to a concentration lower than the drain control criterion of 15 ppm, but involves defects that, as for a decay nuclide, it cannot decrease a radioactivity concentration of the drain control criterion: 1 x 10 2 Bq/cm3 for an x waste solution, and for p decay nuclide, it cannot decrease the same of the drain control criterion: 3 x 10-1 Bq/cm for a ss waste solution.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for processing a radioactive waste solution containing uranium, UD, FP, and TRU as well as fluorine by removing uranium, UD, FP, TRU and fluorine from the radioactive waste solution to reduce radioactive concentration of each element to not more than the drain control criterion.

The present invention provides a method for processing a radioactive waste solution, as set out in Claim 1 or 5. To accomplish the above object, the method for processing the waste solution of the present invention may comprise the steps as shown in Figure 1: a step 13 in which a calcium compound such as Ca(OH)2, CaO, CaC03, etc. and iron chloride are added to an alkaline radioactive waste solution containing uranium which is an a and/or p decay nuclide, uranium radioactive decay nuclide, nuclear fission product, transuranium elements, and fluorine and then the mixture is stirred:: a first filtration step 14 in which precipitates which are agglomerated by stirring of the above step 13 are removed from the stirred solution in the above step 13 by filtration; a first pH adjusting step 15 in which a nitric acid or a nitric acid and iron chloride, if necessary, are added to the filtrate in the above step 14 to adjust the pH to not more than 3; a step 16 in which at least one of a compound selected from the group consisting of a lanthanide compound. a titanium compound. a zirconium compound and a hafnium compound is added to the above pH adjusted solution and then the compound is dissolved therein or mixed therewith; a second PH adjusting step 17 in which an alkaline solution such as a NH40H solution or a NaOH solution is added to the solution or mixed liquid in the above step 16 to adjust the pH to 9 or higher; and a second filtration step 19 in which precipitates which are agglomerated in the above step 17 are removed from the pH adjusted solution of the above step 17 by filtration.

Incidentally. a radioactive waste solution to be stirred in the stirring step 13 can be obtained, for example, as shown in Fig. 1. via a stirring step 11 in which an alkaline solution is added to an uranium-containing solution which is a cylinder washing solution. and the mixture is stirred and adJusted the pH to 10 or more. by a provisionally filtrating step 12 in which uranium precipitates which are agglomerated in the stirring are provisionally filtered to remove the precipitates.

After a calcium compound and iron chloride are added to the radioactive waste solution of the present invention in the stirring step 13. fluorine is mainly removed as a fluoride in the first filtration step 14. Further. in the step 15. the filtrate is made acidic with a pH of not more than 3. then a lanthanide compound. a titanium compound, a zirconium compound or a hafnium compound is dissolved or mixed in the step 16.

Thereafter. the solution or the mixture is returned to an alkaline with a pH of 9 or higher in the step 17, whereby an a and/or ss decay nuclide is removed as agglomerated precipitates of a lanthanide compound. a titanium compound. a zirconium compound or a hafnium compound in the second filtration step 19.

Particularly characteristic feature of the present invention resides in adding a lanthanide compound. a titanium compound, a zirconium compound or a hafnium compound in the step 16 and in simultaneously removing the a and/or ss decay nuclide with these compounds by aggregating and precipitating in the step 19. As the lanthanide compound. there may be exemplified LaCI3, CeCl3. etc.. and as the titanium compound, TiC 14. etc. may be exemplified. Also. as the zirconium compound. ZrCl4 may be exemplified. and as the hafnium compound, there may be exemplified by HfCl4.

BRIEF DESCRIPTION OF THE DRAWINGS The above objects and other objects will be clear from the descriptions of Examples based on the drawings of the present invention as well as the advantages of the invention.

Fig. 1 is a flow sheet showing the processing method of a radioactive waste solution of the present invention.

Fig. 2 is a drawing showing decontamination factors of a radioactivity and ss radioactivity of Examples of the present invention Fig. 3 is a flow sheet showing a conventional processing method of a radioactive waste solution.

DESCRIPTION OF THE PREFERRED EMBODIMENT Next. in order to show the specific embodiment of the present invention. Examples of the present invention will be explained.

ExamPle 1 A NH40H solution (20 cm3) with a concentration of 15N was added to 0. 5 liter of a cylinder washing solution with a fluorine concentration of 340 ppm, an a (uranium) concentration of 6. 96 x 103 Bq/cm3 and a ss concentration of 5. 72 x 103 Bq/cm3. followed by stirring for 30 minutes. Agglomerated precipitates by the stirring were removed by filtration. To the resulting filtrate were added 0. 95 g of CaCOH)2 and 1 cm3 of FeCl3 with a concentration of 37X. and the mixture was stirred for 30 minutes. Agglomerated precipitates by the stirring were removed by filtration. Then. to the resulting filtrate were added 15 cm3 of 6N nitric acid and 1 cm3 of 37% FeCl3 to adjust pH to 2 to 3.

To the pH adjusted solution was added 50 mg of commer- cially available CeC13,7H20 and dissolved. To the solution was added 10 cm3 of a 25% NaOH solution to adjust the pH of the solution to 9 to 10. Precipitates agglomerated by the pH adjustment were removed by filtration. and fluorine, an a concentration and a ss concentration contained in the filtrate were measured. The results are shown in Table 1 and Fig. 2.

Example 2 A cylinder washing solution was processed in the same manner as in Example 1 except for adding 50 mg of commercially available LaCl3 7H20 in place of CeC13. 7H20. Fluorine. an a concentration and a ss concentration contained in the finally obtained filtrate were measured. The results are shown in Table 1 and Fig. 2.

Example 3 A cylinder washing solution was processed in the same manner as in Example 1 except for adding 50 mg of commercially available TiC 14 in place of CeCl3 7H20. Fluorine. an a concentration and a ss concentration contained in the finally obtained filtrate were measured. The results are shown in Table 1 and Fig. 2.

ExamPle 4 A cylinder washing solution was processed in the same manner as in Example 1 except for adding 50 mg of commercially available ZrCl4 in place of CeCl3 7H20. Fluorine. an a concentration and a ss concentration contained in the finally obtained filtrate were measured, The results are shown in Table 1 and Fig. 2.

Table 1 Example 1 Example 2 Example 3 Example 4

Concen- F (ppm) 340 500 400 340 tration before |α(Bq/cm ) 1.2x10 1.2x10 1.2x10 1.2x10 proc essing ss (Bq/cm3) 1. 6x100 1. 6x100 1. 6x100 1.6x10 Concen- F (ppm) 8 < 15 13 7 tration after |α(Bq/cm ) 3.7x10-3 2.4x10-3 2.4x10-3 8.9x10-3 proc essing |ss(Bq/cm ) 2.2x10-1 2.9x10-1 1.3x10-1 1.9x10-1 Decontamination factor of F 4. 3x101 3. 3x101 3. 1x101 4.9x10 Decontamination factor of a 3. 2 x 10 5.0 x 102 5.0 x 102 1.3 x 102 Decontamination factor of ss 7. 3 x 100 5. 5 x 100 1. 2 x 101 8.4 x 10 As clearly seen from Table 1. with regard to the concentrations after processing of Examples 1 to 4. fluorine can be reduced lower than the drain control criterion of 15 ppm.

As for the a decay nuclide such as uranium. the concentration can be reduced not more than the drain control criterion of 1 x 10-2 Bq/cm of the a waste solution. and as for the R decay nuclide such as radioactive decay nuclide of uranium, the concentration can be reduced not more than the drain control criterion of 3 x 10-1 Bq/cm of the ss waste solution.

As described above. in the processing method of the present invention. decontamination factors of the a radioactivity and ss radioactivity are increased 2 order and 1 order, respectively. as compared with the conventional processing method. and concentrations of uranium and a and/or ss decay nuclides other than uranium. as well as fluorine can be each reduced not more than the drain control criterion' S.

Also. since at least one of a lanthanide compound. a titanium compound. a zirconium compound and a hafnium compound, which are easily commercially available and can be used with less amount, is used in place of an expensive ion-exchange resin. there are advantages that occurrence of solid waste material is a little and also waste ion-exchange resin. etc.

which are difficultly processed is not generated so that a processing cost becomes cheap as compared to those of the conventional method.

Claims

1. A method for processing a radioactive waste solution comprising: a first step in which a calcium compound and iron chloride are added to an alkaline radioactive waste solution containing at least one of uranium which is an a and/or p decay nuclide, uranium radioactive decay nuclide, nuclear fission product and trans uranium elements; and fluorine, and then the mixture is stirred; a first filtration step in which precipitates which are agglomerated by stirring in the above step are removed from the stirred solution of the above step by filtration; a first pH adjusting step in which nitric acid is added to the filtrate of the above step to adjust the pH to not more than 3; a step in which at least one compound selected from the group consisting of a lanthanide compound, a titanium compound, a zirconium compound and a hafnium compound is added to the above pH adjusted solution and then the compound is dissolved therein or mixed therewith; a second pH adjusting step in which an alkaline solution is added to the solution or mixed liquid of the above step to adjust the pH to 9 or higher; and a second filtration step in which precipitates which are agglomerated in the above step are removed from the pH adjusted solution of the above step by filtration.

2. The method for processing a radioactive waste solution according to Claim 1, wherein the alkaline solution to be added in the second pH adjusting step is a NH40H solution or a NaOH solution.

3. The method for processing a radioactive waste solution according to Claim 1, wherein the calcium compound to be used in the first step is Ca(OH)2, CaO or CaC03.

4. The method for processing a radioactive waste solution according to Claim 1, wherein iron chloride is added to the filtrate in the first pH adjusting step together with the nitric acid.

5. A method for treating a radioactive waste liquid, substantially as herein described with reference to the accompanying figures, or to Examples 1 to 4.

5. A method for processing a radioactive waste solution, substantially as herein described with reference to the accompanying figures, or to Examples 1 to 4.

Amendments to the claims have been filed as follows 1. A method for treating a radioactive waste liquid comprising: a first step in which a calcium compound and iron chloride are added to an alkaline radioactive waste liquid which contains at least one of an a and/or P decay nuclide, selected from the group consisting of uranium, uranium radioactive decay nuclides, nuclear fission products and transuranium elements; and which contains fluorine, and then the mixture is stirred; a first filtration step in which precipitates which are flocculated by stirring in the above step are removed from the stirred liquid of the above step by filtration; a first pH adjusting step in which nitric acid is added to the filtrate of the above step to adjust the pH to not more than 3; a step in which at least one compound selected from the group consisting of lanthanide compounds, titanium compounds, zirconium compounds and hafnium compounds is added to the above pH adjusted solution and then the compound is dissolved therein or mixed therewith; a second pH adjusting step in which an alkaline solution is added to the mixed liquid of the above step to adjust the pH to a value of 9 or higher; and a second filtration step in which precipitates which are flocculated in the above step are removed from the pH adjusted liquid of the above step by filtration.

2. The method for treating a radioactive waste liquid according to Claim 1, wherein the alkaline solution to be added in the second pH adjusting step is a NH40H solution or a NaOH solution.

3. The method for treating a radioactive waste liquid according to Claim 1, wherein the calcium compound to be used in the first step is Ca(OH)2, CaO or CaC03.

4. The method for treating a radioactive waste liquid according to Claim 1, wherein iron chloride is added to the filtrate in the first pH adjusting step together with the nitric acid.