JPH0797157B2 - Method for recovering radioactive element extractant - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for recovering an eluent extractant in a facility for easily and economically treating a radioactive liquid waste containing transuranium element (TRU) with an extractant. It is a thing.

"Prior Art" As is well known, a method of recovering U / Pu from spent nuclear fuel by reprocessing and vitrifying the remaining high-level radioactive waste liquid has been adopted in Japan. From the viewpoint of waste treatment and disposal, it is most appropriate to separate transuranium element (TRU), which is a long-lived α-emitter contained in high-level radioactive liquid waste, and to effectively store and eliminate it. Conventionally, reprocessing is performed by dissolving spent fuel in nitric acid and performing various redox treatments.
The so-called Purex method, which separates U and Pu by solvent extraction using P (tributyl phosphate), is used.

By the way, in the conventional method for treating radioactive waste liquid,
The high-level radioactive liquid waste after removal of U and Pu is vitrified and stored for storage, but since TRU containing long-term toxicity is included, radioactive waste (glass solidification) is stored and managed. Enormous cost is required.

Therefore, the inventor of the present application has invented a method for treating a radioactive waste liquid having the following structure, which can easily and economically separate and remove TRU from a radioactive waste liquid containing TRU and reduce waste liquid solidified bodies.

In this treatment method, first, U and Pu are separated and removed from the radioactive waste liquid having a high acid concentration by anion exchange or the like, and the radioactive waste liquid containing TRU after U and Pu removal is subjected to CMP (carbamoyl methylene).
phosphonate) or CMPO (carbamoyl methylene phosp
(Hineoxide) impregnated solid support (column) to adsorb TRU in the liquid to the solid support to remove TRU from the waste liquid and elute the TRU adsorbed to the solid support. It is a method characterized by collecting and collecting.

CMP (carbamoyl methylene phosphona) in the above structure
te) or CMPO (carbamoyl methylene phosphine oxid
e) is the extraction of trivalent, tetravalent, and hexavalent actinide elements,
In particular, it is an extractant that has recently been drawing attention as a compound (a bidentate organophosphorus compound) capable of extracting a trivalent actinide element. In this method, by impregnating a solid support such as an ion exchange resin with the CMP and CMPO, flow loss of the relatively expensive CMP and CMPO can be prevented, and the TRU extracted in the CMP and CMPO can be fixed. Making it easy.

For the solid support impregnated with CMP or CMPO, a resin having a large impregnated amount of CMP or CMPO and in which CMP or CMPO is difficult to elute is used. For example, Amberlite XAD-4 (trade name; non-polar polystyrene-DVB resin, giant network structure)
Is preferred. CMP or CMPO on such solid supports
The adsorbent constituted by impregnating (extractant) is prepared by first washing the resin with acetone to remove impurities and then impregnating the dried product with the extractant.

A column is formed by packing the adsorbent thus prepared in a column, and if a radioactive waste liquid containing TRU after removal of U and Pu is passed through this column, the TRU in the liquid is adsorbed to the column. This makes it possible to easily remove the TRU. The TRU adsorbed on the column can be easily eluted by washing with a dilute acid solution, and the TRU can be separated and recovered from other fission products.

"Problems to be Solved by the Invention" By the way, the extractant impregnated in the support as described above is eluted depending on its solubility (to 500 ppm) by passing water through the column of the support. Go. When distilled water is passed through the prepared adsorption column, a large amount of extractant flows out at the initial stage of passing water, and thereafter elution is carried out at a constant concentration (420 ppm). Elution at a constant concentration is due to the solubility of the extractant in water, but the initial large amount of outflow is due to the outflow of excess extractant that could not be removed as an excess extractant in the impregnation step of the extractant.

Since the extractant itself is very expensive in such an initial effluent extractant and the subsequent elution extractant, if it is allowed to flow out as it is, the operating cost is increased, which is not preferable.

"Means for solving problems" The resin (eg Amberlite XAD-4) used as a support for impregnating CMP or CMPO (extractant) originally adsorbs and recovers high molecular organic matter from contaminated water due to organic matter. The adsorbed polymer organic substance can be moved from the resin phase to the liquid phase by using an acetone or methanol solution or the like.

Therefore, utilizing this principle, for the extractant eluted according to the solubility in the aqueous phase from the extractant-impregnated column, an adsorbent column is provided downstream of the extractant-impregnated column to adsorb the eluted extractant, The adsorbent column that has adsorbed the eluent extractant is transferred to the eluent phase with an eluent such as acetone or methanol solution after elution of the transuranium element from this column, and this extractant-containing phase is washed with an alkali, etc., if necessary. , The extractant-containing phase and the aqueous phase are separated, the deteriorated impurities are removed, and then the extractant-containing phase is put under reduced pressure to volatilize and recover the extractant.

For the initial large amount of effluent extractant, after the extraction liquid filled in the solid support column to impregnate the solid support was drawn out from the column,
After washing with about 10 times, the washing solution is passed through the adsorbent column to adsorb the extractant, and then the adsorbent column is washed with an eluent such as acetone or methanol solution, and then the extractant-containing phase is washed. The extractant is volatilized and recovered by placing it under reduced pressure.

[Operation] As described above, according to the extractant recovery method of the present invention, an expensive extractant does not flow out of the radioactive waste liquid treatment system and is not lost. Can be utilized at low cost, and can greatly contribute to economical treatment of radioactive waste liquid.

Hereinafter, the present invention will be described in more detail with reference to Examples.

[Example] Fig. 1 is a schematic configuration diagram of a radioactive waste liquid treatment apparatus suitable for carrying out the method of the present invention.

As is well known, radioactive waste liquid contains a large amount of Americium;
Is included. This radioactive waste liquid usually contains U (VI) and Pu (IV) in addition to the above-mentioned Am, and it is considered that when the concentration of these is high, the adsorption capacity of Am is affected. Therefore, as shown in the figure, first, the waste liquid stored in the waste liquid supply tank 1 is once caused to flow through the anion exchange resin tower 3 together with the concentrated nitric acid solution by the pump 2 to remove the U and Pu elements.
The removed U and Pu components are backwashed with dilute nitric acid solution in tower 3
It is eluted from the ion-exchange resin inside and stored in the U / Pu storage tank 4 for proper recycling.

The effluent (Am waste liquid) after the removal of U and Pu is temporarily stored in the waste liquid storage tank 5, and is supplied from the storage tank 5 to the extraction unit 7 by the pump 6. The extraction unit 7 has two stages of 7a (7a) and 7b in order to increase the amount of waste liquid treated per batch, and the former columns 7a and 7a are filled with CMP-impregnated ion exchange resin or CMPO-impregnated ion exchange resin, A backup column (adsorbent column) for collecting and retaining the eluted extractant is provided in the tower 7b in the latter stage. With this backup column, as described later,
The extractant eluted from the towers 7a, 7a in the first stage can be adsorbed and collected, and the cost loss due to the elution of the extractant can be greatly reduced.

The effluent from which Am has been separated and removed from the extraction unit 7 is temporarily
The fission product can be solidified by sending it to the FP waste liquid storage tank 8 and, for example, treating it with sodium nitrate and performing a temporary solidification treatment.

On the other hand, the extraction tower 7a, such as Am adsorbed on the column in 7a
The TRU is eluted by the normal washing with a dilute nitric acid solution, and the waste liquid containing Am is temporarily stored in the waste liquid storage tank 9 and subjected to vitrification treatment for disposal, or if necessary, by the oxalic acid precipitation method or the like. Collect.

When the TRU recovery is completed as described above, as shown in the figure, the back-up column 7b downstream of the tower 7a is backwashed with the eluent 10 of the acetone or methanol solution tower, and the washing liquid is washed with an alkaline washing tank 11 After washing with an alkali at 1, the liquid-liquid separation phase 12 is separated into an extractant-containing phase and an aqueous phase to remove CMP-deteriorated impurities, and the washed extractant-containing phase is introduced into a decompression tank 13 and decompressed. The extractant is recovered by volatilizing under. The recovered CMP is used for re-impregnation of the ion exchange resin in the towers 7a and 7a.

[Advantages of the Invention] As described above, according to the extraction agent recovery method of the present invention, an expensive extraction agent does not flow out of the radioactive waste liquid treatment system and is not lost. In particular, the characteristics of the extractant having a high ability to extract radioactive elements can be utilized at low cost, and it can greatly contribute to the economical treatment of radioactive waste liquid.

[Brief description of drawings]

FIG. 1 shows an example of a radioactive waste liquid treatment apparatus suitable for carrying out the method of the present invention, and is a schematic configuration diagram of the apparatus. 1 ... Waste liquid supply tank, 2, 6 ... Pump, 3 ... Anion exchange resin tower, 4 ... U / Pu storage tank, 5 ... Waste liquid storage tank, 7 ... Extraction section, 7a ... Extraction tower , 7b …… Backup column (adsorbent column), 8 …… FP waste liquid storage tank, 9 …… Waste liquid storage tank, 10 …… CMP eluent, 11 …… Alkaline cleaning tank 12 …… Liquid-liquid separation tank, 13 ...... Decompression tank.

Claims (1)

[Claims] 1. U and Pu are separated and removed from a radioactive waste liquid having a high acid concentration, and the radioactive waste liquid containing transuranic elements after U and Pu removal is removed by CMP (carbamoyl methylene phosphonate) or CM.
By passing through a solid support column impregnated with an extractant composed of PO (carbamoyl methylene phosphine oxide), the transuranic element is adsorbed on the solid support column to remove the transuranic element from the waste liquid, and A method for recovering an eluent extractant in a radioactive liquid waste treatment facility for eluting and recovering transuranic elements adsorbed on a solid support, wherein an adsorbent column is provided downstream of the solid support column to adsorb the eluent extractant. Then, the adsorbent column adsorbing the eluted extractant is washed with an eluent such as acetone or methanol solution after elution of the transuranium element, transferred to the extractant-containing phase, and the extractant-containing phase is placed under reduced pressure. A method for recovering a radioactive element extractant, characterized in that the extractant is recovered and reused by.