JP4451966B2 - Cleaning method of organic solvent for spent nuclear fuel reprocessing - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for cleaning and regenerating an organic solvent, and more particularly to a method for cleaning an organic solvent used for reprocessing spent nuclear fuel.
[0002]
[Prior art]
Light water-cooled nuclear reactors are currently widely used, but reprocessing of spent fuel is generally performed by the Purex method, and nitric acid aqueous solution is used to dissolve spent fuel debris. Useful substances such as uranium and plutonium dissolved in an aqueous nitric acid solution are extracted using an organic solvent and recovered for reuse. As the organic solvent, for example, a hydrocarbon mixture in which tributyl phosphate (TBP) is dissolved is used. Such an organic solvent is generally regenerated and recycled, but hydrolysis and radiolysis occur at the time of extraction of uranium as described above, and contain decomposition products. Such decomposition products are adversely affected in the reprocessing step, such as a decrease in the recovery rate of uranium and plutonium, a decrease in the decontamination coefficient, cladding, and the formation of emulsions. Organic solvent is reused. That is, in the figure, cleaning aqueous solutions 5a and 5b are brought into contact with the spent organic solvent 3 discharged from the spent fuel reprocessing step 1, and decomposition products (hereinafter referred to as deteriorated solvents) are dissolved in the cleaning aqueous solutions 5a and 5b. And separated as waste liquids 9a and 9b. The recycled organic solvent 11 is returned to the spent fuel reprocessing step 1 for use. As the cleaning aqueous solutions 5a and 5b, an alkaline cleaning solution such as a sodium carbonate aqueous solution or a sodium hydroxide aqueous solution, or a salt-free reagent such as an oxalic acid hydrazine aqueous solution or a carbonate hydrazine aqueous solution is used.
[0003]
[Problems to be solved by the invention]
As described above, in the spent nuclear fuel reprocessing step, there are various kinds of deteriorated solvents generated in the organic solvent. Therefore, if it is attempted to remove these using a cleaning aqueous solution, four extraction operations are required. . For this reason, the processing operation becomes complicated, and four extractors are required, which increases the size of the apparatus, resulting in a high cost for cleaning the organic solvent.
Accordingly, an object of the present invention is to provide a method for cleaning an organic solvent for spent nuclear fuel reprocessing which can be carried out with a simple facility and with a simple processing operation.
[0004]
[Means for Solving the Problems]
In order to solve the above-described problems, according to the cleaning method for spent nuclear fuel reprocessing organic solvent of the present invention, the degraded solvent is separated from the spent organic solvent-containing spent organic solvent used in the extraction of the spent nuclear fuel reprocessing step. Therefore, a supercritical fluid such as carbon dioxide that selectively dissolves an organic solvent is used. That is, in one embodiment of the present invention, the deterioration solvent-containing spent organic solvent by contacting the supercritical fluid dissolving the spent organic solvent for said use the supercritical fluid, the supercritical dissolving the spent organic solvent for said use and dissolved in fluid and cleaning solution to the cleaning solution deterioration solvent was countercurrent contact with the organic solvent and as one likes dissolved in supercritical carbon dioxide, separating the aqueous solution containing the deterioration solvent as waste, after which the organic The supercritical fluid in which the solvent is dissolved is subjected to a vacuum separation operation to separate it into a supercritical fluid and an organic solvent. The separated organic solvent has been regenerated and can be reused for extraction in the spent nuclear fuel reprocessing step.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected to the same part (substance, a process, etc.) over all drawings including drawing regarding a prior art.
Referring to FIG. 1, a cleaning aqueous solution 21 is added to and mixed 23 with the spent organic solvent 3 that has been output from the spent fuel reprocessing step 1. By this mixing, the deteriorated solvent in the used organic solvent 3 is dissolved in the cleaning aqueous solution, and a mixed solution 25 of the organic solvent and the aqueous solution in which the deteriorated solvent is dissolved is obtained. Next, CO ₂ (hereinafter referred to as supercritical carbon dioxide) 27 in a supercritical state (pressure 12 to 20 MPa, temperature 40 to 60 ° C.) is allowed to act on the mixed solution 25 to dissolve the organic solvent 29 in the supercritical carbon dioxide 29. . Due to the dissolution 29 of the organic solvent, the aqueous solution in which the deteriorated solvent is dissolved is separated as the waste liquid 31. The supercritical carbon dioxide 33 in which the organic solvent is dissolved is then depressurized to a pressure of 10 MPa or less by the vacuum separation operation 35, and the organic solvent is precipitated and separated into the carbon dioxide 37 and the regenerated organic solvent 11. As shown in the figure, the regenerated organic solvent 11 is returned to the spent fuel reprocessing step 1 to be reused, and although not shown, the carbon dioxide 37 is recompressed to form supercritical carbon dioxide in a supercritical fluid state. Returned to 27. In the above embodiment, carbon dioxide is used as the supercritical fluid. However, the present invention is not limited to this, and other supercritical fluid may be used.
[0006]
FIG. 2 shows a system diagram of equipment for carrying out the organic solvent cleaning and regeneration method having the above-described steps. The reaction tank 41 receives the used organic solvent 3 and the cleaning aqueous solution 21, mixes them, and receives supercritical carbon dioxide 27. The reaction tank 41 also discharges the liquid waste liquid 31 to an appropriate facility and sends the supercritical carbon dioxide 33 in which the organic solvent is dissolved to the break vessel 43 through the pressure reducing valve 47. Then, in the low-pressure break vessel 43, the regenerated organic solvent 11 and the gas or liquid carbon dioxide 37 are separated. The carbon dioxide 37 is returned to the storage tank 45 and reused.
[0007]
Next, another embodiment of the present invention will be described with reference to FIG. Referring to FIG. 3, the spent organic solvent 3 produced in the same manner as in the above embodiment from the spent fuel reprocessing step 1 is supercritical (pressure 12-20 MPa, temperature 40-60 ° C.). Carbon 27 is allowed to act to dissolve 51 the used organic solvent 3 in supercritical carbon dioxide. The cleaning aqueous solution 21 is further mixed 55 with the supercritical carbon dioxide 53 in which the used organic solvent 3 is dissolved. By this mixing 55, the deteriorated solvent in the used organic solvent 3 is dissolved in the cleaning aqueous solution 21, and the waste liquid 57 composed of the aqueous solution in which the deteriorated solvent is dissolved is separated. The supercritical carbon dioxide 33 obtained by dissolving the organic solvent thus obtained is then depressurized to a pressure of 10 MPa or less by the vacuum separation operation 35, the organic solvent is precipitated, and the carbon dioxide 37 and the regenerated organic solvent 11 are separated. To be separated. The regenerated organic solvent 11 and the carbon dioxide 37 are then treated in the same manner as in the previous embodiment. In this embodiment, a supercritical fluid other than carbon dioxide can be used.
[0008]
FIG. 4 shows a system diagram of equipment for carrying out the organic solvent cleaning and regeneration method described as the second embodiment. The reaction tank 61 receives the used organic solvent (containing a deteriorated solvent) 3, and supercritical carbon dioxide 27 acts on this to dissolve it. Spent organic solvent 3 supercritical carbon dioxide 53 which was dissolved is fed further into the reaction vessel 63, where it is contacted with supercritical carbon dioxide 53 washing solution 2 1 TogaMuko stream. The countercurrent contacting, degradation solvent dissolves in the cleaning solution 2 1, the organic solvent becomes as one likes dissolved in supercritical carbon dioxide. Degradation solvent-containing cleaning solution 2 1 is taken in isolation as waste 57, also supercritical carbon dioxide 33 dissolved organic solvent is fed to break the vessel 43 through a pressure reducing valve 47. The subsequent processing is the same as in FIG.
[0009]
【The invention's effect】
As described above, according to the present invention, a supercritical fluid having selective solubility in which an organic solvent such as tributyl phosphate and n-dodecane is dissolved but an aqueous solution is not dissolved is used. However, since the supercritical fluid can be reused, the amount of waste liquid treated can be reduced and the cost can be reduced.
[Brief description of the drawings]
FIG. 1 is a process diagram showing an embodiment of the present invention.
FIG. 2 is a system diagram of equipment for carrying out the method according to the embodiment.
FIG. 3 is a process diagram showing another embodiment of the present invention.
FIG. 4 is a system diagram of equipment for carrying out the method according to another embodiment.
FIG. 5 is a process diagram showing a conventional method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Reprocessing process of spent fuel 3 Used organic solvent 11 Recycled organic solvent 21 Washing aqueous solution 23 Mixture 25 Mixture 27 Supercritical carbon dioxide 31 Waste liquid 33 Supercritical carbon dioxide 35 dissolved organic solvent Depressurization and separation operation 37 Carbon dioxide 41 Reaction tank 43 Break vessel 45 Storage tank 47 Pressure reducing valve

Claims (1)

The supercritical fluid is brought into contact with the spent organic solvent containing the deteriorated solvent used in the extraction of the spent nuclear fuel reprocessing step, the spent organic solvent is dissolved in the supercritical fluid, and the spent organic solvent is dissolved. and as one likes dissolved and dissolving the washed aqueous solution with a supercritical fluid to the cleaning solution deterioration solvent was countercurrent contact with the organic solvent in the supercritical carbon dioxide, separating the aqueous solution containing the deterioration solvent as waste, thereafter A method of cleaning an organic solvent for reprocessing spent nuclear fuel, wherein the supercritical fluid in which the organic solvent is dissolved is subjected to a vacuum separation operation to separate it into a supercritical fluid and an organic solvent.

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