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UTILISATION OF SUPPORTED LIQUID MEMBRANES FOR THE TREATMENT OF REPROCESSING CONCENTRATE.

Objective

DEVELOPMENT OF NUCLEAR ACTIVITIES AT THE REPROCESSING PLANT OF MARCOULE MUST LEAD TO AN INCREASE OF LOW AND MEDIUM ACTIVITY WASTE, IT IS FORECAST TO SUBSTITUE SOON THE CLASSICAL TREATMENT USING CHEMICAL PRECIPITATION BY A MORE EFFICIENT TREATMENT BY EVAPORATION IN ORDER TO DECREASE THE ACTIVITY DISCHARGED IN THE RHONE.
THIS NEW PROCESS LEADS TO AN INCREASE OF BITUMINIZED WASTES TO BE DISPOSED IN DEEP GEOLOGICAL FORMATION, DUE TO THE HIGH SODIUM NITRATE CONCENTRATION IN THE CONCENTRATE. IT'S THE REASON WHY IT COULD BE ECONOMICALLY INTERESTING TO DECONTAMINATE THIS CONCENTRATE SO THAT THE GREATEST PART WILL BE DISPOSED IN SHALLOW LAND BURIAL AND A VERY SMALL PART IN GEOLOGICAL FORMATION.
TAKING INTO ACCOUNT THE RADIOCHEMICAL CHARACTERISTICS OF THE CONCENTRATE AND TO ALLOW A SHALLOW LAND BURIAL DISPOSAL (FOR INSTANCE CSM) CESIUM STROTIUM AND ACTINIDES MUST BE REMOVED WITH DF HIGHER THAN 50 FOR FISSION PRODUCTS AND 100 FOR ALPHA EMITTERS. THE PROCESS WILL BE ECONOMICALLY INTERESTING IF CONCENTRATION FACTOR EXCEEDS 40.
TO DECONTAMINATE THE CONCENTRATES FROM MARCOULE IT IS INTENDED TO USE SUPPORTED LIQUID MEMBRANES. THIS PROCESS ALLOWS TO TRANSFER SELECTIVELY NUCLIDES FROM LIQUID WASTE TO A STRIPPING SOLUTION, SO THE ACTINIDES CAN BE RECYCLED AND FP IMMOBILIZED IN GLASS.
Reprocessing operations involve the production of liquid waste of medium activity which is treated by evaporation. The distillates are released to the environment. In contrast, all other elements, whether radioactive or not, are concentrated and condensed to solutions of very high salinity. We are interested in decontaminating such concentrates.

Reprocessing operations lead to the production of radioactive medium activity liquid waste which is treated by evaporation, the distillates being discharged into the environment. This, however, leaves elements, both radioactive and nonradioactive, concentrated into solutions of very high salinity. These concentrates from reprocessing plant evaporators have to be stored in geological storage sites in view of their strong caesium, strontium and actinides activity. These elements, however, contained in acid and high sodium nitrated content liquid waste, can be removed by means of selective extractants, using the supported liquid membrane (SLM) technique, which allows the liquid wastes to be stored in surface sites, the actinides and long life fission products being respectively recycled and concentrated into reduced volumes.

The removal of the actinides is done by means of an octyl N N diisobutyl carbamoyl methyl phosphine oxide (CMPO) based liquid membrane, whereas the removal of the caesium and strontium involves crown ethers.

Supported liquid membranes have the advantage, in particular, of producing very small quantities of extractant, but, on account of these very small volumes of extractant, they generally have poor stability. The extractant, the diluent and the phase modifier, that constitute the organic phase impregnating the membrane, play a vital role in SLM stability. The support also affects stability by its nature and geometry.

For the extraction of strontium, the most lipophilic extractant, DtBu 18 C 6, enables higher strontium transfer kinetics to be attained than with DC18 C6. As regards caesium, the extremely lipophilic nDec B21 C7 is the most efficient. Unlike the case of strontium, even with this compound, caesium cannot be quantitatively removed, due to the competition from the very high concentration of sodium ions present in the concentrate.
Stable membranes are obtained with DC18 C6 or DtBu18 C6 diluted in alkylbenzene compounds (hexylbe nzene, tridecylbenzene) with an added phase modifier such as decanol or especially isotridecanol.
The highest strontium transfer kinetics were obtained with the DC18 C6 hexylbenzene isotridecanol mixture.
2.1. EXTRACTION OF ACTINIDES:
2.1.1. CHOICE OF THE COMPONENT AND CONCENTRATION OF THE STRIPPING SOLUTION.
2.1.2. INTEREST OF USING A SECOND MEMBRANE. CHOICE OF THE NAOH CONCENTRATION FOR THE SECOND STRIPPING SOLUTION.

2.2. EXTRACTION OF STRONTIUM:
2.2.1. CHOICE OF THE DILUENT IN ORDER TO IMPROVE THE LIFE-TIME OF THE S.L.M. AND DECREASE THE TRANSFER OF ACIDITY THROUGH THE S.L.M.

2.3. EXTRACTION OF CESIUM:
2.3.1. SYNTHESIS OF B21 C7: FOR REMOVAL OF CESIUM.
2.3.2. CHOICE OF THE DILUENTS ABLE TO DISSOLVE SUBSTITUTED BENZO CROWNS.

2.4. LABORATORY SCALE EXPERIMENTS ON HOLLOW FIBERS MODULES.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Commissariat à l'Energie Atomique (CEA)
Address
Centre D'études De Cadarache Sere-ders
13113 Saint-paul-lez-durance
France