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Content archived on 2024-04-15

DECONTAMINATION OF SOLID ALPHA WASTES AND RECOVERY OF THE PLUTONIUM (PROLIXE FACILITY)

Objective

NUCLEAR ACTIVITIES IN THE RADIOCHEMISTRY BUILDING OF FONTENAY AUX ROSES NUCLEAR RESEARCH CENTER CONCERN PRINCIPALLY THE STUDY OF FUEL REPROCESSING AND THE PRODUCTION OF TRANSURANIUM ISOTOPES. DURING THESE ACTIVITIES SOLID WASTES ARE PRODUCED THAT ARE CONTAMINATED WITH "ALPHA BETA GAMMA" EMITTERS FOR HOT CELLS STUDIES AND WITH A EMITTERS ONLY FOR GLOVE-BOX EXPERIMENTS.
IN ORDER TO IMPROVE THE MANAGEMENT OF THESE WASTES IT HAS BEEN DECIDED TO BUILD NEW FACILITIES :
A/A GROUP OF THREE GLOVE BOXES NAMED ELISE FOR THE TREATMENT OF "ALPHA" ACTIVE SOLID WASTES
B/A HOT-CELL (PROLIXE FACILITY) FOR THE TREATMENT OF "ALPHA BETA GAMMA" ACTIVE SOLID WASTES.

IN THESE FACILITIES WE WILL DEVELOP LEACHING PROCESSES IN ORDER TO :
1/ DECONTAMINATE THESE WASTES EXPECIALLY IN A EMITTERS TO OBTAIN A LEVEL OF ALPHA CONTAMINATION <0,1CI XT -1 OF THE CONDITIONNED WASTES WHICH WILL BE SUITABLE FOR SURFACE SITE DISPOSAL
2/ RECOVER ACTINIDE ELEMENTS, PARTICULARLY THE HIGHLY VALUABLE PLUTONIUM.
THESE TWO ITEMS CONSTITUTE THE MAIN OBJECTIVES OF THE PRESENT PROGRAMME.
In order to improve the management of solid wastes, contaminated with alpha, beta and gamma emitters or with alpha emitters only, it had been decided to build the following new facilities:
a group of 3 glove boxes, named ELISE, for the treatment of alpha active solid waste;
a hot cell, PROLIXE, for the treatment of alpha, beta and gamma emitting solid wastes.

In these facilities leaching processes were developed in order to:
decontaminate these wastes, especially the alpha emitters, in order to obtain a level of residual alpha contamination of less than 0.1 Curies per tonne of the conditioned wastes, which will be suitable for surface site disposal;
recover actinide elements, particularly the highly valuable plutonium, from the leachates.

The processes developed are sufficiently flexible to be able to accommodate solid wastes produced in other facilities. Various types of waste have been studied and laboratory studies have been conducted to develop the leaching process, based on the use of electrogenerated silver(II) species, which is particularly suitable for the dissolution of plutionium oxide.

An important result obtained during the experiments performed in ELISE was related to the recyclability of the leachates after concentration, allowing the minimisation of the generation of secondary wastes. To be able to realise these experiments specific apparatus was designed, built and operated in hot conditions, particularly the silver (II) electrolyser and the cyclone evaporator for leachate concentration. Based on the results obtained on laboratory and pilot scales, it was possible to design conceptual flow sheets for industrial facilities.

In conclusion, it appears that the exhaustive decontamination of alpha and alpha, beta and gamma emitting solid wastes is certainly feasible at an industrial level using leaching processes. This is particularly true for massive metallic wastes. In the case of the other wastes the feasibility of such a goal is still questionable, nevertheless, large plutonium recovery yields are obtainable in the case of the treatment of incineration ashes. For organic solid wastes leaching with electrogenerated reducing agents can be an alternative to the oxidising process.
B.1. WASTES ANALYSIS TO DETERMINE THEIR COMPOSITION AND THE NATURE AND ACTIVITY OF THE RADIOCONTAMINANTS.
B.2. WASTES CRUSHING : CHARACTERIZATION OF THE SIZE OF PARTICLES OBTAINED AFTER THE CRUSHING OF THE WASTES ACCORDING TO THEIR NATURE.
B.3. PRETREATMENT : IN THE SPECIFIC CASE OF THE TREATMENT OF ASHES PRODUCED IN OTHER FACILITY, THE PRETREATMENT PROCEDURE TO ELIMINATE CHLORIDE ION WILL BE DEFINED.
B.4. LEACHING TESTS : ACCORDING TO THE NATURE OF THE WASTES TO BE TREATED SPECIFIC LEACHING EXPERIMENTS WILL BE PERFORMED. DIFFERENT LEACHANTS WILL BE USED : NITRIC ACID, ACIDIC LEACHANTS WITH ELECTROGENERATED REDUCING OR OXIDIZING AGENTS.
B.5. EQUIPMENT DESIGN : THE ELECTROLYZER FOR THE GENERATION OF REDUCING OR OXIDIZING AGENTS WILL BE DEFINED.
B.6. SECONDARY WASTES : AN OPTIMISATION OF THE MANAGEMENT OF SECONDARY WASTE (GAZEOUS WASTES, DISTILLATED)WILL BE REALIZED.THE OPPORTUNITY TO RECOVER SOME CHEMICALS LIKE SILVER WILL BE CONSIDERED.
B.7. RECOVERY AND PURIFICATION OF ALPHA EMITTERS : THE STUDY OF THE RECOVERY OF ALPHA EMITTERS, ESPECIALLY THE PLUTONIUM USING EXTRACTION CHROMATOGRAPHY TECHNIQUE WILL BE REALIZED
B.8. DESIGN OF PROCESS FLOWSHEETS : FOR THE DIFFERENT WASTES TO BE STUDIED, SPECIAL PROCESS FLOWSHEETS WILL BE DESIGNED. A COMPARISON OF THE PERFORMANCE OF THESE PROCESSES WITH THOSE OF CONVENTIONNAL TECHNIQUES WILL BE ACHIEVED.

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Coordinator

Commissariat à l'Energie Atomique (CEA)
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Address
Centre d'Études de Fontenay-aux-Roses
92265 Fontenay-aux-Roses
France

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