During research activities at CEA-Fontenay-aux-Roses solid wastes are produced that are contaminated with a, beta, g emitters (hot-cells studies) and with a emitters only (glove-box experiments). In order to improve the management of these wastes, two facilities are engaged:
- ELISE, a group of glove-boxes for the treatment of a active solid wastes;
- PROLIXE, a hot-cell for the treatment of a, beta, g active solid wastes.
In these facilities, leaching processes were developed in order to:
- decontaminate these wastes, to obtain a level of the conditioned wastes which will be suitable for surface disposal (i.e. a activity < 3.7 GBq/t);
- recover actinide elements and recycle redox agents.
The leaching process is based on the use of electrogenerated oxidizing agents (Ag(II) in nitric acid or reducing agents (Cr(II), Ti(III), V(II) in sulphuric acid, which are particularly suitable to provoke the dissolution of plutonium dioxide.
The study of fuel reprocessing and the production of transuranium isotopes produces solid wastes that are contaminated with alpha, beta, and gamma emitters for hot cells studies and with alpha emitters only for glove box experiments. In order to improve the management of these wastes, 2 facilities are engaged;
ELISE, a group of glove boxes for the treatment of alpha active solid wastes, and PROLIXE, a hot cell for the treatment of alpha, beta, and gamma active solid wastes.
In these facilities, leaching processes were developed in order to decontaminate these wastes, especially in alpha emitters, to obtain a level of residual alpha contamination which will be suitable for surface site disposal; and to recover actinide elements and recycle redox agents. The leaching process is based on the use of electrogenerated oxidizing agents in nitric acid or reducing agents in sulphuric acid, which are particularly suitable to provoke the dissolution of plutonium dioxide.
An electrolytic process for the recovery and the recycling of silver from concentrated leaching solutions has been studied. After laboratory scale experiments, an electrolyzer with a 30 l capacity has been implemented.
The reducing leaching process was studied at laboratory scale, based on the use of electrogenerated powerful reducing agents. The results were very encouraging: high plutonium dissolution yields were achieved and it was found that the process was insensitive to the presence of cellulosic materials.
Approximately 150 kg of metallic wastes contaminated with alpha, beta and gamma emitters have been processed in PROLIXE.
Exhaustive decontamination of these wastes was achieved.
The electrochemical oxidation of organic species has also been investigated to recover alpha, beta and gamma emitters (particularly the plutonium) from contaminated organic materials and to destroy completely some organic compounds.
- oxidizing dissolution of different compounds of plutonium such as fluoride, phosphate, carbide, nitride...; exhaustive alpha decontamination of zircaloy hulls of irradiated mixed oxide fuel by Ag(II) leaching method; electrochemical destruction of organic species.
- characterisation of redox couples, comparison of their performances and choice of reaction media will be realized.
- recycling of electrochemical mediators (the study of processes for recycling of silver will be performed).
Pilot scale experiments:
- silver(II), leaching process: in PROLIXE and ELISE facilities, runs on about 20 kg of different kind (mineral, metallic, organic) of a, beta, g wastes will be achieved. More than 1 500 kg of wastes will be treated in 2 years.
- recovery of actinides and redox mediators: the recovery of actinides will be systematically realized. The recycling of silver will be performed at pilot scale.