History and current status of French dry technologies developments

Bernard Boullis and Philippe Brossard
Radiochemistry and Processes Department, CEA Rhône Valley Center
Nuclear Energy Division of CEA

 

Non aqueous technologies have a long history of research work. Speaking of France, the investigation of a volatilization process to treat irradiated fuels was initiated in the late 50’s and, in collaboration with Russia, the process was developed up to pilot scale in the early seventies.  Due to technical difficulties and a fierce competition with aqueous processes (PUREX) it was not chosen to be implemented in the COGEMA plant of La Hague and studies in the field were more or less shelved.

A renewed interest appears when the issue of highly radioactive waste management raised about 10 years ago.  Indeed, in December 1991, the French Parliament carried an Act specifying the major areas of investigation to determine operational solutions for the back-end of the fuel cycle.  One of the areas should considers separation/transmutation solutions capable of significantly reducing the mass and radio‑toxicity of the long-lived radionuclides that constitute the principal long-term risk.  In that frame it became evident that pyrochemical processes possess unique features that make them best suited to treat long-lived radionuclides transmutation targets. The capability of pyrochemical processes to deal with highly irradiated materials could represent an advantageous alternative to hydrometallurgical processes, which could in some cases prove less compatible with the high burn‑up and short cooling times proposed under some scenarios. The more distant future options, such as dedicated fuel cycles or transmutation in molten salt reactors, provide further impetus for exploring these processes. 

More recently, new concepts for advanced nuclear systems could also benefit from some features of pyrochemical cycles: in situ reprocessing, combined management of all the transuranic nuclides (plutonium and the minor actinides), tight integration with refabrication processes, minimal inventory of radio‑toxic materials confined in the cycle.

For all these potential applications, the main objective for processing irradiated fuels or transmutation targets lies in the ability to quantitatively recover the actinides for recycling.  This key point is at the center of the CEA R&D program in pyrochemistry. The current work focuses primarily at laboratory-scale research without seeking significant technological developments except those that might appear necessary to obtain a preliminary assessment of the operating conditions for the processes investigated. This approach addresses a broad spectrum of possible applications with the following objectives:

q       consolidate our knowledge of the concepts already described or tested elsewhere,

q       explore any promising options,

q       proceed with a preliminary selection of concepts for more thorough investigation of the aspects affecting their possible implementation,

q       perform one or more demonstrations on a few tens of grams of representative irradiated material as exhaustively as possible.

A related objective is to acquire greater basic knowledge of the chemistry of the elements in the proposed media (molten salts), and of process engineering considerations in order to prepare for possible subsequent development of specific applications.