Immobilization in Cement of Ion Exchange Resins
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IMMOBILIZATION IN CEMENT OF ION EXCHANGE RESINS
P. LE BESCOP, P. BOUNIOL, M. JORDA Commissariat a l'Energie Atomique, DRDD/SESD BP n° 6, 92265 Fontenay aux Roses
ABSTRACT Recent studies were carried out in France to improve ion exchange resin solidification in cement-based matrices. Work is conducted on different types of waste - cationic, anionic and mixed-bed resins - under regenerated and loaded states. The main objective is to increase the waste incorporation rate up to roughly 50% (in volume). Hydraulic cement formulas are developed taking into account waste chemistry, in particular the presence of ions which inhibit setting. THE CONTEXT Ion exchange resins (IER) represent the most important waste in terms of " becquerels " generated by French nuclear power plants, essentially pressurized water reactors (PWR). They represent an annual volume of about 900 m3, which must be packaged for disposal. A large part is found in the form of mixed anionic/cationic beds containing borates, the resins being discharged without regeneration. Added to the IER from the French electrical utility EDF is a smaller and diversified production from the COGEMA reprocessing plants and the CEA 3 research centres (a few dozen m /year). These are often regenerated, low-level IER. A large number of IER packaging processes have been investigated worldwide [1], the most widely applied consisting of direct immobilization in cement (Ringhals, Sweden), bitumen (Olkiluoto, Finland) and thermoset polymers (Chooz, France). A rough classification of these different matrices has been established. In France, the reference solution for the time being, for disposal by ANDRA, consists of immobilization in polymers. Some fifteen years ago, unsatifactory tests led EDF to abandon immobilization in cement. The problems encountered consisted essentially of the dimensional instability of the immobilized waste packages, sometimes leading to cracking and bursting of the packages, and often accompanied by very long setting times. Interaction mechanisms (ions exchange, swelling) between the IER and the cement paste in the course of setting, the cause of the problems encountered, have been the subject of many studies [1, 3, 4, 5, 6], and it appears reasonable today to present an IER cementation process to the waste generators, allowing an immobilization volume fraction of about 50%. A patent has been filed accordingly by the CEA [7], extended in particular to the USA. Two variants have been developed in parallel. . On the basis of ANDRA specifications on homogeneous waste packages, the proposal of a packaging process likely to offer containment power compatible with the leach resistance requirements. On the basis of ANDRA specifications on heterogeneous waste packages, the proposal of a packaging process including a peripheral overembedment consisting of a high containment capacity grout, substituting for and performing the r6le of the biological schielding. In this case, the containment guarantee provided by the overembedment is assessed on the Mat. Res. Soc.
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