Different methods to synthesize sodalite, as a matrix for conditioning chloride spent salts from pyroprocesses

Abstract

The pyrometallurgical processing of spent nuclear fuel generates a chloride salt waste containing alkali-metal, alkaline-earth, and some rare-earth fission products. Sodalite, a naturally occurring mineral containing chlorine, has been investigated as an immobilization matrix for this salt waste. To this end different routes for the synthesis of sodalite have been followed: on one hand, direct synthesis from kaolinite, metakaolinite, or from silica and sodium aluminate have been carried out; on the other hand, a synthesis from Zeolite 4A used for preliminary decontamination of the salt by ion-exchange has been performed. The former allows to condition the waste salt as a whole, whenever discarding an entire process salt batch becomes necessary; this is the case when an electrorefiner plant has to be decommissioned, or in the event of a severe process upset; the latter is more suitable for routine operations, which better require the clean-up of the salt and its recycle to the electrorefiner, thus avoiding the production of huge quantities of solidified wastes to be disposed of.