Abstract

The following potential backfill materials have been studied: phillipsite, clinoptilolite, mordenite, montmorillonites, vermiculites, chlorite, kaolinite, labradorite, and shales. Each of these was hydrothermally reacted with Cs/sub 2/MoO/sub 4/, a possible cesium phase in spent fuel elements, in the presence of a bittern brine at 200/sup 0/C for two months under a confining pressure of 300 bars. Analyses of the product solutions indicated that montmorillonites, vermiculites, and zeolites fixed (as determined by resistance to K+ washing) the greatest fractions of the added cesium while other minerals, labradorite, and shales fixed only about 10% of the added cesium. For example, montmorillonite from Arizona and phillipsite from California fixed 47 and 50%, respectively, of the cesium added. X-ray diffraction analysis of the solid products revealed that cesium was fixed in the interlayers of montmorillonite as indicated by the collapse of the c-spacing from 15.5 to 12.1 A. Cesium interaction with clinoptilolite and mordenite zeolites did not result in their alteration or in any new cesium minerals as observed by x-ray diffraction. The cesium aluminosilicate mineral, pollucite, was detected only with phillipsite-cesium interactions in brine unlike in the hydrothermal interaction of these materials with Cs/sub 2/MoO/sub 4/ in deionized water where the presence ofmore » pollucite was found earlier to be pervasive. Powellite, CaMoO/sub 4/, was the only new phase found in all these interactions by x-ray diffraction which resulted from the combination of calcium from brine with molybdenum from Cs/sub 2/MoO/sub 4/. Montmorillonites among clay minerals and zeolites such as clinoptilolite and mordenite seem to be the best backfill materials in salt.« less

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