Hydrothermal Reaction and Dissolution Studies of CsAISi ₅ Or ₁₂ in Water and Brines

Abstract

The alteration of CsAlSi 5 O 12 , a possible host for 137 Cs in tailored nuclear waste ceramics, was studied under simulated nuclear waste repository conditions of 100°, 200°, and 300°C with a confining pressure of 30 MPa. The cesium radiophase was found to be quite stable in water or 3N CaCl 2 , or 3N MgCl 2 but not in 3N NaCl or 3N KCI or a bittern brine. The acid resistance of CsAlSi 5 O 12 can be deduced from its stability in hydrothermal MgCl 2 brine. Possible reaction mechanisms include the formations of pollucite and quartz in deionized water and the formation of Na or K feldspars and quartz in the presence of NaCl or KCl brines, respectively. A comparison of the various cesium aluminosilicates indicates that pollucite (CsAlSi 2 O 6 ) is the best candidate for cesium‐137 immobilization.