INTERACTION OF ALUMINOPHOSPHATE GLASS WIT H WATER AT ELEVATED-TEMPERATURES

Interaction of an Na-Al-P glass (used as a solidifying matrix for radi oactive waste), which contains 3 wt % Cs + 3 wt % SrO, with water at 2 5-30 degrees C and saturated vapor pressure or 200 bar is studied. The run duration is varied from 7 h to 26 weeks. After this period, the N a, Al, Cs, Sr, and P concentrations in the solution are measured and u nder glass alteration is characterized by analytical electron microsco py. microprobe, and X-ray. The glass alteration involves two reciproca l processes, glass dissolution and crystallization of new-formed phase s on the glass surface. This produces two zones: the inner, leached zo ne consisting of block-like glass relicts (30-50% porosity) and the ou ter, deposition zone in which goyazite Sr(Al, Fe)(3)(PO4)(2)(OH)(5) . H2O crystals mainly deposit. The process is complicated by a diffusion ion-exchange removal of Na and Cs from the glass. The activation ener gy of Na and Cs solubilization is about 22 kcal/mol. The Sr concentrat ion in the closed system is controlled by the goyazite solubility. The thermodynamic characteristics of goyazite are derived from the experi mental data. The strontium concentrations are estimated as a function of the solution composition with the experimental data. A rock added t o the system either shows no effect on the Sr concentration (granite) or increases it only slightly (mafic and ultramafic rocks at 300 degre es C). Cesium is virtually not bound by the new-formed phases and rema ins completely in solution. Mafic and ultramafic rocks decrease the eq uilibrium Cs concentration by 1-2 orders of magnitude at 170-300 degre es C but have no effect at lower temperatures.