Study On Leaching Behavior And Model Of HLW-glass Under Repository Conditions

It is a very important thing to protect environment and have a sustained development of nuclear industry to safely dispose high-level radioactive waste. This paper studies on several sections, including the leaching test of simulated HLW-glass under low oxygen repository conditions, analyzing leached glass specimens, studing the glass leaching behavior using geochemistry model and Monte Carlo method, immobilizing Sr with SHS and characterising its products.The leaching behaviors of HLW-glass under repository condition-low oxgen were systemically studied. According to MCC-1 method, the fabricated HLW-glass specimens were leached in static condition for 546d. The compositions of leachate were analyzed by ICP-MS and ICP-AES, and the results showed that the leaching rate and mass loss rate were lower than that at atmosphere, and indicted that glass had less corrosion under low oxgen condition. The leached surfaces were detected by XRD and SEM/XEDS. The results showed no diffraction peak appeared on the surface under 90℃; During the same leaching time, there were some little diffraction peaks appeared on the glass under 150℃ after leaching 182d, which may formed the compound of Ca-Si-Al-Fe-(P), Some expressions are emploied to explain the leaching mechanism. The glass dissolution process and leaching behavior of Si element were controlled by both of ion-diffusion reaction and glass-net dissolution reaction, or more others; the leaching behaviors of Na and B element were controlled by ion-diffusion reactions under 90℃ . The leaching behavior of HLW-glass and pyrochlore-rich synroc under multi-barrier media was respectively studied. The results of mass loss rate showed that pyrochlore-rich synroc had a low mass loss rate with better durability. Especially, the barrier media-granite + Fe3O4 and bentonite + Fe3O4, had more effection on the mass loss rate than others in the first half year. The results of XEDS suggested that U and Ba were enriched on the surface;at the same time, Ca and Ti had a little depleted on the surface ofpyrochlore-rich synroc; the results of XRD and SEM indicated that Fe3O4 can increase the corrosion of glass and pyrochlore-rich synroc; The results of glass mass loss rate showed that bentonite had the most corrosive to the glass specimens among barrier media; the results of XEDS indicated that Ca Fe and Al element were enriched on the glass surfaces, Si and Mg had slightly depleted, and Na was completely depleted.The geochemical model, PHREEQC (2.7 version), was used for calculating the leachate compositions and the sediment phases formed on the glass surface. The results showed that the calculating results were well agreed with the experiment results. The calculating results of the sediment phases were consistent to analysed one. All of these results suggested that the geochemical model-PHREEQC could be a good tool to study the leaching behavior of glass under repository conditions. And the results also suggested that the equilibrium in leaching system was based on the interaction among three parts: the glass, the solution and the sediment phases.A Monte-Carlo model was established based on one component-SiO2 and used for calculation of corrosive depth of glass with different content of SiO2. The study indicted that the more content of SiO2 caused the less corrosion on the glass. The effection of different stochastic value of ion exchange reaction was also investigated. And the results showed, when the stochastic value of ion exchange was lower than that of invert reaction, the glass had less corrosion. On the other hand, the calculating results of the corrosion depth were consistent with the experimental results during 14d, which suggested the Monte Carlo model was suitable for studying the glass corrosion depth during that period. The Monte-Carlo model presented an effective tool to leaching mechanism of HLW glass form.The high-temperature (combustion) self-propagating synthesis (SHS) was used for immobilization of Sr element in perovskite synroc. The preliminary study indicated that the SHS-syn...