Mineralogy and Geochemistry of a Bentonite Pellets Column Heated for 10 years

Abstract A common design of a high-level radioactive waste (HLW) disposal system consists the canisters emplaced in tunnels or shafts, with space between heat-emitting and surrounding rock filled bentonite-based material. Understanding behavior this barrier, particular effect prolonged heating on its properties, is important to assess barrier’s long-term performance. The objective present study was add understanding supply experimental data about state bentonite hydrated heated for long period time. To that end, 50 cm column Wyoming-type pellets at base 140 °C (simulating canister) while synthetic sodium-chloride-rich groundwater including sulfate, calcium, magnesium supplied through upper surface almost 10 y. At end experiment half saturated, but lower water content decreased sharply toward heater, where it close 0%. No relevant mineralogical changes occurred, main component continued be predominantly sodium montmorillonite no structural respect initial one. In area temperatures were >60°C material very dry, however, smectite not able completely develop 1-layer hydrate after 48 h stabilization RH 55%, although expandability fully recovered when liquid water. ions solubilized as result water-content increase transported heater concentrated two distinct areas: calcium chlorides closer than sulfates. contact, microstructure dense packets carbon Na-S-coated cavities. Precipitation calcite sulfates possibly dissolution silica minerals also took place heater.