| Abstract: | Grout formulations have been investigated in Nevada Nuclear Waste Storage Investigations Project, for possible nuclear waste repository sealing applications focused in the Yucca Mountain Area (in welded tuff). A shrinkage compensated cement was chemically modified with siliceous reactants to enhance the chemical compatibility with a siliceous tuff. Fluids in contact with the grouts were measured at 150 °C and 200 °C, and the solids were characterized. Well-crystallized Al-substituted tobermorite and truscottite were observed, and sometimes xonotlite as dominant cementitious phases. Comparisons of solid phases and solution phases are made with a second grout incorporating siliceous modifiers in a Class H cement. Exposures to 150 °C hydrothermal conditions have not produced significant detrimental mechanical behavior of the seal material. The thermal decomposition of ettringite, an expansive calcium sulfate aluminate hydrate, resulted in a small increase in the porosity of the grout, but on a very small fine scale. |
