Hydrothermal Reactivity of Simulated Nuclear Waste Forms and Water-Catalysed Waste-Rock Interactions

Abstract

A key consideration in the long term safe disposal of nuclear wastes is their stability in the repository environment. If the assemblage of waste phases is not in thermodynamic equilibrium with the assemblage of minerals that make up the repository formation, there will be at least a tendency toward chemical reaction between the wastes and the rock. Such reactions are sometimes very similar to naturally occurring geochemical processes and they are greatly enhanced by the presence of water or brine. Heat from young wastes can raise the temperature of the aqueous solutions into the 100 to 400°C temperature range, exactly the temperature range of some of the most reactive fluids in the natural environment. These processes can result in an entirely new object as the long term waste form or “source term” for radionuclides. In this paper we will draw upon recent experimental results to illustrate the nature and implications of hydrothermal interactions. We will consider three waste forms— spent fuel, a glass and a crystalline ceramic—and three repository rock types—basalt, shale and salt. The results presented here extend the concepts developed in our earlier paper (1).