Radiation effects on chemistry

The effects of ionizing radiation on simple solution systems have been studied by computer simulations of radiolysis in salt brine and dilute groundwater. The codes assume a closed homogeneous solution system in which reactants and products cannot enter or leave the system and species cannot diffuse towards or away from the source of radiation. Radiolysis of simple dilute groundwaters appears to be rather insensitive to the expected range of pH, temperature, and pressure in repositories. It is unclear whether this conclusion also holds for salt brine.

The waste-package environment is much more complex than systems that have typically been studied in the past. None of the conceptual models account for potential interactions with the solids present in the waste-package and host rocks. This limitation results primarily from a lack of data and the currént restriction to homogeneous (solution only) reactions. Because the rocks and waste-package materials are the primary pH, Eh, and chemical buffers in the system, radiolysis experiments that neglect their presence cannot definitively address the expected influence of radiation on solution chemistry.

Experimental evidence suggests that radiolysis will not cause significant changes in waste-form leaching, or significant degradation in the physical stability of clays, crystalline host rock, and packing materials. However, experiments in salt suggest that irradiation and heat could produce corrosive species that might affect canister corrosion and waste-form leaching. The possibility of enhanced container corrosion resulting from nitric acid formation in the moist air of an unsaturated tuff repository also warrants attention.