Water Radiolysis and Chemical Production Rates Near Solid-Water Boundaries

Water radiolysis is the dissociation of water molecules by ionizing radiation from the decay of radionuclides. Primary products of water radiolysis include reactive chemicals, such as H2 and H2O2. For this reason, radiolysis is studied in many domains, including nuclear waste, microbiology and planetary evolution. In order to understand the importance of radiolysis in many of these environments, accurate quantification of radiolytic production rates is vital. In this dissertation, I present a new quantitative model calculating radiolytic production rates at solid-water interfaces and apply it to understand the role that radiolysis plays in various environments. This radiolytic model is the first to explicitly calculate radiolytic production due to α-, β- and γ-radiation near solid-water interfaces. We use this model to investigate the effects of radiolytic compounds on the dissolution rate of spent nuclear fuel. The production of rate of H2 and H2O2, which control the dissolution rate of the fuel, depends on the amount and type of radiation surrounding breached nuclear spent fuel rods. Understanding the distribution of radiolytic products is important in assessing different hazards associated with spent fuel storage and the potential release of radionuclides into the environment. We find that in old (1000-year-old) spent fuel α- radiation dominates radiolysis, while β- and γ-radiation control the production rates near young (20-year-old) spent fuel. Radiolysis also is an important process in understanding the extent of life on Earth, as well as possibly providing a means for life on Mars. We investigate the significance of water radiolysis in sustaining microbial communities in Earth’s oceanic crust and the potential extent of radiolysis in wet martian environments (such as the ancient martian surface and the present martian subsurface). These two studies focus specifically on the production of radiolytic H2 as an electron donor. H2 is an important source of energy in these two environments where there other resources for microbes are limited. In the oceanic basaltic aquifer of the South Pacific Gyre, we find that radiolytic H2 production yields depend largely on the width of fractures in basalt and on radionuclide concentrations. We show that in old seafloor (>10 Ma), where there are no other readily available electron donors, radiolytic H2 may dominate and is able to support up to 103 cells in the water adjacent to a square cm of basaltic fracture. The extent of water radiolysis on Mars can be determined for water-saturated martian environments, such as the ancient martian