Abstract

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 surface or the present martian subsurface. Using the fractured rock radiolytic model as well as a previously developed sediment radiolytic model, we calculate potential H₂ production rates for eleven martian lithologies assuming contact with water. The highest rates on Mars are for water-saturated material with the radionuclide concentrations of Acidalia Planitia, a region with surface materials that are enriched in uranium and thorium. We also calculate production rates for the eight proposed Mars 2020 landing sites, assuming water-saturated porosity. Radiolytic H₂ production rates calculated for wet martian sediment and water-filled microfractured rock are comparable to the range of rates calculated for Earth’s South Pacific basement basalt which is known to harbor low concentrations of microbial life.