UC Berkeley

Transition metal hydrides are being researched as moderators for high temperature micro reactor sutilizing HALEU fuels. Their high densities of hydrogen allow for high moderating efficiency per unit volume compared to other high temperature moderators such as graphite. Zirconium hydride is of particular interest due to its low thermal neutron absorption cross-section and its well-established supply chain. However, hydrogen retention is a key concern for the operation of these reactors. In particular, the effects of radiation on hydrogen retention and phase stability are not well understood. While understanding impact of radiation on the mechanical properties is also of high importance. Phase pure δ-ZrHx and ε-ZrHx were fabricated using Zircaloy-4 as a precursor alloy. These samples were thoroughly characterized using a variety of X-Ray Diffraction (XRD) and electron microscopy techniques. In-situ TEM ion irradiations were conducted using 1MeV Kr ions, while ex-situ ion irradiations utilized both zirconium self-ions as well as helium. The key findings of the dissertation are evidence of non-equilibrium phase changes as a result of ion irradiations. It was found using in-situ irradiations that δ-ZrHx transforms into β-Zr metal at temperatures as low as 200°C. While a twin fading phenomena was seen after ex-situ irradiation of ε-ZrHx. Helium implantation of ε-ZrHx resulted in blister formation showing higher ductility in the material than found in previous studies of other hydrides.