UC Berkeley

Coupled extremes such as radiation and corrosion in nuclear environments induce a state in matter that is far from equilibrium. The addition of corrosion increases the complexity of the nonequilibrium problem. Thus, there is a continual need to advance understanding of these coupled effects to ultimately predict material response and enable the design of new materials that can better withstand these combined extreme conditions. The work in this dissertation advances toward a predictive understanding for how point defect transport can drive radiation damage and corrosion.

This dissertation seeks to advance fundamental understanding of defects from radiation damage and oxidation phenomena in structural materials for nuclear reactor applications. The first objective of this research is to validate rate theory predications of radiation damage defect populations in-situ using positron annihilation spectroscopy. This hypothesis is explored using simulation, execution, and discussion of novel positron annihilation spectroscopy experiments. Ultimately, radiation-induced nonequilibrium monovacancy defects were simulated and experimentally observable with positron spectroscopy, and in-situ vacancy concentration showed an increase with increasing dpa. The second objective of this research is to validate theoretical predictions of predominant defect identities within passivating systems. Positron spectroscopy was again used to experimentally connect to previous results from simulations of oxide layer defect behavior, electrochemical studies on oxides, and post-mortem irradiation microscopy studies. Oxidation defect behavior in iron and chromium was quantified as a function of oxidation time, temperature, and irradiation.

Positron annihilation spectroscopy is a monovacancy-sensitive, depth-dependent, nondestructive technique to understand defect behavior, which ultimately governs materials’ radiation and corrosion performance for safety and corrosion protection of new and existing nuclear structural materials. It is hoped that this research will open new doors to advanced characterization and modelling opportunities in the study of nonequilibrium radiation and oxidation defects.