Effects of Gamma Radiation and Gamma-Induced Species on Water Chemistry, Polymers and Fe-, Ni- and Zr-Based Alloys

Doctoral thesis, 2026

Nuclear energy is expected to play an important role in the transition toward low-carbon energy systems. Light Water Reactors (LWRs) dominate the global nuclear fleet, and their safe, reliable, and long-term operation depends on understanding the interactions between radiation, water chemistry, and structural materials that govern corrosion and material degradation.

This thesis investigates the effects of direct gamma irradiation and gamma-induced radiolysis on polymers, aqueous systems, and metallic alloys relevant to LWR operation. Particular attention is given to hydrogen peroxide and other reactive species produced during water radiolysis and their interactions with materials commonly present in reactor systems and laboratory irradiation experiments. The results demonstrate that material interfaces strongly influence the chemistry of irradiated aqueous systems. Investigations of polymer sealing materials revealed that hydrogen peroxide accumulation depends significantly on material choice, highlighting how experimental design and material selection can affect radiation chemistry measurements and contribute to reproducibility challenges. Studies of reactor-relevant alloys further showed that hydrogen peroxide accumulation depends on alloy composition and is governed primarily by radiation-induced processes in solution. Surface analyses indicated only minor modifications of oxide films during irradiation, suggesting that changes in water chemistry are linked more closely to species released into solution than to extensive alterations of alloy surfaces under the investigated conditions. In situ electrochemical measurements under intermittent gamma irradiation revealed an immediate dose-rate-dependent response associated with radiolytically generated reactive species. The results distinguished the roles of short-lived radicals and longer-lived oxidants, identifying hydrogen peroxide as the primary driver of the longer-term electrochemical evolution of the investigated alloy surface. Overall, this thesis shows that the behaviour of irradiated aqueous systems is governed by the interplay between radiation, water chemistry, and material interfaces. The findings contribute to a deeper understanding of radiation chemistry and corrosion-related phenomena in LWR environments and provide guidance for the design and interpretation of future irradiation experiments.