Past exam of the MPhil in nuclear energy course of the University of Cambridge / 2019 / Module NE4 / 2 / c / Solution

Delay cavity nucleation and prevent a large sustained vacancy flux to growing cavities. Select an austenitic alloy composition and heat treatment demonstrated to have low void swelling in the intended spectrum and temperature range; modest composition changes can alter precipitation, segregation and sink evolution. The grade label alone is insufficient.

cold working supplies a dislocation population that can alter defect capture and extend the low-swelling transient. Stable fine precipitates or other engineered sinks can promote defect removal, but capture bias matters as well as sink count. Irradiation and thermal recovery can erase the starting microstructure, so an initially favourable state must be checked at relevant dose. Controlled impurity and helium-producing constituent contents can reduce harmful gas effects, subject to corrosion resistance and phase-stability requirements.

Operating outside a strong-swelling regime, reducing accumulated exposure or replacing components before their qualified limit are complementary measures. Each trades against other constraints such as corrosion, creep, ductility and heat removal. “More cold working” or “more sinks” is not an unlimited prescription. Measurements must separate void swelling from creep; reducing one does not establish that the other was reduced. The pressurised-tube study is a particularly useful control because, after separating stress-enhanced void swelling, its derived creep strains were similar for annealed and cold-worked specimens.^[ref]