A potential emerging issue concerning repair welding of out-of-core PWR components involving tritium exposure and ³He retention

This paper identifies a potential but previously unrecognized risk of helium-induced embrittlement and cracking during repair welding of out-of-core pressurized water reactor (PWR) components exposed to tritium-contaminated coolant. While previous weldability concerns centered on ⁴He accumulation in neutron-irradiated alloys located within the in-core or near-core regions, new measurements show that ³He generated by tritium decay can accumulate in out-of-core components. Because hydrogen isotopes readily diffuse to grain boundaries and become trapped there, significant ³He generation at grain boundaries may lead to cracking during weld repairs. Initial data from far-below-core PWR flux thimble tubes confirm the presence of ³He levels above known cracking thresholds for repair welds. In conclusion, these findings indicate that out-of-core regions should be considered when defining safe weld repair windows in reactors operating for 60–100 years.. Authors: Garner, Frank A. [Radiation Effects Consulting, Richland WA (United States); Texas A & M Univ., College Station, TX (United States)] (ORCID:0000000346902205); Gussev, Maxim N. [Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)] (ORCID:0000000168140737); Song, Miao [Shanghai Jiao Tong Univ. (China)]; Was, Gary S. [Univ. of Michigan, Ann Arbor, MI (United States)]. DOE Contract: AC05-00OR22725. Subjects: Extended PWR lifetimes; Helium-induced repair weld cracking; Out-of-core weld repair challenges; Tritium-induced ³He embrittlement