NRC proposes new reactor embrittlement regulations

The Nuclear Regulatory Commission has proposed amending its regulations regarding embrittlement of pressure vessels in commercial nuclear power reactors. The amendments, which include clarifying the pressurized thermal shock requirements, changing the fracture toughness requirements and establishing new requirements for thermal annealing of a reactor pressure vessel, were prompted in part by NRC`s 1990 inspection of the reactor pressure vessel at the Yankee Rowe nuclear plant in Massachusetts. NRC`s proposed changes would establish a screening criterion for both the rate of irradiation embrittlement or RPV materials and fracture toughness, above which a plant cannot continue to be operated safely.