Management of neutron radiation embrittlement: A view from the United States

One of the main concerns in nuclear power plant operation is protecting the reactor pressure vessel against unstable, brittle fracture. The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code and US Nuclear Regulatory Commission (NRC) regulations prescribe methods for determining plant operating pressure-temperature curves and radiation embrittlement limits that define safety margins for both normal and accident conditions. These limits must be updated periodically using a surveillance testing program to reflect the condition of the steel vessel wall after many years of neutron irradiation. In older plants, these limits may impose significant operational restrictions. Surveillance data may also be useful in demonstrating that, in some plants, the effects of embrittlement are minimal and the life of the vessel can be extended while maintaining adequate margins of safety for plant operation. Decisions involving both life attainment and life extension place new demands on the surveillance program. In some cases, the new demands can be met by minor program adjustments; in other cases, major adjustments are needed to obtain the requisite data. This paper discusses various approaches for managing radiation embrittlement in support of life attainment and life extension decisions. Strategies such as integrated programs, replacement surveillance capsules, and supplemental dosimetry measurements are addressed