Nuclear Executive Update   
An EPRI Progress Report, November 2010
TECHNICAL HIGHLIGHTS
Reactor Pressure Vessel Integrity Primer to Help Manage Radiation Embrittlement

A new primer and associated tutorials will serve as technical resources in managing reactor pressure vessel embrittlement due to neutron irradiation.

EPRI has developed a reactor pressure vessel (RPV) integrity primer (MRP-278, EPRI 1020854) and related presentation materials to support plant personnel responsible for RPV radiation embrittlement and integrity management issues. The primer provides in-depth technical information necessary to implement a radiation embrittlement management program and to assess long-term RPV integrity issues.

Reactor pressure vessels are designed, fabricated, and operated in accordance with industry and regulatory guidelines/requirements to ensure acceptable margins against failure. These margins are maintained during service by implementing inspection and surveillance programs, the results of which are used to periodically assess RPV integrity. One of the major challenges to RPV integrity is embrittlement as a result of neutron irradiation. Neutron irradiation exposure makes the RPV more brittle (reduces ductility and fracture toughness) in the areas adjacent to the core, and the vessel becomes increasingly susceptible to brittle fracture over its operating life.

RPV radiation embrittlement management is an essential component of a continuing nuclear plant maintenance program. The shutdown of the Yankee Rowe plant because of uncertainties related to RPV radiation embrittlement demonstrated the importance of adequately addressing embrittlement issues.

The RPV integrity primer presents background information to understand neutron radiation embrittlement and structural integrity concepts, including an introduction to fracture mechanics based on a previous EPRI primer (EPRI NP-5792-SR, Rev. 1, 1991). These basics are then examined in the framework of regulatory requirements to help understand what is needed for maintaining adequate vessel fracture toughness through current and extended licensed life.

For example, ASME Code and U.S. federal regulations often require conservative assessments that can cause operational hardships or lead to early plant shutdown. By familiarizing responsible utility engineers with the technical bases behind various regulations pertaining to RPV toughness, nuclear power plants can more effectively manage RPV embrittlement over the reactor’s life. Moreover, because many countries rely on ASME Code in setting standards for vessel integrity, the primer is globally applicable.

For more information, contact Kawaljit (Al) Ahluwalia at 650.450.1328 or kahluwal@epri.com.