Aging management of PWR internals components

Light Water Reactors (LWR) in US are normally designed and licensed for a plant life of forty years. However, due to embedded design conservatism and favorable plant operation and maintenance conditions, plants have margins to operate beyond their original designed life. Many US utilities have set a goal to extend plant life to 60+ years through license renewal applications. To achieve this goal, potential degradation of reactor components associated with aging need to be identified and managed. The Standard Review Plan and Generic Aging Lessons Learned (GALL) report issued by the US Nuclear Regulatory Commission (NRC) outline staff's basis on reviewing and accepting the utility aging management program. The Electric Power Research Institute (EPRI) Material Reliability Program (MRP), funded by the US and a number of international utilities, has been conducting research providing data and results to support aging management and the license renewal goal. Reactor internals components due to their proximity to the core absorb significant radiation dosage. They consequently experience radiation induced degradation such as irradiation-assisted stress corrosion cracking (IASCC), embrittlement (i.e., reduction of ductility and fracture toughness), creep/stress relaxation (loss of preload), and void swelling (dimensional changes and ductility loss). These degradation mechanisms, depending on the extent of their effects, may impact structural integrity and functionality of internals components. (authors)