Effective Approaches for Managing Aging Effects in BWR Reactor Coolant System Components for License Renewal

This paper discusses management of aging effects for reactor coolant pressure boundary components in boiling water reactors (BWRs): loss of fracture toughness due to thermal aging and neutron irradiation embrittlement of vessel internals made of cast austenitic stainless steel; cracking of the top guide due to irradiation-assisted stress corrosion cracking; cracking of the core shroud and reactor coolant system piping due to intergranular stress corrosion cracking; cracking of the small bore piping due to high-cycle thermal fatigue; and loss of preload in the pressure boundary bolting. The applicants for license renewal of BWR plants have proposed different approaches for managing these aging effects such that the intended functions of the affected components will be maintained, consistent with the current licensing basis, for the period of extended operation. The NRC staff has performed safety evaluation of these approaches and found them acceptable for adequately managing the aging effects during the period of extended operation. The technical bases for the acceptance are presented in this paper.Copyright © 2003 by ASME