Technical Findings Related to Generic Issue 79. An Evaluation of PWR ReactorVessel Thermal Stress during Natural Convection Cooldown

摘要

The report summarizes work performed by the Nuclear Regulatory Commission staffto resolve Generic Issue 79, 'Unanalyzed Reactor Vessel (PWR) Thermal Stress During Natural Convection Cooldown (NCC).' The report evaluates the effects of an NCC event on PWR reactor vessels (RVs), with particular emphasis on the closure flange region. A conservative independent confirmatory stress analysis of a B&W 177-fuel-assembly RV (B&W 177) was performed by the NRC contractor, and an independent fracture mechanics evaluation was performed by the staff. Based on these and a comparison of geometric similarity between the B&W 177 and other PWR RVs, the NRC staff developed findings that are applicable to all U.S. PWRs.