Survey of BWR Recirculation Line Break Acoustic Loads

Abstract

There have been numerous industry communications over the past six years identifying issues pertaining to incorrectly calculated or erroneously omitted recirculation line break acoustic loads. Acoustic loads caused by a postulated recirculation line break (RLB) loss of coolant accident (LOCA) are one of the required design basis events that must be considered for stress analyses of Boiling Water Reactor (BWR) internal components such as jet pumps, core shrouds, access hole covers, and shroud support assemblies. These acoustic loads must also be considered for fracture mechanics evaluations performed to determine allowable operating periods for flaws detected during in-service inspections. Various organizations have studied the recirculation line break event and have developed methodologies to calculate the associated loads on BWR internal components. In general, loads are calculated in a plant specific and operating condition specific manner. Once these loads are available then the necessary structural evaluations can be performed. Load calculations can be expensive and time consuming. The authors have previously proposed a method for determining plant specific bounding RLB acoustic loads such that a utility can eliminate the need to periodically update the acoustic load calculations for each plant. This paper adds to the body of literature on this topic by providing a survey of BWR shroud acoustic loads, representative of the range of loads expected for the fleet, and provides a bounding load estimate that can be used for any plant in the fleet. The load survey supports previous arguments that the AC loads are expected to be substantially similar from plant to plant, based on the substantial similarity in plant operating conditions and geometry. The bounding load estimate provides significant value in that a utility engineer can rapidly obtain conservative loads to support either plant specific structural evaluations or fleet studies intended to investigate the significance of the load on inspection intervals, flaw tolerance, etc. Cost savings can be realized for utilities and fleet wide insight can be gained from understanding the similarity between RLB acoustic loads across the operating BWR fleet.