Hydrogen management and overpressure protection of the containment for future boiling water reactors

New design and evaluation method for hydrogen management of containment atm osphere have been developed for application in the future boiling water rea ctor (BWR). These are intended as a part of consideration of severe acciden ts in the course of design so as to assure a high level of confidence that a large release of radioactivity to the environment that may result in unac ceptable social consequences can reasonably be avoided. Emphasis on hydroge n management and protection against overpressure failure is based on the in sights from probabilistic safety assessments (PSAs) that late phase overpre ssure (and associated leakage) and molten cerium concrete reaction (MCCI) n eed attention to ensure that containment remains intact, in case energetic challenges to the containment such as DCH (direct containment heating) or F CI (fuel coolant interactions) are practically eliminated by design or reso lved from risk standpoint of view. The authors studied the use of palladium -coated tantalum for hydrogen removal from containment atmosphere in order to avoid pressurization of the containment with small free volume by non-co ndensable gas and steam. Its effectiveness for ABWR (advanced boiling water reactor) containment was evaluated using laboratory test data. Although fu rther experimental studies are necessary to confirm its effectiveness in re al accident conditions. the design is a promising option and one that could be backfitted upon necessity to existing plants for which pressure retaini ng capability cannot be altered. Also new evaluation method for flammabilit y control under severe accident conditions was developed. This method emplo yes a realistic assessment of the amount of oxygen and hydrogen gases gener ated by radiolytic decomposition of water under severe accident conditions and their subsequent transport from water to containment atmosphere. (C) 20 00 Elsevier Science S.A. All rights reserved.