Severe accident progression perspectives for Mark I containments based on the IPE results

Conference · Sun Dec 31 04:00:00 EST 1995

OSTI ID:245537

Lin, C C; Lehner, J R; Pratt, W T ^[1]; Drouin, M ^[2]

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1. Brookhaven National Lab., Upton, NY (United States)
2. Nuclear Regulatory Commission, N. Bethesda, MD (United States)

Based on level 2 analyses in IPE (Individual Plant Examination) submittals accident progression, perspectives were obtained for all containment types. These perspectives consisted of insights on containment failure modes, releases therein, and factors responsible for the results. To illustrate the types of perspectives acquired on severe accident progresssion, insights obtained for (BWR) Mark I containments are discussed here. Mark I containments have high strength but small volumes and rely on pressure suppression pools to condense steam released from the reactor coolant system during an accident. Accidents causing structural failure of the drywell shortly after the core debris melts through the reactor vessel were found to be dominant contributors to risk. Importance of individual containment failure mechanisms depends on plant features and in some cases on modeling assumptions; however the following mechanisms were found important: drywell shell melt-through caused by direct contact with core debris and drywell failure caused by rapid pressure/temperature pulses at time of vessel melt-through. Drywell failure caused by gradual pressure/temperature buildup due to gases and steam released during core/concrete interactions is important in some IPEs. In other IPEs vent was an important contributor. However, accidents that bypass containment (eg interfacing systems LOCA)or involve containment isolation failure were not important contributors to the CDF in any of the IPEs for Mark I plants. These accidents are also not important to risk (even though they can involve large fission product release) because their frequencies of occurrence are so much lower than frequencies of early structural failure caused by other accidents that dominate the CDF.

• Research Organization: Brookhaven National Lab., Upton, NY (United States)
• Sponsoring Organization: Nuclear Regulatory Commission, Washington, DC (United States)
• DOE Contract Number: AC02-76CH00016
• OSTI ID: 245537
• Report Number(s): BNL-NUREG--62800; CONF-9510156--15; ON: DE96011490; IN: SRED--50
• Country of Publication: United States
• Language: English

Related Subjects

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS
22 GENERAL STUDIES OF NUCLEAR REACTORS
BWR TYPE REACTORS
CONTAINMENT
FAILURE MODE ANALYSIS
INFORMATION SYSTEMS
REACTOR ACCIDENTS