SOARCA uncertainty analysis of a short-term station blackout accident at the Sequoyah nuclear power plant

• Published in: Annals of nuclear energy Vol. 145; p. 107495
• Main Authors: Bixler, N.E., Dennis, M., Ross, K., Osborn, D.M., Gauntt, R.O., Wagner, K.C., Ghosh, S.T., Hathaway, A.G., Esmaili, H.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: United States Elsevier Ltd 15.09.2020
• Subjects: Consequence; MACCS; MELCOR; Nuclear; SOARCA; MOC; EF; RCS; SV; MACCS; STSBO; MELCOR; Consequence; UA; EPZ; LCF; SOARCA; LNT; SGTR; Nuclear; BOC; EOC; MCS; ACRS; CCDF; NRC; PRA
• ISSN: 0306-4549; 1873-2100
• DOI: 10.1016/j.anucene.2020.107495

•Uncertainty analysis of consequences of short-term station blackout accident at ice-condenser plant.•Late much more likely than early containment failure, even without igniters.•Only initial hydrogen combustion event had potential to fail containment.•Time in operating cycle, safety valves, U-Zr-O melt temperature drive Cs release uncertainty.•Time in operating cycle, cancer risk factors, containment failure pressure drive cancer risk uncertainty. The U.S. Nuclear Regulatory Commission initiated the state-of-the-art reactor consequence analyses (SOARCA) project to develop realistic estimates of the offsite radiological health consequences for potential severe reactor accidents. The SOARCA analysis of an ice condenser containment plant was performed because its relatively low design pressure and its reliance on igniters make it potentially susceptible to early containment failure from hydrogen combustion during a severe accident. The focus was on station blackout accident scenarios where all alternating current power is lost. Accident progression calculations used the MELCOR computer code and offsite consequence analyses were performed with MACCS. The analysis included more than 500 MELCOR and MACCS simulations to account for uncertainty in important accident progression and offsite consequence input parameters. Consequences from severe nuclear power plant accidents modeled in SOARCA are smaller than previously calculated. The delayed releases calculated provide more time for emergency response actions. The results show that early containment failure is very unlikely, even without successful use of igniters. The modeled behavior of safety valves is very important to this conclusion, but there is sparse data and a lack of established expert consensus on the failure rates under severe accident conditions. Even for scenarios resulting in early containment failure, the calculated individual latent fatal cancer risks are very small. Early and latent-cancer fatality risks are one focus of this paper. Regression results showing the most influential parameters are also discussed.