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Silva, K.*; Ishiwatari, Yuki*; Takahara, Shogo
Proceedings of Probabilistic Safety Assessment and Management Topical Conference; In light of the Fukushima Dai-ichi Accident (PSAM 2013) (USB Flash Drive), 10 Pages, 2013/04
The "cost per severe accident" was introduced as an index to analyze improvement of accident protection and consequence mitigation strategies. This index consists of various costs and consequences converted into monetary values. The evaluations of these costs and consequences were made based on the systematic consequence analysis using level 2 and 3 PSA. The accident sequences were taken from the results of level 2 seismic PSA. The doses to the public and the number of people affected were calculated using the level 3 PSA code OSCAAR. The data obtained from the open documents on the Fukushima Accident are used as much as possible. Sensitivity analyses are carried out to identify the sensitive assumptions or parameters to the cost per severe accident. Base on the results of the sensitivity analyses, optimized accident protection and consequence mitigation strategies are recommended taking into account the various aspects comprehensively using the cost per severe accident.
Kurisaka, Kenichi; Sakai, Takaaki; Yamano, Hidemasa; Nishino, Hiroyuki; Fujita, Satoshi*; Minagawa, Keisuke*; Yamaguchi, Akira*; Takata, Takashi*
Proceedings of Probabilistic Safety Assessment and Management Topical Conference; In light of the Fukushima Dai-ichi Accident (PSAM 2013) (USB Flash Drive), 10 Pages, 2013/04
This study includes a level-1 PSA related to internal events and a seismic event as a representative external event for Japan sodium-cooled fast reactors with passive safety features and a seismic isolation system. For the internal events, it is necessary to evaluate the passive safety features, of which reliability depends on uncertainties of related physical phenomena. In order to consider the reliability of the passive natural circulation, accident sequences leading to core damage result from natural circulation failure were developed, and the annual frequency of the accident sequences was evaluated for the PSA method study. In respects of seismic event, we developed response analysis method considering the coupling effect of horizontal and vertical shaking on the horizontal seismic isolation characteristics, and developed a fragility evaluation model including the effect of seismic non-linearly for the seismic isolation system.
Yamano, Hidemasa; Sakai, Takaaki; Kurisaka, Kenichi
Proceedings of Probabilistic Safety Assessment and Management Topical Conference; In light of the Fukushima Dai-ichi Accident (PSAM 2013) (USB Flash Drive), 11 Pages, 2013/04
This paper provided a failure probability of the natural circulation heat removal function that is expected to actuate only one direct reactor auxiliary cooling system assuming the loss of two primary reactor auxiliary cooling systems. The probability was obtained in the following steps. At first, a reference case was defined through parametric analyses for a realistic evaluation in the PSA. After selecting key uncertainty parameters according to the PIRT, sensitivity analyses were carried out to develop a response surface. Based on this response surface, Monte Carlo calculations were performed assuming appropriate probability distributions of uncertainty parameters, leading to an exceedance probability in terms of temperature difference from the reference case result. In this study, the failure probability was determined above a safety criterion of the coolant boundary temperature. The failure probability of the reference evaluation was very low.
Okano, Yasushi; Kurisaka, Kenichi; Yamano, Hidemasa; Fujita, Satoshi; Nishino, Hiroyuki; Sakai, Takaaki
Proceedings of Probabilistic Safety Assessment and Management Topical Conference; In light of the Fukushima Dai-ichi Accident (PSAM 2013) (USB Flash Drive), 6 Pages, 2013/04