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Kurisaka, Kenichi
NEA/CSNI/R(2012)2, p.61 - 84, 2012/07
Japan Atomic Energy Agency (JAEA) has been preliminarily applied a level-1 PSA to the safety design concept of a loop-type large scale of the Japan Sodium-cooled Fast Reactor (JSFR). As for internal initiators in power operation, typical core damage sequences (i.e., anticipated transients without scram (ATWS), loss of reactor sodium level (LORL), and protected loss of heat sink (PLOHS)) were evaluated to identify dominant failure combinations. The core damage frequency (CDF) was quantified to evaluate the adequacy of the safety design. This evaluation served to improve safety by modifying the decay heat removal system of JSFR. As part of development of reliability evaluation technology, we studied on the quantification of the sodium leak probability depending on the leak flow rate. This study serves to evaluate accident management effectiveness in the sodium-leak-related core damage sequences. As for external initiators, we conducted the seismic margin evaluation based on the seismic fragility evaluation for the principal structures and components, and confirmed that they have sufficient margin against the postulated seismic condition.
Suzuki, Toru; Nakai, Ryodai; Kamiyama, Kenji; Seino, Hiroshi; Koyama, Kazuya*; Morita, Koji*
NEA/CSNI/R(2012)2, p.381 - 391, 2012/07
For the probabilistic safety assessment (PSA) of sodium-cooled fast reactors (SFRs), JAEA consolidated the analytical methodologies and technical basis for all phases/sequences to be evaluated in the Level 2 PSA. In addition to the existing computational codes such as SAS4A, SIMMER-III, DEBNET, ARGO and APPLOHS, JAEA newly developed MUTRAN and SIMMER-LT in order to evaluate the long term behaviors of the material-relocation in the degraded core. These tools enabled the systematic assessment for the in-vessel accident sequences. For the ex-vessel accident sequences, JAEA also improved CONTAIN/LMR taking into account the feature of SFRs and verified the analytical models utilizing the new experiments such as sodium-concrete reaction test. In addition, the technical basis for constructing event trees was compiled, in which the dominant factors having significant effects on the event progression were corresponded to the related experiments and analytical results.
