Development of severe accident evaluation technology (Level 2 PSA) for sodium-cooled fast reactors, 5; Identification of dominant factors in ex-vessel accident sequences

Ohno, Shuji  ; Seino, Hiroshi ; Miyahara, Shinya  

Typical ex-vessel accident sequences in the JSFR are discussed in this paper and dominant behaviors or factors in the sequences are investigated through parametric calculations using the CONTAIN/LMR code. Scenarios to be focused on are, (1) sodium vapor leakage from the reactor vessel and (2) sodium-concrete reaction, which are both to be considered in the LOHRS accident category and might be followed by an early containment failure due to the thermal effect of sodium combustion and hydrogen burning respectively. The calculated results clarify that the sodium vapor leak rate and the scale of sodium-concrete reaction are the important factors to dominate the ex-vessel accident progression. In addition, the results also provide the specific information such as pressure loading value to the containment and the timing of pressurization, which is indispensable as technical base in Level 2 PSA for developing event trees and for quantifying the accident consequences.