Development of seismic countermeasures against cliff edges for enhancement of comprehensive safety of nuclear power plants, 2; Cliff edges relevant to NPP structure modeling

Nishida, Akemi  ; Choi, B.  ; Yamano, Hidemasa   ; Takada, Tsuyoshi*  

In this research, the seismic safety of nuclear power plants (NPP) is treated as a system in which the various cliff edge effects are identified and quantified based on the concepts of risk and defense in depth. A methodology is then developed for avoiding these cliff edge effects. The first step was to carry out a preliminary elastic-plastic analysis of the NPP building system. From the analysis, some knowledge was obtained for the modeling factor dependence of cliff edge effects. Next, a preliminary fragility evaluation of the reactor vessel and piping was carried out; it was found that introducing a horizontal seismic isolation system was very effective for avoiding the cliff edge.