Study on the main design parameters of large seale fast breeder reactor(II); Development of dynamic reliability evaluation technique for decay heat removal system

not registered; not registered ; not registered; not registered; Nakanishi, Seiji; not registered

In a safety design of Fast Breeder Reactor (FBR), high reliability for the decay heat removal systems (DHRSs) is required as well as the reactor shutdown systems in order to define core disruptive accident as the Beyond Design Basis Accidents (BDBAs). Therefore, it had been desired to establish the quantitative reliability evaluation techniques for DHRSs. In the Key Technological Design Study(II), it was represented that a usual fault-tree analysis was insufficient as a reliability evaluation technique for DHRSs and the development of a dynamic analysis tool considering the state transition of the reference plant was required. On the basis of suggestions, the dynamic reliability analysis code DRAC, to which a Markov model is applied, has been developed. In this code, following two time- dependent effects in reliability evaluation are considered. (1)Transition of required removal heat according to the time-dependency of decay heat. (using the Phased Mission method) (2)Transition of plant coolability considering the failure and repair of plant components. (using the Markov model) To verify the analytical capability of this code, the reliability analysis of a typical loop type plant with four IRACSs designed in the Key Technological Design Study(II) was performed as an example analysis for the practical FBR plant. The results of the analysis showed that the reliability of the plant can be easily estimated in cases of all different systems on the design concepts and the dependence of the equipments, and so the applicability of this code for the practical plant was confirmed. After this, we will utilize this code for the reliability analysis in the practical FBR plants design study through both the estimation of the decay heat removal capability by the plant dynamic analysis codes and the application of the failure and repair rate data of the components in the CREDO data-base, etc.