Reliability assessment of passive residual heat removal system using FORM methodology with chaos control

Abstract

Passive safety systems are adopted extensively to increase the inherent safety of the nuclear reactor. However, their stability of operation is more susceptive to thermal hydraulics uncertainty due to the relatively small driving force of passive systems. Coupled with a shortage of pertinent experimental and operational data, its reliability assessment is still a crucial and challenging task. So far, there are no accepted techniques for this problem and they are not yet frozen. Hasofer-Lind and Rackwitz-Flessler method (HL-RF) is an efficient iterative approach to identify the most probable point (MPP) and calculate the reliability. However, the approach may suffer from instability when dealing with highly nonlinear limit state functions (LSFs) or high-dimensional problems. In this paper, a straightforward and efficient method depending on chaos control was proposed to deal with numerical instability and chaos non-convergence problems. The proposed method was utilized to assess the reliability of the passive residual heat removal system (PRHRS) in Integral-type Pressurized Water Reactor (IPWR200). The results showed that it could efficiently and reliably locate MPP and accurately obtain the reliability index.