A Logical Selection of Measures for Quality Assurance on the Integrity of Liquid-Metal Fast Breeder Reactor Primary Boundaries

Abstract

An example of a logical approach to standardization of in-service inspection requirements is introduced, analyzing each measure according to risk reduction factors in order to develop a systematic configuration of safety measures. Comparison of a heavy pressure vessel section fabricated to resist pressure from the many nozzles in a light water reactor vessel with a thin-walled reactor vessel in a liquid-metal fast breeder reactor (LMFBR) operating at high temperatures and low pressure indicated no apparent difference in the failure probability of the reactor vessel. If both large failures and cracks are considered, 10/sup -5//vessel.yr is to be assumed. In assessing the unreliability of the guard vessel, dominant factors are common cause failures and subordinate modes. The coupling factor of the common cause failure of the guard vessel with reactor vessel failure is assumed 10/sup -3/. The subordinate mode failure of the guard vessel when the sodium leak from the reactor vessel is left unattended should be considered in the rate of 10/sup -2//reactor vessel failure. Especially in LMFBRs, visual tests are more practicable than volumetric tests for primary sodium boundaries, and the risk reduction factor by periodic in-service inspections is limited to only 5%.