Effect of delayed link failure on probability of loss of assured safety in temperature-dependent systems with multiple weak and strong links

Abstract

Weak link (WL)/strong link (SL) systems constitute important parts of the overall operational design of high consequence systems, with the SL system designed to permit operation of the system only under intended conditions and the WL system designed to prevent the unintended operation of the system under accident conditions. Degradation of the system under accident conditions into a state in which the WLs have not deactivated the system and the SLs have failed in the sense that they are in a configuration that could permit operation of the system is referred to as loss of assured safety. The probability of such degradation conditional on a specific set of accident conditions is referred to as probability of loss of assured safety (PLOAS). Previous work has developed computational procedures for the calculation of PLOAS under fire conditions for a system involving multiple WLs and SLs and with the assumption that a link fails instantly when it reaches its failure temperature. Extensions of these procedures are obtained for systems in which there is a temperature-dependent delay between the time at which a link reaches its failure temperature and the time at which that link actually fails.

Jon Helton: Pioneer in Uncertainty and Sensitivity Analysis for the Modeling of Complex Physical Systems

“…For repository analysis, we need physically realistic models of the processes of concern and be able to justify simplifications that are made to use the models in a full‐scale risk assessment. In addition, Jon has contributed to the design of analyses to assess the role that weak link/strong link systems have in mitigating the effects of accidents involving high consequence systems (Helton, Johnson, & Oberkampf, 2006a, 2009, Helton, Pilch, & Sallaberry (2014), Helton, Brooks, and Sallaberry (2020a and b)).…”

Probability of loss of assured safety in systems with multiple time-dependent failure modes.

“…[7], a link is assumed to fail at the instant that its failure temperature is reached; Ref. [8] treats the more general situation in which there is a delay between when a link reaches its failure tem perature and when the link actually fails. These differences affect the definitions of the CDFs for link failure time; however, once these CDFs are obtained, PLOAS can be determ ined as indicated in Table 1 for both definitions of link failure time.…”

“…The developments in Refs. [7][8][9][10] always refer to the link properties under consideration as temperature. However, there is no thing in the development of the results in T able 1 that is specific to temperature.…”