(A) study on reliability modeling of DPPS with fault tolerant techniques considering fault detection and process characteristics and human error

Abstract

With the improvement of digital technologies, digital I&C systems have included more various fault tolerant techniques than conventional analog I&C systems have, in order to increase fault detection and to help the system safely perform the required functions in spite of the presence of faults. So, in the reliability evaluation of digital systems, the fault tolerant techniques (FTTs) and their fault coverage must be considered. To consider the effects of FTTs in a digital system, there have been several studies on the reliability of digital model. Therefore, this research based on literature survey attempts to develop a model to evaluate the plant reliability of the digital plant protection system (DPPS) with fault tolerant techniques considering detection and process characteristics and human errors. Sensitivity analysis is performed to ascertain important variables from the fault management coverage and unavailability based on the proposed model. And a method to revise the DPPS fault tree model to consider various FTTs is proposed. In order to consider the effects of FTTs, key characteristics of FTTs are identified based on the litera-ture survey and are adapted to the advanced reliability model. And fault management coverage of FTT has been used for advanced reliability model to reflect the effects of FTTs. From the sensitivity study, the average unavailability between refueling maintenance has been found to strongly depend on fault management coverage of the manual test. Therefore, when applying the FTTs to the system, fault management coverage of the on-line FTTs should be increased. And although the level of human error is high, average unavailability of component could be reduced by applying on-line FTTs. The conventional DPPS fault tree model can be revised to consider the fault management responsibility of FTT based on the fault management process of various FTTs. The advanced reliability model, which considers the effects of FTTs in DPPS, is useful t...