Plant Risk Effect Analysis Focusing on Digital I&C Equipment Failures

Abstract

Safety-critical digital systems have been installed in nuclear power plants and thus their safety effect evaluation has become an emerging issue. The multi-tasking feature of digital instrumentation and control (I&C) equipment could increase the risk factor because the I&C equipment affects the actuation of the safety functions in several mechanisms. In this study, we quantify the safety of the digital plant protection system in Korean nuclear power plants based on probabilistic safety assessment (PSA) technology. Fifteen fault-tree models for the digital reactor-trip system and seven for the safety-feature actuation system are constructed and integrated into the plant safety assessment model. The result of the sensitivity study shows the boundaries of a plant risk and the effect of the digital equipment failures on the total plant risk.

A Quantitative Study on Risk Issues in Safety Feature Control System Design in Digitalized Nuclear Power Plant

“…In order to see the effect of software failures on the system unavailability and the plant risk (CDF), see Authors' previous articles. 6,9) -The issue of the probabilistic treatment of the network communication protocol failure is quite similar to that of the software failure. In the case that the system uses the network for the safety-critical signal transmission, the protocol failure causes the loss of input to the processors.…”

“…The final integrated model consists of about 2176 basic events and 5464 logical gates. The fault trees for the PPS failure are constructed based on the information of the PPS in the Ulchin 5&6 nuclear units, 9) and the fault trees of the ESF-CCS are constructed based on the design data from the APR1400. It should be noted that the ESF-CCS is still in an early design phase, and the modules are still being improved.…”

“…In authors' previous article, 9) the plant risk effects of digitalized I&C equipment failures were addressed with the DPPS and DESFAS of the OPR 1000. The effects of important factors, such as software failure probability and watchdog timer coverage, on the plant-level risk are quantified by using core-damage and large early release frequencies.…”

“…The effects of important factors, such as software failure probability and watchdog timer coverage, on the plant-level risk are quantified by using core-damage and large early release frequencies. This article is an extension of the previous study 9) and aims to address some risk issues regarding the design of new digital safety-critical systems. An engineered safety feature component control system (ESF-CCS) is being developed to meet the design requirements of the APR1400.…”