Effects of control system failures on transients, accidents, and core-melt frequencies at a Babcock and Wilcox pressurized water reactor

Pacific Northwest Laboratory (PNL) performed probabilistic risk analyses to develop estimates of core-melt frequency and public risk associated with control system failures in a Babcock and Wilcox pressurized water reactor. PNL also conducted value/impact analyses of proposed control-system modifications. These analyses were based on failure modes and effects previously identified at Oak Ridge National Laboratory (ORNL). These control system failure modes fall into three main scenarios: (1) overfill of the steam generators, progressing to spillover into the steam lines, (2) ICS hand power failure progressing to steam generator dryout, and (3) ICS automatic power failure progressing to steam generator failure. For each of these modes, two failure sequences were postulated. The results of PNL's probabilistic analysis of failure progression to core damage and value/impact analyses of possible resolutions to prevent these failures are presented in this report. 18 refs., 12 tabs.