Risk Monitoring in Kozloduy NPP – E. Stefanov, L. Kandov, K. Filipov

A Risk Monitoring is one of the specific applications of PSA and is a real-time analysis tool used to determine the point-in-time risk. Risk Monitor calculates the risk for the actual plant configuration defined in terms of the Plant Operational Mode (power operation or one of the shutdown modes), the out of service components, availability of trains of normally operating systems, standby and running mode of trains of operating systems and specifying environmental factors.

The risk measures assessed by Risk Monitors usually include quantitative risk measures such as Core Damage Frequency (CDF) and sometimes the frequency of boiling (for shutdown modes), and qualitative risk measures such as changes of safety functions, safety systems availability and plant transient status (defense-in-depth).

The numerical values associated with quantitative risk measures are quoted in a number of ways which include baseline risk, average risk, point-in-time risk, incremental risk and cumulative risk. These terms are illustrated in the report. This report illustrates risk assessment in case of taking out the high pressure emergency injection pump in operation mode. The point-in-time risk, allowed outage time (AOT) as well as qualitative risk assessment by changes in Safety functions (defense-in-depth) are assessed and presented as results on the operators screen of risk monitor program. The cumulative risk diagram shows the difference in risk level when a high injection pump or an emergency injection pump is taken out of
service in planning mode.

Keywords: risk monitoring, CDF, maintenance planning, risk measures, PSA.