Trend Analysis of Loss of Offsite Power Events

Abstract

This paper presents the results of the trend analysis of Loss of Offsite Power (LOOP) events registered in two reviewed databases. The reviewed databases include the Nuclear Regulatory Commission (NRC) Licensee Event Reports (LERs) database and the IAEA International Reporting System (IRS). Both databases were screened for the relevant events registered in period 1990 to 2012. The statistical analysis of the identified relevant LOOP events is done. The analysis includes assessment of the LOOP initiating event frequency, distribution of the events per year in the analysed period and trend analysis of the identified events. The LOOP frequency is calculated for LOOP events registered in NRC LERs subdivided into four types by cause or location: plant centered, switchyard centered, grid related, and weather related. These four LOOP categories are assessed for two modes of operation (critical and shutdown operation). The number of LOOP events in each year over the analysed period and distribution of events per unit in given year were assessed from the reviewed databases. Trend analysis of the identified events is performed with the utilization of four trend measures. Analysis is done for events registered during power and shutdown operation and their sum. The obtained LOOP frequency for events registered NRC LERs for critical and shutdown mode is comparable to the one assessed in NUREG/CR-6890. Decreasing trend is obtained for the LOOP events registered for events in NRC LER database. Different trends are identified during critical and shutdown modes of operation for the events registered in the IAEA database. The sum of the LOOP events reported during critical and shutdown modes in IAEA IRS show no trend.