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 four reviewed databases. The reviewed databases include IRSN (Institut de Radioprotection et de Sûreté Nucléaire) SAPIDE and GRS (Gesellschaft für Anlagen- und Reaktorsicherheit mbH) VERA database reviewed for time period 1992 to 2011. The Nuclear Regulatory Commission (NRC) Licensee Event Reports (LERs) database and the IAEA International Reporting System (IRS) database were screened for the relevant events registered in period 1990 to 2013. 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. A trend analysis of the identified events was performed with the application of the method for trend analysis of accident data. Four measures of data trends are utilized in the used methodology. The T1 measure compares averages of different parts of the data. The T2 measure compares the first half of the data to the second half while the T3 measure is utilized for identification of the non-monotonic trends. The T4 measure compares the observations with the mean value. The value of the trend measures is calculated for number of events registered during critical and shutdown mode in each year and for sum of events in both modes of operation. The new datasets were generated from the Poisson uncertainty distribution conditionally on number of events and their average. The trend measures were calculated for each generated datasets and compared to the measures values obtained for actual number of events per year. The statistical significance of the trend in the data was assessed from comparison of generated and actual values of measures. With the application of the method a decreasing trend was obtained for the events registered in three databases (IRSN, GRS and NRC). Different trends were identified during critical and shutdown modes of operation for the events registered in IAEA database. No trend was identified for sum of the events reported during critical and shutdown modes.JRC.G.10-Knowledge for Nuclear Security and Safet