Redundant instrument monitoring system

This paper reports on the instrumentation design at the San Onofre Nuclear Generating Station (SONGS), Units 2 and 3, which includes the monitoring of important process parameters by several redundant instrument channels. The Southern California Edison Company (SCE) has installed a system to monitor the calibration status of selected redundant instrumentation in Units 2 and 3 at SONGS. The purpose of the system is to enable identification of instruments which are preforming properly and those whose performance is questionable while the plant in on-line. This information can then be used to justify the calibration of only those instruments that are questionable, thereby reducing the number of calibrations that are required during refueling outages. The Redundant Instrument Monitoring System (RIMS) collects data from the in-plant computer systems, the Plant Monitoring and Critical Functions Monitoring Systems for both Units at 12 minutes intervals. The signals from instrument which monitor the same process parameter are grouped. The average value for each redundant group is then calculated and the deviation of each parameter from the average is determined in terms of percent of calibrated span. Appropriate weighing factors are utilized, based on individual instrument accuracies, to determine the best estimate of the process parameter. The deviations are then trended over time to evaluate changes in the instrumentation calibration status. The time history of these deviations are permanently stored on an optical disk for retrieval at any future date. Result from RIMS are compared with tradition calibration methods at refueling intervals to validate RIMS operation