The Development of HOLLY Code and Single-Point Ex-core Detectors Calibration Method

Abstract

Since the Core Protection System (CPS) and Core Monitoring System (CMS) relay on the ex-core power range detectors to monitor the in-core power distribution, ex-core detectors have traditionally been calibrated monthly or quarterly using multi-points Movable In-core Detectors (MID) flux maps technique that is based on operational information from the current cycle. The HOLLY Code has been developed for six-section ex-core detector calibration, which is based on LOCA Surveillance System (LSS) in PWR. A simple model of LSS (sim-LSS) to monitor in-core fine axial power distribution using six-section ex-core detectors per channel has been developed for HOLLY test and qualification. The calibration parameters include the GK parameters for in-core power level and axial offset, the transfer-sensitivity matrix parameters for six-section in-core power distribution, and so on. The results of HOLLY code and sim-LSS code are reasonable and satisfying. Base on the HOLLY Code, a new single-point calibration method has been developed by replacing an actual power oscillation that would be produced in the core in multi-points calibration, with a simulation of an oscillation using predictive core neutronics solution model. The results of single-point calibration method are in accord with multi-points calibration results which are generated from real core oscillation measurement.