Application of ordinary Kriging interpolation for 3-D power distribution synthesis in core protection calculator

Abstract

The core protection calculator (CPC) is a digital computer equipped with OPR1000 and APR1400 which continuously calculates departure from nucleate boiling ratio (DNBR) and local power density (LPD) to initiate a reactor trip. Current CPC calculates core average axial power shape from 3-level ex-core detector signals using Shape Annealing Matrix (SAM) and cubic spline interpolation. And pseudo hot pin power distribution is calculated by multiplying core average axial power shape and planar radial peaking factor. This pseudo hot pin power distribution methodology shows rapid and conservative results, but excessive conservatism may cause unintended reactor trip. Therefore, in this paper, 3-D power distribution synthesis using in-core instrument signals is applied for CPC in order to calculate the accurate core power distribution. This paper introduces the use of kriging interpolation and artificial neural network (ANN) technique when synthesizing 3-D power distribution in CPC in order to improve the accuracy of DNBR and LPD calculation. This methodology utilizes ordinary kriging interpolation and ANN technique for radial and axial power mapping respectively. The CPC with 3-D power distributions using kriging/ANN can calculate 3-D power distributions with higher accuracy when compared to the current CPCS, with the increase in the minimum DNBR and LPD thermal margins for CPC by 5.7% and 14.4%. Thus, by applying the 3-D power distribution synthesis methodology to the core protection calculator, it is possible to calculate the hot pin power distribution of reactor core more accurately and unintended reactor trip can be prevented.