Application of cubic spline synthesis in core axial power distribution monitoring

A Core Operating Limit Supervisory System (COLSS) is a digital computer based on-line monitoring system that is designed to assist the operator in monitoring of the Limiting Conditions for Operation. A current COLSS calculates axial power distribution based on in-core detector signals using 5th order Fourier series method. It was found that the 5th order Fourier series method is inaccurate for certain axial power shapes, especially saddle power shapes resulting in thermal margin decrease. A cubic spline synthesis was applied to the COLSS in order to improve the axial power distribution monitoring for the various axial power shapes. The results show that the cubic spline synthesis simulates more accurately the axial power shapes, up to 5% in RMS errors, compared to those of the Fourier series