Renormalization of power and burnup independent shape annealing function for excore detectors

This paper describes a predictive mathematical modeling of the excore neutron detectors using a renormalization of power and burnup independent shape annealing function for Korean Optimized Power Reactor (OPR-1000) and demonstrates its validity via comparison with the measurement data. The mathematical model is based on the assembly-wise spatial weighting functions and the core axial spatial weighting functions. Detector responses are estimated through two-step calculations, first the core peripheral power distributions (power distribution of outermost assemblies) are obtained from the three-dimensional power distribution by using the assembly-wise spatial weighting functions and then the relative responses of the axial detector segments are evaluated by applying the core axial spatial weighting functions. To overcome the uncertainty from mathematical modeling, a renormalization scheme is introduced, where the spatial weighting functions are renormalized with respect to the reference measurement data and then used throughout the remaining fuel cycle. Validity tests for the renormalization method show that the detector responses can be estimated very accurately, within 1% error, with the variation of power levels and distributions. The successful application of the renormalization scheme has very important implication that the excore detector system can be accurately modeled in a priori, provided a single measurement is available.