Application of the “best representativity” method to a PWR fuel calculation using the critical experiments at the Toshiba NCA facility

Abstract To judge the applicability of a critical experiment, it is necessary to confirm the similarities of the experiment with actual reactor conditions or equipment. The concept of the “representativity factor” has been well adopted since the late 1970’s, particularly for fast breeder reactors (FBRs) and future reactor studies. In our previous study, we extended this concept to the design of a light water reactor (LWR) system, and derived mathematical formulas for a new numerical evaluation method to correct a physical property of a target system. This method is different from the cross-section adjustment method and the bias factor method. For the first qualification of the method, sample calculations were carried out to correct the effective neutron multiplication factor through critical experiments at the Toshiba Nuclear Critical Assembly (NCA) facility. We also compared the result with that of the Product of Exponentiated experimental values method (PE method) of the extended bias factor methods. A good agreement was observed. The purpose of this study was to demonstrate the applicability of the method to the infinite neutron multiplication factor. Using the method and three kinds of critical experiments of NCA, calculations were performed to correct the infinite neutron multiplication factor of a pressurized water reactor (PWR) fuel assembly. Under combination of NCA critical experiments, the representativity factor became closer to unity. Simultaneously, a correction of the infinite multiplication factor was realized. Results were firstly compared among different combinations of experiments. Comparisons with the results of other calculation methods were also conducted. Whole results were explained with physical considerations.