A study on regional stability analysis methodology with a one-point neutron kinetics model

A methodology for boiling water reactor (BWR) regional stability with a one -point neutron kinetics model is proposed from the higher harmonics viewpoi nt and is verified with the Ringhals-1 stability benchmark test data, A one -point neutron kinetics model for regional stability analysis is derived fr om the spatial neutron diffusion equation using the mode decomposition tech nique. From the derivation, the intermode coupled reactivity coefficient is defined and applied to a frequency-domain BWR stability analysis model. Th e analysis model traces a unit power perturbation and calculates the open-l oop transfer function as the power response to the input perturbation. Comb ined with the aforementioned reactivity coefficient and the asymmetric shap e perturbation that reflects the first azimuthal mode, the first azimuthal mode is excited exclusively without any assumption on the ex-core model. Th erefore, the regional stability can be evaluated with a normal recirculatio n flow model, which is employed for core-wide stability analysis. The metho dology is verified with the Ringhals-1 stability benchmark test data, whose stability conditions were widely distributed and suitable for verification , The results show that the proposed methodology is quite appropriate for B WR regional stability analysis.