Abstract
An analysis method for BWR regional stability is developed in frequency-domain. Conventionally, the energy spectrum of fundamental eigenfunction has been applied to the calculation of first-harmonic void reactivity instead of the spectrum of first-harmonic eigenfunction. In the present method, the fine energy spectra of first-harmonics are applied to the evaluation of void reactivity. The spectra are obtained by assembly calculation considering the geometric bucklings of spatial harmonics.The present method is applied to the Ringhals 1 benchmark test problem. Comparing the present method with the method without the spectrum of first-harmonic eigenfunction, we can estimate the effect of the spectrum on the frequency-domain modal analysis of regional stabilities in BWRs. The decay ratio (DR) of regional stability is also calculated by these two methods. It is found that the latter method tends to underestimate the absolute value of void reactivity by about 10%. By considering the spectra of first-harmonic eigenfunction, the DR of regional stability was estimated larger by about 0.05.
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