The effect of fuel rod dynamics on BWR stability margin

This paper presents a study on the effect of fuel rod dynamics on BWR Stability Margin. Specifically, Boiling Water Nuclear Reactor (BWR) stability predictions using lumped parameter fuel rod models were compared with those using a more detailed distributed parameter nuclear fuel rod model, in which radial variations in power generation were considered. It was found that, when nuclear feedback mechanisms were neglected, both models predicted similar stability margins. However, significantly different margins were obtained when void-reactivity feedback was considered. It was further found that the radial power distribution in a nuclear fuel rod, and the void reactivity coefficient, can have a significant impact on predicted stability margins. This study implies that the nuclear fuel must be accurately modeled in the linear stability analysis of BWR channels, and that simplified fuel dynamics models can lead to large non-conservative errors in the predicted stability margin. (orig.)