Fuel heat transfer modelling in reduced-order boiling water reactor dynamics models

Usually, heat transfer from fuel to coolant is treated as a first-order process in reduced-order boiling water reactor dynamic models, The correctness of this simple approach is investigated by comparing reactor stability predictions of the March-Leuba reduced-order model, with those using a second-order model. The predicted margin to instability, reactor decay ratio and resonance frequency are compared, The first-order model gives correct results, provided that the correct effective fuel time constant is being used, which can be as short as a few seconds