Moderator Temperature Coefficient of Reactivity in Pressurized Water Reactors: Theoretical Investigation and Numerical Simulations

Estimation of the moderator temperature coefficient (MTC) of reactivity of pressurized water reactors by noise analysis is investigated, both theoretically and through numerical simulations. It is found that using local neutron signals, all estimators of MTC will underestimate the actual MTC value, as indeed is observed in all measurements reported in the literature. However, the relative deviation from the actual MTC value remains practically constant over a wide range of MTC values. This suggests that it is possible to calibrate the estimate at the beginning of the fuel cycle and then use this calibration until the end of the fuel cycle. A new estimator is proposed based on integral (point model) concepts. This estimator is found capable of providing the actual value of MTC, provided that coolant velocity fluctuations are at least as strong as coolant inlet temperature fluctuations in inducing neutron and coolant temperature fluctuations.