Theoretical investigation of the MTC noise estimate in 1-D homogeneous systems

In this paper, the accuracy of the noise-based determination of the moderat or temperature coefficient (MTC) is investigated theoretically and quantita tively. It is known from earlier work that the noise method systematically underestimates the MTC. In this paper, it is found that the main reason for the underestimation lies with the radial incoherence of the temperature fl uctuations. The deviation of the reactor response from point-kinetics is an other possible reason, but it was found to play a quite insignificant role. The theory of neutron noise, induced by spatially random perturbations is elaborated and by its help the inaccuracy (bias) of the noise based MTC est imation was quantitatively investigated. It was found that a relatively sho rt correlation length of the temperature fluctuations. which is in agreemen t with experimental evidence, can explain the observed underestimation of t he MTC by the noise method. (C) 2001 Elsevier Science Ltd. All rights reser ved.