An improved response matrix method and its verification by one-dimensional analysis on fast reactors

The current response matrix method based on isotropic (P0) neutron angular distribution has been improved by effectively including a linearly anisotropic (P1) angular distribution. The proposed method does not take into account the P1 component directly, but it includes the effect of this component through consideration of the relation between the P0 and P1 components. The accuracy of the proposed method has been verified by comparing with exact calculation the diffusion length obtained by the present method in a uniform and infinite system: The diffusion length can be evaluated within 1% error. The present method has been further applied to one-dimensional fast reactor systems: The power distribution can be evaluated within 1%, and the neutron multiplication factor within 0.1%ΔK/K, in reference to S16 calculations. This accuracy is comparable to that of a response matrix method in which the Legendre expansion about the angle is performed with components taken up to P1. The proposed method adopts the same number of unknown components of neutron current as in the current response matrix method (order P0). The computing time is thus of comparable order between these two methods, which is much shorter than for the response matrix method using the P1 angular distribution. The proposed method can hence be considered useful for one-dimensional transport problems, and should also have good prospects of proving equally effective for multi-dimensional problems. (auth.)