Burnup Optimization Using Modal Expansion Method

抄録

A method of modal expansion approximation is applied to study a burnup optimization problem. The spatial distribution of the neutron flux is approximated by a linear combination of certain predetermined spatial modes, and one of these modes is regarded as the control mode. A computational procedure that allows fast and sufficiently accurate estimation of the effect of flux shaping on the attainable burnup is described. As numerical example the optimal policy for flux shaping for a one-dimensional slab reactor model with nonlinear feedback effects is sought by this method. By manipulating the flux shape according to the optimal policy, the attainable burnup is increased appreciably over that obtained by the conventional method based on constant flux distribution, when the maximum allowable power peaking factor is large. The optimal policies are determined uniquely in the cases of highly nonuniform fuel loading and smaller values of the maximum allowable power peaking factor, while they become non-unique in the contrary case. The present method is applicable to more general problems such as the optimization of flux shaping of a reactor with multi-zone refueling scheme without much increase in computing effort.