A FISSION-SOURCE ACCELERATION TECHNIQUE FOR TIME-DEPENDENT EVEN-PARITY SN CALCULATIONS

A synthetic scheme for accelerating the convergence of the fission sou rce in time-dependent multigroup even-parity S(n) calculations with do wnscatter is described. The low-order operator associated with this sc heme is a one-group diffusion operator. Thus, this scheme can be thoug ht of as a variant of diffusion synthetic acceleration. A Fourier anal ysis of this scheme is performed, which indicates that it is unconditi onally effective for a spatially infinite model problem. Computational results are presented that show excellent performance of the method i n three-dimensional calculations. Although this method is derived for the even-parity S(n) equations, it can easily be generalized for appli cation to the standard first-order S(n) equations. The accelerated ite ration equations for both the even-parity and first-order S(n) equatio ns are given, but only the even-parity algorithm is computationally te sted.