Calculation of OECD/NEA source convergence benchmark problem no.1 by using MCNP and solving fission matrix equation

摘要

The OECD/NEA source convergence benchmark problem 1: checkerboard storage of assemblies is calculated by using the MCNP-4B continuous energy Monte Carlo code and JENDL3.2 library, Calculated results show that the fission source distributions for the thirty-six cases with various calculation conditions required in the benchmark are affected by the initial source distributions, and not converged because of the weak neutron coupling between fuel assemblies. In order to approximately estimate the converged source distribution, the fission matrix equation for the checkerboard storage is solved with the deterministic method of iterative calculations, where the multiplication factors for the isolated single assembly and the neutron interactions between two assemblies are calculated and applied to the matrix elements. Then we calculate the special case, that is, the assembly-averaged source levels are set to the fission matrix solution and the distributions inside assemblies are assumed to be cosine-like shapes as the initial fission source. Most of the source levels of the major assemblies for this case do not change at all as the generations increase. Thus the fission source distribution is obtained as almost converged.