Effect of mesh division on the fission matrix acceleration method

The fission matrix acceleration method can accelerate the convergence of source distribution in the Monte Carlo(MC) criticality calculation. The inner-outer iteration is introduced to analyze the effect of the mesh division on the fission matrix acceleration method. Its pointed out that the convergence rate increases with a refined mesh to tally the fission matrix but the refined mesh method has its limitation with the consideration of the stability of method. To solve this problem, the mesh changing method is proposed, which can improve the performance of the fission matrix acceleration method further without the increase of order of fission matrix. The improvement is verified by a 1D slab model.