Research on the on-the-fly homogenization method based on RMC code for criticality calculations

Abstract

The applications of traditional deterministic lattice codes are limited in certain cases because they cannot treat closely coupled neutron characteristics and peculiar geometry. Therefore, to use the continuous energy Monte Carlo method and full core homogenization to generate multi-group cross sections has attracted growing interests. In this paper, the on-the-fly homogenization method based on the Monte Carlo code RMC, which generates multi-group cross sections in the frame of full core continuous energy Monte Carlo calculation and then use them in the Monte Carlo multi-group calculation to obtain a more convergent solution, is proposed and implemented. Tests and comparisons for the use of such on-the-fly homogenization method in criticality calculations are conducted using Kaist 1A benchmark and a simplified Lead-cooled reactor. The results show that our on-the-fly homogenization method exhibits similar accuracy with continuous energy Monte Carlo calculation that uses the same number of neutron histories and only costs about half of the computational time. With respect to spatial homogenization schemes, the cell homogenization scheme is the best one which can predict the reference solution especially for problems with strong absorbers. Given a tradeoff between efficiency and accuracy, the hybrid Homogenization scheme, which treats strong absorbers with cell homogenization and others with pin homogenization, can take nearly as much time as the pin Homogenization while achieving nearly the same accuracy as the cell Homogenization.