Application of a new OpenFOAM-based neutron diffusion kinetics solver to pebble-type VHTRs.

• A neutron diffusion kinetics solver DiFOAM V1.0 is developed for pebble type VHTR based on OpenFOAM. • The finite volume method is used to solve neutron diffusion equations and delayed neutron precursor equations. • Two different scale problems including PWR assembly and core benchmark are used to be assessed the accuracy of DiFOAM V1.0. • The accuracy of OpenMC/DiFOAM V1.0 code system applied to pebble type VHTR has been proved. As an advanced reactor type, the pebble type very high temperature gas cooled reactor (VHTR) has the advantages of high safety and high outlet temperature. In this study, the OpenMC/OpenFOAM code system is developed for a neutronic analysis of VHTR. The workflow of OpenMC/OpenFOAM code system consists of two steps: the OpenMC code is used to generate few-group cross sections; then, the OpenFOAM code is used to perform core neutron diffusion kinetics analyses and a neutron diffusion kinetics simulation solver (DiFAOM V1.0) is developed. The finite volume method (FVM) is used to discretize the neutron diffusion kinetics equations. Two scale problems are selected to verified the DiFAOM V1.0 solver. Firstly, the PWR assembly model are compared by DiFAOM V1.0 and Monte Carlo results. The results show that for PWR assembly, the difference of k eff is 41 pcm, and the maximum error of four group normalized flux is −0.0841%. Secondly, 2D-TWIGL benchmark is used to assess the accuracy of DiFAOM V1.0 at core scale, and the calculated results of k eff and normalized power distribution calculated were in good agreement with the benchmark. The above results prove the correctness of DiFAOM V1.0 solver. And for application of VHTR BCC lattice model, the maximum error of four group normalized flux is only −0.826%. [ABSTRACT FROM AUTHOR]