Study on MCNP6 model in the calculation of kinetic parameters for pebble bed reactor

Abstract

When conducting a nuclear reactor transient analysis, the most important parameter, called the kinetic parameter, is required. The calculation of kinetic parameters can be conducted using several methods. The deterministic method is one possible method that relies on the forward and adjoint neutron fluxes to provide the kinetic parameters calculation based on the perturbation theory. In this study, the Monte Carlo transport code MCNP6 was utilized to perform the exact prediction of the kinetic parameters of a pebble bed reactor. The core was modelled with a different fuel composition of uranium loading per pebble,235U enrichment and H/D ratio. It was found that keff strongly depends on the uranium loading, uranium enrichment and H/D ratio while the βeff dependence is insignificant. The increase in the prompt neutron lifetime (ℓ) and mean generation time (Λ) as a function of H/D ratio are insignificant as compared to the decrease of those parameters in the case of uranium loading or uranium enrichment. These results conclude that the selection of uranium loading per pebble,235U enrichment and H/D ratio should be considered carefully for the control and inherent safety performances.