Dancoff factor analysis for pebble bed fluoride salt cooled high temperature reactor

Abstract

In this work, an analytical expression based on a two-region spherical model for a High Temperature Gas cooled Reactor (HTGR), is applied to a Pebble Bed Fluoride salt cooled High temperature Reactor (PB-FHR) to calculate the average Dancoff factor for fuel kernel with various coated particle densities. The results are compared with those obtained by the Monte Carlo (MC) method. It is found that there is a good agreement between the analytical and MC, which implies that the two-region spherical model for the Dancoff factor calculation is applicable to PB-FHR. The Dancoff factors with and without FLiBe salt are both evaluated and compared to analyze the influence of FLiBe salt with different numbers of coated particles. The Dancoff factor with FLiBe salt is smaller than that without FLiBe salt from ∼ 11% to ∼ 3% when the number of coated particles in a fuel pebble increases from 5000 to 60,000. In addition, the effects of temperature and volume fraction of FLiBe salt on Dancoff factor are analyzed. Afterwards, the sensitivity of the infinite multiplication factor (k∞) to the Dancoff factor for a fuel cell of PB-FHR is further analyzed by the neutron transport calculation with a new developed routine. It is found that the infinite multiplication factor increases almost linearly with the increase of Dancoff factor, and a higher density of coated particles will lead to a sharper variation of k∞ with Dancoff factor.