Hybrid Reactivity-Equivalent Physical Transformation Method on Double-Heterogeneous System Containing Dispersed Fuel Particles and Burnable Poison Particles

Abstract

Because of the double heterogeneity of particle-dispersed fuel and particle-dispersed burnable poisons in double-heterogeneous (DH) systems, traditional software for reactor neutronics calculation cannot model and calculate them, and the volume homogenization method may bring large calculation deviations. The traditional reactivity-equivalent physical transformation (RPT) method can equivalently transform a DH system into a single-heterogeneous (SH) system which can be modeled and calculated by proven traditional software for reactor neutronic calculation. The DH system containing both particle-dispersed fuel and particle-dispersed burnable poisons can be treated by the Improved RPT (IRPT) method based on the traditional RPT method. However, when the IRPT method is used to treat the DH system containing particle-dispersed burnable poisons with large absorption cross section, large volume fraction or large particle size, there will be larger calculation deviations in the burnup. The Ring RPT (RRPT) method can not only deal with the problem of dispersed fuel particles that can be handled by the traditional RPT method, but also the problem of dispersed burnable poison particles that make the traditional RPT method invalid because of the large absorption cross section. For DH systems containing both particle-dispersed fuel and particle-dispersed burnable poisons, a two-step RRPT (TRRPT) method can be used. For DH systems containing particle-dispersed burnable poison with a large absorption cross section, a large volume fraction, or a large particle size, TRRPT method has higher calculation accuracy than the IRPT method. In this article, it was found that for DH systems containing both particle-dispersed fuel and particle-dispersed burnable poison, the TRRPT method may be invalid in some situation. Also, a new method named hybrid RPT (HRPT) method has been proposed for DH systems containing both particle-dispersed fuel and particle-dispersed burnable poisons, herein. And then the HRPT are analyzed and studied on the equivalent transformation range of DH systems comparing with the TRRPT method and the IRPT method. It was found that the HRPT method not only has a wider equivalent transformation range of DH systems than the TRRPT method, but also has higher calculation accuracy than the IRPT method. Results of depletion calculations for different types, different volume fractions, and different particle sizes of burnable poisons particles dispersed the DH systems with dispersed particle-type fuel and the comparison with Monte Carlo results of grain models have proved the effectiveness and applicability of HRPT method.