A Full Core Resonance Self-shielding Method Accounting for Temperature-dependent Fuel Subregions and Resonance Interference.

Abstract

This work presents a new resonance self-shielding method for deterministic neutron transport calculation. The new method is a fusion of two types of conventional methods, direct slowing-down equation and integral table based methods. The direct slowing-down method is essentially accurate in terms of using continuous-energy cross section data but is computationally expensive for the reactor assembly or whole core calculation. The integral table based methods use pre-calculated tables so that these methods are much more efficient than directly solving the slowing-down equation. However, the derivation of integral table based methods introduces a couple of approximations, leading to limitations of these methods to treat resonance interference, spatially distributed self-shielding, and non-uniform temperature profile within the fuel rod. To overcome these limitations, the new method incorporates a correction scheme. The conventional iteration of the embedded self-shielding method (ESSM) is still performed without subdivision of the fuel regions to capture the global inter-pin shielding effect. The resultant self-shielded cross sections are modified by correction factors incorporating the intra-pin effects due to radial variation of the shielded cross section, radial temperature distribution, and resonance interference. An efficient quasi-1D slowing-down equation is developed to calculate these correction factors. In essence, the assumption that underpins this new method is that the global Dancoff effect is treated satisfactorily with ESSM, while the effects of radial fuel regions and resonance interference are local phenomena that can be solved with the quasi-1D model. The new method yields substantially improved results for both radially dependent and energy-dependent reaction rates, which help to improve the within-pin physics for multi-region depletion and multiphysics calculations, as well as the overall eigenvalue estimation.