Evaluation of the Need for Discontinuity Factors for Neutronic Modelling of CANDU Low-Void-Reactivity Fuel Lattices
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Abstract
The need for and effectiveness of using assembly discontinuity factors (ADFs) in
neutronic diffusion calculations for low-void-reactivity fuel (LVRF) CANDU lattices was investigated. Two simple configurations were used for this purpose: one consisting of two adjacent fuel cells with different burnups and one consisting of two fuel cells and one reflector cell. Diffusion calculations were performed in two energy groups using homogenized nodes. Four discretization methods were used: Coarse-Mesh Finite
Differences (CMFD), Fine-Mesh Finite Differences (FMFD), Nodal Expansion Method
(NEM) without ADFs and NEM with ADFs. The diffusion results were then compared with
reference results obtained from 69-energy-group transport calculations using detailed
geometrical representations. It was found that using (zero-current) ADFs results in minimal improvement of accuracy and that a better (leakage corrected) homogenization method is needed to further increase accuracy.
neutronic diffusion calculations for low-void-reactivity fuel (LVRF) CANDU lattices was investigated. Two simple configurations were used for this purpose: one consisting of two adjacent fuel cells with different burnups and one consisting of two fuel cells and one reflector cell. Diffusion calculations were performed in two energy groups using homogenized nodes. Four discretization methods were used: Coarse-Mesh Finite
Differences (CMFD), Fine-Mesh Finite Differences (FMFD), Nodal Expansion Method
(NEM) without ADFs and NEM with ADFs. The diffusion results were then compared with
reference results obtained from 69-energy-group transport calculations using detailed
geometrical representations. It was found that using (zero-current) ADFs results in minimal improvement of accuracy and that a better (leakage corrected) homogenization method is needed to further increase accuracy.
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