Abstract
The classical two-step calculation scheme has been extensively used to perform three-dimensional deterministic core calculations thanks to its fast results. On the other hand, direct 3D transport calculations and 2D/1D Fusion methods, mostly based on the method of characteristics, have recently been applied showing a prohibitive computational time for routine design purposes as well as in the context of multiphysics and core depletion calculations, due to current machine capabilities. The Dynamic Homogenization method is here proposed as an alternative technique that may lie between the classical and the direct approaches in terms of precision and performance. In this work, the method is applied to the NEA ”PWR MOX/UO2 Core Benchmark” for a 3D configuration. Comparison of pin power relative errors and computational cost against the two-step and direct approaches are presented.
Highlights
The two-step calculation scheme has been widely used for core modeling and design because of the main advantage of obtaining fast results for different core configurations
The first step of this approach consists of “off-line” 2D calculations for each assembly type, that are typically performed with the method of characteristics (MOC) on a fine spatial and energy mesh with high order angular discretization, to produce a library of homogenized cross sections that are calculated for different physical parameters, such as burnup, moderator density, fuel temperature, etc
For 2D configurations it has been shown that using equivalence parameters improves significantly the quality of the solution of the two-group diffusion core calculation [5,7], and that typical pin power errors found in this literature are reduced from around 10-12% to roughly 5-7% with respect to a reference calculation of a typical LWR at nominal conditions and
Summary
The two-step calculation scheme has been widely used for core modeling and design because of the main advantage of obtaining fast results for different core configurations. Colameco et al extended the application to 2D configurations, introducing in the iterative process an equivalence by discontinuity factors [12] They obtained good agreement against reference transport calculation for a 2x2 cluster in 2D of UOx and MOx assemblies with reflection boundary conditions. Another approximation is introduced for the evaluation of the angular flux on the top and bottom of an axial layer This is done by a 1D calculation performed in transport (Fusion) or by a coarse operator (Hybrid Fusion), but we wanted to avoid this extra cost, by using the information provided by the 3D diffusion solver. NEA Benchmark with 1/8 radial symmetry [15]
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