Recently, a coarse mesh transport method that couples Monte Carlo response function calculations to deterministic sweeps was extended to 2D (x,y) geometry. The deterministic sweeps were used to converge the partial cu...
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Recently, a coarse mesh transport method that couples Monte Carlo response function calculations to deterministic sweeps was extended to 2D (x,y) geometry. The deterministic sweeps were used to converge the partial currents on the coarse mesh boundaries while dealing with the statistical uncertainties in a straightforward fashion. The initial formulation used the cosine-current angular distribution and the spatially flat-flux approximation. This method yielded satisfactory results on the C5G7 MOX benchmark, but knowing that the cosine-current approximation breaks down near regions with strong absorption or in the vicinity of the coarse mesh corners, a new formulation was sought. The angular and spatial approximations were replaced by orthogonal polynomial expansions (Legendre polynomials) to develop a better representation of the partial currents connecting each coarse mesh. The method was then tested on two benchmark problems: a small 2D one group problem and the C5G7 MOX problem. In the first problem, using a 2nd order expansion in all variables (space, polar angle and azimuthal angle) with two segments per edge, we obtain an average pin power, a root mean square and a maximum errors of 0.09%, 0.11% and 0.18%, respectively. The eigenvalue of the coarse mesh method differs from the MCNP reference solution by -0.06%. In the C5G7 MOX benchmark problem, using 2nd polynomials expansions in all variables, the eigenvalue error is 0.06%. The average pin power, the root mean square and the maximum errors are 0.51%, 0.65% and 2.18%, respectively.
At the University of Cincinnati nuclearengineeringprogram, the resurrection of a once moth-balled subcritical reactor facility now provides an ideal laboratory experience to its students. Its simplicity and accessib...
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At the University of Cincinnati nuclearengineeringprogram, the resurrection of a once moth-balled subcritical reactor facility now provides an ideal laboratory experience to its students. Its simplicity and accessibility are among its key features. This article focuses upon supplementing the experimental aspects of this facility via the development of a three-dimensional, full detail, MCNP model of this reactor, while emphasizing the validation of this computational tool against laboratory measurements. The subcritical reactor parameters herein compared include: neutron and photon flux distributions, fission rate, and the subcritical multiplication factor (k-effective), among other relevant parameters of interest
One of the important issues in a nodal diffusion analysis of a PER core is the generation of accurate nodal constants. As compared to a light water reactor (LWR) lattice, in which the variation of the core properties ...
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One of the important issues in a nodal diffusion analysis of a PER core is the generation of accurate nodal constants. As compared to a light water reactor (LWR) lattice, in which the variation of the core properties in the axial direction is relatively weak and therefore a 2-D modeling appropriate, the calculation at the core sub-region level for a PER needs to account for the third spatial dimension because of the complex geometry (double heterogeneity) of packed arrangements of spherical pebbles. The purpose of the present work was to assess the capability of the MICROX-2 code to generate accurate nodal cross sections for PER lattices. This preliminary evaluation was based on comparison to a continuous-energy, doubly heterogeneous MCNP reference model. The terms of the comparison were the infinite medium multiplication factor, the few-group cell-homogenized total, capture and fission cross-sections, and the spectral indices. The principal phenomena covered by these choices pertain to resonance treatment and double heterogeneity. The models developed here do not attempt to evaluate the effect of packing randomness at either heterogeneity level. Such a study will be discussed elsewhere. The double heterogeneity of the lattice cell was fully modeled in the MCNP reference model. The cell-homogenized few-group cross sections and spectral parameters were calculated in MCNP by using the reaction rates and flux tallies. A spherical geometry model was used with MICROX-2. The analysis was completed at cold, room temperature (296 K) and at hot operating conditions (1073 K). For consistency, the same cross section data files were used for generating both the pointwise cross sections for MCNP and the fine-group cross sections for MICROX-2. Results showed significant differences between the MCNP and the MICROX-2 results, especially in the thermal and resonance energy range.
Recently, a coarse mesh transport method was extended to 2-D geometry by coupling Monte Carlo response function calculations to deterministic sweeps for converging the partial currents on the coarse mesh boundaries. M...
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ISBN:
(纸本)0894486837
Recently, a coarse mesh transport method was extended to 2-D geometry by coupling Monte Carlo response function calculations to deterministic sweeps for converging the partial currents on the coarse mesh boundaries. More extensive testing of the new method has been performed with the previously published continuous energy benchmark problem, as well as the multigroup C5G7 MOX problem. The effect of the partial current representation in space, for the MOX problem, and in space and energy, for the smaller problem, on the accuracy of the results is the focus of this paper. For the MOX problem, accurate results were obtained with the assumption that the partial currents are piecewise-constant on four spatial segments per coarse mesh interface. Specifically, the errors in the system multiplication factor and the average absolute pin power were 0.12% and 0.68%, respectively. The root mean square and the mean relative pin power errors were 1.15% and 0.56%, respectively.
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