Heterogeneous effects in fast breeder reactors
Name
856918347.pdf
Size
12.12 MB
Format
Adobe PDF
Checksum (MD5)
3a6f170e331a67333daac359ae314fa0
Author(s)
Gregory, Michael Vladimir
Driscoll, Michael J.
Lanning, David D.
Date Issued
1973
Publisher
Cambridge, Mass. : Massachusetts Institute of Technology, Dept. of Nuclear Engineering, [1973]
Series/Report no.
MITNE ; no. 142
COO (Series) ; 2250-1
AEC research and development report
Abstract
Heterogeneous effects in fast breeder reactors are examined through development of simple but accurate models for the calculation of a posteriori corrections to a volume-averaged homogeneous representation. Three distinct heterogeneous effects are considered: spatial coarse-group flux distribution within the unit cell, anisotropic diffusion, and resonance self-shielding. An escape/transmission probability theory is developed which yields region-averaged fluxes, used to flux-weight cross sections. Fluxes calculated by the model are in substantial agreement with S 8 discrete ordinate calculations. The method of Benoist, as applied to tight lattices, is adopted to generate anisotropic diffusion coefficients in pin geometry. The resulting perturbations from a volume-averaged homogeneous representation are interpreted in terms of reactivities calculated from first order perturbation theory and an equivalent "total differential of k" method.
Resonance self-shielding is treated by the f-factor approach, based on correlations developed to give the self-shielding factors as functions of one-group constants. Various reference designs are analyzed for heterogeneous effects. For a demonstration LMFBR design, the whole-core sodium void reactivity change is calculated to be 90e less positive for the heterogeneous core representation compared to a homogeneous core, due primarily to the effects of anisotropic diffusion. Parametric studies show at least a doubling of this negative reactivity contribution is attainable for judicious choices of enrichment, lattice pitch and lattice geometry (particularly the open hexagonal lattice). The fuel dispersal accident is analyzed and a positive reactivity contribution due to heterogeneity is identified. The results of intra-rod U-238 activation measurements in the Blanket Test Facility are analyzed and compared to calculations.
This activation depression is found to be of the order of 10% (surfaceto- average) for a typical LMFBR blanket rod and is ascribed to the effect of heterogeneous resonance self-shielding of U-238. Heterogeneous effects on the breeding ratio are studied with the conclusions that accounting for resonance self-shielding reduces the total breeding ratio by over 10%, but heterogeneous effects are not important for breeding ratio calculations.
Description
"January, 1973."
Also issued as a Ph. D. thesis written by the first author and supervised by the second and third author, MIT, Dept. of Nuclear Engineering, 1973
Includes bibliographical references (pages 259-266)
Persistent DSpace Link
