Heterogeneity effects of stainless steel subassembly walls in FBR blankets
Abstract
The neutron absorption in stainless steel in a fast reactor with fuel rods lumped into a hexagonal lattice surrounded by the subassembly wall, may be considerably less than that calculated from conventional homogeneous approximations. This is particularly the case for the softer neutron spectra of blanket regions. A methodology is developed to treat the heterogeneity effect of stainless steel subassembly walls in a fast reactor blanket; it is applied to the blanket in the new FBBF (Blanket III). Heterogeneous resonance absorption within the subassembly wall is calculated with integral transport theory for multiple scattering. A multiple scattering treatment is important because of the high scattering cross section of stainless steel. In addition, the transitional self-shielding effect near the subassembly walls is evaluated with integral transport theory for a double-interface system. The calculation of transitional self-shielding leads to a difference in the capture rate in the near-wall clad as compared to the homogeneous calculation. This capture rate increment in the near-wall clad is combined with the capture rate of the subassembly wall to describe the total heterogeneity effect of the subassembly wall. The combined capture rate is used to generate a "revised" macroscopic cross section with an improved smearing method of the subassembly wall in a triangular mesh. Self-shielding within the subassembly wall due to major resonances reduces the VITAMIN-E cross sections for stainless steel in the subassembly wall by 3% to 65%. These heterogeneous self-shielded group constants for the stainless steel subassembly wall are smeared in the corresponding "near-wall" triangles. Due to a smaller stainless steel capture cross section, the stainless steel capture rates are first obtained to be smaller by 3% for the heterogeneous treatment compared to the conventional homogeneous values. However, an increased transmission due to an increased self-shielding in stainless steel overcomes a decrease in the stainless steel capture rates and eventually yields larger values with increasing penetration into the blanket. The increased flux increases the U$\sp{238}$ capture and fission rates by 6% from the conventional homogeneous values. The reaction rates in the blanket are accounted for by the flux behavior resulting from an increased transmission with increasing penetration into the blanket.
Degree
Ph.D.
Advisors
Ott, Purdue University.
Subject Area
Nuclear physics
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