Resonance self-shielding

The orbackground concept for calculating resonance self-shielding the capture and fission resonances may be in error by 0.1 to 0.2% in kg the errors due to an improved correction for anisotropic down scattering are about as large. These relatively small corrections cannot account for the large discrepancies observed for Pu-fueled assemblies. The recent and probably more reliable results for o-Pu will give only a small improvement. 

The measured and predicted spectra were normalized to a constant value of integrated fissions and are compared In Fig. 2. The results demonstrate the need for consideration of unresolved resonance self-shielding in U, and suggest that the U absorption cross-section data may be slightly high at low energies (100 eV < E < 2 keV). 

The analysis of the measurements was accomplished using first-order perturbation theory in two dimensions, using ENDF/B-68 cross-secUim data and corrected for resonance self-shielding. The corrections were determined from a of the self-shielding factor vs Op, where Op was calculated for each sample in the cell environment. Further corrections were applied to the B... 

D. WINTZER, "BOterogeneity Calculati ms including Space D ndent Resonance Self-Shielding, Fast Reactor Physics, II, 237, IAEA, Vienna (1968). 

The neutron multiplication factor (Keff) of each benchmark core was calculated using the Monte Carlo criticality code KENO IV. The 123-group XSDRN cross-section set was used. Resonance self-shielding was accounted for in the U isotope only. Self-shielding corrections were made with the NIT AWL code from the AMPX package. ... 

All calculations were based on 29-group diffusion theory using ENDF/B-IV data which had bMn collapsed through the MC-2-II and SDX modules of the ARC system. Platewise resonance self-shielding of both the intermediate mass and isotopes was treated explicitly. 

All of the analyses utDized the SCALE 27 neutron-group cross-section library based on ENDF-IV. The resonance isotopes were corrected for resonance self-shielding via the Nordheim Integral treatment in the NITAWL code. Prior criticality studies using this library on several EPRI critical experiments indicated that for rite coolant-to-fuel voliune ratio and corresponding lattice pitch of the TMI design cote, the K-effective calculated would range from 0.98 and 0.99. 

---