Comparison of ENDF/B-VI and preliminary ENDF/B-VII results for the MCNP criticality validation suite
- Russell D.
An initial assessment of the impact of preliminary data proposed for ENDF/B-VII has been made using the MCNP criticality validation suite. Relative to ENDF/B-VI, the data changes primarily involve high-energy elastic and inelastic scattering in the uranium isotopes and {sup 239}Pu, as well as resonance parameters for {sup 238}U. The criticality validation suite is a collection of 31 benchmarks taken from the International Handbook of Evaluated Criticality Benchmark Experiments. It contains cases for a variety of fuels, including {sup 233}U, highly enriched uranium (HEU), intermediate-enriched uranium (IEU), low-enriched uranium (LEU), and plutonium. For each fuel type, there are cases with a variety of moderators, reflectors, spectra, and geometries. The cases in the suite are summarized in Table I. Three sets of calculations were performed for the suite using the MCNP5 Monte Carlo code. The first set employed nuclear data from ENDF/B-VI Release 8, the final release for ENDF/B-VI. The second set employed preliminary ENDF/B-VII data generated by group T-16 at Los Alamos National Laboratory for the uranium isotopes and for {sup 239}Pu but retained ENDF/B-VI data for all other nuclides. The third set was the same as the second except that a new set of {sup 238}U resonance parameters generated by researchers at Oak Ridge National Laboratory (ORNL) was added to the T-16 evaluation. The MCNPS calculations were run with 5,000,000 active neutron histories for all but two cases in the suite. Only 3,000,000 active histories were used for those cases, SB-5 and Zebra-8H, because they require substantially more computer time per history than the other cases. Nonetheless, the standard deviation for k{sub eff} from those cases is comparable to those for other cases in the suite. The results from these calculations are presented in Table II. The preliminary ENDF/B-VII data produce marked improvements in k{sub eff} for bare spheres of {sup 233}U (Jezebel-233), HEU (Godiva), and plutonium (Jezebel and Jezebel-240) as well as the other unreflected HEU and plutonium cases (Tinkertoy02 (c-11) and Pu Buttons, respectively). Furthermore, the reactivity swings between those bare spheres and the corresponding Flattop cases (which enclose the sphere inside an annulus of normal uranium) are substantially decreased. The changes also significantly improve k{sub eff} for BIG TEN and for HEU and plutonium spheres immersed in water (Godiver and Pu-MF-11, respectively). In addition, inclusion of the ORNL resonance parameters for {sup 238}U produces a significantly better value for k{sub eff} for B&W XI (2), a lattice of LEU fuel pins in water, and ORNL-II, an unreflected sphere of uranyl nitrate solution enriched in {sup 233}U. At the same time, the preliminary ENDF/B-VII data produce worse results for thermal lattices of {sup 233}U and HEU pins in water (SB-2 1/2 and SB-5, respectively), for the bare IEU sphere (IEU-MF-03) and the IEU sphere reflected by graphite (IEU-MF-04), for a plutonium sphere reflected by thorium (THOR), and for a MOX lattice in water (PNL-33). Furthermore, k{sub eff} for the uranium cases with intermediate spectra remains substantially underpredicted, while k{sub eff} for the plutonium case with an intermediate spectrum (HISS/HPG) continues to be significantly over-predicted. In conclusion, preliminary ENDF/B-VII data for the uranium isotopes and {sup 239}Pu produce improvements for most of the cases with fast spectra, BIG TEN, and the lattice of LEU fuel pins in water. However, improvements still are needed in some areas, particularly those cases with intermediate spectra.
- Research Organization:
- Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 977394
- Report Number(s):
- LA-UR-04-0123; LA-UR-04-123; TRN: US1002910
- Resource Relation:
- Conference: Summary only
- Country of Publication:
- United States
- Language:
- English
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