Program - Brookhaven National Laboratory

LA-UR-12-23712
The ENDF/B-VII.1 [1,2] nuclear data library was released in December, 2011 ... five years after the release
of ENDF/B-VII.0 [3]. Integral data testing of the library has relied heavily upon Critical Safety benchmarks
defined in the International Criticality Safety Benchmark Evaluation Project Handbook [4]. We
have calculated the critical eigenvalue for hundreds of these benchmarks, spanning a range of fuel systems
( 233 U, HEU, LEU, 239 Pu) under various moderating and reflected conditions. The desired outcome of any
critical eigenvalue calculation will be (i) accurate results obtained with previous evaluated cross sections
should remain accurate, irrespective of any changes in the underlying evaluated cross section files; (ii) poor
results should be improved if there are substantial changes in the underlying cross section evaluations, and
(iii) poor results should not improve if there have not been any changes in the underlying nuclear data.
We show examples of all three outcomes, with particular emphasis on benchmarks containing 233 U, 239 Pu,
beryllium and lead. Benchmarks containing these materials were not calculated as accurately as desired
with ENDF/B-VII.0 and they received limited attention during the development of ENDF/B-VII.1. We
now have a several year window were evaluators and data validators can iterate on potentially improved
data sets that could become incorporated in the next generation evaluated data file. We also show comparisons
between the latest ENDF/B-VII.1, JEFF-3.1.2 and JENDL-4.0 libraries. There remain significant
differences in selected cross sections from the “Big 3” nuclides, 235,238 U and 239 Pu that the international
community should work to resolve in the next several years. In some instances, the bare 239 Pu sphere
commonly known as Jezebel for example, accurate eigenvalues are obtained with all three libraries. This
suggests that at least one, and more likely all three, evaluated files is yielding an accurate eigenvalue for
the wrong reason; an observation that casts doubt on the predictive capability of all three files.
[1] M.B.Chadwick et al., “ENDF/B-VII.1 Nuclear Data for Science and Technology: Cross Sections, Covariances,
Fission Yields and Decay Data,” Nuclear Data Sheets, 112, 2887 (2011). [2] A.C.Kahler et al.,
“ENDF/B-VII.1 Neutron Cross Section Data Testing with Critical Assembly and Reactor Experiments,”
Nuclear Data Sheets, 112, 2997 (2011). [3] M.B.Chadwick et al., “ENDF/B-VII.0: Next Generation Evaluated
Nuclear Data Library for Nuclear Science and Technology,” Nuclear Data Sheets, 107, 2931 (2006).
[4] J.B.Briggs, editor, “International Handbook of Evaluated Criticality Safety Benchmark Experiments,”/
NEA/NSC/DOC(95)03, revised and updated annually.
FE 2 11:00 AM
Comparison of ENDF/B-VII.1 and ENDF/B-VII.0 Results for the Expanded Criticality
Validation Suite for MCNP and for Selected Additional Criticality Benchmarks
Russell D. Mosteller
(retired)
Results obtained with the ENDF/B-VII.0 and ENDF/B-VII.1 nuclear data libraries are compared for a
substantial number of criticality benchmarks. Results from the ENDF/B-VI nuclear data library also
are included for historical perspective. The calculations were performed with the MCNP Monte Carlo
code. The cases include the 119 benchmarks in the expanded criticality validation suite for MCNP and 23
additional benchmarks. Specifications for all of the benchmarks are taken from the International Handbook
of Evaluated Criticality Safety Benchmark Experiments. The full paper will contain the results for all 142
benchmarks. The 119 benchmarks in the expanded criticality validation suite are divided into five classes
of fuel: 233 U, highly enriched uranium (HEU), intermediate enriched uranium (IEU), low enriched uranium
(LEU), and plutonium. The 233 U, HEU, IEU, and plutonium benchmarks are subdivided farther according
to spectrum – fast, intermediate, or thermal. The LEU category includes only thermal cases, since LEU
can reach a critical condition only with a thermal spectrum. Succinct descriptions of each of the 119 cases
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