Abstract
We describe neutron cross section covariances for 78 structural materials and fission products produced for the new US evaluated nuclear reaction library ENDF/B-VII.1. Neutron incident energies cover full range from 10-5eV to 20 MeV and covariances are primarily provided for capture, elastic and inelastic scattering as well as (n,2n). The list of materials follows priorities defined by the Advanced Fuel Cycle Initiative, the major application being data adjustment for advanced fast reactor systems. Thus, in addition to 28 structural materials and 49 fission products, the list includes also 23Na which is important fast reactor coolant. Due to extensive amount of materials, we adopted a variety of methodologies depending on the priority of a specific material. In the resolved resonance region we primarily used resonance parameter uncertainties given in Atlas of Neutron Resonances and either applied the kernel approximation to propagate these uncertainties into cross section uncertainties or resorted to simplified estimates based on integral quantities. For several priority materials we adopted MF32 covariances produced by SAMMY at ORNL, modified by us by adding MF33 covariances to account for systematic uncertainties. In the fast neutron region we resorted to three methods. The most sophisticated was EMPIRE-KALMAN method which combines experimental data from EXFOR library with nuclear reaction modeling and least-squares fitting. The two other methods used simplified estimates, either based on the propagation of nuclear reaction model parameter uncertainties or on a dispersion analysis of central cross section values in recent evaluated data files. All covariances were subject to quality assurance procedures adopted recently by CSEWG. In addition, tools were developed to allow inspection of processed covariances and computed integral quantities, and for comparing these values to data from the Atlas and the astrophysics database KADoNiS.
| Original language | English |
|---|---|
| Pages (from-to) | 3075-3097 |
| Number of pages | 23 |
| Journal | Nuclear Data Sheets |
| Volume | 112 |
| Issue number | 12 |
| DOIs | |
| State | Published - Dec 2011 |
| Externally published | Yes |
Funding
We are grateful to numerous colleagues for useful discussions and criticism. The authors appreciate the valuable assistance of Ramon Arcilla in covariance processing with the code NJOY. We also are grateful to Boris Pri-tychenko for his efforts with the EXFOR module of the quality assurance system and to Gustavo Nobre , Annalia Palumbo, and David Brown for their careful work in checking the covariance libraries. We wish to thank ANL and INL reactor analysts led by M. Salvatores and G. Palmiotti for most useful feedback. We acknowledge support provided by the United States DOE Nuclear Criticality Safety and Advanced Fuel Cycle Initiative programs. This work was sponsored by the Office of Nuclear Physics, Office of Science, U.S. Department of Energy under contract No. DE-AC02-98CH10886 with Brookhaven Science Associates.