PRELIMINARY CROSS SECTION AND NU-BAR COVARIANCES FOR WPEC SUBGROUP 26

We report preliminary cross section covariances developed for the WPEC Subgroup 26 for 45 out of 52 requested materials. The covariances were produced in 15- and 187-group representations as follows: (1) 36 isotopes (16O, 19F, 23Na, 27Al, 28Si, 52Cr, 56,56Fe, 58Ni, 90,91,92,94Zr, 166,167,168,170Er, 206,207,208Pb, 209Bi, 233,234,236U, 237Np, 238,240,241,242Pu, 241,242m,243Am, 242,243,244,245Cm) were evaluated using the BNL-LANL methodology. For the thermal region and the resolved and unresolved resonance regions, the methodology has been based on the Atlas-Kalman approach, in the fast neutron region the Empire-Kalman method has been used; (2) 6 isotopes (155,156,157,158,160Gd and 232Th) were taken from ENDF/B-VII.0; and (3) 3 isotopes (1H, 238U and 239Pu) were taken from JENDL-3.3. For 6 light nuclei (4He, 6,7Li, 9Be, 10B, 12C), only partial cross section covariance results were obtained, additional work is needed and they do not report the results here. Likewise, the cross section covariances for 235U, which they recommend to take from JENDL-3.3, will be included once the multigroup processing is successfully completed. Covariances for the average number of neutrons per fission, total ν-bar, are provided for 10 actinides identified as priority by SG26. Further work is needed to resolve some of the issues and to produce covariances for the full set of 52 materials