Covariance Evaluation for Actinide Nuclear Data in JENDL-4

Abstract

Covariances of actinide nuclear data stored in JENDL-4.0 have been evaluated based on available experimental data and reaction model calculation. The covariance matrix was basically deduced applying the consistent method with the nuclear data evaluation. For the fast neutron fission cross sections of 6 major actinides of 233,235,238 U and 239,240,241 Pu were evaluated simultaneously with experimental data of both cross sections and their ratios using the least-squares code SOK, resulting in giving the covariance matrices that has correlations between the data of dierent nuclei. For the minor actinide, the least-squares fitting code GMA was used for fission cross section evaluation. The covariances were obtained from the same calculation. For other reaction cross sections, covariances were evaluated using KALMAN code with the sensitivities calculated by CCONE code. Covariances for other data such as resonance parameters and average numbers of fission neutrons were also evaluated. The evaluated covariance data have been complied to the ENDF-6 format files. The JENDL-4.0 library contains covariance data of (1) average number of neutrons per fission (MF = 31), (2) resonance parameters (MF = 32), (3) cross sections (MF = 33), (4) angular distributions of elastic scattering (MF = 34), and (5) prompt fission spectra (MF = 35) for all 79 actinides.