Fission product and actinide data status in ENDF/B

The fission product and actinide data atatus in ENDF/B-4 and -5 are summarized, and the needed improvements in these files are described together with the planned expansion of data for ENDF/B-6 in the areas of fission-product yields and cross sections. The general content is compared between ENDF/B-4 and -5, and the dominant changes from the version 4 to 5 are shown. The expansion of decay spectral data for ENDF/B-5 improved the shape of the aggregate spectra, but worsened the magnitude as compared with those in ENDF/B-4. The ''Pandemondium'' problem is discussed is connection with these results. The planned expansion for ENDF/B-6 is presented for the data of fission product yield, decay data and the neutron cross sections of fission products and actinides. The specific nuclides and energies scheduled to have yield data are summarized. In ENDF/B-6, the delayed neutron spectra for individual nuclides are added to calculate the conventional aggregate time-group spectra and the total delayed neutron yields. The cross section data for several primary fuel nuclides are reevaluated for Version 6. The update plans of the cross section evaluation for fission products and higher actinides are summarized. (Asami, T.)