Reevaluation of the 235U crosss sections for ENDF/B-VI

The ENDF/B-VI 235U resonance representation of the neutron cross sections in the resolved energy range has been included in several nuclear data libraries throughout the world; it is the cross-section representation used in the European files, the Joint Evaluation File, and the Japanese files, Japanese Evaluated Nuclear Data Library. Consequently, the 235U evaluation has undergone several tests. The French Laboratory, CEN Cadarche, has indicated that the current 235U parametric representation gives a value of the capture cross section 13% lower than that expected in integral calculations for the energy range 22.6 to 454 eV. In addition, it has been found that the ENDF/B-VI parametric representation of the 235U cross sections is unable to resolve a long-standing problem to properly predict the desired capture-to-fission ratio, the α ratio. These results clearly point out deficiencies in ENDF/B-VI in reproducing integral results