Nuclear Data Evaluation for Reactor Applications

In past years, nuclear analysts had to rely on a limited amount of nuclear data for reactor design. In that time, the need for nuclear data was driven by the thermal and fast reactor programs. In a thermal reactor, the fissions of importance all take place below 4 eV. Because of this, evaluations for thermal applications emphasized this region. In a typical fast reactor, however, the most important fission range shifts upwards to the 10's to 100's of keV region, and this led to evaluations that emphasized this range. Nuclear criticality situations involve an energy spectrum that peaks in the 10's to 100's eV range, and need critical attention to the cross sections in this range. Since all of these systems produce fission neutrons at high energies-500 keV to a few MeV-attention has been given to this energy range. As noted, the region most neglected is the epithermal region; however, calculational experiences suggest many nuclides need improvements in all energy regions