Nuclear data needs for application in nuclear criticality safety programs

In nuclear criticality safety applications, a number of important uncertainties have to be addressed to establish the required criticality safety margin of a nuclear system. One source of these uncertainties is the basic nuclear data used to calculate the effective multiplication factor of the system. Before criticality safety calculations are performed, the bias and uncertainties of the codes and cross sections that are used must be determined. Cross-section data are measured, evaluated, and tested prior to their inclusion in nuclear data libraries. Traditionally, nuclear data evaluations are performed to support the analysis and design of thermal and fast reactors. The neutron spectra characteristic of the thermal and fast systems used for data testing are predominantly in the low- and high-energy ranges, with a relatively minor influence from the intermediate-energy range. In the area of nuclear criticality safety, nuclear systems involving spent fuel elements from reactors can lead to situations very different from those most commonly found in reactor analysis and design. These systems are not limited to thermal or fast neutron spectra and may have their most significant influence from the intermediate energy range. This requires extending the range of applicability of the nuclear data evaluation beyond thermal and fast systems. The aim here is to focus on the evaluated nuclear data pertaining to applications in nuclear criticality safety.