The basic nuclear physics that are required in modelling and simulation of nuclear systems cannot be derived from first principles but must be carefully measured. Quantities such as the interaction probabilities between neutrons and different nuclei vary by orders of magnitude between different isotopes and incident neutron energies. For typical systems such as nuclear fission reactors, the incident energies of importance span values between thousandths of an electron volt to millions of electron volts and complete knowledge of all these areas is required.
Since the earliest days of nuclear engineering, nuclear nations have performed experiments to carefully measure nuclear reaction quantities. These are essential for the design and construction of all nuclear reactors and national 'library' projects were established to collect all of these measurements. In the 1960s the EXFOR database was established as a collaboration between the US National Nuclear Data Center, the precursor to the NEA Databank, the IAEA and the Russian Nuclear Data Center, storing neutron-induced differential reaction measurements. Over time this database has grown to include hundreds of thousands of datasets that serves as an invaluable starting point for all nuclear data evaluation.
The NEA has been at the forefront of nuclear data experimental work with several initiatives:
The HPRL serves as the international reference for nuclear data needs. It is based on a detailed process that reviews the impact of new measurements and allows decision-takers to understand what and why new measurements need to be made. When these and other measurements are completed, the NEA Databank works directly with the experimental facilities to translate the results into the standardised EXFOR format for inclusion in the database stored at the IAEA.
Other initiatives, such as the work on nuclear data standards in WPEC subgroup 7 and target accuracy requirements of subgroup 26, allow leading experts from around the world to collaborate on the analysis of experimental needs, resulting in new entries to the HPRL and ultimately resulting in new measurements to improve nuclear data.
The NEA's nuclear data evaluation co-operation activities involve the following evaluation projects: ENDF (United States), JENDL (Japan), ROSFOND/BROND (Russia), JEFF (other Data Bank member countries) and CENDL (China) in close co-operation with the Nuclear Data Section of the International Atomic Energy Agency (IAEA).
The expert group is responsible for managing the activities related to the High Priority Request List (HPRL) for nuclear data, in particular for guaranteeing that the entries are up-to-date and well-motivated by current interests in the field of nuclear energy and other nuclear applications.