New criticality benchmarks and progress in NEA experimental data evaluation and preservation efforts for nuclear criticality, reactor physics and radiation shielding

The NEA organised the annual technical review group and task force meetings of key experimental data evaluation and preservation projects, namely the International Criticality Safety Benchmarks Evaluation Project (ICSBEP), the International Reactor Physics Experiments Evaluation (IRPhE) Project, as well as the International Radiation Shielding Experiments Database (SINBAD) on 16-19 April 2024. Hosted by Lawrence Livermore National Laboratory (LLNL) in the United States, the meetings brought together 95 experts – experimentalists, practitioners, and modelers – from 17 countries to review candidate evaluations and work in progress.

Three new and one major revision of criticality benchmark evaluations have been approved for inclusion in the next edition of the ICSBEP Handbook:

  • A fundamental physics evaluation assessing pulsed-neutron die-away response of polyethylene and polymethyl methacrylate targets to validate thermal neutron scattering laws;
  • A critical setup of plutonium metal plates separated by lead and reflected by copper to measure lead void reactivity coefficients in plutonium systems;
  • A critical set up of highly enriched uranium plates with hafnium to validate hafnium data in the thermal, intermediate, and fast neutron energy regimes; and
  • A major revision of a critical setup of a highly enriched uranium sphere reflected by natural uranium which is a reference experiment.


Ten data sets from various facilities in Canada, France, the Netherlands, Switzerland, and the United States have been discussed as candidates for later submission as IRPhE evaluated benchmark, with several expected to be submitted as soon as 2025.

The nine subgroups of the Shielding Integral Benchmark Archive and Database (SINBAD) Task Force presented their latest advancements in expanding the database with four new datasets and enhancing the quality of existing datasets. The SINBAD has now been fully migrated to NEA GitLab, and novel open-source software development strategies have been embraced. The development will move forward in agile, iterative, and modular manner, and SINBAD licensees can provide direct feedback and proposals for improvements of the existing data sets.

The meeting participants also had the opportunity to visit LLNL’s Laboratory Space including the Inherently Safe Subcritical Assembly and the Pulsed-Neutron Die-Away Experiment at Radiation Calibration Laboratory’s Low Scatter Facility, as well as the National Ignition Facility (NIF).

Organising these meetings in conjunction has proved to contribute to the fruitful exchanges across communities and sectors for the mutual benefit of all experimental data evaluation and preservation efforts in nuclear science. The next NEA benchmark evaluation meetings will take place in spring 2025.

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