Progress on the reevaluation and validation of the n+233U neutron cross sections. (1st December 2021)

• Record Type: Journal Article
• Authors: Pigni, Marco T.; Capote, Roberto; Trkov, Andrej
• Is Part Of: Annals of nuclear energy. Volume 163(2021)
• Publication Date: 2021-12-01
• Subjects: R-matrix -- 233U -- Fissile nuclide -- Validation -- Nuclear data -- Evaluated data; Nuclear energy -- Periodicals; Nuclear engineering -- Periodicals; 621.4805
• DOI: 10.1016/j.anucene.2021.108595
• Languages: English
• ISSNs: 0306-4549

Abstract

Highlights: 233 U is of fundamental importance for criticality safety and thorium-based fuel cycle (or Th/U fule cycle). Significant updates to the 233U evaluation are aimed to improve integral benchmarks. Updates are for the prompt fission spectrum, thermal constants, and R-matrix analysis. Current analysis showed improved criticality for a selected set of benchmarks. Future plans to extend n+ 233 U evaluated data up to 2.5 keV are discussed. Abstract: The set of 233 U resonance parameters of the ENDF/B-VIII.0 nuclear data library was adopted from the previous ENDF/B-VII.1 evaluation using the external levels to update the thermal values. Adoption of IAEA 2017 thermal standards ( σ f = 533.0 ± 2.2 b, σ c = 44.9 ± 0.9 b, and ν ‾ tot = 2.487 ± 0.011 ) and of the IAEA-recommended thermal-neutron induced prompt fission neutron spectrum (PFNS) with average PFNS energy of 2.030 ± 0.013 MeV requires a re-evaluation of 233 U neutron cross sections in the resolved resonance region. A newly produced evaluation is being tested on benchmarks carefully selected from the Handbook of International Criticality Safety Benchmark Experiments (ICSBEP) which are highly sensitive to 233 U data. An important goal of this work was to eliminate the strong negative gradient of the calculated effective multiplication factors with respect to the epithermal fission fraction observed in the validation of the ENDF/B-VIII.0 library for those assemblies. A significant improvement in integral performance of critical 233 U solutions is observed for the newly proposed evaluation. Further work addressing the fast neutron region is needed.