PRELIMINARY RESULTS OF THE NEA FHR BENCHMARK PHASE I-A AND I-B (FUEL ELEMENT 2-D BENCHMARK)

Under the auspices on OECD-NEA, a benchmark has been initiated to assess state of the art modelling and simulation capabilities for Fluoride salt-cooled High-temperature Reactors (FHRs) with TRISO fuel embedded in fuel plates (“planks”) of hexagonal fuel elements. Benchmark phases I-A and I-B involve reactor physics analysis of a representative fuel element, without and with depletion. Several configurations are considered (e.g., unrodded and rodded configuration, presence of burnable absorbers, variable enrichment). Parameters compared include multiplication factor, reactivity coefficients, flux distribution, neutron spectrum and isotopic composition change with burnup. Seven organizations from four countries are taking part in this blind-benchmark exercise, using Monte Carlo and deterministic methods. Given the complex combination of materials and geometry, the FHR benchmark is expected to be challenging, particularly for deterministic codes. As the nuclear data libraries underpinning both deterministic and Monte Carlo methods have had limited testing for FHR systems, and molten salt systems in general, the benchmark aims to provide feedback to both the nuclear data community as well as molten salt reactor designers with regards to the variance of results with different nuclear data sources. This paper reports on the current results submitted and provides comparisons and analysis. Overall, the observed agreement is satisfactory, although notable differences are identified in specific cases, suggesting need for further in-depth analysis of those cases.