Nuclear data V&V analysis for fusion applications: integral benchmarks and decay data

Nuclear data V&V analysis for fusion applications: integral benchmarks and decay data

Nuclear data V&V analysis for fusion applications: integral benchmarks and decay data 150 150 UKAEA Opendata
UKAEA-CCFE-CP(23)09

Nuclear data V&V analysis for fusion applications: integral benchmarks and decay data

Recent studies of the neutron irradiation conditions predicted in the plasma-exposed first wall of a conceptual design of fusion DEMO power plant implementing the SPECTRA-PKA code have shown the importance of taking into consideration per-channel analysis of the high-energy threshold reactions for an accurate evaluation of their contribution to damage creation for a number of fusion-relevant elements. Another vital aspect of paying due attention to various neutron-induced reaction pathways in fusion environment that arises after the power plant shutdown is residual decay power assessment. Computation of the decay power performed by FISPACT-II relies on a large volume of nuclear data, both neutron activation-transmutation cross-sections and radioactive decay data. Validation and verification (V&V) benchmark exercises are needed to test both the performance of the code and the quality of the latest releases of the nuclear databases.

Several of these “benchmarks” have been developed for neutron-irradiation applications with FISPACT-II, including an integro-differential validation, which compares, amongst other things, the available experimental differential data from the EXFOR database to reaction cross-section evaluations read from data-libraries by FISPACT-II. Another V&V benchmark exercise relied on the fusion decay heat measurements performed by the Japan Atomic Energy Agency (JAEA) at their fusion neutron source (FNS) facility.

For each irradiation case in the FNS-benchmark, FISPACT-II simulations apply each of the major nuclear cross-section libraries: TENDL-2017, JEFF-3.3, ENDF/B-VIII.0, EAF2010, and IRDFF-1.05. Detailed pathways analysis in this validation effort has recently shown that while codes such as FISPACT-II generate pathway contributions from each possible reaction into the total time-dependent decay heat release, the accuracy of this allocation depends entirely on the quality (and inclusion) of the cross-sections which are the subject of the validation. For instance, the results for tungsten, osmium, niobium and nickel (M. Gilbert, J.Ch. Sublet, 2019) showed that either the nuclear data for certain reactions need adjustment (re-evaluation) or that some reaction channels (pathways) to important isomeric states were completely missing, and thus should be properly embedded in the future versions of the libraries. This work will present the results of the ongoing detailed analyses for the FNS experiment results for the elements relevant in the radiation and spectroscopy measurements (i.e. platinum, europium, gold), in addition to the materials that are primarily considered in fusion activation analysis.

Furthermore, the intermediate results for the updating of the nuclear decay data library used for fusion activation analyses will also be discussed. The decay library currently used by FISPACT-II is almost a decade old and needs to be updated and then validated according to the available updates in the experimental data. The work will primarily be focussed on the decay files for the radionuclides identified as critical/important for DEMO activation, dose-rate, decay heat, and waste analyses. The review of the current status of decay data for fusion activation applications will be performed to identify any discrepant data (based on experimental validation) and to also assess if there are any available updates (from published experimental data) for fusion-critical radionuclides.

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PHYSOR 2020, University of Cambridge, United Kingdom, 29 March - 2 April 2020