Speaker
Description
Design engineering of future fusion experimental devices and near-commercial power plants are considering a variety of materials for the construction – some known and applied in the wider nuclear industry and some under development. When used in the extreme neutron environments predicted for the in-vessel components of future commercial and near-commercial magnetic-confinement fusion power plants, nuclei of these materials will undergo frequent nuclear reactions with the neutrons, resulting in transmutation and activation. The production of short- and medium-lived radionuclides (half-lives of the order of minutes to months) will create radiological issues to solve relating to the operation and maintenance of fusion reactor components, for example due to on-load and post-operation decay heat requiring additional cooling capacity. Meanwhile, the creation of longer-lived nuclides (half-lives from decades to centuries or more) will potentially create challenges when decommissioning fusion reactors because the nuclear waste may be too severe (to highly activated) for near surface repositories. Whilst such fusion wastes are less radiotoxic than those generated in fission at long timescales, the radioactivity-based criteria for licencing storage facilities could present conditions for similar long-lived waste problems as those faced with fission.
Accurate and reliable predictions of the nuclear response of materials using evaluated nuclear data libraries are a critical part of the design activities. Computational validation activities, comparing experimental decay heat measurements to simulations with different nuclear libraries [1,2], demonstrate that modern nuclear data libraries generally perform well. However, there are still areas for improvement, particularly for some of the more exotic materials being considered in the novel concepts being explored for fusion – for example, decay-heat predictions for iridium and osmium do not match well with experimental measurements after fusion-neutron exposure. Such discrepancies and the need to reduce uncertainties, which would otherwise result in engineering design including unacceptably large and costly safety margins, prompted an effort to perform new measurements.
In this paper we discuss the experimental set-up for a campaign of irradiations and $\gamma$-spectroscopy measurements at the UK-based 14 MeV ASP-accelerator. Previously [3], comparison of simulations with the analysed results from measurements on Mo – a candidate fusion armour material – have demonstrated how the database of experimental measurements, covering ~20 different metallic elements in more than 300 separate experiments, can be used to benchmark inventory code predictions with FISPACT-II [4] – the transmutation and activation simulation platform developed at UKAEA. The analysis and interpretation has been revised and improved in the present work. Results for fusion relevant materials, including W and Cr, are discussed.
Using this experimental experience, particularly an appreciation of the analysis and interpretation difficulties, we make recommendations for how future experiments should be conducted, such as targeted irradiation times and optimized measurement approaches.
.
This work is part funded by the RCUK Energy Programme [grant number EP/T012250/1].
.
[1] M.R. Gilbert, J.-Ch. Sublet, “Experimental decay-heat simulation-benchmark for 14 MeV neutrons & complex inventory analysis with FISPACT-II” Nuclear Fusion 59 (2019) 086045
[2] M.R. Gilbert, O.V. Vilkhivskaya, J.-Ch. Sublet, “Fusion decay heat validation, FISPACT-II & TENDL-2019, ENDF/B-VIII.0, JEFF-3.3, EAF2010, and IRDFF-II nuclear data libraries” UKAEA report UKAEA-CCFE-RE(20)04. Available from fispact.ukaea.uk
[3] M.R. Gilbert, L.W. Packer, T. Stainer, “Experimental validation of inventory simulations on molybdenum and its isotopes for fusion applications” Nuclear Fusion 60 (2020) 106022
[4] J.-Ch. Sublet, J.W. Eastwood, J.G. Morgan, M.R Gilbert, M. Fleming, W. Arter, “FISPACT-II: An Advanced Simulation System for Activation, Transmutation and Material Modelling“ Nuclear Data Sheets 139 (2017) 77–137. See fispact.ukaea.uk