Journal of Nuclear Materials 554 (2021) 153014 Contents lists available at ScienceDirect Journal of Nuclear Materials journal homepage: www.elsevier.com/locate/jnucmat Quantitative analysis of rhenium in irradiated tungsten P. Warnicke a,∗ , H. Ramanantoanina b , J. Li c , Y. Dai a , M. A. Pouchon a a Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland b Department of Chemistry, Johannes Gutenberg University, D-55128 Mainz, Germany c Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, PR China a r t i c l e i n f o Article history: Received 5 June 2020 Revised 9 March 2021 Accepted 10 April 2021 Available online 15 May 2021 Keywords: XANES EXAFS Tungsten Rhenium Transmutation Plasma-facing material Spallation neutron irradiation a b s t r a c t Pure tungsten (W), irradiated to 3.5 dpa in a target of the Swiss neutron spallation source (SINQ), was characterized using high-sensitivity HPGe gamma ray spectroscopy to identify the present radionuclides. Synchrotron X-ray absorption spectroscopy was used to quantify the amount of Re produced in the irra- diated W. An atomic concentration of 0.61% Re in the irradiated W was determined from the height of the L3-edge X-ray absorption edge jump. Analysis of the local atomic structure from the extended X-ray absorption fine structure (EXAFS) spec- tra indicates that rhenium (Re) produced in the system is mainly coordinated by W atoms and partly coordinated by void defects. First-principles density functional theory calculations confirm a positive for- mation energy for a double Re defect in the system, supporting the conclusion that Re cluster formation is suppressed. © 2021 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) I. Introduction Tungsten (W) is increasingly considered a promising material for spallation targets and for plasma facing components, e.g. the divertor, in nuclear fusion devices such as ITER due to its high melting point, high thermal conductivity, low thermal expansion, and low physical sputtering yield. At the same time, irradiation in- duced effects in W are commonly observed as increased harden- ing and embrittlement [1–5]. Pure W is brittle at room temper- ature and has a ductile transition at about ~300°C. Irradiation at doses of 0.1 dpa (displacements per atom) reduces the ductility of W to below 1% and the material shows completely brittle behav- ior at 500°C [1]. Changes in the mechanical properties stem from microstructural changes in the material. In the low temperature regime (below ~1000°C), nanometer sized defect clusters, disloca- tion loops, voids and precipitates may form in matrix and on grain- boundaries depending on crystallinity (i.e. polycrystalline or single crystal [6,7]), irradiation dose, and temperature [2,6–11]. These mi- crostructural changes are accompanied by chemical impurities pro- duced by the irradiation. Irradiation-induced elements such as rhenium (Re) can be pro- duced at relatively high rates in W during irradiation in fission and ∗ Corresponding author. E-mail address: [email protected] (P. Warnicke). fusion nuclear reactors by nuclear reactions or afterwards via de- cay [2]. Naturally occurring W consists of five stable isotopes, W- 180, W-182, W-183, W-184, and W-186. During irradiation of W with neutrons, transmutation can take place via neutron capture (n,γ ), followed by decay: 180W (n,γ ) −→ 181W EC −→ 181Ta 182W (n,γ ) −→ 183W 183W (n,γ ) −→ 184W 184W (n,γ ) −→ 185W β− −→ 185Re 186W (n,γ ) −→ 187W β− −→ 187Re A small fraction of tungsten (0.12 at.%) consists of W-180. This isotope transmutes via neutron capture to W-181, which decays via electron capture to stable Ta-181. W-182 and W-183 transmutes via neutron capture to W-183 and W-184, respectively. The two major isotopes occurring in natural tungsten are W-184 (30.7 at.%) and W-186 (28.6 at.%). W-184 transmutes via neutron capture to W- 185, which decays to Re-185 via β - decay with a half-life T 1/2 of https://doi.org/10.1016/j.jnucmat.2021.153014 0022-3115/© 2021 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)
Quantitative analysis of rhenium in irradiated tungsten
Jun 14, 2023
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