Atomistic simulations of helium, hydrogen, and self-interstitial diffusion inside dislocation cores in tungsten

Journal Article · 10 January 2020 · Nuclear Fusion

DOI: https://doi.org/10.1088/1741-4326/ab6061 · OSTI ID:1604004

Mathew, Nithin  ^[1]; Perez, Danny  ^[1]; Martinez Saez, Enrique ^[1]

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1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

Tritium retention and microstructural modifications due to helium accumulation are two of the main concerns regarding plasma-facing materials in fusion applications. Crystal defects in tungsten (W), such as grain boundaries and dislocations, can serve as traps or channels for diffusion of hydrogen (H) and helium (He), and, as such, can affect the transport of these species. In this work reported herein, we study the diffusion of hydrogen, helium and self-interstitial atoms (SIA) inside screw and edge dislocations in W using molecular dynamics simulations. Stable sites for interstitials in dislocations are identified using a free-volume analysis and energy barriers for diffusion are predicted using a combination of the nudged elastic band (NEB) method and finite temperature molecular dynamics simulations. Overall, the simulations predict higher energetic barriers for He and H diffusion in both screw and edge dislocations compared to the bulk. However, the diffusion mechanism in both dislocations are shown to differ: simulations predict that interstitials are constrained to move in short channels inside the edge dislocation core so that long-range diffusion along the dislocation line happens only with the motion of the dislocation. In contrast, 1D diffusion of the interstitial along the dislocation core, independent of dislocation motion, is observed for screw dislocations.

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC), Advanced Scientific Computing Research (ASCR). Scientific Discovery through Advanced Computing (SciDAC); USDOE Office of Science (SC), Fusion Energy Sciences (FES)
• Grant/Contract Number: 89233218CNA000001; SC0008875; AC02-05CH11231
• OSTI ID: 1604004
• Report Number(s): LA-UR-19-28989; TRN: US2104174
• Journal Information: Nuclear Fusion, Vol. 60, Issue 2; ISSN 0029-5515
• Publisher: IOP ScienceCopyright Statement
• Country of Publication: United States
• Language: English