151. MODELING OF HYDROGEN RETENTION IN THE BULK OF METALLIC PLASMA FACING COMPONENTS

Department: Mechanical & Aerospace Engineering
Research Institute Affiliation: Center for Energy Research (CER)
Faculty Advisor(s): Sergei Krasheninnikov | Roman Smirnov
Award(s): Honorable Mention

Primary Student
Name: Jerome Guterl
Email: jguterl@ucsd.edu
Phone: 858-405-7807
Grad Year: 2015

Abstract
The inventory of tritium in the vacuum vessel of the ITER device has been identified as a critical plasma wall interaction issue for safety and operational reasons . Consequently, it is essential to understand mechanisms of both short- and long-term retention of hydrogen isotopes in the ITER first wall. The wall components will be exposed to various plasma conditions during nominal ITER operations and can reach high temperatures (T~800K) that will affect both the wall surface (material erosion, co-deposition, hydrogen adsorption, etc.) and the bulk (hydrogen implantation, creation of trap sites, bubbles, etc.). These processes induce hydrogen retention in wall material, experimentally observed both in the near-surface region and in the depth of the bulk. However, there is currently no relevant model for the dynamic plasma interaction processes involved in long-term fuel retention in magnetic fusion environment. In this paper, we present a theoretical analysis and modeling of the long-term hydrogen retention in a metallic wall in ITER operational conditions. Here we take into account only the major mechanisms affecting hydrogen retention in a thick wall, including hydrogen implantation, desorption, diffusion, and trapping in the bulk, as well as transport of the traps and wall erosion. The theoretical analysis of the two-component (free hydrogen and mobile trapping sites) dynamical system is carried out by considering coupled diffusion-reaction equations with advective terms. We classify the different retention regimes based on relative rates of the processes involved and strength of coupling of the density profiles in the bulk. The dynamics of hydrogen retention in the wall including all the considered processes is investigated numerically by using recently developed First wAll simulation CodE (FACE). However, numerical modeling does not always reach a steady state due to large difference in the time scales of particle transport in the narrow implantation layer and in the bulk. To resolve this issue, we develop an analytical model of the implantation layer in both high and low hydrogen recycling regimes that allows us to treat the layer as a boundary for the bulk. The model is applied to analyze retention as a function of the wall temperature and is in good agreement with experimental data on hydrogen retention in beryllium. The different aspects of hydrogen retention in the wall bulk material in application to ITER conditions are discussed. Ref: J. Roth, et al., J. Nucl. Mater.390-391 (2008) R.A. Causey, J. Nucl.Mater.300 (2002) R.A. Anderl,et al., J.Nucl.Mater.273 (1999)

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