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Hongjie Zhang Purge gas flow impact on tritium permeation Integrated simulation on tritium permeation in the solid breeder unit FNST, August 18-20, 2009

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FNST 2009 Issues Tritium behavior in blanket is a complicated phenomenon which consist of tritium generation, tritium permeation, purge gas thermo- fluid and nuclear heating No single integrated program of theory, computer modeling to simulate tritium behavior in blanket units. Handling of 3D complicated large scale geometry Objective Develop a predictive capability of tritium and hydrogen permeation from breeding zones to the coolant in the helium cooled pebble-bed blanket. Construct 3-D convection-diffusion models Integrated with thermal- fluid analysis in TBM unit Take into account the tritium generation rate distribution and nuclear heating rate distribution. Provide predictive capabilities, and Assist solid breeder design Motivations and Objectives

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FNST 2009 COMSOL model Set-up Convection-diffusion model with imported velocity and temperature profiles Apply Law-boundary conditions at gas-metal interface. Works on 2-D or 3-D small scale geometry Memory issue for large-scale geometry Sctetra model Extend CFD code for tritium permeation assessment in TBM unit Add multi-species permeation / Isotope permeation Support Law-dependent boundary condition or Rate-dependent boundary condition at gas-metal interface Support 3-D complex geometry at large scale Previous work and Recent advancement Two multi-physics models based on different codes were developed

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FNST 2009 Ω breeder Model Domain Ω structure Ω coolant Methodology Develop a 3-D multi-species convection-diffusion permeation model Integrated with thermal-fluid analysis in porous media to account for the effects of purge stream convection and the accompanying velocity and temperature profile Model domain: 1.the purge flow region 2.the structure 3.the coolant. H2, T2, and HT are transported by diffusion and convection in the two fluid phase diffusion is the only transport mechanism in the structure phase B.C.s at the gas-structure interface should ensure The flux continuity The concentration discontinuities C1C1 C3C3 Solid c2c2 c2c2 T2 Diffusion across a film T T2

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FNST 2009 Reflects the variations of porosity and transport in the bed near the wall regions Governing equations To obtain the convective part of the flux, velocity distributions can be introduced by solving the N-S equation based on Brinkman model of a flow in a packed bed. Considering the wall effect, which reflects the variations of porosity and tritium transport in the bed near the wall regions, the calculation uses the following governing equations: Momentum conservation equation Energy conservation equation Diffusive species conservation equation

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FNST 2009 Experiments: Permeation of deuterium through a palladium membrane, which was accompanied by co-permeation of hydrogen were performed. Two cases were compared: Permeation of D2 only through Pd membrane (0.025mm, 825K, 865K) Co-permeation of H2 D2 through Pd membrane(0.025mm, 825K) Calculated permeation flux agree well with the experimental results for both cases Modal Validation - Co-permeation of deuterium and hydrogen through Pd, K. Kizu, A. Pisarev, T. Tanabe, J. of Nuclear Materials, 289(2001) 291-302 Case 1 D2 permeation flux as a function of upstream deuterium pressure HD H2 D2 permeation flux in co-permeation measurements as a function of effective deuterium pressure PD=P(D2)+P(HD)/2 and at a fixed value of effective H2 pressure PH=P(H2)+P(HD)/2=0.063Pa. Case 2 H2 D2 partial pressures from P_H2 : 0.06 ~ 0.0035 P_D2 : 0.0001 ~ 1

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FNST 2009 Model Application - multi-physics simulation in a TBM unit As a part of integrated multi-physics modeling capability, able to Evaluate temperature profile, velocity profile, chemical composition Calculate Tritium Concentration, Tritium permeation flux, and other parameters of interest Handle any 3-D large scale geometry Multi-physics simulation in a TBM unit Tritium production rate distribution in the radial direction Heating rate distribution in the radial direction TBM unit Purge gas inlet Purge gas outlet Coolant channels

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FNST 2009 Model Application - multi-physics simulation in a TBM unit Purge gas streamline Tritium concentration in breeder Temperature Low velocity field will appear in the Left-Bottom corner and Right-Top corner, which will affect tritium concentration slightly. Tritium permeation over the production decreases quickly as the average purge gas velocity increases Tritium concentration is impacted by production rate, Velocity and Temperature profiles

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FNST 2009 Conclusion 3-D multi-species convection-diffusion permeation model Integrated with thermal-fluid analysis in porous media are assessed to provide predictive capabilities and assist solid breeder design Benchmark cases agree well with experimental results, and more benchmark with available data can be done As a part of integrated multi-physics modeling capability, able to Evaluate temperature profile, velocity profile, chemical composition Calculate Tritium Concentration, Tritium permeation flux, and other parameters of interest Handle 3-D large scale geometry Simulation in a TBM unit show that parameters such as temperature distribution and purge gas flow can strongly affect tritium transport. Under reasonable purge velocity profile, increasing the inlet velocity is an effective method to reduce tritium permeation to the coolant.

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FNST 2009 Thank you

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