Transient gasification in an NBG-18 coolant channel of a VHTR prismatic fuel element |
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| Affiliation: | 1. Institute for Space & Nuclear Power Studies, University of New Mexico, Albuquerque, NM, USA;2. Chemical & Nuclear Engineering Department, University of New Mexico, Albuquerque, NM, USA;3. Mechanical Engineering Department, University of New Mexico, Albuquerque, NM, USA;1. Institute of Nuclear and New Energy Technology, Collaborative Innovation Center of Advanced and Safety Nuclear Energy Technology, Key Laboratory of Advanced Reactor Engineering and Safety of Ministry of Education, Tsinghua University, Beijing 100084, China;2. Huaneng Nuclear Power Development Co. Ltd, Beijing 100031, China;1. Institute for Space and Nuclear Power Studies, The University of New Mexico, Albuquerque, NM, USA;2. Nuclear Engineering Department, The University of New Mexico, Albuquerque, NM, USA;3. Mechanical Engineering Department, The University of New Mexico, Albuquerque, NM, USA;4. Chemical and Biological Engineering Department, The University of New Mexico, Albuquerque, NM, USA;1. Dept. of Mechanical Engineering, University of Saskatchewan, Saskatoon, SK S7N 5A9, Canada;2. Materials Science and Technology Division, Los Alamos National Laboratory, NM 87545, USA;3. Dept. of Physics and Engineering Physics, University of Saskatchewan, Saskatoon, SK S7N 5E2, Canada;1. Department of Electrical and Computer Engineering, Ecole de Technologie Superieure (ETS), Montreal, Canada;2. Department of Electrical and Computer Engineering, Concordia University, Montreal, Canada;1. National Research Nuclear University “MEPHI” (Moscow Engineering Physics Institute), Kashirskoe sh. 31, Moscow, Russia;2. Nuclear Physics Institute of the CAS, Řež 130, 250 68, Řež, Czech Republic;3. National Science Centre “Kharkov Institute of Physics and Technology”, Kharkov, Ukraine;4. Department of Low-temperature Physics, Charles University, V Holešovičkách 2, 180 00, Prague, Czech Republic;5. Institute for Neutron Physics and Reactor Technology, Karlsruhe Institute of Technology, 76344, Eggenstein-Leopoldshafen, Germany |
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| Abstract: | This paper investigates the transient gasification of NBG-18 nuclear graphite with atmospheric air ingress in a 0.8-m long coolant channel of a prismatic Very High Temperature Reactor fuel element. Analysis varied the initial graphite and air inlet temperature, To, from 800 to 1100 K at air inlet Reynolds number, Rein = 5, 10 and 20. The analysis employs a Generic Interface that couples a multi-species diffusion and flow model to readout tables of the CO and CO2 production fluxes. These fluxes are functions of the graphite local surface temperature, oxygen partial pressure and graphite weight loss fraction and calculated using a chemical-reactions kinetics model for the gasification of nuclear graphite. The analysis accounts for the heats of formation of CO and CO2 gases, the heat conduction in the graphite sleeve, and the change in the oxygen partial pressure in the bulk gas flow mixture along the channel. Transient calculations performed up to a weight loss fraction of 0.10 at the entrance of the channel, t10. They include the local graphite surface temperature and composition of bulk gas flow, the local and total graphite weight losses and the local and total production rates of CO and CO2 gases. The heat released in the exothermic production reactions of these gases increases the local graphite surface temperature, accelerating its gasification. At the end of the calculated gasification transient, t = t10, the graphite weight loss is highest at the channel entrance and decreases rapidly with axial distance into the channel, to its lowest value where oxygen in the bulk gas flow is depleted. Increasing To decreases t10 and the total graphite loss, while increasing Rein decreases t10 but increases graphite loss. |
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