Analysis on hydrogen risk mitigation in severe accidents for Pressurized Heavy Water Reactor |
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| Affiliation: | 1. School of Nuclear Science and Technology, Xi''an Jiaotong University, No. 28 Xianning West Road, Xi''an, Shaanxi 710049, PR China;2. Shanghai Nuclear Engineering Research & Design Institute, 29 Hongchao Road, Shanghai 200233, PR China;3. Department of Nuclear Engineering and Radiological Sciences, University of Michigan, 2200 Bonisteel, Ann Arbor, MI 48109, USA;1. Department of Physics, Lanzhou University of Technology, Lanzhou 730050, China;2. College of Electrical and Information Engineering, Lanzhou University of Technology, Lanzhou 730050, China;1. Forschungszentrum Jülich, Institute for Energy and Climate Research (IEK-6), Juelich, Germany;2. RWTH Aachen University, Institute for Reactor Safety and Reactor Technology, Aachen, Germany;1. Nuclear Safety Institute of the Russian Academy of Sciences, Moscow, Russia;2. Moscow Institute of Physics and Technology, Russia;1. Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600036, Tamil Nadu, India;2. Safety Research Institute, Atomic Energy Regulatory Board, Government of India, Kalpakkam 603102, Tamil Nadu, India |
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| Abstract: | Hydrogen source term and hydrogen mitigation under severe accidents is evaluated for most nuclear power plants (NPPs) after Fukushima Daiichi accident. Two units of Pressurized Heavy Water Reactor (PHWR) are under operating in China, and hydrogen risk control should be evaluated in detail for the existing design. The distinguish feature of PHWR, compared with PWR, is the horizontal reactor core surrounded by moderator in calandria vessel (CV), which may influence the hydrogen source term. Based on integral system analysis code of PHWR, the plant model including primary heat transfer system (PHTS), calandria, end shield system, reactor cavity and containment has been developed. Two severe accident sequences have been selected to study hydrogen generation characteristic and the effectiveness of hydrogen mitigation with igniters. The one is Station Blackout (SBO) which represents high-pressure core melt accident, and the other is Large Break Loss of Coolant Accident (LLOCA) at reactor outlet header (ROH) which represents low-pressure core melt accident. Results show that under severe accident sequences, core oxidation of zirconium–steam reaction will produce hydrogen with deterioration of core cooling and the water in CV and reactor cavity can inhibits hydrogen generation for a relatively long time. However, as the water dries out, creep failure happens on CV. As a result, molten core falls into cavity and molten core concrete interaction (MCCI) occurs, releasing a large mass of hydrogen. When hydrogen igniters fail, volume fraction of hydrogen in the containment is more than 15% while equivalent amount of hydrogen generate from a 100% fuel clad-coolant reaction. As a result, hydrogen risk lies in the deflagration–detonation transition area. When igniters start at the beginning of large hydrogen generation, hydrogen mixtures ignite at low concentration in the compartments and the combustion mode locates at the edge of flammable area. However, the power supply to igniters should be ensured. |
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| Keywords: | PHWR Hydrogen source term SBO LLOCA Igniters |
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