Research and development activities for cleanup of the Fukushima Daiichi Nuclear Power Station
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Research and development activities for cleanup of the Fukushima Daiichi Nuclear Power Station Toshiki Sasaki1, Shuji Kaminishi2, Yasuaki Miyamoto1, and Hideyuki Funasaka1 1 Headquarters of Fukushima Partnership Operations, Japan Atomic Energy Agency, 2-2-2 Uchisaiwai-cho, Chiyoda, Tokyo 100-8577, Japan 2 Nuclear Fuel Cycle Department, Tokyo Electric Power Company 1-3 Uchisaiwai-cho, Chiyoda, Tokyo 100-8560, Japan ABSTRACT The Fukushima Daiichi nuclear power station accident and restoration works have produced significant volume of radioactive waste. The waste has very different characteristics from usual radioactive waste produced in nuclear power stations and it requires extensive research and development for management of the waste. R&D works such as analysis of the waste properties, hydrogen generation by radiolysis and diffusion in a storage vessel and corrosion of storage vessels, etc. have been performed for characterization and safe storage of the waste. The detailed R&D plan for processing and disposal waste will be established by the end of FY2012. INTRODUCTION Fukushima Daiichi nuclear power station (NPS) consists of six BWRs. Units 1, 2, and 3 were operating at rated power level while 4, 5, and 6 were in cold shutdown when a magnitude 9.0 earthquake occurred offshore of Japan’s east coast in the afternoon on March 11, 2011. The operating units auto-scrammed on reactor protection system trip. The earthquake immediately devastated all off-site AC power supply to the station. On-site emergency diesel generators were automatically kicked in to supply power for emergency systems. However, a series of tsunamis with their greatest height of approximately fifteen meter began hitting the site about forty minutes later the earthquake and killed most of on-site emergency AC/DC power supply by flooding diesel generators, switchgear rooms, DC batteries and so forth. Units 1-3 lost core cooling to remove decay heat that lead to fuel degradation and core melt. Hydrogen produced in damaged cores caused explosions blowing off top of reactor buildings in units 1, 3, and 4. The accident produced radioactive gaseous, liquid, and solid wastes. TEPCO estimated approximately 500PBq of radioactive iodine and cesium was released into the air and the sea after the accident [1]. Significant gaseous releases have stopped since Reactor Pressure Vessel (RPV) temperatures decreased well below 100Û C till the end of 2011 using the temporarily installed core cooling system supplying cooling water to the damaged cores [2]. Approximately 400 tons of cooling water is injected to damaged cores everyday even more than five hundred days after the accident via piping of primary water lines to remove decay heats [3]. Injected cooling water is not lead to any outlet lines after heat removal but spills on Primary Containment Vessel (PCV) floors through accident-made pressure boundary openings, flows through basement floors of reactor/turbine/utility buildings and is pumped out and recycled after decontamination.
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