Cleanup technologies following Fukushima
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Cleanup technologies following Fukushima By Angela Saini Feature Editor Tadafumi Koyama
T
he accident at Fukushima Daiichi happened almost six years ago, but the after-effects will stretch on for many decades. Scientists and engineers remain in the early stages of the enormous task of cleaning the site and making it safe. Melted fuel debris must be cleared and stored, thousands of tons of contaminated water must be managed, and the reactors must be protected to stop any more radioactive material from escaping. Only then can engineers get to the heart of the problem—decommissioning. To date, the job is far from complete. According to a spokesperson for the Tokyo Electric Power Company (TEPCO), which operates the plant, it will take another 30 to 40 years to complete all the processes toward decommissioning. So far, unbroken fuel rods have been removed from the cooling pool of one reactor unit, with work on another unit expected to begin in 2017, followed by another two in 2020. The job demands many new technologies, including materials. “It is important to work on basic research in materials science and engineering, as well as research and development for
practical use,” in order to achieve all this, added the spokesperson for TEPCO. On-site cleanup is being carried out by TEPCO, in conjunction with large corporations, including Toshiba, Hitachi, Kurion, Kajima, and Taisei, contracted to assist and supply technology. Solutions to problems are also being developed by Japan’s International Research Institute for Nuclear Decommissioning (IRID), the Japan Atomic Energy Agency, the Central Research Institute of Electric Power Industry, and various universities around the world. To cope with the complexity of all the different research needs, the Japanese government created a Nuclear Damage Compensation and Decommissioning Facilitation Corporation in 2014 to manage the research activities on the road to decommissioning. According to Hirofumi Kenda, president of IRID, “One of the most challenging issues for Fukushima Daiichi is the high radiation dose rate in the reactor buildings due to contamination by cesium-137, whose half-life is 30 years. Because of that environment, access by personnel is restricted, and remote operating and sensing technologies are required in all circumstances.” Cesium137 is both a strong gamma emitter and able to move in a soluble format, which makes it doubly dangerous.
Robot helpers Although there are many thousands of workers at the site, it is unsafe for them to enter the plant itself because of the high radiation levels. The alternative has been to use robots. Swimming and crawling robots, for example, developed by Japanese multinational Hitachi, investigate leakages from the reactors. A robotic water boat meanwhile surveys leakages inside the reactor containment vessel. And one type of decontamination robot used on the upper floors deploys a high pressure water jet, while another type uses blasts of dry ice. An important materials challenge is to develop electronics, especially semic
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