FUKUSHIMA
serious incident at the nuclear power plant in Ohkuma, Fukushima, Japan, about 300 km northeast of Tokyo. All of the units at Fukushima Daiichi are owned by Tokyo Electric Power Company (TEPCO). This article summarises the impacts of the incident in both the short and long term. The Fukushima Daiichi Nuclear Power
M
Plant is on Japan’s northeast coast directly on the Pacifi c Ocean. It is comprised of six large commercial nuclear reactors. The particulars of each reactor and its status at the time of the earthquake and subsequent tsunami are listed in the box, right: Units 1, 2, 3, and 4 are clustered close
arch 11, 2012, marked the one-year anniversary of the earthquake and tsunami that resulted in the
together in a line near the waterfront. Units 5 and 6 are clustered together several hundred yards away, also near the waterfront. The units that were operating at the time of the incident immediately shut down as they are programmed to do upon a large earthquake in their vicinity. Up until this point in time everything was working as it should.
What happened at Fukushima? The major issue with the Fukushima units was the loss of onsite and off site normal and emergency power caused primarily by the tsunami. All western light water reactors (that is, Boiling Water Reactors and Pressurised Water Reactors) are designed to operate on emergency onsite power (usually provided by diesel generators or batteries) in the event the
plant trips off line and can no longer produce power needed to run cooling systems. At Fukushima, the tsunami knocked out internal power circuits, fl ooded and contaminated emergency diesel fuel systems, and fl ooded battery areas. It also impeded the ability to get emergency power from off site sources since most transmission lines were destroyed. The lack of onsite or off site normal or
emergency power was especially acute for the units which were operating at the time of the incident. The heat produced by radioactive fi ssion products peaks shortly after a unit trips off line. If pumps cannot circulate cooling water through the reactor and the spent fuel pool, eventually water in the reactors boils and the fuel becomes uncovered. Uncooled and uncovered fuel eventually begins to
HOW FAR? 30 | CHEMICAL, BIOLOGICAL & NUCLEAR WARFARE | 2012/02
HOW WIDE?
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