Engineers at Japan's stricken Fukushima Dai-ichi nuclear power plant have abandoned their attempt to stabilize reactor Number 3 by flooding it with water, finding that melting fuel rods had created a hole in the chamber, allowing some 3,000 tons of contaminated water to leak into the basement of the reactor building—raising concerns about groundwater contamination. Plant operator TEPCO now says it will pump the 4,000 tons of water out to be transferred to a waste-disposal facility before pumping in new water and installing a "self-circulating" system. The Nuclear and Industrial Safety Agency has approved the new plan—but it appears to carry its own risks. The temperature in reactor No. 3 has been rising since the beginning of the month, reaching more than 200 degrees Celsius (392 Fahrenheit).
TEPCO insists the new plan, which will also be applied in reactors 1 and 2, will not upset the timetable issued last month, in which the company says it will achieve a "cold shutdown" of the reactors within nine months—meaning that water temperatures inside the reactors will be reduced to less than 100 degrees (212 Fahrenheit). The company also plans to build "shells" around the reactor buildings to contain contaminated water, as well as to shield the damaged buildings from late summer typhoons.
TEPCO now admits that a meltdown of nuclear fuel likely occurred [2] at reactor No. 1 within a day of the March 11 earthquake and tsunami. The melted fuel is now believed to have created holes that allowed water to leak from the reactor core, and the company is examining the possibility that this has happened at reactors 2 and 3 as well. There is growing talk among nuclear industry-watchers that a so-called "China Syndrome"—in which fuel melts through the reactor building and into the earth—may already be underway. (Kyodo [3], Kyodo [4], Japan Today [5], Radio Australia [6], NYT [7], VOA [8], The Guardian [9], May 17; BBC News [10], May 15; Nature.com News Blog [11], May 13)
Speculation that the meltdown at reactor No. 1 was caused by a loss-of-coolant accident initiated by the earthquake itself—not, as official accounts have had it, by the resultant power outage—now appears confirmed. TEPCO said May 16 that radiation levels inside reactor 1 were measured at 300 milli-Sieverts an hour within hours of the earthquake—-meaning that fuel melting already had begun. Writes the Nuclear Information and Resource Service: "For melting to have begun that early, coolant must have been lost almost immediately. It's now believed that fuel melted and dropped to the bottom of the containment—melting a hole into it, within 16 hours. Most likely, a major pipe carrying cooling water to the core was damaged by the earthquake, which should lead to a new evaluation of the ability of key reactor components to withstand seismic events." (NIRS [12], May 16)
The International Atomic Energy Agency (IAEA [13]) is to send a team to Japan to investigate the Fukushima disaster from May 24 to June 2. The team of some 20 nuclear experts will make "a tentative assessment" of the crisis, with their findings to be delivered at a ministerial meeting on nuclear safety to be hosted by the agency from June 20-24 in Vienna. (Mainichi Japan [14]) May 17, 2011
See our last post on the Fukushima disaster [15].
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