– Nuclear fuel has melted through base of Fukushima plant (Telegraph, Jun 9, 2011):
The nuclear fuel in three of the reactors at the Fukushima Dai-Ichi nuclear plant has melted through the base of the pressure vessels and is pooling in the outer containment vessels, according to a report by the Japanese government.
The findings of the report, which has been given to the International Atomic Energy Agency, were revealed by the Yomiuri newspaper, which described a “melt-through” as being “far worse than a core meltdown” and “the worst possibility in a nuclear accident.”
A spokesman for Tokyo Electric Power Co. said the company is presently revising the road-map for bringing the plant under control, including the time required to achieve cold shutdown of the reactors.
In a best-case scenario, the company says it will be able to achieve that by October, although that may have to be revised in light of the report.
Water that was pumped into the pressure vessels to cool the fuel rods, becoming highly radioactive in the process, has been confirmed to have leaked out of the containment vessels and outside the buildings that house the reactors.
Tepco said it is trying to contain the contaminated water and prevent it from leaking into the sea, but elevated levels of radiation have been confirmed in the ocean off the plant.
The radiation will also have contaminated the soil and plant and animal life around the facility, making the task of cleaning up more difficult and expensive, as well as taking longer.
The experts have also yet to come up with a plan for decommissioning the ruined plant. Studies have estimated that the cost of the accident at Fukushima may rise as high as $250 billion over the next 10 years.
The pressure vessel of the No. 1 reactor is now believed to have suffered damage just five hours after the March 11 earthquake and tsunami, contrary to an estimation released by Tepco, which estimated the failure at 15 hours later.
Melt-downs of the fuel in the No. 2 and No. 3 reactors followed over the following days with the molten fuel collecting at the bottom of the pressure vessels before burning through and into the external steel containment vessels.
The fuel appears to be stable at present as it is being cooled by water pumped into the vessels, although it will complicate the emergency recovery plan put forward by the government.
The report comes after Japan’s Nuclear and Industrial Safety Agency doubled its initial estimate of the amount of radioactivity that was released from the plant in the days immediately after it was destroyed by the tsunami.
In early April, the agency said some 370,000 terabecquerels escaped from the facility. It now believes that figure was 770,000 terabecquerels. One terabecquerel is a trillion becquerels, the standard measure of radiation, while the permissible level of iodine-131 for vegetables and fish is 2,000 becquerels per kilogram.
Combined, the two announcements will raise further questions about the true scale of the problem at the plant and the measures being taken to get the situation under control.
“The recovery effort at the plant is likely to be more difficult as they will not be able to use their previous plan to contain the fuel,” Yoshiaki Oka, a professor of nuclear science at Tokyo’s Waseda University told The Daily Telegraph.
“So it may take longer and be more difficult, but it is something they have to do.
“But we now know that this happened at the very beginning of the accident, so I see no particular additional affects on human health,” he said.