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Sunday, April 3, 2011
Irradiated water swamps Tepco
Restarting cooling systems takes a back seat to storage, disposal
The government and Tokyo Electric Power Co. have been struggling for three weeks to end the Fukushima No. 1 nuclear crisis but are being stymied by the need to remove massive amounts of highly radioactive water.
The highest priority is to extract the contaminated water in the flooded basements of some of the reactor turbine buildings, whose electric systems must be checked in order to cool fuel rods inside the reactors and spent fuel pools.
But little progress appears to have been made in the last few days, with Tepco continuing to transfer contaminated water from tank to tank to store it.
Experts said this is difficult and time-consuming, and new measures are needed quickly because the existing tanks will reach capacity.
Tsuyoshi Misawa, a reactor physics and engineering professor at Kyoto University's Research Reactor Institute, said it is unclear when the water removal will be completed, especially as the water in the No. 2 reactor turbine building is possibly leaking from its pressure vessel.
As for the flooded No. 1 turbine building, Tepco was pumping the water into a condenser tank but was forced to transfer it to another vessel after the tank got full. The work reduced the water in the basement from a depth of 40 cm to about 20 cm.
Work to remove contaminated water from reactors 2 and 3, however, has yet to start. The crucial task of restoring electricity for the reactor cooling systems has meanwhile been delayed.
Experts warned that condenser tanks won't be able to hold all the water.
"I think some facility to store a massive amount of water will be needed," Kyoto University's Misawa said, adding it will be a huge task to properly dispose of the vast amounts of contaminated water.
While the government has mulled anchoring tankers by the plant to store the water and building a facility to properly dispose of it, the city of Shizuoka announced Friday it will provide its mega-float, a huge barge, to Tepco for storing the water.
Tepco estimates the vessel can store about 10,000 tons of water, while the amount of water detected in the plant has reached around 13,000 tons.
While removing the water is expected to take time, possible damage to pressure vessels might mean radioactive substances will keep leaking.
Misawa said it is highly possible the No. 2 reactor's pressure vessel is damaged, since the water in its turbine building is extremely contaminated, showing surface-level radiation in excess of 1,000 millisieverts per hour.
Radionuclide analysis of that water showed it contains not only volatile iodine-131 and cesium-134, but also the more stable lanthanum-140 and barium-140. All four substances are believed to have come from atomic fission, meaning "some part of the pressure vessel is probably damaged," Misawa said.
But at the same time, the reactor does not appear to be in a dangerous enough state to cause another hydrogen explosion because its temperature is hovering around 180 degrees, he said. Hydrogen only emerges when the temperature rises high enough to start the fuel rods' zirconium casings burning, allowing them to react with the water in the pressure vessel.
Meanwhile, experts welcomed France's support, given the country's experience and knowledge of nuclear power.
French President Nicolas Sarkozy met with Prime Minister Naoto Kan on Thursday and promised its support, while Anne Lauvergeon, CEO of French nuclear power company Areva SA, also pledged support when she met with Economy, Trade and Industry Minister Banri Kaieda.
"The knowledge and experience of Tepco and people engaged in domestic nuclear-related fields are limited amid the crisis," said Hiromi Ogawa, a former engineer at Toshiba Corp. who managed the company's nuclear power generation project.
Areva has experience of handling previous nuclear accidents, including Three Mile Island and Chernobyl.
Assuming the situation at Fukushima No. 1 is eventually brought under control, the challenge of decommissioning reactor Nos. 1 through 4, which Tepco Chairman Tsuneyoshi Katsumata has said is probably unavoidable, awaits. But decommissioning damaged nuclear power plants is a very lengthy, tricky and expensive project.
Even shutting down a regular nuclear plant requires time and money. At the nation's first nuclear power plant in Tokai, Ibaraki Prefecture, which ended operations in 1998, it took three years just to remove spent fuel rods. Work to complete the process is slated to end in 2020 and cost a total of ¥89 billion, according to some media reports.
Ex-Toshiba engineer Ogawa said that when decommissioning a normal plant there are a limited number of places where the radiation level is high, so even though the work is time-consuming, it can advance according to plan.
But "it is going to be very different in the case of Fukushima," he said, as places that are not supposed to have high levels of radiation have been contaminated, such as the basement floor of the No. 2 turbine building.
The fact that the quake and tsunami damaged machines such as cranes that are vital to remove spent fuel will increase the level of difficulty and require considerably more time and funds, Ogawa said.