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Saturday, May 14, 2011
Holes in reactor 1 mean road map needs major overhaul
Tokyo Electric Power Co. will have to change its road map for stabilizing the Fukushima No. 1 power plant because it will take longer than expected to install a cooling system with circulating water for heavily damaged reactor No. 1, experts said Friday.
Tepco said Thursday it found that the water level in the reactor's pressure and containment vessels was much lower than it had estimated and said both had developed holes or cracks.
The utility is still pumping massive amounts of water into the vessels to cool the fuel rods inside the pressure vessel.
"Tepco will have to review its plan in the road map dramatically. We now know Tepco has much more work to do, such as locating cracks and holes and sealing them," said Hiromi Ogawa, a former engineer at Toshiba Corp. who managed its nuclear power generation project.
Industry minister Banri Kaieda echoed Ogawa, telling journalists Friday that the holes at the bottom of the containment vessel are "a major factor requiring a change in how to stabilize the situation."
Tepco is working to gain control over reactors 1, 2 and 3 in line with the road map announced April 17.
According to the plan, Tepco aims to start reducing the amount of leaked radioactive substances in three months and achieve cold shutdown, the status in which the water temperature in the pressure vessel drops below 100 degrees and the fuel rods are being stably cooled, in six to nine months.
Tepco has not injected water into the containment vessels for reactors 2 and 3, and it did not deny the possibility that those vessels may be as badly damaged as reactor No. 1's.
"Tepco was going to establish a cooling system of circulating water from (reactor 1's) containment vessel to the pressure vessel and back again, but it may have to establish the system so that water in the basement of the reactor building will be circulated to the pressure vessel and from there to the containment vessel, depending on where and how many holes there are," Ogawa said.
Sealing holes in the containment vessel will probably be "very difficult" because workers will have to go very close to the spot where highly radioactive water keeps flowing out, he said.
Even the floor of the reactor building may have cracks, and if so, a cooling system that is circulating water inside it will leak, Ogawa said.
However, leaks from the reactor building would probably not be as bad as from the containment vessel, and sealing cracks in the reactor building is probably less dangerous than fixing those in the containment vessel, he said.
Shinichi Morooka of Waseda University, who specializes in nuclear reactor engineering, agreed with Ogawa. Even though Tepco will not be able to meet the deadline it spelled out in the April 17 road map, "I believe Tepco has been doing the best job it could possibly do" since April 17, he said.
The temperature in the pressure vessel is about 100 to 120 degrees, according to Tepco. But that doesn't mean the utility is about to achieve cold shutdown, Ogawa said.
"Cold shutdown is achievable with water temperature less than 100 degrees only if the fuel rods are neatly placed. Now a chunk of mixed melted rods and zirconium is in the bottom of the pressure vessel and the temperature at the center of the chunk is probably higher," he said.