Defect concealed in Fukushima No. 4 reactor: engineer

Bloomberg

The No. 4 reactor at the Fukushima No. 1 nuclear plant may have been relying on flawed steel to hold the radiation in its core, according to an engineer who helped build its containment vessel four decades ago.

Coping with the unthinkable: A resident explains his fears during a town hall meeting Tuesday in Kawamata, Fukushima Prefecture, on radiation exposure from the nearby Fukushima No. 1 nuclear power plant. AP PHOTO

Mitsuhiko Tanaka says he helped conceal a manufacturing defect in the ¥20 billion steel vessel installed at the reactor while working for a unit of Hitachi in 1974. The reactor, which Tanaka has called a "time bomb," was shut for maintenance when the March 11 earthquake triggered a tsunami that disabled cooling systems at the plant, leading to explosions and radiation leaks.

"Who knows what would have happened if that reactor had been running?" Tanaka, who turned his back on the nuclear industry after the Chernobyl disaster, said in an interview last week. "I have no idea if it could withstand an earthquake like this. It's got a faulty reactor inside."

Tanaka's allegations, which he says he brought to the attention of the Ministry of Economy, Trade and Industry in 1988, when it was the Ministry of International Trade and Industry, and chronicled in a book two years later called "Why Nuclear Power is Dangerous," have resurfaced after the nation's worst nuclear accident on record. The No. 4 reactor was hit by explosions and a fire that spread from adjacent units as the crisis deepened.

Hitachi spokesman Yuichi Izumisawa said the company met with Tanaka in 1988 to discuss the work he did to fix a dent in the vessel and concluded there was no safety problem. "We have not revised our view since then," Izumisawa said.

Kenta Takahashi, an official at METI's Nuclear and Industrial Safety Agency, said he couldn't confirm whether the agency's predecessor, the Agency for Natural Resources and Energy, had conducted an investigation into Tanaka's claims. Naoki Tsunoda, a spokesman at Tokyo Electric Power Co., said he couldn't immediately comment.

Tanaka says the reactor pressure vessel inside the No. 4 reactor was damaged at a Babcock-Hitachi foundry in Kure, Hiroshima Prefecture, during the last step of a manufacturing process that took 2 1/2 years and cost billions of yen. If the mistake had been discovered, the company might have been bankrupted, he said.

Inside a blast furnace the size of a small airplane hanger, the reactor pressure vessel was being treated one last time to remove welding stress. The cylinder, 20 meters tall and 5.8 meters in diameter, was heated to more than 600 degrees, a temperature that softens metal.

Braces that were to have been placed inside during the blasting were either forgotten or fell over when the cylinder was wheeled into the furnace. After the vessel cooled, its walls were warped, Tanaka said.

Δημοσίευση: Μαρτίου 30, 2011