The Yomiuri Shimbun
Hydrogen has been detected in a pipe at the No. 1 reactor at the Fukushima No. 1 nuclear power plant, but there is no possibility it will cause an explosion "in the immediate future," the plant's operator said Friday.
According to Tokyo Electric Power Co., hydrogen of at least 10,000 parts per million was detected at two spots in a pipe passing through the containment vessel on the reactor building's first floor. This concentration was higher than TEPCO had anticipated.
Although TEPCO is not certain how much hydrogen is still inside the vessel, the utility believes it is possible the concentration of the highly flammable gas is higher than had been assumed.
In air and liquid, 10,000 ppm is equivalent to 1 percent. Air containing at least 4 percent hydrogen and 5 percent oxygen is at risk of causing explosion.
TEPCO has been injecting nitrogen into the containment vessel since April so it is assumed there is virtually no oxygen. As a result, the utility ruled out the possibility of an explosion "in the immediate future."
The hydrogen was detected during an examination of the pipe before installation of a radioactive gas purification system inside the containment vessel. TEPCO said it had closely examined the hydrogen concentration and would inject nitrogen into the pipe to flush out the remaining hydrogen.
TEPCO said it had expected hydrogen would still be inside the containment vessel, but that it would have no effect on the radioactive gas purification system.
The nuclear plant's Nos. 1, 3 and 4 reactors were damaged by hydrogen explosions in the days after the March 11 earthquake and tsunami knocked out the plant's cooling systems.
(Sep. 24, 2011)