4 Avril 2012
April 5, 2012
A system that injects nitrogen into the containment and pressure vessels of the Nos. 1, 2 and 3 reactors at the crippled Fukushima No. 1 nuclear power plant stopped for nearly 1-1/2 hours Wednesday, Tokyo Electric Power Co. said.
Hydrogen levels within the vessels did not rise because the injections resumed soon after, TEPCO said.
According to the utility and the Nuclear and Industry Safety Agency, a plant worker discovered that no nitrogen was being injected into the vessels at about 10:55 a.m. It was soon confirmed that the pumps had stopped.
A backup system was started at 12:16 p.m., and nitrogen injections resumed at 12:30 p.m.
Nitrogen is being pumped into the vessels to push highly explosive hydrogen, generated through a radiation-cooling water reaction, out of the vessels.
TEPCO and the agency believe it would take 30 hours without the injections for the hydrogen concentration to rise as high as 4 percent, at which point there is a risk of explosion.