Tepco Injects Boric Acid in Fukushima Plant

By Tsuyoshi Inajima – Feb 7, 2012 12:56 AM GMT+0000

Tokyo Electric Power Co. injected boric acid into a reactor at its crippled Fukushima nuclear plant to prevent an accidental chain reaction known as re- criticality after temperatures rose in the past week.

The temperature of the No. 2 reactor was 70.1 degrees Celsius (158 degrees Fahrenheit) as of 6 a.m. today, according to preliminary data, Akitsuka Kobayashi, a spokesman for the utility, said by phone. The reading fell from 72.2 degrees at 5 a.m. this morning, and is below the 93 degrees that’s used to define a cold shutdown, or safe state, of the reactor.

Since Feb. 1, temperatures at the bottom of the No. 2 reactor vessel have risen by more than 20 degrees Celsius, according to the company’s data. Tepco, as the utility is known, and the government announced that the Fukushima plant reached a cold shutdown on Dec. 16, nine months after the Tohoku earthquake and tsunami destroyed the nuclear station, and caused three meltdowns and radiation release.

Tepco increased the rate of water being injected into the unit to 13.5 cubic meters per hour from 10.5 cubic meters per hour at 4:24 a.m. today, it said. A cold shutdown describes a reactor’s cooling system operating at atmospheric pressure and below 93 degrees Celsius, according to the U.S. Nuclear Regulatory Commission.

Tepco switched to different piping to inject water on Jan. 26, Kobayashi said. This may have led to insufficient water reaching the melted fuel, he said.

No traces of xenon 135, which is associated with nuclear fission, were found when Tepco conducted a gas sampling of the reactor yesterday, the company said in an e-mailed statement late yesterday.

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