Possible Nuclear Fission at Fukushima Reactor

SFGate:  Nov. 2 (Bloomberg) -- Tokyo Electric Power Co. detected signs of possible nuclear fission at its crippled Fukushima atomic power plant in northern Japan, raising the risk of more radiation leaks.

The company, known as Tepco, began spraying boric acid on the No. 2 reactor at 2:48 a.m. Japan time in an attempt to prevent accidental chain reactions. Tepco said it may have found xenon, which is associated with nuclear fission, while examining gases taken from the reactor, according to an e-mailed statement today.

The amount of detected xenon is "very small" and results of the utility's analysis may be wrong, said Hiroyuki Usami, a spokesman for Tepco. No significant changes in temperatures and pressures of the reactor and radiation levels at the site have been detected, he said.

The discovery comes almost eight months after the March 11 earthquake and tsunami wrecked the Fukushima Dai-Ichi plant, causing a loss of cooling and the meltdowns of three reactors. The incident, the worst nuclear disaster since Chernobyl in 1986, was responsible for the biggest discharge of radioactive material into the ocean in history, according to a study from a French nuclear safety institute.

Nuclear fission, even if it has occurred, is unlikely to be sustained as Tepco started injecting boric acid into the reactor, said Tadashi Narabayashi, a former reactor safety researcher at Toshiba Corp. and now a nuclear engineering professor at Hokkaido University.

Tepco and the government have said they are on track to bring the damaged reactors into a safe state known as cold shutdown by the end of the year. The company has been mixing boron, an element that absorbs neutrons and hinders nuclear fission, with cooling water in the reactors to prevent accidental chain reactions.

Shares Slide

Shares of Tepco slid as much as 6.1 percent, the biggest intraday loss since Oct. 21, and traded 4.5 percent lower at 296 yen as of 9:05 a.m. on the Tokyo Stock Exchange. The benchmark Nikkei 225 Stock Average slid 1.7 percent.

Tepco and the Japan Atomic Energy Agency are reexamining the gases, said Toshiyuki Koganeya, a spokesman for the Nuclear and Industrial Safety Agency, the government regulator.

Even if Tepco's analysis is correct, nuclear fission would be taking place in a "very restricted part" of the reactor, said Koganeya. The regulator believes fuel accumulated at the bottom of the pressure vessel and containment vessel is unlikely to start melting again, he said.

Fukushima has sustained damaged at four of its six reactors at the Dai-Ichi plant.

French Study

The radioactive cesium that flowed into the sea from the plant was 20 times the amount estimated by Tepco, according to the Institute for Radiological Protection and Nuclear Safety, which is funded by the French government.

The oceanic study estimates 27,000 terabecquerels of radioactive cesium 137 leaked into the sea from the Fukushima plant, north of Tokyo.

Separately, Kyushu Electric Power Co. said it plans to restart the No. 4 reactor at its Genkai nuclear station in southwestern Japan last night, the first atomic facility to resume operations since the Fukushima disaster.