No sustained nuclear fission at Fukushima

The operator of Japan's quake-damaged Fukushima Daiichi nuclear power plant said Thursday radioactive xenon detected at one of the reactors was not the result of sustained nuclear fission, but a case of spontaneous fission."Based on further examination, we judged the discovery of xenon in the No. 2 reactor at the plant was caused by spontaneous fission that occurs in any idle reactor, and we don't see any fresh problems at the No. 2 reactor," Tokyo Electric Power Co. (TEPCO) spokesman Junichi Matsumoto told a press conference.TEPCO said Wednesday it has detected signs of nuclear fission, as small amounts of xenon-133 and xenon-135 were found in gas samples from the No. 2 reactor building late Tuesday, and injected water and boric acid to stop further nuclear reactions as a precaution. Both are byproducts of a nuclear fission and have a short half-life of five days and nine hours respectively, suggesting that a nuclear fission took place recently.Matsumoto also reiterated that the incident does not have major impact on the utility's schedule to bring the damaged reactors to a safe condition known as cold shutdown by the end of the year.The magnitude-9.0 earthquake and tsunami on March 11 had knocked out cooling systems at the six-reactor Fukushima complex, 230 km north of Tokyo, triggering explosions and radiation leaks. The world's worst atomic disaster since Chernobyl in 1986 also resulted in the meltdown of nuclear fuel in the No. 1 to 3 reactors.