Charles Digges: Chain Reaction Scare at Fukushima

Last week, technicians and observers warned of a possible chain reaction in Fukushima Daiichi's destroyed reactor No.2 has now been determined to be a "spontaneous fission incident", a process of radioactive decay that does not involve a chain reaction. The fears behind a possible chain reaction centered on the discovery of xenon gas as a possible harbinger of further fuel melts at the reactors, three of which experienced full meltdowns after the plant was hit by a 9.0 magnitude earthquake and tsunami in March. But both the plant's owner, Tokyo Electric Power Co (TEPCO) and nuclear physicist Katsutada Aoki have said that the presence of xenon is not an indication that the wrecked fuel in the reactors has re-achieved "criticality" or a sustained chain reaction of nuclear fission. "The discovery of xenon in the reactor is no reason to fear anything serious," Aoki, an expert in nuclear engineering who headed the the reactor physics division of the Atomic Energy Society of Japan, told the Japan Times. TEPCO said this week that it considered the source of the xenon to be a spontaneous fission, because technicians had injected boric acid into the reactor vessel to reduce the likelihood of chain fission reactions, but was still able to detect xenon.