The operator of the tsunami-hit nuclear power plant in Japan said yesterday that substances found in a reactor could be a result of nuclear fission, a possible setback in efforts to shut the plant down safely. But analysts said a higher risk of radiation was unlikely.
The Fukushima Daiichi plant was struck by a devastating earthquake and tsunami in March and released radiation into the atmosphere, the world's worst nuclear crisis since Chernobyl 25 years ago.
Tokyo Electric Power said it discovered xenon, a substance produced as a byproduct of fission, in the No 2 reactor, and had poured in water and boric acid, an agent that helps prevent nuclear reactions, as a precaution.
"It can be assumed that isolated criticality took place for a short period of time judging from the presence of xenon," Tepco spokesman Junichi Matsumoto said. Criticality is when controlled nuclear reactions take place. Nuclear plants harness the resulting heat to produce electricity.
Richard Wakeford, at Manchester University, was sceptical. He said: "Nuclear criticality requires delicate conditions. It seems unlikely that these exist at Fukushima ... Also, criticality would be accompanied by a burst of radiation, which I would have expected to be detected."