TOKYO - The operator of tsunami-hit nuclear power plant in Japan said on Wednesday it had found substances in a reactor which could be a result of nuclear fission, a possible setback in efforts to bring the plant to a safe, cold shutdown this year.
The Fukushima Daiichi nuclear power plant was struck by a devastating earthquake and tsunami in March and has released radiation into the atmosphere ever since.
Tokyo Electric Power said that it discovered xenon, a substance produced as a byproduct of fission from the No 2 reactor, and had poured in a mixture of 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 told reporters.
Criticality is a state when controlled nuclear reactions take place and nuclear power plants harness the resulting heat to produce electricity.