Nuclear officials in Japan are reassuring the public after scientists at the crippled Fukushima nuclear plant detected small amounts of xenon — a radioactive gas that could indicate nuclear fission is taking place — inside one of the plant's reactors.

Officials said Wednesday there has been no increase in temperature, pressure or radiation levels at the plant's number two reactor. However the Tokyo Electric Power Company, which operates the plant, has begun injecting boric acid, which neutralizes nuclear reactions, into the reactor as a precaution.

Nuclear fission is the process by which atoms break apart, producing energy. But TEPCO officials stressed that any fission taking place inside the reactor has not reached the stage of “criticality,” at which point it would become self-sustaining.

TEPCO officials said the discovery of the Xenon was not expected to affect plans to bring all the reactors at the Fukushima plant to a state of cold shutdown by the end of this year.

The plant has been leaking radiation since a massive earthquake and tsunami on March 11 knocked out its cooling systems, leading to core meltdowns in three of the six reactors.

Tens of thousands of people have been evacuated from areas around the plant, and elevated radiation levels have been detected in food and water as far away as Tokyo.