The operator of the crippled nuclear power plant in Japan said Wednesday it had found signs that nuclear fission is continuing unexpectedly in one of the reactors, even as workers attempt to bring the plant to a cold shutdown.
Utility officials said they detected gas inside the No. 2 reactor at the Fukushima Dai-ichi nuclear facility that indicated the presence of radioactive xenon, which is likely the byproduct of recent nuclear fission.
Tokyo Electric Power, or Tepco, said as a precaution, it was pouring a mixture of water and boric acid into the reactor, which should help prevent nuclear reaction.
The amount of xenon detected was small and there was no rise in the reactor's temperature or pressure, Tepco insisted.
But because the half-life of the isotopes detected is short, it's likely the xenon was created recently – within the last 10 days or so.
Nevertheless, officials said the level was so low that further tests would be required to confirm the measurements were not an error.
"We have confirmed that the reactor is stable and we don't believe this will have any impact on our future work," TEPCO spokesman Osamu Yokokura told the Associated Press.
He said no radiation leaks outside the plant were detected. The country's nuclear safety agency said the situation was stable and that the small amounts of radioactive material did not present a risk to the public.
The No 2 reactor is one of three at the plant that started to melt down on March 11, after the facility's cooling system lost power following a magnitude-9 earthquake and tsunami.
Tepco has been working to stabilize the facility ever since and recently said it was close to declaring it had reached a "cold shutdown," meaning the temperatures at the reactors are constant and controlled.
Even so, a Japanese government panel says it will take at least 30 years to safely decommission the facility. And a 20-kilometre exclusion zone around the facility remains in effect.
Before the Fukushima disaster, Japan relied on nuclear power for about one-third of its electricity. These days, 43 of the country's 54 reactors are offline for inspections or mechanical troubles.
Meanwhile, a reactor in southern Japan was restarted this week and brought back online -- the first to start generating electricity since the March earthquake.
