There are signs of fresh trouble at the crippled Fukushima nuclear power plant in Japan.
Concern that nuclear fission may be occurring has prompted Tokyo Electric Power Company to spray boric acid into one of the reactor buildings at the Fukushima-1 power plant.
The utility confirms a "very small amount" of radioactive xenon gas has been detected at the number two reactor - one of three crippled after a magnitude 9.0 earthquake and subsequent tsunami hit the facility on March 11.
Both Xenon 133 and 135, which have been detected, are by-products of nuclear fission. The substances themselves are not considered a health risk.
Professor Andrew Stuchberry heads the nuclear physics department at Australian National University.
"The most likely source of them [radioactive xenon gas emissions] is from some nuclear fission taking place. The fact their response is to add boric acid, which eats neutrons, that should stop the fission process," he said.
Stuchberry characterizes this development as "a little bit of a surprise" but says there is no reason for the public, so far, to be overly concerned.
"If there's a little bit of fission taking place in the core I would think it would be relatively limited. There's certainly no chance that anything is going to explode. I don't think there'll be large amounts of heat generated that would affect safety," he said. "I would hope that there wouldn't be any additional radiation release associated with this. With the little information we have at the moment and the action being taken I wouldn't get too alarmed."
TEPCO officials say this latest incident should not delay their goal of bringing all the plant's reactors to a state of cold shutdown by the end of this year.
The plant has been leaking radiation since its cooling system was knocked out by the mega-quake and tsunami nearly eight months ago. That triggered apparent core meltdowns in three of the six reactors. Towns and villages in a 20-kilometer radius of the plant were evacuated. Elevated radiation levels have been detected in food, water and soil as far away as Tokyo.
A French nuclear safety institute says the Fukushima disaster has generated the largest-ever discharge of radioactive materials into the ocean. The incident is the worst nuclear disaster since the 1986 Chernobyl meltdown.
A Japanese government panel says it will take at least 30 years to safely decommission the Fukushima nuclear plant.