The radiation leak from an earthquake-damaged power plant is decreasing, Japanese officials said Saturday, amid fears of a nuclear meltdown after a blast that levelled the structure housing a reactor.
The explosion on Saturday at the Fukushima Daiichi plant north of Tokyo crumbled much of the reactor building. Japanese news footage showed smoke billowing into the air, and only the building's metal frame was left standing.
Friday's massive 8.9-magnitude quake and the powerful tsunami it spawned ravaged Japan's northeastern coast, killing at least 586 people. Thousands of others were still unaccounted for on Saturday.
The twin disasters prompted Japan to declare states of emergency for five nuclear reactors at two power plants, with the Fukushima station raising the most concern. The plant's Unit 1 lost power and, consequently, its cooling abilities, which could cause a pressure buildup in the reactor.
But Japan's government spokesman Yukio Edano played down worries of a nuclear catastrophe, saying the metal vessel enveloping the reactor itself was still intact, despite the destruction of the building around it.
"We have confirmed that the walls of this building were what exploded, and it was not the reactor's container that exploded," he said.
Tokyo Power Electric Co., which runs the Fukushima Daiichi plant, said four workers were being treated in hospital for minor injuries after the explosion.
Edano said radiation around the plant did not increase after the explosion and was actually decreasing. He added that pressure in the reactor was also down.
Officials are nevertheless taking no chances, and on Saturday doubled the evacuation radius to 20 kilometres from 10 kilometres. Some 51,000 residents in what was considered the danger zone near the Fukushima plant were evacuated after the explosion.
According to Reuters, Japanese authorities have told the United Nations Atomic Energy Commission the government is preparing to hand out iodine to residents to help protect them from radiation exposure.
"People in the danger zones have been told to cover their mouths and noses with wet cloths," said freelance reporter Craig Dale, speaking to the CBC News on Saturday.
He added there were also instructions for residents to be aware of the possibility of "internal exposure" and to avoid eating fruits and vegetables until they get the all-clear from authorities.
A jet stream, or air current, could well carry radioactive fallout as far as B.C., the CBC's Belle Puri reported.
The worst-case scenario would be a Chernobyl-scale catastrophe, with explosions destroying the reactors and sending a deadly plume of radioactivity into the atmosphere. The Chernobyl accident 25 years ago in Ukraine spewed radiation over much of Europe after a nuclear reactor exploded and caught fire.
But such a scenario would be highly unlikely in Japan, said Jim Walsh of the Massachusetts Institute of Technology, who is an expert on nuclear threats.
If the containment vessel around the reactor has not been touched, it should act as a layer of defence to prevent radiation from escaping, he told CBC's Mark Kelly.
The main issue is how to cool down the reactor, which has already been shut down.
Walsh said the concern was that with an increase in temperature and pressure, the fuel for the reactor could melt.
"And if it melts and somehow escapes the reactor vessel and touches the air, it will explode."
Japanese officials are continuing to monitor radiation levels in the area. Pressure at the Fukushima reactor was double its normal level, prompting officials to release slightly radioactive vapours to reduce pressure.
"They're venting some of the steam now because one way to reduce the temperature and pressure is to let some of the air out of that, even if it's mildly radioacitve," Walsh said. "That's better than the alternative."