a nationally televised statement, Prime Minister Naoto Kan said radiation spread from the four stricken reactors of the Fukushima Dai-ichi nuclear plant along Japan’s northeastern coast. The region was shattered by Friday’s 9.0-magnitude earthquake and the ensuing tsunami that is believed to have killed more than 10,000 people, plunged millions into misery and pummelled the world’s third-largest economy.
Japanese officials told the International Atomic Energy Agency that the reactor fire was in a fuel storage pond — an area where used nuclear fuel is kept cool — and that “radioactivity is being released directly into the atmosphere”.
Long after the fire was extinguished, a Japanese official said the pool might still be boiling, though the reported levels of radiation had dropped dramatically by the end of the day.
That reactor, Unit 4, had been shut down before the quake for maintenance.
If the water boils, it could evaporate, exposing the rods. The fuel rods are encased in safety containers meant to prevent them from resuming nuclear reactions, nuclear officials said. But they acknowledged that there could have been damage to the containers. They also confirmed that the walls of the storage pool building were damaged.
Experts noted that much of the leaking radiation was apparently in steam from boiling water. It had not been emitted directly by fuel rods, which would be far more virulent, they said.
Less clear were the results of the blast in Unit 2, near a suppression pool, which removes heat under a reactor vessel, said plant owner Tokyo Electric Power Co.
The nuclear core was not damaged but the bottom of the surrounding container may have been, said Shigekazu Omukai, a spokesman for Japan’s nuclear safety agency.
Though Kan and other officials urged calm, yesterday’s developments fuelled a growing panic in Japan and around the world.
In the worst case scenario, one or more of the reactor cores would completely melt down, a disaster that could spew large amounts of radioactivity into the atmosphere.
“I worry a lot about fallout,” said Yuta Tadano, a 20-year-old pump technician at the Fukushima plant, who said he was in the complex when the quake hit. “If we could see it, we could escape, but we can’t,” he said, cradling his four- month-old baby, Shoma, at an evacuation centre.
Hundreds of aftershocks have shaken Japan’s northeast and Tokyo since the original offshore quake.
Officials expect the death toll to rise to at least 10,000 but have only been able to confirm a far lower toll — about 3,300.
Japan’s Chief Cabinet Secretary Yukio Edano told residents in the Fukushima Dai-ichi danger zone: “Please do not go outside. Please stay indoors. Please close windows and make your homes airtight... These are figures that potentially affect health. There is no mistake about that.”
Weather forecasts for Fukushima were for snow and wind Tuesday evening, blowing southwest toward Tokyo, then shifting and blowing east out to sea. That’s important as it shows the direction a possible nuclear cloud might blow.
- Chief Cabinet Secretary Yukio Edano said radiation levels near the stricken plant on the northeast coast reached as high as 400 millisieverts (mSv) an hour, thousands of times higher than readings before the blast, but later gave a lower figure.
- Exposure to 350 mSv was the criterion for relocating people after the Chernobyl accident.
- People are exposed to natural radiation of about 2 mSv a year.
- A typical chest X-ray involves exposure of about 0.02 mSv.
- Exposure to 100 mSv a year is the lowest level at which any increase in cancer is clearly evident.
- A single 1,000 mSv dose causes radiation sickness such as nausea. A single dose of 5,000 mSv would kill about half of those exposed to it in a month.
- “Very acute radiation... is unlikely for the [overall] population,” said Lam Ching-wan, a chemical pathologist at the university of Hong Kong.
Source: the World Nuclear Association and the Atomic Energy Council, Taiwan