Japanese authorities ordered most of the 800 workers at the Fukushima Daiichi nuclear power plant to leave the site yesterday after a fire broke out in a pool holding spent fuel rods for reactor No. 4. The fire sent plumes of highly radioactive smoke billowing into the atmosphere, forcing the government to expand the affected zone around the plant to a radius of 30 miles.
The 50 workers who remained behind waged a courageous, high-risk battle to contain the blaze. Officials said the fire eventually was put out, and by late Tuesday in Japan the radiation levels around the Fukushima plant began to drop.
Plant managers apparently have decided to rotate small crews at the plant as they struggle to cool down the most heavily damaged unit, reactor No. 2, by pumping in seawater using firefighting equipment. The cooling system has failed for three of the reactors at the complex, and containment buildings housing two of them have been shattered by huge hydrogen explosions. Experts believe reactor No. 2 has experienced a partial meltdown of its reactor core of radioactive fuel rods.
But late Tuesday Japan’s nuclear watchdog said a pool storing spent fuel rods at that fourth reactor had overheated and reached boiling point and had become unapproachable by workers. The fire earlier Tuesday morning was sparked by a hydrogen explosion caused by rising temperatures at the fuel pool, which released radioactivity directly into the atmosphere. The government said late Tuesday that radiation levels at the plant also appeared to be falling sharply from earlier in the day.
The fourth reactor had been turned off and was under refurbishment for months before the earthquake and tsunami hit the plant on Friday. But the plant contains spent fuel rods that were removed from the reactor. If these rods had become dry, they could overheat and catch fire. Officials said that is almost as dangerous as the fuel in working reactors melting down because the spent fuel can also spew radioactivity into the atmosphere.
In a brief address to the nation, Prime Minister Naoto Kan announced that everyone — including immobile hospital patients — must evacuate from a 20-mile zone around the crippled plant. Kan also said that anyone remaining within 30 miles of the plant site must stay indoors. The prime minister said there is “a very high risk” of further leakage, but he urged the island nation to remain calm.