Already-grave conditions at the Fukushima Daiichi nuclear plant worsened Sunday with the highest radiation readings yet, compounding both the risks and challenges for workers trying to repair the facility’s cooling system.
Leaked water sampled from one unit Sunday was 100,000 times more radioactive than normal background levels — though the Tokyo Electric Power Co., which operates the plant, first calculated an even higher, erroneous, figure that it didn’t correct for several hours.
Tepco apologized Sunday night when it realized the mistake; it had initially reported radiation levels in the leaked water from the unit 2 reactor as being 10 million times higher than normal, which prompted an evacuation of the building.
After the levels were correctly measured, airborne radioactivity in the unit 2 turbine building still remained so high — 1,000 millisieverts per hour — that a worker there would reach his yearly occupational exposure limit in 15 minutes. A dose of 4,000 to 5,000 millisieverts absorbed fairly rapidly will eventually kill about half of those exposed.
Tests also found increased levels of radioactive cesium, a substance with a longer half-life, the Japanese safety agency said.
“Because these substances originate from nuclear fission, there is a high possibility they originate from the reactor,” said Hidehiko Nishiyama, the agency’s deputy director-general, at a news conference. He said that it was likely that radiation was leaking from the pipes or the suppression chamber, and not directly from the pressure vessel, because water levels and pressure in the vessel were relatively stable.