TOKYO — Already-grave conditions at the Fukushima Dai ichi nuclear plant worsened today as highly radioactive iodine seeping from the complex appeared to be making its way into seawater farther away than previously thought after officials reported the highest radiation readings yet.
Leaked water sampled from one unit Sunday was 100,000 times more radioactive than normal background levels. The Tokyo Electric Power Co. had calculated an even higher, erroneous figure that caused workers to flee before the company corrected the reading hours later.
Airborne radioactivity in the unit 2 turbine building was so high that a worker would reach his yearly occupational exposure limit in 15 minutes.
Chief Cabinet Secretary Yukio Edano repeated today that Unit 2’s contaminated water appeared to be due to a temporary partial meltdown of the reactor core. He said the spike in radiation appeared limited to the unit.
But new readings show contamination in the ocean about a mile farther north of the nuclear site than before. Radioactive iodine-131 was found just offshore from Unit 5 and Unit 6 at a level 1,150 times higher than normal, Hidehiko Nishiyama, a Nuclear and Industrial Safety Agency spokesman, told reporters today.
Earlier, a magnitude-6.5 quake off the northeast coast briefly prompted a tsunami warning.
There were no immediate reports of injuries or damage, but the quake — one of dozens that have shaken Japan in the past two weeks — added to the sense of unease.
The March 11 magnitude-9 quake off the northeast coast triggered a tsunami that barreled onshore and disabled the Fukushima plant, complicating a disaster that is thought to have killed 18,000 people.
The confusion in the effort to stave off a full-scale nuclear meltdown underscores the immense challenges in trying to restart the cooling systems. Seventeen workers have been exposed to high levels of radiation, including three hospitalized last week, as technicians conducted nuanced electrical work in dark conditions that one expert termed “hellish.”
“To a layman, you’d be scared to death,” said Lake Barrett, a nuclear engineer who directed the cleanup after the 1979 Three Mile Island accident. “You’re working with saltwater around your feet. This is not the way electricians usually work.”
The Associated Press contributed to this report.
