Pumping seawater into the plants produced high pressures and vapors that the company vented into its containment structures and then into the air, raising concerns about radioactivity levels in the surrounding area where people have already been evacuated. The utility said that at one of the huge, complicated reactors, a safety relief valve was opened manually to lower the pressure levels in a containment vessel.
But the limited vapor emissions were seen as far less dire than the consequences of failure in the fight against a more far-reaching partial or complete meltdown that would occur if the rods blazed their way through the reactor’s layers of steel and concrete walls.
The potential size of the area affected by radioactive emissions could be large. A state of emergency was declared briefly at another nuclear plant called Onagawa after elevated radioactivity levels were detected there. Later Japanese authorities blamed the measurement on radioactive material that had drifted from the Fukushima plant more than 75 miles away, according to the International Atomic Energy Agency.
The IAEA noted that forecasts said winds would be blowing to the northeast, away from the Japanese coast, over the next three days.
Tokyo Electric said that radioactivity levels both inside the plant and at its nearby monitoring post were higher than normal. The Nuclear Energy Institute, an industry group in the United States, reported that the highest recorded radiation level at the Fukushima Daiichi site was 155.7 millirem at 1:52 p.m. on March 13; radiation levels fell to 4.4 millirem by the evening. The Nuclear Regulatory Commission’s radiation dose limit for the public is 100 millirem per year.
In addition to one worker hospitalized for radiation exposure, two others felt ill during stints in the control rooms of Fukushima Daiichi units 1 and 2.
While Tokyo Electric said it also continued to deal with cooling system failures and high pressures at half a dozen of its 10 reactors in the two Fukushima complexes, fears mounted about the threat posed by the pools of water where years of spent fuel rods are stored.
At the 40-year-old Fukushima Daiichi unit 1, where an explosion Saturday destroyed a building housing the reactor, the spent fuel pool, in accordance with General Electric’s design, are placed above the reactor. Tokyo Electric said that it was trying to figure out how to maintain water levels in the pools, indicating that the normal safety systems there had failed too. Failure to keep adequate water levels in a pool would lead to a catastrophic fire, said nuclear experts, some of whom believe that unit 1’s pool may now be outside.
“That would be like Chernobyl on steroids,” said Arnie Gundersen, a nuclear engineer at Fairewinds Associates Inc. and a member of the public oversight panel for the Vermont Yankee nuclear plant, which is identical to the Fukushima Daiichi unit 1.
Gundersen said the unit 1 pool could have as much as 20 years of spent fuel rods, which are still radioactive
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