TOKYO and LOS ANGELES — Radiation levels spiked inside and outside the Fukushima Daiichi nuclear power plant Thursday, slowing work on the facility once again and once more throwing into doubt the integrity of the containment vessels that hold the fuel rods.
Tokyo Electric Power Co. officials said levels of radioactive iodine in water at the plant spiked to levels 10,000 times permissible limits, preventing workers from getting near the water.
Engineers have been pumping water out of the tunnels in the basements of the facilities and into holding areas in an attempt to permit access to areas where workers are trying to restore electricity to the cooling pumps that could ultimately bring the situation at the stricken facility under control. But they cannot do so when radiation levels are that high.
The iodine is the primary gaseous byproduct of fission of uranium in the fuel rods that power the plant and its presence in water suggests that, at the very least, the cladding that encases the uranium fuel pellets has cracked, permitting the gas to escape. The good news is that radioactive forms of iodine have a half-life of about an hour or less, so that the radioactivity should quickly decay if no further release occurs.
Engineers speculated that the radiation spikes may be coming from a partial meltdown of the fuel core of reactor No. 1. It appears that small segments of the melted fuel rods in that reactor are undergoing what is known as "localized criticality," emitting brief flashes of heat and radiation.
Levels of radioactive iodine in seawater off the coast at the plant have also risen, according to Japan's nuclear safety agency. The agency said Thursday that levels of the isotope in water about 350 yards off the coast had risen to 4,385 times the permissible level, up about a third from levels the previous day.
The agency said levels of cesium-137, a much more dangerous isotope because its half-life is 30 years, were about 527 times the permissible level at the site. Environmental experts fear that the cesium could get into plankton and then into fish, where it could eventually make its way into the human food chain.
And even while radiation levels are rising at the plant, public broadcaster NHK said Thursday that many workers at the facility do not have radiation monitoring badges. Tepco, which owns the facility, confirmed the report, noting that much of its supplies had been destroyed in the magnitude 9 Tohoku earthquake and the tsunami that followed it.
But company officials said that the leaders of each team of workers have a badge and that workers without badges are assigned to areas with low radiation risk.
Fears of radiation may also be hampering recovery of bodies in the immediate area around the nuclear facility. Fukushima prefecture still has 4,760 people missing, and media reports suggest that authorities fear looking for them because of the radiation.
But police say all public areas have been cleared of bodies. They conceded that some bodies could still be inside buildings, but they do not believe the numbers are high.
(Makinen reported from Tokyo and Maugh reported from Los Angeles.)