TEPCO: Melted fuel eroded containment vessel floor at Fukushima reactor
The No. 1 reactor building of the Fukushima No. 1 nuclear power plant (Asahi Shimbun file photo)
Most of the fuel rods that melted in the pressure vessel of the No. 1 reactor of the stricken Fukushima nuclear power plant dripped into the containment vessel and ate into it, according to Tokyo Electric Power Co.
Cesium-137 deposits 50 times more than previous record
TSUKUBA, Ibaraki Prefecture--Nearly 30,000 becquerels per square meter of cesium-137 fell on Tsukuba in March as a result of the accident at the Fukushima No. 1 nuclear power plant, the government's Meteorological Research Institute said Dec. 1.
The amount was 50 times higher than the previous record level of 550 becquerels, which was measured in Tokyo in 1963 and was the result of deposits from atmospheric nuclear tests.
The MRI, affiliated with the Japan Meteorological Agency, said the cesium-137 deposits in Tsukuba in April fell to less than one-tenth the March level, and by summer fell further to several tens of becquerels per square meter, approximately the same levels found in the aftermath of the 1986 Chernobyl accident, researchers said.
"It may take decades for the figures to come down to levels before the Fukushima accident," said Yasuhito Igarashi, a laboratory head at the MRI's Atmospheric Environment and Applied Meteorology Research Department.
Meanwhile, analysis of seawater collected in April and May found that radioactive substances spewed by the stricken Fukushima No. 1 plant fell over broad areas in the North Pacific. Fallout was also detected near the West Coast of the United States.
The research institute estimated that the Fukushima plant discharged at least 3,500 trillion becquerels each of cesium-137 and cesium-134 into the ocean. It forecast that the radioactive material will spread east across the North Pacific on surface ocean current before drifting southwest on deeper ocean currents. Part of the radioactive materials carried by mid-depth ocean currents will return to seas near Japan's coast in 20-30 years, the scientists said.
"Continual surveys are necessary across all areas of the North Pacific," said Michio Aoyama, a laboratory head at the MRI's Geochemical Research Department.
The MRI has been engaged in radioactivity measurements since 1954.
On March 31, the budget for fiscal 2011, which was to start the next day, was abruptly frozen, and the researchers were told to suspend the measurements. The latest findings are a fruit of efforts by scientists who ignored that order and continued with the measurements.
In meltdown, Japan dodged even bigger disaster
It turned out that the disaster at Japan's Fukushima Dai-ichi power plant was much worse than was first thought. After last spring's tsunami, one reactor suffered a meltdown. CBS News correspondent Lucy Craft details how close it came to burning into the earth.
Recently, reporters got their first look at the devastation left in the wake of the accident, with heavily reinforced buildings torn to shreds after a series of meltdowns and explosions, But as CBS News found out this week, the damage was even worse: Rector 1 almost had a full meltdown.
A new report revealed that molten nuclear fuel burned through the 8-foot concrete walls of the first protective casing surrounding the reactor's core, and then ate 3/4 of the way through the second casing.
The meltdown stopped within a foot of the container's steel bottom, 25 feet above the earth's surface.
Masanori Naitoh is a nuclear engineer who has reviewed the plant's findings. "It was a close call," he said. "The meltdown may have been even worse. But we can say the containment held."
Held, according to the report, because of the huge efforts to dump a continuous flood of seawater on the reactors to cool the nuclear cores. If it had burned through, it would have contaminated the ground water and the soil. No one knows how far it would have spread.
One man who experienced the accident firsthand was Yukio Takayama, a veteran firefighter who was sent to Fukushima six days after the accident.
He said: "It reminded me of a haunted house -- total silence, billowing smoke, eerie. With fires, you can feel the heat or smell the gas. At Fukushima, it was all the more frightening, because the danger was invisible."
So far, he has no signs of radiation poisoning. Nor do any of the other 32 members of his squad. But at the time, they weren't sure they'd come back alive. And they didn't believe the government's assurances.
"The TV was saying, there was no meltdown, no radiation leaks, nothing to worry about," Takayama recalled. "But when you saw the damage, you knew this was no ordinary accident."
The plant's operator says it is on schedule for a "cold shutdown" by the end of this year -- that's when fuel has cooled enough to no longer pose a threat. But it's a long process. Dismantling the reactor and cleaning up the plant could take 30 years.