The estimate of much higher levels of radioactive caesium-137 in the atmosphere comes from a worldwide network of sensors that was studied by the Norwegian Institute for Air Research in a report authored by Andreas Stohl .
The Norwegian study says the Japanese government estimate came only from data in Japan, and that would have missed emissions blown out to sea. Its says that Fukushima Daiichi radioactive releases equal 40 percent of those from the Chernobyl disaster in 1986.
A study by the French Institute for Radiological Protection and Nuclear Safety also stated that the amount of caesium-137 that flowed into the Pacific from the coastal plant is some 30 times more than was estimated by the plant’s owner, Tokyo Electric Power Co (TEPCO).
More caesium in the sea
According to the French report, an estimated an estimated 27.1 quadrillion becquerels of caesium-137 spilled into the ocean between March 21 to mid-July, Kyodo news agency reported. A quadrillion is equivalent to 1,000 trillion.
Of the amount, 82 percent had flowed into the sea by April 8, according to the study, which noted that the amount released as a result of the disaster triggered by the March 11 earthquake and tsunami was unprecedented.
The French report also said the Pacific was polluted at an exceptional speed because the plant stands in a coastal area with strong currents, though it said the impact of the contamination on marine life in remote waters is likely to wane from this autumn on.
But the institute warned that a significant degree of pollution would remain in waters off the coast of Fukushima Prefecture as caesium-137 has a half-life of around 30 years.
Norway confirms July estimates from Japan
The Norwegian study confirms general figures that were released by TEPCO and Japan’s Nuclear and Industrial Saftey Agency(NISA) in July, which also put the rate of contamination at 40 percent that of Chernobyl.
The revisions by TEPCO and NISA at that time where shocking, as NISA had held over the months since the disaster that radioactive contamination was only some 10 percent of Chernobyl.
TEPCO also confirmed at that time that Fukushima Daiichi’s reactor Nos 1,2 and 3 had experienced full meltdowns within hours of the crippling earthquake and tsunami, which left the plant with no primary, back-up or battery coolant systems.
Japan’s revelations about the scale of the disaster, some four months after the quake, cast further shadows on the nuclear establishment there, which has been show time and again to have withheld critical information.
Norwegian report zeros in on caesium
The primary difference between the figures now being released by the Norwegian Institute for Air Research and those estimates releases last July by TEPCO is that the Norwegian study focuses on caesium-137.
According to the Norwegian study, Japan had early in the summer estimated some 15,000 terabecquerels of cesium had been released into the atmosphere.
A terabecquerel is a trillion becquerels, a commonly used measure of the radiation emitted by a radioactive material.
The new report from Stohl and co-authors estimates about 36,000 terabecquerels of caesium-137 were release from March 11 through April 20. That’s about 42 percent of the estimated release from Chernobyl, the report says, according to the Associated Press.
In July, NISA had estimated that some 777,000 terabecquerels of radiation in total had been released during the first week after the March 11 disaster, but did not isolate specific isotopes. The agency had previously estimated 370,000 terabecquerels released in the first month.
The Norwegian Institute for Air Research went further to say that Japanese studies of caesium releases had not considered health implications of the caesium related radiation, according to the AP. Caesium-137 can last for decades in the environment and release cancer causing agents.
Measuring radiation a flawed science
Bellona’s executive director and nuclear physicist Nils Bøhmer has long said that putting exact figures on radiation released from Fukushima are premature.
The disaster is only now being brought under some level of control, with hopes that cold shutdown can be achieved at Fukushima Daiichi’s reactors by the end of the year.
But the site is still emitting considerable amounts of radiation.
As to fixing the disaster at 40 percent of Chernobyl, Bøhmer pointed out that that was an inexact science as Soviet era radiation reports may not have been reliable.
Most experts say that the true emissions from Chernobyl were 1.5 to 2.5 times as high as the 777,000 terabecquerels that the Soviet Union acknowledged. Assuming that the true emissions from Chernobyl were twice the official figure, the Fukushima nuclear accident has released 20 percent as much as Chernobyl, according to NISA’s July estimate.
Stohl acknowledged the difficulties of measuring radiation in an interview with AP and said emission estimates are so imprecise that finding twice the amount of cesium isn’t considered a major difference. He said some previous estimates had been higher than his.
Stohl also told the AP that his study found cesium-137 emissions dropped suddenly at the time workers started spraying water on the spent fuel pool from one of the reactors. That challenges previous thinking that the pool wasn’t emitting cesium, he said.
NISA officials contacted by Bellona on Monday said they could not yet comment on the Norwegian report because they had not reviewed it yet.
The report also says about a fifth of the cesium fell on land in Japan, while most of the rest fell into the Pacific Ocean. Only about 2 percent of the fallout came down on land outside Japan, the report concluded.
Experts have no firm projections about how many cancers could result because they’re still trying to find out what doses people received. Some radiation from the accident has also been detected in Tokyo and in the United States, but experts say they expect no significant health consequences there.
Still, concern about radiation is strong in Japan. Many parents of small children in Tokyo worry about the discovery of radiation hotspots even though government officials say they don’t pose a health risk. And former prime minister Naoto Kan has said the most contaminated areas inside the evacuation zone could be uninhabitable for decades.