In the last two days, workers monitoring radiation levels at Japan’s Fukushima Daiichi nuclear power plant have detected “hot spot” areas on the site, where pockets of air contain such high doses that standing in those spots for an hour would result in acute poisoning and likely lead to death within weeks.
Thankfully, the workers who detected the danger zones where radiation exceeded 10 sieverts per hour, did so quickly.
"Three plant workers were exposed to a dosage of four millisieverts while they were monitoring radiation," a Tokyo Electric Power Company spokeswoman told AFP. "We are still checking the cause of such high levels of radioactivity." Four millisieverts is the typical background radiation most people living in a city receive in a year.
A handout from TEPCO, distributed through Reuters, shows a gamma ray image of the location of where the workers detected the first known hot spot: at the base of a ventilation shaft between the power plant’s No. 1 and No. 2 reactors. TEPCO reported measurements of over 10 sieverts (10,000 millisieverts) per hour at the base of the vent on Monday afternoon. On Wednesday TEPCO announced another site, on the floor inside reactor No. 1, had been found with 5 sieverts (5,000 millisieverts) of radiation per hour, the Associated Press reported.
A monitoring map from August 3 (above) showed that other areas around the site had levels no higher than 2015 microsieverts or about .002 sieverts per hour. [NOTE CORRECTION: the readings in the monitoring map are not in millisieverts as was mistakenly first reported].
TEPCO, says that the areas are restricted and have been cordoned off. They are currently considering shielding as a countermeasure.
Nuclear engineer Gary Was of the University of Michigan told CNN that the gamma-ray camera should help identify if radioactivity resulted from reactor waste products, bits of nuclear fuel or both. He suggested that the location of the hot spot at the base of the emergency ventilation shaft makes it likely that the radioactive material came from air and steam released to relieve pressure inside the reactors during the meltdowns and channeled through the air system filters.
"As they were venting, either intentionally or unintentionally, the building air was being sent through filters," Was said. Those filters may have been concentrating radioactive particles "into one spot," he said.
IMAGE 1: Gamma-ray imagery showing the bottom of a ventilation stack standing between Fukushima Daiichi nuclear power plant's No. 1 and No. 2 reactors, where radiation exceeding 10 sieverts (10,000 millisieverts) per hour was found as shown in red. (Courtesy of Yoshikazu Nagai, TEPCO)
IMAGE 2: Map of the Fukushima-Daiichi Nuclear Power Plant (TEPCO).
IMAGE 3: Map from the status report of the radiation dose measured on Aug 3, 2011 at 9 pm local time (TEPCO).
IMAGE 4: The troubled Fukushima-Daiichi Nuclear Power Plant off the coast of Japan as seen from south of the plant. (Photo by Toshifumi Tanuichi/Getty Images)
Tags: Earthquakes, Engineering, Nuclear Accidents, Nuclear Science, Tsunami
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