More workers were drafted for the frontline of Japan’s biggest nuclear disaster as radiation limits forced Tokyo Electric Power Co. to replace members of its original team trying to avert a nuclear meltdown.
The utility increased its workforce at the Fukushima Dai- Ichi plant to 322 yesterday from 180 on March 16 as it tried to douse water over spent nuclear fuel rods to prevent them melting and leaking lethal radiation. Levels beside exposed rods would deliver a fatal dose in 16 seconds, said David Lochbaum, a nuclear physicist for the Union of Concerned Scientists and a former U.S. Nuclear Regulatory Commission safety instructor.
The permissible cumulative radiation exposure was more than doubled three days ago to extend the time nuclear workers could legally spend onsite. Radiation was measured at 20 millisieverts per hour near the site’s administration building, Hikaru Kuroda, the utility’s maintenance chief, told reporters today. An hour’s exposure there would equate to the most workers are typically allowed in one year, frustrating efforts to cool nuclear fuel.
“The risk is that material will be released, and the dose rates around the vicinity of the reactor buildings will be so high that the workers will not be able to get in there and do anything,” said Peter Burns, former chief executive officer of the Australian Radiation Protection and Nuclear Safety Agency. “Then you have a more or less cascading situation.”
Workers are being ordered to leave the plant, located 135 miles (220 kilometers) north of Tokyo, before radiation dosages reach the maximum permissible level, said a spokesman yesterday for the utility who declined to give his name.
“Monitors have shown large radiation numbers in some places,” Chief Cabinet Secretary Yukio Edano said at a briefing today. Overall, levels aren’t high enough to be harmful, he said.
Radiation exposure levels are measured in millisieverts. Exposure totaling 100 millisieverts over a year is the lowest level at which any increase in cancer is evident, according to the World Nuclear Association in London. The cumulative maximum level for nuclear workers was increased to 250 millisieverts from 100 millisieverts by Japan’s health ministry on March 15.
“Once they have reached that limit, they can’t go in the plant anymore,” said John Price, a Melbourne-based consultant on industrial accidents and former safety policy staffer at the U.K.’s National Nuclear Corp. “You shouldn’t be doing that sort of work ever again,” Price said by phone yesterday.
“A worker receiving a dose of 100 millisieverts from these emergency operations will have a future risk of a serious cancer from this dose of less than 1 percent,” said Richard Wakeford, a professor of epidemiology at the University of Manchester’s Dalton Nuclear Institute in the U.K. That compares with a risk of dying from cancer in the absence of this radiation exposure of about 20 to 25 percent, Wakeford said in an e-mail today.
Nine Tokyo Electric employees and eight subcontractors suffered exposure to their face not requiring hospital treatment, two policemen needed radiation decontamination, and some firemen exposed to radiation are under investigation, the International Atomic Energy Agency said on its website yesterday.
Control Room Evacuated
Operators evacuated a central control room for about 45 minutes on March 16 amid concerns that a containment vessel at the plant’s reactor No. 3 was damaged and leaking radiation, the agency said. Two employees who were wearing full-face masks in the main control room complained of discomfort and were taken to the plant’s industrial doctor, according to the report.
“The fact they were evacuated means that they were getting very high surges of doses that were just too high to permit them to keep working,” said Evan Douple, associate chief of research at the Radiation Effects Research Foundation in Hiroshima.
Releases of radiation so far have been localized and in the immediate vicinity of the plant, Gerry Thomas, chair in molecular pathology at London’s Imperial College, said March 16 in a telephone interview.
“They are pulling the workers back if they think there is going to be a spike, which is a sensible precaution,” said Thomas, who studied the aftermath of the 1986 nuclear disaster at Chernobyl, Ukraine. “It doesn’t mean that anything nasty would happen to them if they were still there. If you can avoid getting a radiation dose, you avoid it.”
About 200,000 people from across the former Soviet Union were involved in the recovery and clean-up of Chernobyl in 1986 and 1987, receiving average radiation doses of about 100 millisieverts, according to the World Nuclear Association.
The highest doses were received by about 1,000 emergency workers and onsite personnel during the first day of the accident, when radiation doses rose as high as 20,000 millisieverts. Twenty-eight workers died of acute radiation syndrome within a few weeks, the association said on its website.
Control-room workers in Fukushima would be wearing full- length overalls and face masks that probably use a carbon filter or bottled oxygen supply to prevent the inhalation of contaminated particles, consultant Price said.
Radiation reached 400 millisieverts per hour on March 15 at the plant’s No. 3 reactor. The exposure limit for a nuclear industry employee is 20 millisieverts a year, averaged over five years, according to the nuclear association.
“What we are seeing now is, really, heroics,” said Seth Grae, chief executive officer of Lightbridge Corp., a nuclear consultancy in McLean, Virginia.
The on-site team is likely foregoing sleep and food, and working with minimal light as levels of radiation rise, according to Gennady Pshakin, a former International Atomic Energy Agency official.
“They are like the Spartans, standing up against all that’s thrown against them,” said Pshakin, who has worked in the nuclear industry for 40 years, referring to the people of ancient Greece who fended off military attacks for centuries. “They are probably working on thin air,” he said by phone from Obninsk, the site of the world’s first nuclear power plant.
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