N-plant bravehearts reach OD limit, hand over charge

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 Daiichi plant to 322 on Thursday from 180 on the previous day 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 US Nuclear Regulatory Commission safety instructor.
The permissible cumulative radiation exposure was more than doubled three days ago to extend the time nuclear workers could 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 . 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 CEO of Australian Radiation Protection and Nuclear Safety Agency. “Then you have a cascading situation.”
Workers are being ordered to leave the plant, 220km north of Tokyo, before radiation dosages reach the maximum permissible level, said a spokesman for the utility.
“Monitors have shown large radiation numbers in some places,” chief cabinet secretary Yukio Edano said at a briefing. Overall, levels aren’t high enough to be harmful, he said.
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 consultant on industrial accident. “You shouldn’t be doing that sort of work ever again.”
One plant worker was exposed to 106.3 millisieverts, Japan’s Nuclear and Industrial Safety Agency said. “A worker receiving a dose of 100 millisieverts will have a risk of serious cancer,” said Richard Wakeford, a professor of epidemiology at the University of Manchester.