How dangerous are the levels of radioactivity?
Having initially reported high levels of radiation - of about 100 milliSieverts per hour near the leaked water within the moat - officials had to concede later that the equipment used to take the readings had an inadequate scale. When newer equipment was brought in, it was established that the levels of beta radiation had actually been 18 times higher. Subsequent readings have been up to as much as 2,200mSv per hour. While still extremely high, experts say that, properly protected, workers can still operate in such an environment.
"What is vital is whether this is beta or gamma radiation; the Japanese nuclear watchdog has said the radiation is beta," says Prof Paddy Regan, at the University of Surrey, UK. "Workers can get close to the source of beta radiation without a significant radiological hazard, because the beta particles lose their energy in the air (radioactivity lost after about 10cm) and assuming the source is not airborne. As long as the radioactive particles are not deposited on the skin, inhaled or ingested, the hazard is much smaller than if the radiation had been for a whole body gamma ray exposure of the same dose."
And although the public understandably finds any talk of radioactivity alarming, the overall emissions at Fukushima need to be kept in some perspective. According to Dr Ken Buesseler, senior scientist at the Woods Hole Oceanographic Institution, US, the release of the radioactive element caesium from Fukushima, for example, is between a 10th and a third of what was released from the accident in Chernobyl, and perhaps one fortieth of what was released by the hundreds atmospheric nuclear bomb tests in the last century.
How does Fukushima's location exacerbate the water problems?
There are steep hills behind the Fukushima plant. Rainwater runs down from those hills, through the ground on which the plant is built and out into the ocean. Radioactivity readings offshore have not fallen in the way many experts say they should have, indicating that this groundwater is picking up radioactive elements on its journey. Tepco is working on a series of plans to stop more radioactive water getting into the ocean, including erecting steel barriers and injecting chemicals into the earth to create an impermeable layer.
What is the eventual solution to the stored water issue?
Tepco has changed its inspection protocols for the storage tanks and claims this should pick up any future problems much earlier. But given the huge volumes of water being handled at the site, it is likely that Tepco will have to introduce bigger, more robust storage tanks at some point - similar in scale to the crude oil depot tanks for which there is good local technology in Japan. The water itself needs to be filtered, to take out the most radioactive elements. This "cleaned" water is likely then to go into the Pacific. Even before then, such is the volume of contaminated cooling water coming out of the reactors that Tepco may be forced simply to release some water unfiltered into the ocean.
