nuclear-news

The distinctive “fingerprint” of the Fukushima radiation fallout

The real fallout from Fukushima, Maclean’s  Colby Cosh January 8, 2015 On the verge of the new year, scientists from the federal Department of Fisheries and Oceans issued the first systematic report of measurements on the spread of radioactive seawater from Japan’s damaged Fukushima nuclear reactor to the coast of British Columbia. …….Accurate measurements of the Fukushima plume are possible because humans wisely stopped testing nuclear weapons in the atmosphere in 1980. There is still a “fallout background” of radiation lingering in the world’s oceans from these nuclear tests—and, of course, from those two nuclear explosions that did not quite have the character of tests. But every kind of radioactive isotope has a different rate of decay, usually expressed as a “half-life,” and the short-lived ones from nuclear testing are all gone.

This means that the 2011 Fukushima disaster left a distinctive “fingerprint” of fast-decaying radioactives that cannot be attributed to any other source. So that’s what the scientists measuring the plume look for—fanning out between Vancouver Island and Japan on Canadian Coast Guard oceanographic vessels, gathering up seawater from various depths, and pumping it through ion exchangers to extract the telltale radioactive cesium that spewed out of the damaged reactor.

In 2011, the measurements along the B.C.-Japan line looked just like usual. But the levels of cesium-134, which can only have come from Fukushima, suddenly increased about 1,500 km off the continental shelf when samples were taken in 2012. In 2013 the “fingerprint” of Fukushima seems to have reached the shelf itself.

Cesium-134 degrades fast. What physicists and doctors have been concerned about is the equal amount of cesium-137 spilled at Fukushima: that isotope has a half-life of 30 years, so most of whatever reaches B.C. now will be around for a while. The radiation emitted by the fallout background—the cesium-137 presently left in the ocean by past nuclear testing—works out to about one becquerel per cubic metre of seawater. That figure has now doubled. The total peak level of ocean radioactivity off Canada’s Pacific Coast is expected to reach somewhere between three to five becquerels per cubic metre before beginning to drop back down……..

Overall, the authors of the paper expect the Fukushima plume to make B.C. ocean water as radioactive as it was in the 1980s…….

January 10, 2015 - Posted by Christina Macpherson | 2 WORLD, oceans, radiation