By Jeremy Hsu, LiveScience Contributor:[1]


A radioactive plume of water in the Pacific Ocean from Japan's Fukushima nuclear plant, which was crippled in the 2011 earthquake and tsunami, will likely reach U.S. coastal waters starting in 2014, according to a new study. The long journey of the radioactive particles could help researchers better understand how the ocean’s currents circulate around the world.


Ocean simulations showed that the plume of radioactive cesium-137[2] released by the Fukushima disaster[3] in 2011 could begin flowing into U.S. coastal waters starting in early 2014 and peak in 2016. Luckily, two ocean currents off the eastern coast of Japan — the Kuroshio Current and the Kuroshio Extension — would have diluted the radioactive material so that its concentration fell well below the World Health Organization’s safety levels[4] within four months of the Fukushima incident. But it could have been a different story if nuclear disaster struck on the other side of Japan.


“The environmental impact could have been worse if the contaminated water would have been released in another oceanic environment in which the circulation was less energetic and turbulent,” said Vincent Rossi, an oceanographer and postdoctoral research fellow at the Institute for Cross-Disciplinary Physics and Complex Systems in Spain.


Fukushima’s radioactive water release has taken its time journeying across the Pacific. By comparison, atmospheric radiation from the Fukushima plant began reaching the U.S. West Coast within just days of the disaster back in 2011. [Fukushima Radiation Leak: 5 Things You Should Know[5] ]


Tracking radioactivity’s path


The radioactive plume has three different sources: radioactive particles falling out from the atmosphere into the ocean, contaminated water directly released from the plant, and water that became contaminated by leaching radioactive particles from tainted soil.



The release of cesium-137[6] from Fukushima in Japan’s more turbulent eastern currents means the radioactive material is diluted to the point of posing little threat to humans by the time it leaves Japan’s coastal waters. Rossi worked with former colleagues at the Climate Change Research Centre at the University of New South Wales in Australia to simulate the spread of Fukushima’s radioactivity in the oceans — a study detailed in the October issue of the journal Deep-Sea Research Part 1.


Researchers averaged 27 experimental runs of their model — each run starting in a different year — to ensure that the simulated spread of the cesium-137 as a "tracer" was not unusually affected by initial ocean conditions. Many oceanographers studying the ocean’s currents prefer using cesium-137 to track the ocean currents because it acts as a passive tracer in seawater, meaning it doesn't interact much with other things, and decays slowly with a long half-life of 30 years.


“One advantage of this tracer is its long half-life and our ability to measure it quite accurately, so that it can be used in the future to test our models of ocean circulation and see how well they represent reality over time,” Rossi told LiveScience. “In 20 years' time, we could go out, grab measurements everywhere in the Pacific and compare them to our model.”


Journey across the Pacific Rim


The team focused on predicting the path of the radioactivity until it reached the continental shelf waters stretching from the U.S. coastline to about 180 miles (300 kilometers) offshore. About 10 to 30 becquerels (units of radioactivity representing decay per second) per cubic meter of cesium-137 could reach U.S. and Canadian coastal waters north of Oregon between 2014 and 2020. (Such levels are far below the U.S. Environmental Protection Agency’s limits for drinking water.)


By comparison, California’s coast may receive just 10 to 20 becquerels per cubic meter from 2016 to 2025. That slower, lesser impact comes from Pacific currents taking part of the radioactive plume down below the ocean surface on a slower journey toward the Californian coast, Rossi explained.


A large proportion of the radioactive plume from the initial Fukushima release won't even reach U.S. coastal waters anytime soon. Instead, the majority of the cesium-137 will remain in the North Pacific gyre — a region of ocean that circulates slowly clockwise and has trapped debris in its center to form the “Great Pacific Garbage Patch[7] ” — and continue to be diluted for approximately a decade following the initial Fukushima release in 2011. (The water from the current power plant leak would be expected to take a similar long-term path to the initial plume released, Rossi said.)


But the plume will eventually begin to escape the North Pacific gyre in an even more diluted form. About 25 percent of the radioactivity initially released will travel to the Indian Ocean and South Pacific over two to three decades after the Fukushima disaster, the model showed.


You can follow Jeremy Hsu on Twitter @jeremyhsu . Follow us @livescience , Facebook & Google+ . Original article on LiveScience. [8] [9] [10] [11] [12]



Copyright 2013 LiveScience[16] , a TechMediaNetwork company. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.



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  • In this combination photo, Tayo Kitamura, 40, kneels in the street to caress and talk to the wrapped body of her mother Kuniko Kitamura, 69, after Japanese firemen discovered the dead body in the ruins of her home in Onagawa, Japan, on March 19, 2011, top, and a newly built home sits at the site of the now-cleared but destroyed area on Wednesday, Feb. 22, 2012. (AP Photo/David Guttenfelder)




  • A few homes have been rebuilt in the year since an earthquake and tsunami roared across Japan's coastline, killing 19,000 people. But most communities remain unrecognizable, and their residents' futures uncertain. (AP Photo/David Guttenfelder)




  • The tsunami that slammed into Japan's coastline one year ago was merciless, sparing little in its path. Homes were reduced to rubble, cars tossed about like toys, and boats -- such as this one photographed in Kesennuma, Japan, on March 28, 2011 -- flung from the sea into streets and onto roofs. The ocean's fury, and the earthquake that preceded it, left around 19,000 people dead, hundreds of thousands homeless, and sparked the worst nuclear crisis the world had seen in a quarter century. (AP Photo/David Guttenfelder)




  • In this combination photo, Japanese vehicles pass through the ruins of the leveled city of Minamisanriku, Japan, on March 15, 2011, top, four days after the tsunami, and vehicles pass through the same area on Thursday, Feb. 23, 2012. (AP Photo/David Guttenfelder)




  • The earthquake and tsunami, which killed around 19,000 people, delivered one of their worst hits to the once-scenic, blue-collar fishing town of Minamisanriku, Japan, photographed here on March 15, 2011. The wall of water spared little in its path, sweeping away nearly every business and every job, and leaving more than half the town's residents dead or homeless. (AP Photo/David Guttenfelder)




  • A year after the earthquake and tsunami people across Japan and leveled this town, there are hints of progress _ the main roads are free of debris, and some temporary houses have been built. But many in Minamisanriku, and elsewhere across Japan's battered coastline, remain in a hellish state of limbo. (AP Photo/David Guttenfelder)




  • In this combination photo, a ship washed away by the tsunami sits in a destroyed residential neighborhood in Kesennuma, northeastern Japan, on March 28, 2011, top, and the same ship sits on the same spot on Thursday, Feb. 23, 2012. (AP Photo/David Guttenfelder)




  • A year after an earthquake and tsunami ravaged the country's coastline and killed around 19,000 people, many of the boats carried inland by the wall of water have been removed. But some, like this one, remain _ providing a stark reminder of nature's fearsome power. (AP Photo/David Guttenfelder File)




  • One year later, more than 3,200 people presumed killed in the earthquake and tsunami have yet to be found. They are among the 19,000 people who lost their lives on March 11, 2011. (AP Photo/David Guttenfelder)




  • In this combination photo, Japanese residents of Kesennuma, northeastern Japan, pass through a road that was cleared by bulldozer through the ruins of the city on March 17, 2011, six days after the tsunami, top, and people cross the same street on Thursday, Feb. 23, 2012. (AP Photo/David Guttenfelder)




  • In the days after the earthquake and tsunami ravaged Japan's coastal towns, the bulldozers began to arrive, clearing away the rubble that littered the roads, such as this street in Kesennuma, Japan, photographed on March 17, 2011. Those tasked with clearing away the wreckage faced a monstrous task: towering piles of twisted metal and wood, boats perched atop roofs, mountains of family heirlooms, sodden furniture and children's toys. They also faced the grim reality that many of the 19,000 people killed lay entombed in the rubble, waiting to be discovered. (AP Photo/David Guttenfelder)




  • One year after a powerful tsunami battered Japan and killed around 19,000 people, the streets have been cleared and the wreckage removed from town centers. But the process of destroying all that debris has been slow, with much of it still sitting in huge mountains in temporary holding areas. (AP Photo/David Guttenfelder)




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