Laboratories outside Japan have validated the results. Marine radioactivity levels from the nuclear disaster have fallen, but questions remain years after the meltdown. Continue reading IAEA Affirms Japan’s Fukushima-Related Radioactivity Monitoring
by WHOI Media Relations
Published 2 October 2017
Scientists have found a previously unsuspected place where radioactive material from the Fukushima Dai-ichi nuclear power plant disaster has accumulated—in sands and brackish groundwater beneath beaches up to 60 miles away. The sands took up and retained radioactive cesium originating from the disaster in 2011 and have been slowly releasing it back to the ocean.
“No one is either exposed to, or drinks, these waters, and thus public health is not of primary concern here,” the scientists said in a study published October 2 in the Proceedings of the National Academy of Sciences. But “this new and unanticipated pathway for the storage and release of radionuclides to the ocean should be taken into account in the management of coastal areas where nuclear power plants are situated.”
The research team—Virginie Sanial, Ken Buesseler, and Matthew Charette of Woods Hole Oceanographic Institution and Seiya Nagao of Kanazawa University—hypothesize that high levels of radioactive cesium-137 released in 2011 were transported along the coast by ocean currents. Days and weeks after the accident, waves and tides brought the cesium in these highly contaminated waters onto the coast, where cesium became “stuck” to the surfaces of sand grains. Cesium-enriched sand resided on the beaches and in the brackish, slightly salty mixture of fresh water and salt water beneath the beaches.
But in salt water, cesium no longer “sticks” to the sand. So when more recent waves and tides brought in salty seawater from the ocean, the brackish water underneath the beaches became salty enough to release the cesium from the sand, and it was carried back into the ocean.
“No one expected that the highest levels of cesium in ocean water today would be found not in the harbor of the Fukushima Dai-ichi nuclear power plant, but in the groundwater many miles away below the beach sands,” said Sanial.
The scientists estimated that the amount of contaminated water flowing into the ocean from this brackish groundwater source below the sandy beaches is as large as the input from two other known sources: ongoing releases and runoff from the nuclear power plant site itself, and outflow from rivers that continue to carry cesium from the fallout on land in 2011 to the ocean on river-borne particles. All three of these ongoing sources are thousands of times smaller today compared with the days immediately after the disaster in 2011.
The team sampled eight beaches within 60 miles of the crippled Fukushima Dai-ichi Nuclear Power Plant between 2013 and 2016. They plunged 3- to 7-foot-long tubes into the sand, pumped up underlying groundwater, and analyzed its cesium-137 content. The cesium levels in the groundwater were up to 10 times higher than the levels found in seawater within the harbor of the nuclear power plant itself. In addition, the total amount of cesium retained more than 3 feet deep in the sands is higher than what is found in sediments on the seafloor offshore of the beaches.
Cesium has a long half-life and persists in the environment. In their analyses of the beaches, the scientists detected not only cesium-137, which may have come from the Dai-ichi plant or from nuclear weapons tested in the 1950s and1960s, but also cesium-134, a radioactive form of cesium that can only come only from the 2011 Fukushima accident.
The researchers also conducted experiments on Japanese beach samples in the lab to demonstrate that cesium did indeed “stick” to sand grains and then lost their “stickiness” when they were flushed with salt water.
“It is as if the sands acted as a ‘sponge’ that was contaminated in 2011 and is only slowly being depleted,” said Buesseler.
“Only time will slowly remove the cesium from the sands as it naturally decays away and is washed out by seawater,” said Sanial.
“There are 440 operational nuclear reactors in the world, with approximately one-half situated along the coastline,” the study’s authors wrote. So this previously unknown, ongoing, and persistent source of contamination to coastal oceans “needs to be considered in nuclear power plant monitoring and scenarios involving future accidents.”
By Matt McGrath
17 August 2017
Originally published by BBC News
Radioactive iodine from nuclear reprocessing plants in the UK and France has been detected deep in the waters near Bermuda.
Scientists say the contaminants take a circuitous route travelling via the Arctic Ocean and down past Greenland.
Researchers believe the radioactivity levels are extremely low and present no danger.
However, scientists can use the iodine to accurately map the currents that transport greenhouse gases.
One scientific consequence that arose from the testing of nuclear bombs in the atmosphere in the 1950s was that their radioactive fallout provided a powerful global tracer of water circulation and deep-ocean ventilation.
Other sources of radioactive material for scientists to track water movements have been the nuclear reprocessing plants at Sellafield in the UK and at La Hague in France.
Contaminants have been legally released from these sites for more than 50 years. One in particular, Iodine-129 (129I), has been very useful for scientists tracing the ocean currents that help pull down greenhouse gases into the waters.
“What we have found is that by tracing radioactive iodine released into the seas off the UK and France, we have been able to confirm how the deep ocean currents flow in the North Atlantic,” said lead researcher Dr John Smith from the Bedford Institute of Oceanography, in Canada.
“This is the first study to show precise and continuous tracking of Atlantic water flowing northward into the Arctic Ocean off Norway, circulating around the arctic basins and returning to the Nordic seas in what we call the ‘Arctic loop’, and then flowing southward down the continental slope of North America to Bermuda at depths below 3000 metres.”
Scientists have used other molecules as tracers, specifically chlorofluorocarbons that were once used in refrigeration. But 129I, which has a half-life of 15.7 millions years, retains the initial imprint of its input history over a long period of time.
Another advantage for researchers is that 129I is relatively easy to detect at extremely low levels.
“In many ways this is a bit like the old ‘stick in a stream’ game we used to play as kids,” said Dr Smith.
“What people call ‘pooh sticks’ in England, where you would drop a buoyant object in the water and observe where it comes out. Of course, it would be much better if these markers were not in the ocean at all, but they are, and we can use them to do some important environmental science.”
This new study is part of an international project called GEOTRACES that uses geochemical markers to follow ocean currents.
The scientists say that 129I has been measured as far south as Puerto Rico, but the expectation is that it will continue to flow southward into the South Atlantic and eventually spread throughout the global ocean.
“The advantage of using 129I as a transient tracer in oceanography is the long half-life of this isotope compared to the circulation times, and the fact that it is largely soluble in seawater,” said Dr Núria Casacuberta Arola from ETH, Zurich, who wasn’t involved with the study.
“Now, major efforts are also devoted to find other artificial radionuclides with similar sources and behaviour than 129I so that the more tools we have, the better we will understand the ocean circulation.”
The research has been presented at the Goldschmidt2017 conference in Paris.
In June 2013, Steve Fradkin hiked the rugged coast of Washington State’s Olympic National Park to count the stars. In the summertime, the lowest tides expose the slippery rocks of the intertidal zone from daybreak until noon. Perfect conditions for spotting Pisaster ochraceus, the five-armed purple, orange and red sea stars common to Pacific waters along the western edge of the United States. Continue reading The wasting of the stars: A look into the largest ocean epidemic in recorded history
After my tour at the University of Ottawa, the day continued with a tour of the Radiation Protection Bureau facilities over at Health Canada on the south side of the city. After clearing through security, Drs. Jean-Francois Mercier and Michael Cooke, showed Cole and I around the lab spaces that are used by the Canadian Radiological Monitoring Network and where InFORM samples are run. Continue reading An InFORMal Gathering – Part 2