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 Jay T. Cullen
The purpose of this post is to conduct a thought experiment to arrive at (I hope) a useful estimate of how much radioactive contamination might occur if North Korea detonates a thermonuclear weapon in the lower atmosphere over the North Pacific Ocean. There are a significant number of unknowns, not the least of which is the fundamental uncertainty as to whether the rogue nation has successfully tested a Teller-Ulam style thermonuclear weapon or not. I explain my assumptions and compare the resulting global release of radioisotopes that represent a radiological health concern from such a test to the amounts recently released from the Fukushima Daiichi Nuclear Power Plant (FDNPP) disaster, the Chernobyl disaster and aggregate atmospheric weapons testing in the last century. I invite comments and an accounting of the approach used here and how it might be improved. Continue reading North Korean Atmospheric Thermonuclear Test: How much contamination can we expect?
The purpose of this post is to report on a recently published, peer-reviewed study that investigated the levels of Fukushima derived contamination in migratory Pacific predators. The post is part of an ongoing effort to inform interested members of the public what the scientific community is finding about the impact of the Fukushima Daiichi Nuclear Power Plant (FDNPP) disaster on the environmental and human health. Madigan and colleagues looked for radiocesium (134Cs, half life ~ 2 years; 137Cs, half life ~30 years) in a variety of large, predatory organisms in the North Pacific Ocean between 2012 and 2015. Their results were as follows:
- Fukushima derived 134Cs could not be detected in any of the organisms with the exception of a single olive ridley sea turtle with trace levels (0.1 Bq kg-1 dry weight)
- Levels of 137Cs varied in the organisms but were generally unchanged compared with levels measured in organisms prior to the FDNPP disaster (pre-2011)
- Levels of 137Cs were roughly 10 to 100-fold lower in the organisms than levels of naturally occurring Potassium-40 (40K)
- Neither the levels of radiocesium or 40K approach levels known to represent a significant health risk to the animal or human consumers
These direct measurements of contamination levels in marine predators suggest that assuming that Pacific organisms will accumulate detectable FDNPP contamination is unwise. Similarly, anxiety and speculation about the dangers of radiocesium bioaccumulation in the face of such data seems unfounded.
Between 2012 and 2015 a total of 91 different organisms from a variety of predatory marine groups were sampled and analyzed for the presence of radiocesium contamination and naturally occurring 40K. The human made isotope 134Cs, with its relatively short ~2 year half life, serves as a fingerprint of FDNPP contamination as all other human sources are sufficiently distant in the past to have completely decayed away in the environment. Organisms sampled and their radioisotope content are reported in the following table:
With the exception of a single olive ridley sea turtle no detectable (<0.1 Bq kg-1 dry weight) trace of FDNPP 134Cs contamination was found. Levels of 137Cs found in the organisms were similar to levels measured pre-Fukushima. In addition, the 137Cs levels were less than 0.2% of US FDA levels of concern (370 Bq kg-1 wet weight) and less than 0.05% of US FDA derived intervention levels (1200 Bq kg-1 wet weight). Simply stated levels in these organisms would have to be >1600-fold higher to be designated unfit for market. The levels and ionizing radiation dose to consumers from naturally occurring 40K dwarfed those from FDNPP radiocesium. Radiocesium derived ionizing radiation doses were <1% of those from 40K. Neither the doses from 40K or cesium isotopes approached, even remotely, those known to affect the health of the organisms or consumers of these organisms.
These results are consistent with those of the Integrated Fukushima Ocean Radionuclide Monitoring (InFORM) project. Ongoing, scientifically rigorous, monitoring of the marine environment provides the best evidence with which to gauge the risk that the FDNPP meltdowns represent for marine and public health here in North America.
by Mari Yamaguchi
July 21, 2017
Originally published by the Associated Press
TOKYO (AP) — An underwater robot captured images of solidified lava-like rocks Friday inside a damaged reactor at Japan’s crippled Fukushima nuclear plant, spotting for the first time what is believed to be nuclear fuel that melted six years ago. Continue reading Possible Melted Fuel Seen for First Time at Fukushima Plant