Error in Study Suggests Fukushima Releases Greater Than Chernobyl

By Jay T. Cullen

Distribution of soil activity concentration due to 134Cs and 137Cs within 80 km of the Fukushima Daiichi nuclear power plant. Considering radioactive decay, the activity concentrations in the graph were corrected to July 2, 2011 From Koo et al. (2014)

The purpose of this post is to address an error in a recently published review of current release estimates from the Fukushima Dai-ichi nuclear power plant disaster that began in March 2011. The post is part of an ongoing effort to communicate results of scientific studies aimed at understanding the impact of Fukushima on the health of the North Pacific and residents of the west coast of North America. In a recent review paper published in Progress in Nuclear Energy by Koo and colleagues this July, compiled estimates of atmospheric and ocean releases from Fukushima were presented. Due to an error in interpretation they suggest that direct ocean releases were a factor of 4 greater than atmospheric releases of radiologically significant isotopes like 131-I (~8 day half life) and 137-Cs (~30 year half life). This error inflates release estimates and has been reported on to suggest Fukushima releases exceed Chernobyl’s. Accurate estimates of releases from Fukushima suggest that they are about an order of magnitude less than those from Chernobyl in 1986.


The study of Koo and others (link to a ResearchGate upload) estimated atmospheric releases of 131-I, 137-Cs and the noble gas 133-Xe (half life ~ 5 days) from the Fukushima Dai-ichii nuclear power plant. Their estimates compared with previously published estimates are reported in the following table (Table 2 from paper):

Summary of source terms released into the atmosphere from units 1–3. Koo et al. (2014)

Similar to previous work, for example, they estimate the atmospheric release of 137-Cs from the plant to be 10-50 PBq or somewhere between 3 and 17 kg of the isotope. Given the core inventories of reactors 1-3 this release represents about 4% of the inventory at the time of the meltdowns in March 2011.

The authors make a significant error when they begin their estimate of direct releases from Fukushima to the ocean when they state the following in section 2.2.2. Release from the primary system into the sea:

It is reported that, of the total radioactivity released from the units 1–3 into the environment, more than 80% of it flowed into the sea (Hoeve and Jacobson, 2012 and Christoudias and Lelieveld, 2013), implying that 4 times more radioactivity was released to the sea than to the atmosphere.

Bolds are mine. In stating that 80% of the total radioisotope releases flowed into the sea they fundamentally misinterpret the studies they cite. What the study of Christoudias and Lelieveld (2013), and other studies not referenced here in the diary, actually show and establish is that (quoting from the Christoudias and Lelieveld work):

We calculated that about 80% of the radioactivity from Fukushima which was released to the atmosphere deposited into the Pacific Ocean.

This is a fundamentally different than the interpretation Koo and colleagues use in their study. By wrongly interpreting that atmospheric releases represent 20% of the total release they assume that direct ocean releases are 4 fold greater than the 4% of core inventories (10-50 PBq) or 16% of core inventories of 137-Cs in March 2011. This error greatly increases the estimated total releases from the plant (atmosphere + direct ocean).

It is very likely that this incorrect approach will lead others to conclude that total releases from Fukushima are greater than those from Chernobyl. For example a back of the envelope calculation assuming the 4% of the total core inventory of 137-Cs (760-820 PBq according to the table above) was released to the atmosphere and 16% to the ocean would lead to a total release of ~152-164 PBq. Such a calculation was done by a popular news aggregator and editorial site that has a history of misinterpreting and misinformation the public about Fukushima. This estimate, not surprisingly, is at great odds with existing estimates based on measurements and modeling.

Best estimates to date suggest that:

1. atmospheric releases of 137-Cs were 19.4 +- 3.0 PBq through the end of March 2011
2. direct ocean discharge of 137-Cs to the Pacific in addition to atmospheric deposition are in the range 2.3 to 26.9 PBq
3. About 19.5 +- 5% of releases were deposited to land while about 80% ended up in the Pacific Ocean

A report reviewing the most recent peer reviewed studies which reaches these conclusions was summarized in a post here.

Releases of isotopes that represent potential radiological health threats given their respective total activities and/or their significant half lives (e.g. 131-I and 137-Cs) were about an order of magnitude (factor of 10 times) lower than the releases from the Chernobyl disaster in 1986 (see reports here and here for example). More and more observations are being made globally by the international scientific community which will help to improve source term and release estimates. I will report on these studies as the data becomes available.

I have contacted the authors to bring their attention to this problem with their study.

Kelp Watch 2014 Update: No Fukushima Derived Radiocesium Detected in West Coast Kelp

By Jay T. Cullen

Dan Harrison, Executive Director of InFORM partner organization Raincoast Education Society (http://raincoasteducation.org/) sampling kelp for Kelp Watch 2014 in Tofino, BC Canada.

The most recent results of Kelp Watch 2014 , a program dedicated to monitoring for the presence of Fukushima sourced radionuclides off our Pacific Coast, are reported in this post. This post is the latest contribution to a series dedicated to the dissemination of information about the impacts of the Fukushima Dai-ichi disaster on the North Pacific Ocean ecosystem and on North American public health. New results from the second sampling period (June to August 2014) of Kelp Watch 2014 were just released and can be found here. As with previously reported results here and here no radioactive isotopes from Fukushima were detected in kelp growing at sampling sites spread across the eastern Pacific coast. However, significant quantities of the short lived radioisotope 131-Iodine (half life ~8 days) continued to be found in Los Angeles County and San Diego in southern California. Rather than being transported across the Pacific these isotopes were likely released locally in waste water that carries significant 131-I because of its application in nuclear medicine to treat thyroid maladies. The absence of 134-Cs in kelp suggest that ocean transport of Fukushima contamination has yet to reach North American coastal water.


Kelp Watch 2014 is a joint initiative between Dr. Steven Manley (Department of Biological Sciences, California State University- Long Beach) and Dr. Kai Vetter (UC Berkeley and Lawrence Berkeley National Laboratory). The program involves the analysis of kelp samples collected by citizen-scientists along the Pacific coast for Fukushima derived radioisotopes. Because of their sedentary existences and propensity to concentrate isotopes in their tissues kelp are useful sentinel organisms with which to monitor the timing and extent of the Fukushima impacted plume of seawater as it progressively affects more of the North American west coast.

Samples were collected June to August of this year at various sampling locations along the coast with some kelp obtained from Chile and Tasmania (where little Fukushima impact is expected) to serve as reference locations.

Stations where samples of kelp were obtained for Kelp Watch 2014

Full results for the second sampling period can be found here along with details about the goals and approach of Kelp Watch 2014.

Because of its relatively short half life of ~2 years radioactive 134-Cs serves as a useful tracer of Fukushima impact as it was released in significant quantities, with many other isotopes, into the environment after the disaster in March 2011. All other legacy sources of the human produced isotope have occurred far enough in the past that any 134-Cs present in the environment faithfully reflects release from Fukushima. Similar to previous work by this program all samples of kelp collected from the Pacific by Kelp Watch 2014 in June to August of this year had no detectable (detection limit ~ 0.04 Bq/kg dry weight of kelp) levels of 134-Cs suggesting that isotopes from Fukushima are not significantly affecting radioisotope activities in these organisms to date.

The authors summarize findings about 134-Cs and its longer lived cousin 137-Cs (half life ~30 yr) as follows:

Cesium-137 was detected in all West Coast samples at very low levels. This isotope is still detectable in the marine environment due to above-ground nuclear weapons testing that took place mostly in the 1950s and 1960s. The very low limits set on the shorter-lived Cesium-134 mean that the Cs-137 cannot be directly tied to the Fukushima releases and is more likely due to these “legacy” sources.

Significant Iodine-131 (131-I, half life ~8 days), which can represent a significant radiological health risk given its propensity to concentrate in the thyroid gland and induce cancer, activities continue to be detected (up to 251 Bq/kg at Long Beach CA) in southern California kelp samples. This 131-I is not likely from Fukushima given that ocean transport is quite slow relative to 131-I decay. Kelp Watch 2014 attributes the presence of 131-I to local sources which are likely waste water inputs to the coastal ocean that contains 131-I from nuclear medical applications in hospitals and clinics in the area.

Ongoing monitoring of seawater and marine organism activity concentrations of radioisotopes from Fukushima will help to determine the likely impacts on the ecosystem and public health along North America’s Pacific coast resulting from the disaster. As always, I will report new results as they are made available and we look forward to more work from this quality monitoring program.

Sampling Event in Victoria this Wednesday Oct. 15 at 4PM Ogden Point Breakwater: Calling all citizen scientists

Happy Thanksgiving everyone.  The InFORM team is calling all interested citizen scientists in Victoria to attend the first seawater sampling event this coming Wednesday, Oct. 15 at the Ogden Point Breakwater at 4PM (map shown below).  We will meet at the Breakwater entrance and talk informally about the project and go through a quick sampling orientation followed by grabbing some seawater for radioisotope analysis.  If the mood strikes you can stay for a drink and socialize at the Breakwater Bistro afterwards to meet fellow volunteers.  If you can make it this Wednesday please indicate so on the poll below.  If you can’t attend this event it does not mean that you will not be involved in the project.

Breakwater copy

Powell River Peak Covers the InFORM Project

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Link to the article here

Seawater testing project ramps up
Citizen scientists aid in tracking coastal radiation
by Chris Bolster | reporter@prpeak.com

Published: Wednesday, October 8, 2014 12:42 PM PDT
A seawater testing project on BC’s coast is ramping up to record the arrival of Japanese radiation leaked into the sea from the Fukushima Daiichi nuclear power plant disaster.

On March 11, 2011, the plant on the north east coast of Japan was hit by a tsunami triggered by a 9.0 magnitude earthquake. Three of the six nuclear reactors at the plant went into meltdown and a day later started to leak radioactive material into the Pacific Ocean. It is known as the largest nuclear incident since Chernobyl in 1986.

Dr. Jay Cullen is a chemical oceanographer at the University of Victoria who is leading the three-year project.

Starting this month, Cullen and his team will be coordinating about 600 citizen scientist volunteers in 14 coastal communities who will be collecting seawater samples monthly to send to the lab.

“The project itself is building on the success of more modest testing programs the Department of Fisheries and Oceans (DFO) and Health Canada have been carrying out since the triple meltdown at Fukushima Daiichi in March 2011,” said Cullen.

DFO and Dr. John Smith have been making measurements in the north east Pacific and the Arctic oceans looking for radionuclides from Fukushima in seawater, he said.

Cesium-137, a signature isotope of Fukushima, was first detected about 1,500 kilometres offshore in 2012. In June 2013 it was detected off the west coast of Vancouver Island.

Cullen’s project will track the arrival of the plume of contaminated seawater being transported on North Pacific ocean currents.

“It’s to track its arrival and look for the maximum activities of these isotopes which will dictate what the risk is to the public,” Cullen said, adding that estimates suggest peak levels will reach BC during the next three years.

Scientist have measured low levels of radioactive material in seawater for decades.

“If you look at the activity of some of the isotopes which present the greatest health risks like Cesium-137 or Strontium-90 those levels peaked in the mid-1960s as a result of weapons testing,” said Cullen.

Currently there is only a slight trace of the chemicals from the disaster, he said.

“If you lived here in the 1970s or 80s the radioactivity of seawater and fish was likely greater than what we expect to be resulting from Fukushima,” he added.

Readers interested in the most recent scientific studies on the radiation-contaminated seawater or more information on the project, can visit Cullen’s blog or the study’s website.

Update on Fukushima Plutonium Releases to the Pacific Ocean

By Jay T. Cullen

This post reports on the most recent study of plutonium releases from Fukushima to the Pacific Ocean. The post contributes to an ongoing effort to report peer-reviewed studies on the impact of the triple meltdowns at the Fukushima Dai-ichii nuclear power plant on the health of the Pacific ecosystem and residents of the west coast of North America. Plutonium is an alpha-emitting isotope that carries significant radiological health risks if internalized with risk of exposure increasing with the activity of Pu isotopes in the environment. Previous work indicates that 239,240-Pu releases from Fukushima were about 100,000 and 5,000,000 times lower than releases from the Chernobyl disaster in 1986 and 20th century weapons testing respectively. Initial measurements of Pu isotopes in seawater and marine sediments off the coast from Fukushima indicated no detectable change occurred in Pu inventories in the western Pacific after the disaster. More recent and more expansive work supports earlier studies drawing the conclusion that up to two years after the accident the release of Pu isotopes by the Fukushima accident to the Pacific Ocean has been negligible.


A paper by Bu and colleagues was recently published in the peer-reviewed journal Environmental Science and Technology which investigated the activity of Pu isotopes marine sediments collected within 30 km of the Fukushima reactor sites. 239,240,241-Pu and radiocesium isotopes (134-Cs and 137-Cs) were measured. Given that Pu is a particle reactive element that would tend to be concentrated in sediments such measurements should help to determine the extent and degree of Fukushima derived Pu in the marine environment. Sample collection sites are indicated in the map below.

Map showing the locations for (a) sediment samples collected within the 30 km zone around the FDNPP site and (b) sediment samples collected outside the 30 km zone around the FDNPP site in previously published studies by Bu and colleagues.

Relatively high activities of 134-Cs and 137-Cs and a decay corrected ratio near 1 indicated that the sediments were indeed contaminated with Fukushima derived radionuclides.

137-Cs activities and 134-Cs/137-Cs activity ratios in the marine sediments (decay corrected to 15 March 2011) determined by Bu et al. 2014. The blue dashed line represents the 134Cs/137Cs activity ratio fingerprint of the radiocesium released by the Fukushima disaster.

In contrast to the clear imprint of Fukushima derived Cs on the marine sediments the activities of 239,240-Pu and 241-Pu were low compared with the background level before the accident. The Pu activity ratios (240-Pu/239-Pu and 241-Pu/239-Pu) suggested that the Pu detected was the result of global fallout and the pacific proving ground (PPG) close-in fallout resulting from atmospheric weapons testing in the 20th century. The following figure is a mixing diagram that helps to determine the relative contributions to the observed Pu contamination of marine sediments off the Japanese coast.

Mixing plot of 241-Pu/239-Pu atom ratio vs 240-Pu/239-Pu activity ratio in Fukushima sediments compared with Pu compositions of global weapons fallout, Fukushima release, and the Pacific Proving Ground weapons fallout. The closed orange circles (soil and litter samples) and closed black circles (aerosol samples) represent the Fukushima source; the closed pink circle represents the global weapons test fallout; the closed blue circles represent the surface sediment samples collected outside the 30 km zone; the open black circles represent sediment samples within 30 km of the Fukushima site; the closed violet circle represents Sagami Bay sediment samples; the closed wine colored circles represent Pacific Proving Ground source.

The mixing diagram indicates that the isotopic ratio of Pu in marine sediments is inconsistent with a significant release of Fukushima Pu to the marine environment. The isotopic composition of Pu in marine sediments is consistent with Pu deposited during atmospheric weapons testing in the last century.

While initial releases from the plant and ongoing releases due to groundwater infiltration and terrestrial runoff have been negligible thus far according the authors they rightly point out that significant inventories of Pu are insecurely stored at the Fukushima site. So far estimates suggest that about 2.3×10^9 Bq of 239,240-Pu or 580 milligrams of the isotopes have been broadcast to the environment from Fukushima. Bu et al. (2014) estimate that contained within the roughly 270,000 tons of radioactive liquid waste stored in large tanks at Fukushima there exists approximately a further 1×10^8 Bq of 239,240-Pu. Given that future earthquakes or other events could mobilize this Pu, continued monitoring of Pu isotopes in the marine environment is necessary and prudent.

Release, Dispersion and Fate of Radioactive Strontium From Fukushima in the Northwest Pacific Ocean

By Jay T. Cullen

The purpose of this diary is to summarize recent models and measurements of the release of strontium-90 (90-Sr, half life 28.8 yr) to the ocean resulting from the triple meltdowns at the Fukushima-Daiichi nuclear power plant in March 2011. This post is part of an ongoing series aimed at understanding the impact of the disaster on the North Pacific Ocean and residents of the west coast of North America. 90-Sr is a beta-emitting element that is a radiological health concern given its relatively long half life and similar chemistry to the nutrient calcium (Ca). Previous peer-reviewed work indicate that releases of 90-Sr were about 30-10,000 fold less than 137-Cs and similar to the release of 90-Sr from the Chernobyl disaster in 1986 and about 600-fold lower than the releases from atmospheric weapons tests that peaked in the mid-1960’s. Given maximal release rates after the disaster, modeled activities of 90-Sr in the marine foodweb and in fish that accounts for bioconcentration and accumulation predict maximal dose rates from Fukushima to human consumers three orders of magnitude less than doses owing to the presence of 137-Cs in marine products and thus well below maximum dose limits thought to be detrimental to public health.


A 3D numerical model designed to track the dispersion and fate of 90-Sr in the waters and biota of the northwest Pacific Ocean was published by Maderich and colleagues in the peer-reviewed journal Science of the Total Environment. The authors used a dynamic model including the marine food chain to assess the fate of 90-Sr in the northwest Pacific from 1945-2010 and the radiological health risk from Fukushima through marine 90-Sr exposure pathways from 2011-2040. The model is designed to predict the dispersion of 90-Sr derived radioactivity in the water, sediments and the transfer of the isotope through the marine foodweb resulting in doses to humans through the consumption of marine products. The model accounts for transfer of 90-Sr from the terrestrial environment to the ocean over time and tracks the transfer of the isotope from phytoplankton, zooplankton, molluscs, crustaceans to fish as shown schematically in the following figure.

Schematic of radionuclide transfer in the Maderich et al. (2014) model.

The model domain in the northwest Pacific is shown in the following figure which identifies numbered model compartments.

The compartment system. Shaded boxes represent the deep water boxes (> 1000 m). The compartments representing estuaries of large rivers (174 — the Chang Jiang River, 173 — the Huanghe River and 175 — the Han River) are shown by arrows with numbers of compartments. The location of NPPs are indicated by filled circles. Letter “F” represents the Fukushima Dai-ichi NPP. The intermediary regional compartment no. 176 around the FDNPP is also indicated.

The model well predicts the temporal evolution of 90-Sr in the northwest Pacific post World War II. The figure below compares measurements of 90-Sr with model output for numbered compartments of the model domain which show good agreement.

Calculated concentrations of 90Sr in surface waters for box no. 37 (A) and no. 30 (B) in the East China Sea, and for box no. 96 (C) in the Korea/Tsushima Strait and for box no. 149 (D) in the East/Japan Sea. Predicted concentrations in the East China Sea were estimated with and without considering riverine inputs.

The calculated activities of 90-Sr in water, bottom sediment and marine biota are in good agreement with measurements made in the coastal area around Fukushima before the accident. Fewer direct measurements of 90-Sr exist compared to Cs isotopes because the analysis of 90-Sr requires significantly more sample processing and handling to separate it from other beta-emitters. For this reason the model assumes that 90-Sr releases from Fukushima to the ocean are related to 137-Cs releases in ratios determined by direct measurement after the disaster. While releases are ongoing the model determined that the activities in sediments and marine foodstuffs depend primarily on the initial releases in March and April 2011 when rates of release were greatest. Using a conservative estimated release of 640 TBq (TBq = 10^12 Bq) the model predicts the following individual dose rates to Japanese consumers of sea organisms where the average consumer eats 23.4 kg of fish, 2 kg of crustaceans, 1.3 kg molluscs and 3.7 kg of macroalgae per year. It was also assumed that 50% of the fish consumed included the organisms bones.

Individual dose rates for Japanese consumers of 90-Sr contaminated seafood in box 176 and 90 of the model domain before and after Fukushima.

The maximum dose rate in the coastal region at Fukushima was 0.66 microSv/yr which is an order of magnitude greater than the maximal dose rate from 90-Sr released through weapons testing in 1959. This maximal dose rate from 90-Sr is three orders of magnitude less than the dose rate from 137-Cs in the most contaminated marine environment off of Fukushima Daiichi. Given mixing and dilution of the contaminated plume of seawater the annual doses owing to 90-Sr from Fukushima are much less significant in model domains distant from the disaster site. The authors considered a worst case scenario where the public only consumed seafood from the Fukushima coast over the course of a year which resulted in a dose rate of 15 microSv/yr which is well below dose rates thought to represent a significant radiological health risk for the public.

While the modeled activities of 90-Sr in fish agrees well with limited measurements made in fish the model tends to slightly underestimate the activity of 90-Sr in fish. More measurements of this radionuclide in seawater, sediments and biota will improve our understanding of how 90-Sr moves through the environment. Ongoing releases of 90-Sr from the Fukushima site also dictate that monitoring of the levels in the marine environment are necessary and prudent to determine the radiological health risk to seafood consumers.

Authors Lower Fukushima Cesium in North Pacific By Order of Magnitude

By Jay T. Cullen

Introduction

One of the goals of the InFORM project is to make measurements of radionuclides in the North Pacific Ocean to determine maximum activities that will determine impacts on the marine ecosystem and residents of the west coast. The purpose of this post is to bring to the attention of readers a recently published correction to a prominent model that predicts the activity of Fukushima derived Cesium-137 (137-Cs, half life ~30 years) in seawater of the North Pacific. The diary is part of an ongoing series aimed at discussing research addressing the impact of the Fukushima nuclear disaster on the health of the North Pacific Ocean and inhabitants of North America’s west coast. Predictions of a model by Rossi and colleagues published in Deep-Sea Research in 2013 of the evolution of the plume of seawater contaminated by the Fukushima triple meltdowns are an order of magnitude too high. Rather than a range of ~1-30 Bq/m^3 reported previously maximum activities off the west coast of North America are likely to be ~3 Bq/m^3 or about more than 25 times lower than maximum activities measured in the Pacific in the mid-20th century resulting from atmospheric weapons tests. These activities are not likely to represent significant radiological health risks to the North Pacific ecosystem or residents of the North American west coast.


A paper by Rossi et al. (2013) used a Lagrangian model to predict the temporal and spatial evolution of the seawater plume contaminated by the Fukushima nuclear disaster beginning in March 2011. The model predicted a range of 10-30 Bq/m^3 137-Cs in waters off the coast of North America at 49 degrees North latitude as demonstrated in the figure shown below:

Activities of 137-Cs predicted by the Rossi et al. (2013) model on the continental shelves of North America at two latitudes and off Hawaii over time.

This model predicted higher maximum 137-Cs activities in seawater in the North Pacific compared with a similar model published by Behrens et al. (2012) that had maximum activities off of North America reaching only ~1-2 Bq/m^3.

Recently, after comments from Professor Michio Aoyama of Japan, Rossi and colleagues recognized an error in their model and have published a correction to their 2013 study here. The error resulted in a factor of 10 overestimation of maximum activities of 137-Cs in the Pacific such that maximum 137-Cs off N. America will likely be between 1 and 3 Bq/m^3. The corrections to the model do not affect the conclusions of the study and results from the 2013 study are easy scaled to the more accurate values given the Langrangian approach used by the authors in the original work.

The figure below shows the time evolution of the plume at various latitudes along the international date line and compares the model output with measurements made by Aoyama et al. (2013) along the international dateline at about 40 degrees N in 2012.

Activities of 137-Cs predicted by the Rossi et al. model along the international dateline in the N. Pacific over time at various latitudes.

The factor of 10 lower activity correction better agrees with the Behrens et al. (2012) modeling study and measurements of 137-Cs in seawater made by Japanese and North American scientists.

Maximum activities of ~1-3 Bq/m^3 as the heart of the contaminated plume reaches the North American coast in the coming 2 year period are roughly 25-fold lower than 137-Cs activities in the North Pacific circa 1960 resulting from atmospheric weapons testing. Therefore, it is unlikely that 137-Cs activities of 3 Bq/m^3 or associated radionuclides released at lower total activities from Fukushima will represent significant health risks to the North Pacific ecosystem.

Ongoing monitoring of radionuclide activities in the North Pacific is required to ground-truth models of Pacific Ocean circulation and plume evolution and to provide the best information to determine likely impact to residents of North America.