Category Archives: Japan

Comparing the Environmental Impacts of the Chernobyl and Fukushima Disasters

Estimated total atmospheric source term for Fukushima compared to Chernobyl in PBq (PBq = 10^15 Bq). From Steinhauser et al. (2014) SciToTEnviron

By Jay T. Cullen

This post reports on a recently published peer reviewed study by Steinhauser and colleagues in the journal Science of the Total Environment (behind pay wall) comparing the Chernobyl and Fukushima nuclear accidents. The post is part of an ongoing effort to communicate the results of scientific studies into the impact of the Fukushima disaster on the environment. A majority of the radioactivity released from both Chernobyl and Fukushima can be attributed to volatile radionuclides (noble gases, iodine, cesium, tellurium). In contrast, the amounts of more refractory elements (including actinides like plutonium), released by Chernobyl was ~four orders of magnitude (10,000 fold) higher than releases from Fukushima. The most cited source term for Chernobyl is 5300 PBq (excluding noble gases) while a review of published studies of Fukushima carried out by the authors above allow an estimate for the total atmospheric source term of 520 (a range of 340–800) PBq. Monitoring of air, soil and water for radionuclides after the respective accidents indicate that the environmental impact of Chernobyl is likely to be much greater than the Fukushima accident. The post is relatively information dense as I have provided data tables for those who are interested in the estimates and the peer-reviewed studies from which they come. Apologies up front to those who find such information tedious. Continue reading Comparing the Environmental Impacts of the Chernobyl and Fukushima Disasters

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.

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

Plutonium in the Pacific Ocean From Fukushima

By Jay T. Cullen

Introduction

This post is part of an ongoing series that represents an effort to communicate peer-reviewed scientific studies of the impact of the Fukushima nuclear disaster on the North Pacific Ocean and residents of the west coast of North America. A frequently asked question of those involved in monitoring the health of the North Pacific is why more measurements of the long lived, alpha-emitting isotopes of plutonium (239-Pu half-life 24,100 years; 240-Pu 6,570 years) are not being made given the potential for these isotopes to pose radiological health risks. Measurements of air, soil and water indicate that Pu was released and broadcast into the environment as a result of the triple reactor meltdowns with estimates of the source on the order of 2.3×10^9 Bq of 239,240-Pu or 580 milligrams of the isotopes. Measurements of isotope composition and activity of Pu in seawater and sediments off the coast of Japan indicate that there was no detectable change resulting from the nuclear disaster (behind pay wall). Given that the Fukushima signal is not detectable in the ocean off Japan relative to legacy sources from atmospheric weapons testing in the 20th century there is likely little information in making the same measurements in the eastern Pacific off of North America.


Members of the public are concerned about the presence of the alpha-emitting isotopes of Pu and have been asking why measuring for these elements in seawater and marine biota is not a priority of the InFORM network. The purpose of this diary is to explain why such measurements are less likely to provide information about the plume and its impacts.

A recently published paper by Bu and colleagues in the peer-reviewed Journal of Chromotography A reports the development of a new method to determine Pu isotopes in small (20 – 60 liters) samples of seawater and measurements made of these isotopes off the coast of Japan from July 2011 to January 2013 until the present. Locations where samples were collected are shown in the figure below:

Map showing seawater collection stations from the western North Pacific and Tokyo Bay since the FDNPP accident.

For all the seawater samples analyzed by Bu and colleagues, the 239-,240-Pu activities and 240-Pu/239-Pu atom ratios where found to be 0.00043 to 0.0056 Bq m^-3 and from 0.227 to 0.284, respectively. The results are summarized in Table 4 of the paper and are shown below:

 

Before the Fukushima accident in March 2011, Pu isotopes were being monitored off the coast of Japan to assess the radiological impact of the nuclear plants on the marine environment. The 239-,240-Pu activities before the meltdowns were below 0.0083 Bq m^−3 and 0.022 Bq m^−3 respectively, with 240-Pu/239-Pu atom ratios between 0.173 and 0.322. These ratios represent the influence of the Pacific Proving Ground nuclear weapon test site, which was characterized by a high 240-Pu/239-Pu atom ratio (0.30–0.36). Results after the Fukushima disaster were typically in the background data range, suggesting no detectable Pu contamination from the accident in the marine environment ~30 km offshore of the Fukushima Dai-ichi reactor complex. This conclusion is consistent with findings from previous studies of Pu isotopes in marine sediments in the western North Pacific after the Fukushima accident.

Given the absence of isotopic and concentration anomalies thus far in the western Pacific resulting from the Fukushima meltdowns there is not very much information to be gained about the evolution of the contaminated seawater plume in time and space. Similarly, the impact of the Fukushima disaster on the health of marine ecosystem with respect to Pu isotopes will be difficult to quantify relative to weapons testing background levels that persist in the environment.

On the Methodology Used to Make the Measurements (If You are Interested, IYI)
The approach used by Bu and colleagues to measure Pu isotopes at such low concentrations and activities involves applying sector field high resolution inductively coupled mass spectrometry. The instrument is able to separate chemical species by their respective mass to charge ratios using a strong electromagnetic field downstream of the plasma ionization source. Great pains were taken maximize the instruments sensitivity to measure the isotopes of interest 238-U, 239-Pu, 240-Pu, and 242-Pu. To remove the seawater matrix (cations and anions that would reduce instrument sensitivity) and elements with mass to charge ratios that would interfere with Pu detection like 238-U the seawater samples were purified using ion selective resins held in columns by passing them through successive loading and elution steps. This process is summarized in the following flow diagram from the paper:

Flow chart of the analytical procedure for the determination of Pu isotopes in seawater by anion-exchange chromatography and SF-ICP-MS.

The preconcentration and sensitivity of SF-ICP-MS allows for the very low detection limits required to quantify Pu in relatively small (20 – 60 L) volumes of seawater.