This post is part of an ongoing series that endeavors to report measurements of Fukushima derived radionuclides in the environment to help determine the likely impact on ecosystem and public health in western North America. One of the goals of the InFORM project is to provide quality measurements of Fukushima derived radionuclides in the North Pacific to help verify model predictions of ecosystem and public health impacts of the disaster. The purpose of this post is to summarize results of a recent peer reviewed study by Kaeriyama and colleagues published in Environmental Science & Technology who measured radioactive isotopes of cesium (137-Cs half life ~30 yr and 134-Cs half life ~ 2 yr) in the western North Pacific Ocean to help track the location and movement of the Fukushima contaminated seawater plume.
The purpose of this blog is to bring to the attention of interested readers a recent peer-reviewed, open-access study published in the Journal or Radiological Protection . The investigators describe the design and manufacture of a whole body sensor whose purpose is the detection of 137-Cs (half-life ~30 years) in children who were proximate to radionuclide releases after the triple meltdowns at the Fukushima-Daiichi nuclear power plant which began in March 2011. Health impacts of the disaster are likely to be most acute in Japan given that levels of radionuclides in air, soil and water resulting from the disaster were higher compared to levels measured and expected on the west coast of North America. The detector in question (called BABYSCAN) is demonstrated to have a detection limit of better than 50 Bq/body and has been installed in a hospital in Fukushima. Because children are most vulnerable to the impacts of ionizing radiation, 100 Fukushima children were scanned for the presence of 137-Cs and none were found to have detectable levels of the isotope in their bodies. Larger scale measurements of the population will be reported as the long term impacts of low levels of ionizing radiation present owing to the Fukushima disaster warrant further study.
As a result of the radionuclides released to the atmosphere after the meltdowns in March 2011 at the Fukushima-Daiichi nuclear power plant, Fukushima Prefecture was contaminated with radioactive cesium (134-Cs and 137-Cs) and other isotopes, which pose radiological health risks to the resident population. As would be expected for parents around the world, parents of small children in Fukushima Prefecture have great concern about the internal exposure experienced by their offspring.
The paper by Hayano and colleagues describes the design and manufacture of a whole body scanner designed specifically for the purpose of detecting gamma-emitting isotopes that have been internalized by children. The instrument was first installed at the Hirata Central Hospital in Fukushima Prefecture in December 2013. The design principles, implementation and the initial operating experience are reported in the paper.
The age distribution of the first 100 children who were selected for isotope counting are given in the figure below:
Given the experimental conditions the minimum detectable activity (MDA) for 137-Cs (Bq/body), was calculated for each subject and plotted against weight for each child as shown below.
The detection limit of BABYSCAN for 137-Cs, one of the most significant isotopes with respect to radiological health risks released from Fukushima, is better than 50 Bq/body. Despite this low detection limit, 137-Cs was not detected in any of the first 100 children scanned from the most contaminated areas of Japan in Fukushima Prefecture. Ongoing analyses will be carried out on a larger-scale with BABYSCAN and reported in publications by the investigators in the future. I will report on data as it becomes available.
This diary is part of an ongoing series here that aims to report measurements of Fukushima derived radionuclides in the North Pacific Ocean to help determine the likely impact on ecosystem and public health in western North America. The purpose of this diary is to report the results of a recently published study by Kumamoto and colleagues in the open-access journal Scientific Reports. The study measured the activity of Fukushima derived cesium (Cs), a tracer for other radionuclides, in the upper 1000 meters of the western Pacific Ocean along the 149 degree E meridian as of winter 2012. These measurements indicate that 10-60% of the total Fukushima derived 134-Cs in the North Pacific has been transported to the south at a depth of ~300 m below the surface. This result is surprising as most models suggest that transport would be primarily to the east toward North America. The study demonstrates that the amount of Fukushima derived radionuclides being transported to the east towards North America is lower than predicted by previous models and provides important information on the circulation of the ocean.
The disaster at the Fukushima Dai-ichi Nuclear Power Plant (FDNPP), precipitated by the earthquake and tsunami on March 11, 2011, resulted in meltdowns at Units 1-3 and a massive release of radionuclides to the North Pacific Ocean by direct discharges from the plant and by deposition of radionuclides released to the atmosphere. While a suite of radionuclides were released, 134-Cs is a useful tracer of Fukushima impact. 134-Cs has a relatively short half-life (~2 years) that unequivocally fingerprints a Fukushima source. It was also released in large quantities and therefore poses a potential radiological threat to organisms. 134-Cs was released along with 137-Cs (half-life = ~30 years) in a 1:1 ratio from Fukushima.
Scientists use a variety of units to measure radioactivity. A commonly used unit is the Becquerel (Bq for short) which represents an amount of radioactive material where one atom decays per second and has units of inverse time (per second). Another unit commonly used is disintegrations per minute (dpm) where the number of atoms undergoing radioactive decay in one minute are counted (so 1 Bq = 60 dpm).
Estimates of direct release of Cs to the ocean were on the order of 11-15 PBq (10^15 Bq) while the deposition of Cs to the surface of the ocean were about 5.8-30 PBq. In 2012 the authors of the study occupied a series of stations along 149degree E as shown in the figure below:
In addition the surface plume of radionuclides that has been modeled and detected (by InFORM team member Dr. John Smith of DFO) in surface currents heading to the east toward North America depth distributions of 134-Cs in the western Pacific show that a concentrated plume of Fukushima derived radionuclides has been transported to the south at a depth of 300 meters:
Based on the integration of the activity of Cs over the depth the authors estimate that about 6 Pbq (10^15 Bq) are present in the subsurface feature being transported to the south. This represents on the order of 10-60% of the total radiocesium that was introduced to the Pacific by the disaster. This helps to explain the lower activities being measured in the eastern Pacific compared to what models predict and suggests that maximum activities on the west coast of North America will likely fall toward the lower end of model predictions that were in the range of 2-30 Bq/m^3. Simply stated more of the radioactive elements released from Fukushima to the Pacific Ocean are headed south rather than east to North America in the plume than previously thought.
More direct measurements of radioactive elements in the North Pacific Ocean through the InFORM project will help to determine what activities are likely on the west coast of North American as the plume arrives from 2013 onward. The measurements or radionuclides in seawater, combined with measurements of radioactive elements in marine organisms, will help to assess the risk of exposure of west coast residents to radionuclides from Fukushima.
A Twitter user interested in the InFORM network asked the following question today:
“…do you have a public list of all products in Fukushima emissions?”
It is important to realize that release estimates are not fully constrained and that estimates improve as more and more measurements are made in the environment. A useful, peer-reviewed, open access study that summarizes release estimates is Povinec et al. (2013) published in the journal Biogeosciences. Table 1 from this study is shown below and can be maximized by clicking the image:
Full references for the table are available in the Povinec paper by following the link given above. Estimates of plutonium released by the Fukushima disaster are provided in this summary with peer-reviewed studies linked to within the document. Measurements of Pu in soil, air and water suggest that 1 to 1,000,000 fold less Pu was released from Fukushima compared to 137-Cs emissions given above.
Below we present near comprehensive inventories of radionuclides in the reactor cores of Units 1,2 and 3 and in the spent fuel pools of Units 1,2,3 and 4 at the time of the accident as reported by:
Nishihara, K., H. Iwamoto, K. Suyama. 2012. Estimation of Fuel Compositions in Fukushima-Daiichi Nuclear Power Plant. Japan Atomic Energy Agency, Tokai. Japan.
The following information has been modified from:
Tables in the pdf file given just below contain information on the radionuclide, grams of radionuclide present, half-life of element, activity in Bq and ratio to 137-Cs in the core or spent fuel respectively.