Radioactive Hot Particles in Japan: Full Radiation Risks not Recorded



Radioactively-Hot Particles in Japan; New Study Shows Full Radiation Risks are not Recorded

The article details the analysis of radioactively hot particles collected in Japan following the Fukushima Dai-ichi meltdowns. Based on 415 samples of radioactive dust from Japan, the USA, and Canada, the study identified a statistically meaningful number of samples that were considerably more radioactive than current radiation models anticipated. If ingested, these more radioactive particles increase the risk of suffering a future health problem…



Radioactively-hot particles detected in dusts and soils from Northern Japan by combination of gamma spectrometry, autoradiography, and SEM/EDS analysis and implications in radiation risk assessment

by Marco Kaltofen (Nuclear Science and Engineering Program, Department of Physics, Worcester Polytechnic Institute) and Arnie Gundersen (Fairewinds Energy Education), Dec 2017 :

Radioactively-hot particles detected in dusts and soils from Northern Japan… Radioactive particles from Fukushima are tracked via dusts, soils, and sediments; Radioactive dust impacts are tracked in both Japan and the United States/Canada; Atypically-radioactive particles from reactor cores are identified in house dusts… After the March 11, 2011, nuclear reactor meltdowns at Fukushima Dai-ichi, 180 samples of Japanese particulate matter (dusts and surface soils) and 235 similar U.S. and Canadian samples were collected and analyzed… Samples were collected and analyzed over a five-year period, from 2011 to 2016.



Detectable levels of 134Cs and 137Cs were found in 142 of 180 (80%) Japanese particulate matter samples… U.S. and Canadian samples had detectable 134Cs and 137Cs in one dust sample out of 32 collected, and four soils out of 74… The mean in Japan was skewed upward due to nine of the 180 (5%) samples with activities > 250 kBq kg− 1 [250,000 Bq/kg]… 300 individual radioactively-hot particles were identified in samples from Japan; composed of 1% or more of the elements cesium, americium, radium, polonium, thorium, tellurium, or strontium.



Some particles reached specific activities in the MBq μg− 1 level and higher [1,000,000,000,000,000 Bq/kg]… Some of the hot particles detected in this study could cause significant radiation exposures to individuals if inhaled. Exposure models ignoring these isolated hot particles would potentially understate human radiation dose.



Study: Radioactive Hot Particles Still Afloat Throughout Japan Six Year After Fukushima Meltdowns

Radioactive particles of uranium, thorium, radium, cesium, strontium, polonium, tellurium and americium are still afloat throughout Northern Japan more than six years after a tsunami slammed into the Fukushima Daiichi Power Plant causing three full-blown nuclear meltdowns. That was the conclusion reached by two of the world’s leading radiation experts after conducting an extensive five-year monitoring project.

Arnie Gundersen and Marco Kaltofen authored the peer reviewed study titled, Radioactively-hot particles detected in dusts and soils from Northern Japan by combination of gamma spectrometry, autoradiography, and SEM/EDS analysis and implications in radiation risk assessment, published July 27, 2017, in Science of the Total Environment (STOLEN).

Gundersen represents Fairewinds Associates and is a nuclear engineer, former power plant operator and industry executive, turned whistleblower, and was CNN’s play-by-play on-air expert during the 2011 meltdowns. Kaltofen, of the Worcester Polytechnic Institute (WPI), is a licensed civil engineer and is renowned as a leading experts on radioactive contamination in the environment.

415 samples of “dust and surface soil” were “analyzed sequentially by gamma spectrometry, autoradiography, and scanning electron microscopy with energy dispersive X-ray analysis” between 2011 and 2016. 180 of the samples came from Japan while another 235 were taken from the United States and Canada. The study further clarifies, “Of these 180 Japanese particulate matter samples, 57 were automobile or home air filters, 59 were surface dust samples, 29 were street dusts (accumulated surface soils and dusts) and 33 were vacuum cleaner bag or other dust samples.”

108 of the Japanese samples were taken in 2016, while the other 72 were gathered in 2011 after the meltdowns. Gundersen and Kaltofen tapped 15 volunteer scientists to help collect the dust and soil — mostly from Fukushima Prefecture and Minamisouma City. “A majority of these samples were collected from locations in decontaminated zones cleared for habitation by the National Government of Japan,” the study revealed. For the 108 samples taken in 2016, an “International Medcom Inspector Alert surface contamination monitor (radiation survey meter) was used to identify samples from within low lying areas and on contaminated outdoor surfaces.”

A Fairewinds Associates’ video from 2012 features Gundersen collecting five samples of surface soil from random places throughout Tokyo — places including a sidewalk crack, a rooftop garden, and a previously decontaminated children’s playground. The samples were bagged, declared through Customs, and brought back to the U.S. for testing. All five samples were so radioactive that according to Gundersen, they “qualified as radioactive waste here in the United States and would have to be sent to Texas to be disposed of.” Those five examples were not included as part of the recently released study, but Gundersen went back to Tokyo for samples in 2016. Those samples were included, and were radioactive, and according to Gundersen were “similar to what I found in Tokyo in [2012].”


Furthermore, 142 of the 180 samples (about 80 percent) contained cesium 134 and cesium 137. Cesium 134 and 137, two of the most widespread byproducts of the nuclear fission process from uranium-fueled reactors, are released in large quantities in nuclear accidents. Cesium emits intense beta radiation as it decays away to other isotopes, and is very dangerous if ingested or inhaled. On a mildly positive note, the study shows that only four of the 235 dust samples tested in the United States and Canada had detectable levels of cesium from Fukushima.

Cesium, due to its molecular structure, mimics potassium once inside the body, and is often transported to the heart where it can become lodged, thereafter mutating and burning heart tissue which can lead to cardiovascular disease. Other isotopes imitate nutritive substances once inside the body as well. Strontium 90 for example mimics calcium, and is absorbed by bones and teeth.

“Different parts of the human body (nerves, bones, stomach, lung) are impacted differently,” Kaltofen told EnviroNews in an email. “Different cells have radio-sensitivities that vary over many orders of magnitude. The body reacts differently to the same dose received over a short time or a long time; the same as acute or chronic doses in chemical toxicity.”

In contrast to external X-rays, gamma, beta or alpha rays, hot particles are small mobile pieces of radioactive elements that can be breathed in, drunk or eaten in food. The fragments can then become lodged in bodily tissue where they will emanate high-intensity ionizing radiation for months or years, damaging and twisting cells, potentially causing myriad diseases and cancer. The study points out, “Contaminated environmental dusts can accumulate in indoor spaces, potentially causing radiation exposures to humans via inhalation, dermal contact, and ingestion.”

The study also explains, “Given the wide variability in hot particle sizes, activities, and occurrence; some individuals may experience a hot particle dose that is higher or lower than the dose calculated by using averaged environmental data.” For example, a person living in a contaminated area might use a leaf blower or sweep a floor containing a hefty amount of hot particle-laden dust and receive a large does in a short time, whereas other people in the same area, exposed to the same background radiation and environmental averages, may not take as heavy a hit as the housekeeper that sweeps floors for a living. People exposed to more dust on the job, or who simply have bad luck and haphazardly breathe in hot radioactive dust, are at an increased risk for cancer and disease. High winds can also randomly pick up radioactive surface soil, rendering it airborne and endangering any unsuspecting subject unlucky enough to breath it in.

Hot particles, or “internal particle emitters” as they are sometimes called, also carry unique epidemiological risks as compared to a chest X-ray by contrast. The dangers from radiation are calculated by the dose a subject receives, but the manner in which that dose is received can also play a critical factor in the amount of damage to a person’s health.

“Comparing external radiation to hot particles inside the body is an inappropriate analogy,” Gundersen told EnviroNews in an email. “Hot particles deliver a lot of energy to a very localized group of cells that surround them and can therefore cause significant localized cell damage. External radiation is diffuse. For example, the weight from a stiletto high heal shoe is the same as the weight while wearing loafers, but the high heal is damaging because its force is localized.”

Kaltofen elaborated with an analogy of his own in a followup email with EnviroNews saying:

Dose is the amount of energy in joules absorbed by tissue. Imagine Fred with a one joule gamma dose to the whole body from living in a dentist’s office over a lifetime, versus Rhonda with exactly the same dose as alpha absorbed by the lung from a hot particle. Standard health physics theory says that Fred will almost certainly be fine, but Rhonda has about a 10 percent chance of dying from lung cancer — even though the doses are the same.

External radiation and internal hot particles both follow exactly the same health physics rules, even though they cause different kinds of biological damage. Our data simply shows that you can’t understand radiation risk without measuring both.

Some isotopes, like plutonium, only pose danger to an organism inside the body. As an alpha emitter, plutonium’s rays are blocked by the skin and not strong enough to penetrate deep into bodily tissue. However, when inhaled or ingested, plutonium’s ionizing alpha rays twist and shred cells, making it one of the most carcinogenic and mutagenic substances on the planet.

“Measuring radioactive dust exposures can be like sitting by a fireplace,” Dr. Kaltofen explained in a press release. “Near the fire you get a little warm, but once in a while the fire throws off a spark that can actually burn you.”

“We weren’t trying to see just somebody’s theoretical average result,” Kaltofen continued in the press release. “We looked at how people actually encounter radioactive dust in their real lives. [By] combining microanalytical methods with traditional health physics models… we found that some people were breathing or ingesting enough radioactive dust to have a real increase in their risk of suffering a future health problem. This was especially true of children and younger people, who inhale or ingest proportionately more dust than adults.”

“Individuals in the contaminated zone, and potentially well outside of the mapped contaminated zone, may receive a dose that is higher than the mean dose calculated from average environmental data, due to inhalation or ingestion of radioactively-hot dust and soil particles,” the study says in summation. “Accurate radiation risk assessments therefore require data for hot particle exposure as well as for exposure to more uniform environmental radioactivity levels.”

Radioactively-hot Particles Detected in Dusts and Soils from Northern Japan by Combination of Gamma Spectrometry, Autoradiography, and SEM/EDS Analysis and Implications in Radiation Risk Assessment


Dr. Marco Kaltofen – Nuclear Science and Engineering Program, Dept. of Physics, Worcester Polytechnic Institute

Arnie Gundersen – Chief Engineer, Fairewinds Energy Education, Community Research Fellow University of Vermont 

Complete Methodology: 

The purposes of the study were to identify and collect samples with a high potential to contain radioactively-hot particles for microscopic examination, to determine if local hot spots of contamination existed at the time of the Fukushima Dai-ichi meltdowns, and finally to document whether any hot spots persisted five years after the accidents.

Samples of 180 Japanese house dusts, car engine filters, HVAC filters, street dusts and fine surface soils were collected and shipped to Worcester Polytechnic Institute for radioisotope analysis. A total of 235 US and Canadian samples of similar matrices were collected between 2011 and 2015. Of these 180 Japanese particulate matter samples, 57 were automobile or home air filters, 59 were surface dust samples, 29 were street dusts (accumulated surface soils and dusts) and 33 were vacuum cleaner bag or other dust samples. All filters were in service on or after March 11, 2011, the date of the initial releases from the Fukushima Dai-ichi reactors.

Of the 180 samples from Japan, 108 were collected in Japan during 2016 while the remaining 72 samples were collected during 2011. These samples included fine surface soils, sediments from drainage areas, and soils from floor mats. Dusts were collected from bulk and surface dust accumulations; including air handling fans, residential air filters, vacuum cleaner bags, automobile air filters, public restroom ventilation fans and from surfaces at public transportation points throughout northern Japan. This study used a mix of samples submitted by volunteers and by the authors. There were controls on the volunteers’ methods used to select samples, however direct sampling oversight was limited. Fifteen scientists and volunteer citizen-scientists collected these samples in areas across Japan, but predominantly in Fukushima Prefecture and Minamisoma City. Sampling locations were in publicly-accessible areas such as bike paths, roadways, sidewalks and public buildings. Permits were received to sample in restricted areas where post-Fukushima meltdown decontamination work was in progress. A majority of these samples were collected from locations in decontaminated zones cleared for habitation by the National Government of Japan.

Sample collection

Sample collection was biased by performing a preliminary visual survey to facilitate collection from areas where fine particulate matter can accumulate, such as low spots on roads or rooftops, air handling fan blades, floor mats and rooftops. For the 2016 sample set (108 of 180 samples), an International Medcom Inspector Alert surface contamination monitor (radiation survey meter) was used to identify samples from within low lying areas and on contaminated outdoor surfaces. Screening introduces a bias to the soil sample set allowing for maximum probability of collecting particulate matter that might contain hot particles. Indoor dusts, HVAC system dusts and auto air filters were randomly selected and no survey meters were used nor were surface radiation measurements taken prior to dust sample collection.

At the time of the 2016 sampling campaign, mapped surface activity data was available from Safecast, an open citizen-led group that collected activity data via a standardized device of their own design, the bGeigie. Uncontaminated areas in Japan (as mapped by have bGeigie-measured activities on the order of 0.08 uSv/hr. or less. Areas of known contamination are on the order of 0.16 uSv/hr. and higher. More than 90 percent of the samples in this study come from the areas Safecast-mapped as 0.16 uSv/hr. and higher (Figure 1). This indicates that the data are more representative of the contaminated zone, rather than of Japan as a whole. Mapping via the Safecast bGeigie proceeds with a plastic alpha and beta shield around the detector element. This makes the device essentially a gamma activity monitor. Thirteen of the 2016 samples from Japan were measured by the primary instrument (Ortec NaI well gamma photon detector) and the bGeigie. With the shield present on the bGeigie so that both devices measured gamma energy only, the R2 value between the two sets was 0.97, a good fit (Figure 2). Without the shield the bGeigie also accumulated beta and alpha energy, so the fit was poorer, with R2 = 0.15. The strong correlation between the bGeigie in gamma mode and the Ortec spectrometer is added evidence that the sampling methodology provides data that is more representative of the contaminated areas in northern Japan, and less so for Japan as a whole.

For each 2016 sample collection location point, a photograph was taken to provide an image of where the sample was collected as well as a record of the GPS location. All Japanese samples were air dried at ambient temperature prior to analysis, then shipped internationally to Worcester Polytechnic Institute in Worcester, MA, USA, for analysis.

Motor vehicle engine air filters process large volumes of air. In Japan private vehicles average 65 liters of gasoline use per month. (Schipper 2009) This fuel requires approximately 638 cubic meters of air for complete combustion. This is about 30 cubic meters per day, which is in the same order of magnitude as a working adult tidal air volume of 10 to 20 cubic meters per day. It was hypothesized that engine air filters in routine use and first installed prior to March 11, 2011 would provide an approximation of the amount of radioactive dusts present in ambient air for each driving region.

Bulk dust and street dust/soil samples were air dried at ambient temperatures prior to analyses. Dust samples containing macroscopic objects and excessive pet hair were sieved to pass a 150 micron brass ASTM #100 screen. Samples were divided and separately screened by gamma spectroscopy to determine if activity was heterogeneously distributed within samples. Samples were sequentially divided if necessary, based on gamma-screening results.

Dust was mechanically removed from automobile and HVAC filters. Motor vehicle air filters varied in usage from nearly new to as much as 55,000 logged kilometers of use. Sample results for dust samples were reported on a kBq kg-1 basis. Eight filter samples with detectable activities but with dust that could not be quantitatively removed from filter media were assigned a dust mass of 1.0 g. This introduced a low bias to these samples. Nine samples had activities greater than 0.25 MBq kg-1. To ensure safe transport, these samples were mass-limited to 3 grams before shipping from Japan.

Included in this set of nine atypically-radioactive samples, was a 300 mg sample of street dust received from a location about 10 km from the Fukushima-Dai-ichi accident site in Namie-machi, Futaba-gun, Fukushima Prefecture. This is in the restricted zone, close to but just outside of the exclusion zone. A very similar sample was collected from Iitate. The particulate matter samples were analyzed by sodium iodide gamma spectrometry. One vacuum bag received from a home in Nagoya, Japan, yielded subsamples with no detectable radioactivity above background, despite a sizable amount of activity for the bag as a whole. (Nagoya is 433 km from Fukushima Dai-ichi). By sample division and hot particle isolation with a pancake detector, a single 1 cm by 2 cm glass slide was prepared, with a small number of microscopic dust particles (with activity > 1 MBq ug-1) mounted via double sided adhesive tape.

Analyses of the samples proceeded sequentially by NaI gamma spectrometry, autoradiography of high activity samples, and scanning electron microscopy / energy dispersive X-ray analysis (SEM/EDS) of individual radioactively-hot particles identified by autoradiography (Moody 2015). Autoradiographs were prepared from the highest specific activity samples using blue-sensitive X-ray film, followed by SEM/EDS analysis of autoradiographically positive portions of the sample. Air filter media that had positive gamma spectrometry results were mounted in a single layer onto double sided adhesive paper sheets. These sheets with dusts were then attached to 3 mm thick copper plates. Vehicle and HVAC air filters were prepared by cutting the filter media from their frames, and mounting the filter media on 3 mm thick copper plates. A sheet of blue-sensitive Xray film was sandwiched with the mounted filters, and exposed in a dark photographer’s box for seven days. The autoradiographs used MidSci® classic blue autoradiography film BX and D76 processing.

All gamma spectrometry data are corrected for geometry, and were standardized against a known activity of 137Cs. Gamma photon analyses used Ortec® NaI and Canberra® GeLi flat plate photon detectors. An Ortec® NaI well detector and 1K MCA were also used. Counting efficiency @ 662 keV was found to be 30% based on use of a certified calibration standard from an Eckert & Ziegler Isotope Products standard source, manufactured and certified on Sept. 12, 2011, with 40.12 nCi of 137Cs. The 137Cs in the standard used for quantitation and any Fukushima-related 137Cs in the samples were of the same approximate age, therefore no 137Cs decay correction is warranted in this five-year study. Nuclides not amenable to gamma spectrometry, such as strontium, were not analyzed in this study.

Samples with evident gamma spectral peaks for uranium, thorium or plutonium were selected for SEM/EDS analyses. All particles were mounted as a monolayer on a 25 mm OD Ted Pella, Inc., PELCO® tape tab-covered aluminum SEM stub. If necessary to improve particle conductivity, the samples were carbon or gold coated prior to SEM/EDS analysis. SEM/EDS work was tested commercially at Microvision Laboratories of Chelmsford, MA, using a Bruker® X-Flash® Peltier-cooled silicon drift detector (SDD). The electron beam current was 0.60 nAmperes, accelerated at a voltage of < 0.5 to 60 keV.

Want to look at the numbers? Click below to download the complete data sheet of our samples (.xlsx). 

Activities as radio-cesium

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Maps of Safecast data and sample sites in Japan

july 27 2017 2.jpg(Above-left) Safecast map with dark blues representing low contamination

(Above-right) Map of study sample areas using same Safecast color scheme

Boat tracks and other clutter have been removed from this graphic.

Japan Radiation Interactive Map

(Above) Browse the location, supplementary info and photographs of samples taken in Japan with our interactive sample map created by Ben Shulman-Reed, Fairewinds Energy Education program researcher. 

Safecast bGeigie data vs. Ortec NaI gamma spectroscopy data


Japanese dusts and sediments presented by specific activity in kBq kg-1

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Distribution of total radiocesium activities in particulate matter samples from Japan

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Gamma spec Ibaraki Prefecture, analyzed April 11, 2011



Tokyo vehicle air filter image (Left) and 7 day exposure autoradiograph (Right) Corresponding auto exposed points on the X-ray film are connected by red lines.

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SEM image of hot particle, magnification 5000 X.

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(Top) SEM/EDS spectrum showing one nodule of hot particle with 15.6% Cs, 16.7% Te, 1.2% Rb, 0.61% Po.  (Bottom) second nodule with 48% Te, 1.2% Po, 0.18% Dy (analyzed 12/18/2013).

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To read more at :

Fukushima Insoluble Radioactive Particles (part 3)



We are presenting here a transcription of an NHK TV documentary (note1) on insoluble radioactive particles found in Fukushima and in the Tokyo metropolitan region. This is the 3rd part of the 3 parts.

Her is the 1st part :

Here is the 2nd part :


As you can see below, small insoluble radioactive particles are dispersed in the Tokyo metropolitan area. We believe that this represents serious health problems for the population in terms of internal irradiation, since the insoluble radioactive particles remain in the body for a long time. For anybody who would stay in this metropolitan area, further radioprotection against internal irradiation would be required.




Takeda: I will ask Yuichi Moriguchi, who is carrying out investigations on radio-contamination caused by the accident, including the insoluble radioactive particles, how many of such insoluble radioactive particles exist and in what range of area?

Moriguchi: There are many different sizes of particles, but relatively large particles have been found only near the nuclear power plant. On the other hand, we know that the smaller particles were transported far by the wind and reached the Kanto region.



Kamakura: Please see here for the details.
Mr. Moriguchi and his colleagues have divided the insoluble radioactive particles into two major types.  They are called type A and type B.
Those of type A are comparatively small with a size of 10 micrometers or less. A lot of them are spherical. What is called a cesium ball is of this type. Since they are small in size, these particles are likely to reach the lungs by breathing.
On the other hand, those of the type B are comparatively large, by more than several tens of micrometers, and most of them are of distorted shape. Because the particle is large, it is not possible to enter the lungs, but it may adhere to the skin and mucous membranes.





Kamakura: Please see here for the details.
Mr. Moriguchi and his colleagues have divided the insoluble radioactive particles into two major types.  They are called type A and type B.
Those of type A are comparatively small with a size of 10 micrometers or less. A lot of them are spherical. What is called a cesium ball is of this type. Since they are small in size, these particles are likely to reach the lungs by breathing.
On the other hand, those of the type B are comparatively large, by more than several tens of micrometers, and most of them are of distorted shape. Because the particle is large, it is not possible to enter the lungs, but it may adhere to the skin and mucous membranes.

The areas where each type are scattered are gradually coming to be known.
A relatively large, heavy type B particle has been found within 20 kilometers of the Fukushima Daiichi nuclear power plant. On the other hand, small light type A particles are found in the Kanto region.







According to the simulation in the paper published by the meteorological laboratory, the type A particles were diffused like this by the wind on March 14-15 immediately after the accident.

Takeda: Smaller type A particles flew to the Kanto region immediately after the accident. Could you explain more?

Moriguchi: This is exactly what we are researching right now. The other day I presented a paper at an Academic society. We knew that radioactive materials had reached the Kanto area on March 15, but we found that there were insoluble radioactive particles among them. We are trying to clarify right now as to why they arrived there. We are coming to know gradually that the radioactive materials are likely to have been discharged at a certain time.

Takeda: Just for confirmation: these are the ones that flew in the period between March 14 and 15?

Moriguchi: Yes, that’s right.

Takeda: Do you have any estimation of the amount that has been transported in the wind?

Moriguchi: As a whole, I still don’t know how much has been scattered, but as for what flew to the Kanto area on March 15, we have the result of another research group, according to which 80% to 90% of the radioactive materials are composed of this insoluble type A particle. I think that it’s necessary to evaluate the influence carefully because it has reached a considerably large area from Fukushima Prefecture to the Kanto region.

Takeda: Mr. Kai, what is your opinion of the health effect of the A type?

Kai: In the case of radiation, there are external and internal radiation effects. According to the report of the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), the influence of external radiation is larger. Therefore, although it is necessary to review the effects of internal radiation due to the discovery of such insoluble particles, the over-all effects including external radiation do not change much, even when the effects of internal radiation have changed. However, the evaluation of internal radiation needs to be reviewed properly in any case.

Takeda: The UNSCEAR has evaluated that there is no health impact due to the amount of radiation in the metropolitan area. Is there a possibility that this evaluation is reversed?

Kai: In that sense, the influence of the internal radiation exposure will change, but I do not think that their evaluation will be revised, because it is assumed that the influence of external exposure is larger.



Kamakura: On the other hand, there are people who had been evacuated and recently returned to the vicinity of the nuclear power plant.
What are the reactions of the local governments about this insoluble radioactive particle?
For example, the environmental policy section of Okuma town says: “No special measures have been taken, but when people enter a difficult-to-return area, we tell them to wear a protective suit and a mask, and to be careful not to blow up the dust when cleaning the room.”
As you can see, all municipalities are basically dealing with the protective measures that have been carried out so far such as avoiding adhesion to the body and inhaling radioactive materials.

Takeda: Mr. Moriguchi, the evacuation orders have been lifted near the nuclear power plant, and some people have started to return. What are the points to be careful about?

Moriguchi: The decontamination work is done, and the evacuation orders are lifted because the radiation dose has dropped, but the fact is that the decontamination work was carried out only outdoors. Moreover, even in places where the radiation dose is comparatively low, there are areas where such radioactive particles entered residential rooms immediately after the accident. Therefore, I think it is necessary to take the radioprotection seriously.







Takeda: There is another problem that researchers are concerned about in the issue of  insoluble radioactive particles. It is a problem called “re-scattering”, that is to say, particles are re-raised and scatted from the areas where decontamination has not been done, including the site of the nuclear power plant. In fact, a case of re-scattering was already observed in the past.
On August 19, 2013, at Fukushima Daiichi nuclear power plant, following the decommissioning plan, the debris removal work was on the way at the reactor #3. But… the radiation dose increased on the premises. The workers’ body pollution occurred.





At this time, Kyoto University’s research group observed an increase in atmospheric radioactive materials at a point about 26 kilometers away from the nuclear power plant. In addition, insoluble radioactive particles were collected at observation facilities between the nuclear power plant and the Kyoto University observation point.







The research group at Kyoto University simulated the scattering of radioactive particles based on the weather data of the day.  As a result, it was learned that the particles that had been lifted in the debris removal work had scattered over a wide range and reached the observation point.

Takeda: What is your point of view about the health effect of this re-scattering?

Kai: I think that the dose is relatively small, but it is important to take the measurements properly and keep watching. I think that it is especially important to pay attention to measurement results of the round the clock dust monitors installed in the vicinity of the nuclear power plant.

Takeda: How about you, Mr. Moriguchi? What do you think of the measures to take against the problem of re-scattering?

Moriguchi: About the re-scattering, if a big problem happens, most probably it will be in connection with the decommission work. So this is the first thing to be careful about.

Takeda: Another thing: what are the effects of insoluble radioactive particles on the agricultural crops?

Moriguchi: They are actually monitored rigorously. The monitoring in the atmosphere is done as well as the rigorous control of farm products. I think that it is important to diffuse the information thoroughly.

Takeda: You mean that we can trust the products which are put in the market?

Moriguchi: I think that the monitoring is done well.

Takeda: Mr. Moriguchi and Mr. Kai are continuing the research to find out the range of  the scattered particles, and also to evaluate the irradiation dose. They are hoping to have the results by the end of the fiscal year (the end of March).
Researchers are currently trying to clarify the risks of insoluble radioactive particles. And we are going to continue our investigations.
This may cause anguish to some people, but we think that it’s important to receive the information calmly for now.


Note 1: Close-up Gendai, Genpatsu jiko kara 6 nen, Michi no hoshasei ryushi ni semaru (Approaching radioactive particles six years from nuclear accident) (diffusion: 2017 June 6)


Fukushima Insoluble Radioactive Particles (part 2)


We are presenting here a transcription of an NHK TV documentary (note1) on insoluble radioactive particles found in Fukushima and in the Tokyo metropolitan region. This is the 2nd part of the 3 parts.

Here is the first part.









Insoluble radioactive particles that do not dissolve in water.

This characteristic is supposed to make a big difference when considering health effects.

In the past, radioactive cesium emitted in the nuclear accident was thought to be carried away adhering to water-soluble particles called aerosols in the atmosphere. When it touches the water the particle melts and the cesium diffuses and gets diluted. The same is true when it is inhaled in the lungs; the water-soluble cesium melts into the body fluid and spreads thinly throughout the body. Then it is supposed to be discharged gradually by the metabolic activity, and decreases by half from 80 to 100 days in the case of adults.



Insoluble radioactive particles, on the other hand, do not dissolve in body fluids. For example, if they adhere to the alveoli at the furthest areas of the lungs, it may take years to discharge. Even with the same amount of cesium, the dose of lung exposure is about 70 times higher than in the case of water-soluble cesium in the case of adults. As for the infants who are more radiosensitive, the dose of exposure is supposed to be approximately 180 times higher.







In fact, this insoluble radioactive particle has not been identified in past nuclear accidents. Why was it emitted in the accident of the Fukushima nuclear power plant?

Yukihiko Sato, who is doing research on this particle, is focusing on the insulation material that contains glass components. It is used in parts such as piping in the nuclear power plant.

A special electron microscope is used to analyze the proportion of elements contained in the radioactive particles and in the insulation material.

The top is radioactive particles, and the bottom is the insulation material.

The proportion of elements, such as silicon and oxygen, which are the main components of glass, is well matched.











From this, Mr. Sato thought about the scenario where the radioactive particle formed as follows:

Radioactive cesium was emitted from the melted nuclear fuel in the event of the accident. It first filled the reactor. Then, it leaked into the reactor containment building.

Cesium was absorbed in the insulation material in the building.

After that, a nuclear reactor building blew up by hydrogen explosion.

As the insulation material melts and becomes glass, cesium is taken in. And with the explosion, it became small particles as it dispersed in the blast.









The radioactive particles found by Sato are in diameter from 0.5 to 500 micrometer. Their shapes vary from a smooth round one to a rugged one.



Tatsuhiko Sato of the Japan Atomic Energy Agency.

He simulated the health effects of insoluble radioactive particles using a program to calculate the behavior of each ray. For the simulation, he used a particle of the size which enters the lung, and which is actually found. He compared the simulation of the insoluble radioactive particles remaining to adhere to the same spot on the surface of the organ, and that of the same amount of radioactive material adhered uniformly on the surface.







In the case of uniform adhesion, even after 24 hours, blue and light blue areas are spread out indicating that the radiation dose is low.











On the other hand, in the case of the particle, the dose near the spot increases locally and orange and red areas are expanding.



Even with the same quantity of radioactive materials, the health effect may change.





In fact, there are data of people who may have inhaled insoluble radioactive particles. This is a survey of TEPCO employees who had a large amount of exposure during the nuclear accident.







The amount of the radioactive materials in the body is examined regularly, and the graph in red shows that the value of the vicinity of the chest is comparatively high. While the radioactive cesium that had spread throughout the body decreased over time, only around the chest the speed to decrease was slow. The inhaled insoluble radioactive particles are suspected to remain in the lungs.





However, researchers say that the amount is not significant enough to worry about the health effects, according to the International Commission on Radiological Protection.

Takeda: Mr. Michiaki Kai is a specialist in the radio-induced health damages and radioprotection.

If the insoluble radioactive particles stay in the body, the radiation dose may increase locally. And according to some experts, it is necessary to investigate the health effects. What is your opinion?

Kai: First of all, you know that the dose is a measure of health effects. However, when we compare the dose, you cannot compare the cases of smaller and larger exposures ranges. In general, the greater the exposures range, the greater the health impact is. In that sense, the larger the average dose of an organ or an entire system is, the greater the impact is. Therefore, it is important to evaluate the average organ dose even in the case of the insoluble particle. However, there is a possibility that the dose becomes high very locally, so it is important to evaluate it properly, since some people worry about it. This is why such an evaluation is carried out.

Takeda: The overall exposure more than local exposure is …

Kai: If it is the same dose, the impact on health is larger if the range of exposure is wider.

Takeda: You mean that the impact is larger, but it is also necessary to examine a local exposure.

Kai: I think that it is necessary to examine it properly.

(To be continued in the Part 3)


Note 1: Close-up Gendai, Genpatsu jiko kara 6 nen, Michi no hoshasei ryushi ni semaru (Approaching radioactive particles six years from the nuclear accident) (diffusion: 2017 June 6)


Fukushima Insoluble Radioactive Particles (part 1)



We are presenting here a transcription of an NHK TV documentary (note1) on insoluble radioactive particles found in Fukushima and in the Tokyo metropolitan region. Since it is quite heavy with images, it will be uploaded in 3 parts.

These particles contain cesium, which has the property to dissolve in water. However, in the case of these particles, the cesium was taken into glass-like particles during the Fukushima Daiichi NPP accident before it was blown away by the explosion. These particles do not dissolve in water, and as a consequence the cesium will remain longer both in the environment and in the human body, which will modify the impact of radioactive materials on the environment and on health.

Here the video in Japanese:

Takeda: A round particle like a marble.
Rugged particles like asteroids.
Presently, the researchers are paying attention to them.



Very small particles contain radioactive cesium.
Therefore, sometimes they are called “cesium balls”.
They are radioactive particles emitted during the TEPCO Fukushima Daiichi nuclear power plant accident.





Their existence came to light recently and the investigation is ongoing.
The reason why researchers pay attention is their nature of not dissolving in water.
They are called “insoluble radioactive particles”.
Because of this characteristic, they are considered to stay in the environment for a long time.
 If inhaled, they may remain in the human body for a long time, but the impact is not yet fully known.
While the evacuation orders are being lifted, the researchers began to raise their voices that they should communicate the information known at this stage.










Six years since the accident.
The reality of the insoluble radioactive particles has gradually become clear.
This is the latest research report.





First, these are the areas where evacuation orders were issued following the Fukushima Daiichi nuclear power plant accident.
In areas where decontamination works have been completed, evacuation orders have been lifted from the end of March and the return movement of the population has begun.
It is in this context that in this year, the research presentations on insoluble radioactive particles have come out in succession.



Kamakura: Among the radioactive material released during the accident, it is radioactive cesium that is still regarded as a problem. Especially this cesium 137. Most of the radioactive materials that remain in the environment are cesium 137 because they are released in large quantities and have a long half-life of 30 years. Until now, cesium has been thought to dissolve in water and gradually become diluted in the environment. However, cesium is found in insoluble state that does not dissolve in water.



Takeda: Many aspects of the insoluble radioactive particles remain unknown, such as where they exist and in what quantity, or how they affect the health.
Today, we wanted to share the information known to us at this point, including the things that remain unclear yet, in order to provide a base to make decisions on this issue.
First of all, we shall see what the insoluble radioactive particles are.
And then, we will have a look to see in what measure the impact on health is known.











A symposium was held in March this year on the irradiation due to the nuclear accident.
Tatsuhiko Sato of the Japan Atomic Energy Agency presented a paper on the health effects of insoluble radioactive particles, which were hardly known so far.









Where are insoluble radioactive particles located?
We accompanied various investigations in difficult-to-return areas.
We entered a building abandoned since immediately after the accident.
We collected dust accumulated in a room.
We took it back to the lab and analyzed it….
A number of black dots emerged. It shows that there are radioactive materials.
We carried out a further examination of the part where the black dots are located.
We came to a small particle.







This is an insoluble radioactive particle.
The measurement has proven that radioactive cesium of approximately 60 becquerels is included in the particle of about 200 micrometers.
There are 27 buildings in the survey. In all the buildings similar radioactive particles have been found.

(to be continued in Part 2)


Note 1: Close-up Gendai, Genpatsu jiko kara 6 nen, Michi no hoshasei ryushi ni semaru (Approaching radioactive particles six years from nuclear accident) (diffusion: 2017 June 6)


The Different Dangerosity of Some Radioactive Elements.

One night in July 2013, Xavier Nast, a French antinuclear activist, who many years before used to work at COGEMA, presently named AREVA, took the time to explain me the diffrence between some of the radioactive elements, in terms of their dangerosity.
As Xavier Nast told me, nothing is worth practical exercises to understand what is not always obvious at the first explanation.
Since the beginning of the Fukushima accident, everyone understands the situation as he/she perceives it, and everyone is right it is very serious indeed, but still we haven’t seen almost anything yet. And what we may risk to see and understand?
When sharing the “galette des rois”in France, some king cakes in the old days were stuffed with a a small gold coin (a gold Napoleon). If a greedy one swallowed it inadvertently, he will have to wait one to two days to recover it but his health will not be affected.
Imagine the coins gold plated and filled with actinides (highly toxic alpharadio transmitters) such as they all weigh 6 grams, have a diameter of 21 mm and the same visual appearance:
A) An Uranium 238 filled gold plated coin
B) A Plutonium 239 filled gold plated coin
C) A Plutonium 238 filled gold plated coin
D) A Polonium 210 filled gold plated coin
We will not see any difference in appearance and weight.
However the threshold for the lethal dose of an inhaled monolithic dust is:
0.835gram for A (Uranium 238)
0.000 000 4 gram for B (Plutonium 239)
0.000 000 001 6 gram for C (Plutonium 238)
0.000 000 000 007 gram for D (Polonium 210)
This means that the lethal dose of these coins could destroy:
6 lives for A (Uranium 238, there is a lot)
13,475,000 lives for B, more than Paris Metropolis population (Plutonium 239,there is a lot)
3,700,000,000lives for C, more than half of mankind (Plutonium 238 is rare)
850 billion lives for D, 120 times the world population. (Polonium 210 is very rare)
Yet these coins A, B, C and D have not caused you any damage after being swallowed, not even long after.Because they were all covered with a tenth mm of gold , which prevented the huge flow of alpha particles to destroy even just a little of your digestive tract.
Conclusion:alpha emitters radionuclides must remain CONFINED.
We therefore better have no nuclear plant to explode, especially one of those nuclear plants using MOX, as MOX fuel consists of 7% plutonium 239 mixed with depleted uranium, such as the ones we have many in France.
Knowing this, are you still willing for them to continue using their deadly nuclear technology? Do you still believe that civil nuclear is safe?