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No way to find hot spots with dosimeter at 1m from the ground

Special thanks for their very important work to Kurumi Sugita of the Fukushima 311 Voices Blog and to Mr Yoichi Ozawa of the citizen’s measurement group named the “Fukuichi Area Environmental Radiation Monitoring Project“.
We have published several articles in this blog saying that to protect the population the Japanese goverment should take into account the soil contamination as well as the radiation dose in the air.  The policy to open the evacuation zones and encourage the population to return to live there (with the end of financial compensation and relocation aid) is based only on the airborn radiation dose measurements (the evacuation order is lifted when the radiation dose is under 20mSv/year).  We have been saying that this is very dangerous, even  criminal, for the air radiation dose rate (indicating the amount of radioactive dose received by a person within a certin period time) is useful with a well-identfied fixed source of radiation, but is not adequate to reveal the overall environmental contamination after a nuclear accident. It doesn’t account for the internal radiation exposure induced health hazards (note 1).
Now we would like to point out another problem related to hotspots: it is nearly impossible to find hotspots by the usual measuring practice of the airborn radiation dose rate (in sieverts per unit of time).  To illustrate this difficulty, we are translating here a Facebook post of Mr Yoichi Ozawa of the citizen’s measurement group named the “Fukuichi Area Environmental Radiation Monitoring Project“.
 
Here are the radiation dose rates, captured vertically above a highly radioactive substance (“black substance” or “black dust”) of 4,120,000 Bq/kg, measuring 79 μ Sv/h.
Below are measurements at different distances from the ground.
5cm:9.112 μSv/h
50cm:0.630 μSv/h
1m:0.251 μSv/h
Nov 30 2017.jpg
Conclusion: it is impossible to discover micro-hotspots right under your feet when you walk around measuring radiation doses at 1m of distance from the ground.
Measuring device:
Aloka TCS172B
Measurements carried out by Mr Yoichi Ozawa.
For 0cm from the ground, Aloka TCS172B, which cannot measure over 30µSv/h, was replaced by Polimaster PM1703M and Radex RD1706. The value is the average of the measurements of these two devices.  
 
Here is the video of the measurement.
As we can see from the graph above, the value in terms of Sieverts decreases drastically with the distance from the ground. At 1m, which is the usual reference height to measure the radiation dose rate, the value becomes very small even with the soil of over 4 million Bq/kg, which is absolutely enormous (note 2).
Some readers might be familiar with the image of a Japanese citizen measuring  radioactivity with a device at about 1m from the ground. This practice, almost unknown before the Fukushima Daiichi nuclear accident, has become widespread among citizens, although it has become rather a rare practice nowadays as many people have more or less become accustomed to live with radiation. Besides the fact that it is hard to live a life worrying about radiation around the clock and some people prefer to stop thinking about it, this “normalisation” of radiation is strongly enforced by a governmental security campaign. One of the methods employed is to focus on the external irradiation risk, neglecting the internal irradiation risk, by spreading the knowledge and data only in terms of the radiation dose in the air (measured by Sieverts), at the expense of other measurements such as the radiocontamination density in soil (surface contamination density in terms of Becquerel/unit of surface).
One of the now well-known problems of radiocontamination of the environment is that the contamination is not homogeneous, but dispersed with what is called a hot spot. This is a serious problem for the population, as the absorption of radioative particles contained in these hot spots can cause internal irradiation related health damage. And as we see above, it is extremely difficult to detect these hotspots, from 1m and above, even with the extremely highly contaminated substance such as “black dust”.
It is widespread belief among the public that if the value of the airborn radiation dose at 1m from the ground is under 0.23µSv/h (note 3), it is safe. This value, diffused by the authorities as well as by media, is indeed applied as the lower limit to carry out decontamination work.  Yet, as we have seen, even with the extremely highly contaminated substance such as “black dust”, at 1m, the radiation dose is only 0.25µSv/h, that is to say, only slightly over the limit of the 0.23µSv/h, which is believed to be the “safety level”.
It is unfortunate to say that for most of the residents taking the measurements of the airborn radiation dose by themselves, the values they observe have become rather an “encouraging” factor to continue living there or to return to live, than an alarming factor, as these values do not reveal but rather conceal the presence of hotspots which can cause internal radiation exposure induced health damage.
It is difficult to find hotspots anyway.  So when the soil contamination is high (see the concentration maps in this blog, for Namie, Minamisoma), it is better to keep the zone closed, continuing to aid the evacuated people.
 
Note 1: In opposition to the external radiation exposure which occurs when the human body is exposed to an external source, the internal radiation exposure is an exposure from inside the body due to the incorporation of radioactive particles through ingestion, inhalation or adhesion to skin.
Note 2: This extremely high level of contamination is understandable, for what is measured here is the infamous “black substance” or “black dust”, a kind of Cyanobacteria, about which we invite you to listen to podocast of Marco Kaltofen with English transcription.
Note 3: In fact, the 0.23µSv/h value is problematic in itself.  This is based on the 1mSv/year value following the ICRP (International Commission on Radiological Protection) recommendations on the public health.  However,  the 0.23µSv/h value is not the result of a simple division of 1mSv by 365 days x 24 hours. The calculation of 0.23µSv/h presupposes that people stay inside for 16 hours/day and that the radiation is reduced by 60% because of the building structure.  Then, the background of 0.04µSv/h is added. (1000µSv÷365÷(8 + 〈16×0.4〉) + 0.04  But in the real life in rural areas such as Fukushima, people spend more time outdoors.  Besides, some recent research has shown that in some cases the radiation dose can be higher indoors than outdoors because of the infiltration of hot particles. Thus, the reality is much more complex to apply uniformly the value of 0.23µSv/h as a safety threshhold. Lastly, many people in Fukushima were victimes of the initial exposure right after the accident. For such population, any exposure, whatever the quantity is, is to be avoided.
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December 1, 2017 Posted by | Fukushima 2017 | , , , | Leave a comment

Fukushima 6 Years After: No Return to Normal

 

The Japanese government is set to lift evacuation orders in heavily contaminated areas around Fukushima. It will cut compensation and housing support to survivors, who are still struggling six years later.

Their basic rights to health, housing, and environment are being violated. The government is desperately trying to minimize the disaster at the expense of survivors in an attempt to revive the dying nuclear industry and suffocate other cleaner energy sources. We must say no!

Greenpeace has just published report on the Fukushima disaster entitled “No return to normal”. They made a study of the potential doses of the inhabitants who would return to the evacuated areas, with a focus on Iitate-mura. http://www.greenpeace.org/japan/Global/japan/pdf/NRN_FINweb4.pdf

The report is based on many on-site measurements and makes lifetime dose assessments. It should be noted that the samples were taken by the citizen laboratory Chikurin, founded with the support of the ACRO. http://chikurin.org/

The authorities planned to lift the evacuation order at the end of March in Iitaté-mura, except in areas classified as difficult return zones, as well as in the Yamakiya district of Kawamata. Compensation will stop within one year. This concerns more than 6,000 people in Iitate who are facing a dilemma, as in all the other contaminated territories.

Greenpeace recalls that decontamination concerns only areas close to dwellings and cultivated fields and that forest covers 75% of this mountainous area. Even in areas where decontamination work has been carried out, the doses remain high. Greenpeace carried out measurements of soil contamination and dose in 7 dwellings to estimate the exposure for people who would return. This varies between 39 and 183 mSv over 70 years from March 2017. This may exceed the limit of 1 mSv / year which is the dose limit in normal time and the total dose of 100 mSv from which the Japanese authorities admit that there is an increased risk of cancer. The doses taken at the beginning of the disaster are not taken into account in this calculation.

In its calculations, the government estimates that the dose rate is reduced by 60% in homes due to the screening effect of the walls. But the measurements made by Greenpeace in a house show that the reduction in exposure is not as strong.

Source: http://fukushima.eu.org/fukushima-6-ans-apres-rapport-de-greenpeace/

Translation Hervé Courtois

February 22, 2017 Posted by | Fukushima 2017 | , , , , , , | Leave a comment

Radioactive contaminant levels can’t be read at 31 Fukushima temp waste sites

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FUKUSHIMA — It may be impossible to measure the radioactive contaminant concentrations of water leeching from soil and other waste produced by the Fukushima nuclear disaster cleanup at 31 temporary waste storage sites in Fukushima Prefecture due to a planning flaw, a Board of Audit inspection has found.

The cleanup waste is put in bags, put in piles and covered with a waterproof tarp at the temporary disposal sites. These piles are built atop a low convex mound of earth, which is also covered with a tarp and is supposed to funnel the water leeching out of the waste into underground tanks. Contaminant concentration measurements are then taken from these tanks.

However, though many temporary disposal sites have been built on soft ground such as agricultural land, apparently no provisions were made for land subsidence — the earth being pushed down by the pressure of the waste bags — during planning.

The Board of Audit chose 34 of the 106 disposal sites in the prefecture for inspection. The 34 sites were spread across five municipalities, had waste piles five to six bags (or about 5 meters) high, and had been established in the four years up to fiscal 2015. Of these, the earth beneath the waste stack had subsided — going from convex to concave — at 31 sites, meaning contaminated water was also not flowing into the storage tanks. It is possible the water is collecting in the tarps.

There are 15 such sites in the Fukushima Prefecture town of Kawamata, five in the town of Namie, four each in the city of Tamura and the village of Iitate, and three in the town of Naraha. The subsidence of the earth bases hasn’t been confirmed, but the Board of Audit has pointed out that if contaminated water is pooling in the tarps, it could impact future operations to move the waste to a mid-term storage site. It has also called on the Environment Ministry, which operates the sites, to take necessary measures to rectify the problem.

The ministry told the Mainichi Shimbun, “The stacks are designed so that contaminated water won’t escape even if the land underneath subsides, and no harm has been done by the treatment of the water. The waste bags themselves have been replaced with waterproof versions, but we would still like to consider ways to reinforce the ground (under the piles), such as by using sand in the middle.”

http://mainichi.jp/english/articles/20161024/p2a/00m/0na/017000c

October 25, 2016 Posted by | Fukushima 2016 | , , , , | Leave a comment