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 : https://fukushima311voices.wordpress.com/2017/07/14/insoluble-radioactive-particles-part-1/
Here is the 2nd part : https://fukushima311voices.wordpress.com/2017/07/14/insoluble-radioactive-particles-part-2/
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.
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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)
https://fukushima311voices.wordpress.com/2017/07/16/insoluble-radioactive-particles-part-3/
Fukushima 311 Watchdogs 
Reblogged this on 20 millisieverts per year.
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