Tag Archives: Fukushima Dai-ichi Plant

8/28/2011 Extremely High First Year Radiation Doses Predicted by Japanese Government in some areas

8/28/2011 Extremely High First Year Radiation Doses Predicted by Japanese Government in some areasby Gordon Edwards: Background: Deposits of radioactive fallout from Fukushima are highly variable, depending on weather conditions, precipitation, and nature of the releases — which include not only gases and vapours, but also “hot particles”, sometimes called “nuclear fuel fleas”, which are tiny but solid radioactive “cinders” from the disintegrated fuel elements. For those who may not know, MEXT is Japan’s Ministry of Education, Culture, Sports, Science & Technology. A note about the numbers: In Canada, the maximum extra radiation exposure allowed (by regulation) for a member of the public is 1 mSv per year. In the nuclear industry, any worker who is exposed to 1 mSv or more per year must receive special training. In North America, the maximum occupational exposure for an atomic worker is 50 mSv per year. In Germany, the maximum occupational exposure for an atomic worker is 20 mSv per year.

8/23/2011 Email From: Ko-ichi Nakamura: 8/23/2011 Greetings, I am forwarding Dr. Saji’s latest daily update by Ko-ichi Nakamura: (Dr. Saji is Ex-Secretariat of Nuclear Safety Commission, Japan). He is now retired, independent from any government or industry group. The following web sites may be your good source of info, what is going on everyday. http://jaif.or.jp/english/ http://www.tepco.co.jp/en/press/corp-com/release/
Best regards, Ko-ichi Nakamura

8/23/2011 Email From: Genn Saji: Dear Colleagues: 161th-165th day!:

I. Extremely high first year doses predicted by MEXT. MEXT announced their estimation of the first year doses (starting from the day of the accident), at the 50 representative spots within the 20 km “vigilance (off-limit)” zone in view of the government intention of allowing re-habilitation of the evacuees. According to their measurements, the dose rates are orders of magnitude different within the same zone in Fukushima Prefecture. Among the extremely high doses recorded are these: 508.1 mSv at Koirino, Okuma-cho, 223.7 mSv at Kawafusa, Namie-cho, 172.4 mSv at Futaba-cho, 115.3 mSv at Koryougahama, Tomioka-cho, 53.1 mSv at Kanaya, Kotaka-ku, Minamisouma-shi.

Thirty five out of 50 locations exceeded the Government guideline of the first year dose of 20 mSv. The dose rates are greatly different even in the same district. For example, at Namie-cho, it was only 4.1 mSv at Kitaokusebashi, located only 8 km from the Fukushima Daiichi. I think overall dose maps have been shown in DOE/NNRI website by indicating above 20 mSv, however, these individual values higher than 20 mSv are the first released by MEXT.

Further studies of these phenomena are very important, I believe, since there are two possibilities. One is that these highly contaminated spots are induced by the black-rain/fallout as droplets from the plumes, mostly in a liquid state. The other case is that highly radioactive solid fuel particles were included in the plume which fell out during the plume passage.

In this case, the surface concentration should be much more localized than the first case. In the first case, the removal of wider surface soil should be necessary for decontamination. Whereas, in the second case, it is essential to locate the hot particles and remove them.

Being influenced by these facts, the Government is now saying that there will be some areas where rehabilitation will not be possible for an extended [number of] years, typically several tens of years. Mr. Edano, Chief Secretary of Diet, said on August 21 that the government is going to contact with the local communities to explain these prospects. It was reported that the government is going to purchase these areas, however, the local people may refuse to sell due to a strong affection towards their homelands. The Government is shifted to lent [forced to rent] the lands for decontamination until re-habitation will become feasible.

Through watching results of various decontamination activities being performed in Fukushima, I got an impression that decreasing the soil activation by one order of magnitude may be feasible, such as by removing the surface soil as well as disposing weeds and fallen leaves, reduction of two orders of magnitude may not be practical, due to secondary contamination possibilities. I once thought it is essential to decontaminate the very highly contaminated corridor stretching towards NW direction towards the Iitate-mura [village], however, I begin to think it will not be feasible if we consider secondary radiation doses expected for the workers. It is because most of these regions are in a Mountain district (Abukuma mountain chain).

The recent observation [recently observed] activities are now showing that a large fraction of radioactivity seems to be absorbed in leaves and barks of the trees. For decontamination, we need to dispose these biomass mass safely, As in the case of the “Red Forest” stretching towards the west direction from the Chernobyl reactor, the decontamination may be impossible. The Government should clearly explain to the affected people what can be done and what will be impossible, considering the secondary radiation risk.

II. Update of internal exposure in livestock

Since I covered this subject in July 30 as [Update #134], this issue is being reported almost every day in Japanese media. I would like to update this since another route of contamination [of beef] was discovered recently. It has been generally understood that the major pathway was through rice straw feed mainly produced in Fukushima, contaminated from the straw left in the paddy field at the time of the plume passage, through a rice straw feed –> cattle.

However, stocked beef meet from 12 cattle was found contaminated as high as 2.0E+3 Bq/kg, [2,000 becquerels per kilogram] twice the temporary guideline. The meat was produced at Namiemachi (10-30 km from Fukushima Dai-ichi) in April. This rancher has not used the rice straw feed, instead he was feeding with imported hay, all stored in a barn. The local government [guessed] that the contaminated air passing through the barn may have contaminated the hay. In view of this, the Fukushima Prefecture is requesting the Government to lift the restriction of marketing cattle from Fukushima, since they are now ready to perform monitoring of each cattle.

I first suspected the pathway is from inhalation, however, due to high retention factor of radioactive aerosol in vegetation, the prominent pathway seems to be through contaminated straw or hay feed.

III. Update of the water purification system

The new zeolite sorption process, developed by Toshiba/Shaw Group has started to commission on August 18, showing DFs as below for Line B:

Species pre-processing post-processing DF
(Bq/cm3) (Bq/cm3) Decontamination Factor
I-131 ND (<7200) 5.8 <1,200 Cs-134 1,100,000 21 52,000 Cs-137 1,300,000 23 57,000 The DFs were found to be approximately 10 time lower than expected, however, it is an order of magnitude better than Kurion's process. Because of the reasonably good performance, TEPCO configured this system to run parallel to the existing system. The parallel operation improved the total capacity of the water purification system by a factor of 1.5 with 70 tons/h, starting from the night of August 19. This started to reduce the total volume of the highly contaminated water. If everything works as planned, the backlog inventories may be clarified in several month. Partly being helped from this, all of the temperature readings of the [Fukushima Dai-ichi Unit 1 plant] went below the boiling point on 11 PM on August 19. The temperature readings of [Units 2 and 3] are still 118.4/126.4, [degrees Celsius] respectively. Genn Saji