Top Japan advisor resigns in protest over radiation protection for schools

[Mainichi Shimbun] Cabinet nuclear advisor resigns in protest over government response to plant crisis

A nuclear advisor to the Cabinet has resigned in protest against government stopgap measures that deal with the ongoing nuclear crisis in Fukushima Prefecture.

Toshiso Kosako, 61, a University of Tokyo professor specializing in radiation safety, submitted a letter of resignation to the Prime Minister's Office on April 29.

...

In particular, Kosako protested against the government's decision to revise the maximum permissible level of radiation exposure among children up to 20 millisieverts per year, saying, "Should I approve that decision, I would no longer be a researcher. I would not want my children to be exposed to that amount of radiation."

Kosako revealed the Cabinet did not accept his advice that outdoor school activities for elementary and junior high school students near the crippled power station be restricted to prevent them from being exposed to over 1 millisievert of radiation per year.

"It is quite rare for nuclear power plant workers dealing with radioactive materials to be exposed to 20 millisieverts of radiation per year. I cannot allow infants and children to be exposed to such high levels of radiation from an academic as well as humanitarian point of view."

[Forbes] Criticism up on Japan govt handling of nuke crisis

In a tearful news conference, Kosako said he could not stay and allow the government to set what he called improper radiation limits of 20 millisieverts an hour for elementary schools in areas near the plant.

"I cannot allow this as a scholar," he said. "I feel the government response has been merely to bide time."

I am not a health physicist (i.e. radiation expert), but I think Professor Kosako is correct. 20 mSv/year (which is also the evacuation threshold) is not a dose to be subjected to without good cause. It is ten times background radiation; it is comparbale to a CT scan every year. Based on ICRP recommendations, 20 mSv (1 year) should be estimated to cause an excess fatal-cancer risk of 0.1% (general population -- for children this should be higher?):

[Google Books excerpt] Radiobiology for the radiologist By Eric J. Hall, Amato J. Giaccia

Admittedly there is signficiant uncertainty about such a prediction, as 20 mSv is a sufficiently low dose that emprical data does not exist (you can only extrapolate from known effects at much higher doses). The Health Physics Society, for instance, recommends against quantiative estimation below 50 mSv (5 rem). But 20 mSv is pretty close to 50 mSv; I should think there's a good chance there are substantial health risks at this dose rate, even if the linear extrapolation is an overestimate.

As a related issue (one I've been repeatedly bringing up), some people in yet-to-be-evacuated areas have already received doses of up to 20 mSv (in Namie, measured), or maybe 50 mSv (extrapolated). Actually these are outdoors doses, so actual exposures are attenuated (by maybe a half).

MIT publishes study on nuclear fuel cycles

[MIT] The Future of the Nuclear Fuel Cycle

1-year cumulative dose in Fukushima prefecture

[NHK] Science ministry releases Fukushima radiation map

Estimated cumulative dose over one year (in milliSieverts), starting from March 11, to someone spending 8 hours a day outdoors:

http://www.asahi.com/national/gallery_e/view_photo.html?national-pg/0426/TKY201104260415.jpg

What's the bold line (black) at 20 mSv mean? According to reports (e.g. this NYT article), 20 mSv over one year is the Japanese government's threshold for evacuation. So if I interpret correctly, that enclosed area is likely to be evacuated within a month or so, for a long period of time. (Since much of the dose comes from long-lived ¹³⁷Cs, this could be a very long time. A permanent-exclusion zone.) That's around 500 km² in there, which based on district-level population densities probably encloses (very roughly) around 50,000 people.

Some related data sources are

• MEXT radiation monitoring data (measurements)
• Independent academic radiation survey (with more isotopes)
• NNSA monitoring data (mostly overflights)

More detailed isotope analysis from Iitate, from an academic source

Somehow I've overlooked this! It is two weeks old; it is a survey by a team of academics, hosted on Kyoto University's Reactor Research Institute:

Interim Report on Radiation Survey in Iitate Village area conducted on March 28th and 29th

Soil analysis of 8 isotopes:

Note the ¹³⁷Cs levels on the order of ~1 MBq/m². This validates previous measurements (see MEXT page for their latest data). MEXT's daily ¹³⁷Cs readings in this area have been fluctuating by almost two orders of magnitude -- maybe (?) they are measuring in different locations, moving in and out of hot spots (note the units are different here, Bq/kg of soil):

("Island Soil" is a mistake for "Inland Soil"). As a common reference point: the Kyoto University report describes the flowerbed soil sample as averaging 21 kBq/kg ¹³⁷Cs, and 749 kBq/m² in terms of area. Maybe this suggests a conversion factor (it's consistent with the earlier media reports).

They also extrapolate back from soil samples to estimate past dose rates -- they infer up to 200 μSv/hour on March 15, or 5 mSv/day, in Magata (where they measured their highest fallout levels). Based on their calculation, the accumulated dose there would be around 50 mSv to date, going up to 95 mSv over 90 days . Note these are outdoor doses (standing above soil); they say being inside a wooden framed house would reduce this by 1/2.

These are the radiation dose equivalents of multiple CT scans. I would definitely not stick around here for extended periods -- and indeed, the Japanese government is planning evacuations for this area.

Note that this survey is geographically limited (map below). The highest dose rates there (colored red) are 18 - 20 μSv/hour; apparently they extend higher further south (into the "stay indoors" zone). As being reported by Kyodo News and others, the NSC estimates the accumulated dose in the 20 - 30 km ring to be <50 mSv, and over 100 mSv in some areas of the (evacuated) 20 km zone.

For comparison, here's the map from the NNSA overflights in approximately the same time period. Not clear to me if "R" is short for "roentgen", or if they've misabbreviated "rem".

A comment on N. American 131I milk contamination non-story

Slightly-modified comment I wrote on Barry Brook's blog.

According to EL's EPA link [1], iodine-131 activities in milk were measured at 3.2 pCi/L in Arizona, 8.9 pCi/L in Arkansas, and 18 pCi/L in Hawaii; the EPA's MCL is 3 pCi/L [2], which was exceeded. But this MCL is for life-long exposure, whereas this ¹³¹I will decay in a few days; it is completely harmless, despite exceeding MCL. For example the FDA's derived intervention level for ¹³¹I in milk is 170 Bq/kg or 4,600 pCi/kg [2,3]; this is 250x higher than the highest activities detected.

EPA administrator Lisa Jackson testified about this today: she says the same thing I'm saying: [4]

Early precipitation samples collected by EPA indicated low levels of radioactivity. Given the sampling results in other environmental media, EPA expected to find very low levels of radiation in precipitation samples. Similar findings are to be expected in the coming weeks as radioactive materials are dispersed through the air from Japan. While the levels in some of the rainwater exceed the applicable Maximum Contaminant Level (MCL) of 3 pCi/L for drinking water, it is important to note that the corresponding MCL for iodine-131 was calculated based on long-term chronic exposures over the course of a lifetime 70 years. The levels seen in rainwater are expected to be relatively short in duration and are not expected to present any threat to public health.

Results from samples of milk taken March 28, 2011 in Phoenix, Arizona and Los Angeles, California showed approximately 3 pCi/L of iodine-131, which is more than 1,500 times lower than the Derived Intervention Level set by the U.S. Food and Drug Administration. These types of findings are to be expected in the coming days and are far below levels of public health concern, including for infants and children. Iodine-131 has a very short half-life of approximately eight days, and the level detected in milk and milk products is, therefore, expected to drop relatively quickly. Additional information about the broader federal response can be found at: http://www.usa.gov/Japan2011.

Take the whole-body CEDE of ¹³¹I by ingestion. [5] (Disclaimer, I am not a health physicist). At a CEDE of 1.44*10^-8 Sv/Bq, drinking 1 L/day of MCL 3 pCi/L water gives you an accumulated dose of 40 μSv or 4 mrem (the base regulatory definition [6]) after 70 years. (This is, of course, nothing. You get 17,000 mrem (17 rem) of natural radiation in the same time period). If instead you have a one-shot ¹³¹I release, which gives you an initial ¹³¹I level of 3 pCi/L which then decays, you ingest a total of 1 L/day * 3 pCi/L * (8.0 days / ln(2)) = 34.7 pCi, for a total dose of 18.4 nSv or 1.84 μrem. This is ridiculously negligible. With the Hilo measurement, 18 pCi/L, this goes up to 110 nSv or 11 μrem.

Now, for contrast; in Fukushima prefecture dairy farms, milk ¹³¹I levels had been measured [7] up to 1,510 Bq/kg (L), or 40,810 pCi/L. Under the same assumptions as above, if you were to drink 1 L/day of this milk (which you couldn't been it was not sold), you could get a total dose of 250 μSv (25 mrem), over the few weeks it would take for the iodine to decay. Four orders of magnitude higher than in the US (but still not really harmful).

[1] http://epa.gov/japan2011/rert/radnet-sampling-data.html#milk

[2] http://www.atsdr.cdc.gov/csem/iodine/standards_regulations.html

[3] http://www.fda.gov/ICECI/ComplianceManuals/CompliancePolicyGuidanceManual/ucm074576

[4] http://yosemite.epa.gov/opa/admpress.nsf/0/16cf19b9b7f7014a85257870006dd410?OpenDocument

[5] http://researchcompliance.uc.edu/radsafety/isotope/isds-I131.html

[6] http://water.epa.gov/drink/contaminants/index.cfm#Radionuclides

[7] http://online.wsj.com/article/SB10001424052748704021504576209854015156320.html

Fukushima rated INES level 7

[Kyodo News] Japan raises nuke accident severity level to highest 7 from 5

My summary:

• The rating is based on the amount of radiation released
• Cumulative radiological release estimated at 370 PBq (NISA), 630 PBq (NSC)
• NSC had earlier estimated rate of radiological release of 10 PBq/hour, over "several" hours
• These activities are in terms of ¹³¹I "equivalent" (see INES User's Manual Appendix I)
• Estimated cumulative doses of up to: >100 mSv (within 20 km exclusion zone), 50 mSv (20-30 km "stay indoors" zone), >1 mSv up to 60 km northwest, 40 km south-southwest
• Unclear if this is outdoors dose (I assume it is)

Here's the NISA press release:

[NISA] INES Rating on the Events in Fukushima Dai-ichi Nuclear Power Station by the Tohoku District - off the Pacific Ocean Earthquake

It gives these estimates of the radiological discharge:

For comparison, I've dug up a more comprehensive estimates for the discharge from the Chernobyl disaster. Keep in mind that the dispersal mechanisms are different -- there's no core fire at Fukushima.

http://titania.sourceoecd.org/vl=2140418/cl=16/nw=1/rpsv/~4292/v3n1/s1/p1l

Japan to extend evacuation zone within a month; using threshold of 20 mSv/year

As I foretold, several towns outside of the current 20-km (30-km recommended) zone will now see long-term evacuations, due to potential hazards of accumulated radiation dose. These evacuations are not urgent and are not going into effect immediately, rather sometime within the next month. The new zone is not a circular radius around Fukushima Daiichi, but rather focused around areas of fallout in the northwest direction.

[NYT] Strong Aftershock as Japan Urges More Evacuations

Yukio Edano, the government’s chief cabinet secretary, said in the capital on Monday that the government would order parts of five villages and cities that are outside the current zone to prepare to evacuate. The fear is that these areas are being exposed to radiation equivalent to at least 20 millisieverts a year, he said, which could be harmful to human health over the long term. Evacuation orders will come within a month for Katsurao, Namie, Iitate and parts of Minamisoma and Kawamata, Mr. Edano said.

The threshold for evacuation is

...to reach the Japanese government’s threshold level for evacuations: radiation accumulating at a rate of at least 20 millisieverts per year.

Monitoring outside the current 20-km zone measured integrated doses up to 14.5 mSv (since March 23), and current dose rates up to 22.1 μSv/hour (24-hour average). These are probably underestimates since the start of monitoring was several days after the initial radiation release, apparently excluding the periods of higher dose rate (as indicated by aerial monitoring).

[MEXT] Readings of integrated Dose at Monitoring Post out of 20 Km Zone of Fukushima Dai-ichi NPP

Significantly, these are outdoor doses (probably higher than what people are actually exposed to). Further, there is significant spatial variation -- most area has much lower dose rates than the highest measured, although this suggests some hotspots might have higher, unmeasured doses.

(Update: according to the Nuclear Safety Commission of Japan, the total dose in the unevacuated 20-30km ring is estimated to have been around 50 mSv. It's unclear if this is the outdoor or indoor dose (in this zone, residents had been cautioned to stay indoors).

As the timescales indiciate, much of the dose comes from long-lived radioisotopes like Cs-137 (see MEXT dust sampling and my earlier comments). So it's conceivable that there will be areas which will remain closed (no permanent residents) for very long timescales -- decades.

US industry source: spent fuel pieces found outside, covered over with bulldozers

According to a western nuclear industry executive, quoted on condition of anonymity:

Broken pieces of fuel rods have been found outside of Reactor No. 2, and are now being covered with bulldozers, he said. The pieces may be from rods in the spent-fuel pools that were flung out by hydrogen explosions.

[New York Times] Millions Without Power After Japan Aftershock

This is supported by the previously leaked NRC assessment, which stops short of identifying "very high dose rate material" as spent fuel pieces:

Fuel particulates may have been ejected from the pool (based on information of neutron emitters found up to 1 mile from the units, and very high dose rate material that had to be bulldozed over between Units 3 and 4. It is also possible the material could have come from Unit 3).

[NRC Reactor Safety Team] NRC threat assessment of Fukushima risks

There is an inconsistency: the executive says the fuel pieces were found outside Unit 2, while NRC says it was between Units 3 and 4. The Reactor Safety Team speculates the source was the spent fuel pool of either Unit 3 or 4. Unit 4 was the one with the full-core offload, where the entire core was in the storage pool for maintenance. According to the document, those assemblies were 105 days old at the time; and according to JAIF, there were a total of 1,331 assemblies in that pool.

(It's unclear to me whether NRC's "particulates" refers to dust-size particles, or whether the executive's "pieces" refers to larger fragments).

High-resolution damage photos are hosted on Cryptome:

http://cryptome.org/eyeball/daiichi-npp/daiichi-photos.htm

Here's one of them, of the area between Unit 4 (left) and Unit 3 (right) where the NRC says the "very high dose rate" material was found (click to see high-res version):

An idea about the faulty 134I reading

There's been some speculation (e.g. at Arms Control Wonk) that the detection of short-lived fission products and activation products are evidence of intermittent nuclear criticalities. While it's been suggested that some isotope identifications are probably errors (computer confusion of one gamma-ray peak with another of very similar energy), one problem not resolved in the media is, how to explain the improbably high activities observed? For example, the erroneous measurement of 78 Curies/liter of iodine-134 in turbine hall puddles -- a fission product with a 53 minute half life. Yomiuri Shimbun reports TEPCO as concluding it was actually cobalt-56, or maybe cesium-134 (they backtracked twice). But such high activity levels of these longer-lived fission products would be even more confusing.

I suggest a simple explanation for this absurdity. Take a look again at this set of faulty measurements (leftmost column; I've appended this table at the end of this post). We see 2.9×10⁹ Bq/cm³ (or 78 Ci/L) ¹³⁴I, t_1/2 = 53 minutes. But look at the time! (Top rows, first page). This sample was obtained at 8:50, and measured (by gamma spectrometry I speculate) at 18:50 of the same day -- 10 hours later. Eleven ¹³⁴I half lives later.

So what's the meaning of the reported figure? To report the measured activity of ¹³⁴I, after 99.96% of it had decayed away, would be mostly meaningless. I speculate that TEPCO had, rather, inferred the original ¹³⁴I activity by taking the measured activity and working backwards. That is, compensated for 11.32 half-lives of decay by just multiplying them back in (a factor of 2,558x). This would be fine -- if the isotope really was ¹³⁴I.

But suppose the true contaminant was really a long-lived isotope, half-life of months (Co-56) or years (Cs-134). Then the decay would have been negligible; and the back-calculation would have introduced an error factor of 2,558x. The actual activity would then have been 3 orders of magnitude lower than the reported one, or about 1.13×10⁶ Bq/cm³ (31 mCi/L) of a long-lived isotope. Which would be consistent with the other measurements.

Update: Cyril R points out that tellurium-134, t_1/2 = 41.8 minutes, β-decays to ¹³⁴I, which would alter the calculations (by a small factor).