Wednesday, March 23, 2011

Update on Dose Readings in Japan

This is a quick post to summarize the newest and best things on the new I have my hands on to assess the state of the dispersion of radioactive gases from Fukushima I.

Best Sources of Understandable Information

Firstly, a great new blog called Where are the Clouds? They are doing a fantastic job of following the new developments and actively contributing to the body of knowledge regarding dose rate readings and atmospheric plume modeling in the wake of the disaster. These are the professionals.

A fantastic new graphic has appeared showing the plant site dose readings from the start through the "hottest" (radiological) days at the site. You can probably read this graph for half an hour. Credit to R.C. Hoetzlein, and many thanks for releasing it for all uses. There are still a few issues related to the units and comparisons, but otherwise amazing.

Tepco reorganizes monitor readings

I imagine it's hard for reporting offices to navigate the incredibly disjointed press releases coming from Tepco. A few days ago, they were in the main list of press releases on their home page. But then they moved it to a new page of releases of nothing but monitor readings specific to the plant. I had been coming back to the NYTimes graph for what the site readings are now giving, but it seems they stopped right about the time Tepco moved the page.

Maybe they never got the memo. Or maybe they became bored of it. The most recent graph I see now is still a few days old, but as I've looked at the reports, not much has changed. On top of that, Tepco has released local area data that the NYTimes has graphed fairly well (this covers a lot of Fukushima Prefecture). Additionally, Tepco has updated this information over time, which gives a little bit more interesting picture than the confusing site readings.

Of course, there is still bad information out there. The NYTimes published a map supposedly showing the dose rates at different radii from the plant, which would seem to any ordinary reader to predict nausea, vomiting, and hair loss at 5 miles away from the plant. The only problem is that it was made with no information specific to Fukushima I, aside from an assumption that fuel was failed, core melt occurred, containment was breached, etc. It's hard to identify just how wrong this graph is, because it doesn't even give enough information to know (i mean, exposure time). Thankfully, other bloggers have been identifying this as a misuse of a model from an old and otherwise well-intentioned paper. And anyway, to get an idea of what doses people in Japan are facing, you can just keep reading.

What is Happening to Dose Rates in Japan?

Note, in order to convert to Japan time right now, switch am and pm, then add 1 hour. To convert back to EST, switch am/pm and subtract an hour.

There have been 2 major onsets of radiation spread over areas to the southwest of the Fukushima Daiichi plant. The first was very early on Tuesday 3/15 (Japan time). I've gone back and plotted the dose rates in Ibaraki Prefecture monitoring stations to compliment the previous graph I posted.

Note that this is in log scale now. Ibaraki Prefecture is much closer to Fukushima than Tokyo and correspondingly has much higher dose rates, and yes, will have greater long term effects as well. Fukushima Prefecture, of course, is hit harder than any other. Let's return to Tokyo. How have things changed there? A second wave of artificial radiation has clearly appeared. The following shows the dose rates as the first and second major Southwest winds pushed the plume over the Tokyo area.

One can easily identify the two transit dates the plume made through Tokyo. One is 3/15 in the morning and another is 3/21 in the morning. For 3/15, atmospheric data shows a line going straight through the Tokyo area, which is expected. If that wasn't enough evidence for you, the wind patterns at all altitudes on 3/21 and 3/22 show the plume traveling toward Tokyo and even further.

Mindblowing Analysis from the NNSA

Last post I was praising the public data feed from Japan's national network of detectors. The US, of course, has some impressive technology itself, and the DOE has come out with this bombshell (download in pptx format). The tool is called the Aerial Monitoring System, and obviously they send a plane around that constantly takes readings and quickly flies back and fourth over an area to get an incredible map of dose readings.

These images are showing a local perspective (left) and larger perspective (right). You can see the path the craft takes in the lines that are shown. They show units of mR/hr. For many kinds of radiation, 1 R= 1 rad = 1 rem. 1 rem = 0.01 Sv, and the limit for radiation workers in the US is mSv, or 5 rem (equivalent dose). The red color in the graphs indicates 12.5 mR/hr, and if this was absorbed for a day, that would be 0.3 R, and the equivalent dose (adding extra weighting for more damaging particles) would be some amount more than that.

Without getting into specifics, a 12.5 mR/hr area should really be avoided to whatever extent possible, but there should be differences between the readings from the air and the dose on the ground. Either way, the most important thing to avoid is internal dose. There is no reason to panic. The Japanese authorities have been making decisions to tell people not to eat certain farm products among other measures, these are all reasonable as far as I can tell but firmly based on the precautionary principle.

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