I often do things the hard way before doing them the easy way. It is very nice to have an internet tool that one can check to see the state of something they are thinking about, like radiation dose rates over an area. As I was mentioning in my last post, I found the release of information about the on-site levels at the Fukushima I plant a little difficult to parse. Today I've found a reporting site for radiation levels all over the nation of Japan, it's called the System for Prediction of Environment Emergency Dose Information (SPEEDI). You can imagine it is particularly interesting today. Have a look at their Japanese page:
They also have an English version, but it lacks all the cool tools. They have 16 different reporting sites, typically with about a dozen different monitoring locations each. Not surprisingly, these are almost entirely associated with nuclear power plants, nuclear research facilities (such as associated with the JAEA), and educational institutions.
There locations are currently not reporting, including the Fukushima I plant itself. If you are looking for data, graphs, and resources for that, well I am too. Here is what I have so far.
New York Times graphic
Graph made by a German Wikipedian
A data/graph project on Paddon
My last post
I would not be surprised if there are better illustrations by the time I post this, but this is what I know of. Back to the national radiation readings.
Much of the concern so far has referenced Tokyo. Not that other areas equally far from the plant are not also subject to the same elevated dose, but Tokyo has one of the largest metropolitan areas in the world. A small effect over a large number of people can be very significant. We have no readings for Tokyo, but we do have some in Kanagawa Prefecture (thank you GNF), which is right next to it. You can also get 7-day graphs of dose. But each monitoring station is different and there are 12 of them in Kanagawa Prefecture, and it turns out that matters a great deal to both the background dose and the profile of the elevated radiation levels. I apologize for the quality, but here is my mashup.
Regarding the chart, most detectors were not operational right after the earthquake, which I find completely understandable. The area was then unaffected until early on the 15th. After that, clearly elevated radiation levels occurred and have been sustained. Yes, it's not dangerous, but we're talking about Kangawa Prefecture, which is 157 miles away from the plant. Other locations, closer by are getting much more. Just have a look at Ibaraki, the 5th in the list here, although you would probably have figured that out on your own since it's 10x the dose rate of all the others right now.
So, I've answered many of my own questions and hopefully this answers the same for you. Even though this is the case, I still believe it to be unhelpful and sensationalist for a news organization to go announce simply "radiation levels in Tokyo 20 times normal", for several reasons, not least of which because it's cherry picked. A spike in levels is just that, a spike, and after those spikes the area is experiencing close to twice background.
Q: Has the Tokyo area been exposed to significant radiation compared to natural, directly from the plant?
Yes, this is clearly the case
Q: Is this dangerous?
It is not to the people in Tokyo. This enters into the debate of the impact of low-level radiation. People in that area are not being exposed to more radiation than what they would probably get during a Mount Fuji hiking trip. However, other areas closer to the plant do need to be paying attention.