So says the Fukushima prefectural government, after more than one and a half year since the start of the Fukushima I Nuclear Power Plant accident. Supposedly, it took them all these days to analyze the data that was retrieved from the 19 monitoring posts around the two nuclear power plants (Fukushima I and II), and only now the prefectural government is sheepishly admitting the radiation levels were much, much higher than it has been telling the residents.
What's more, though the prefectural government doesn't say it explicitly, the spikes in radiation levels correlate not to the explosive events but the vents, if you look at the charts published by the Fukushima prefectural government.
First, from Asahi Shinbun Fukushima Edition (9/22/2012):
On September 21, Fukushima Prefecture announced the result of air radiation survey conducted in March last year around Fukushima I Nuclear Power Plant. The reading in Kamihatori in Futaba-machi, 5.6 kilometers northwest of the nuclear plant, was 1,590 microsieverts/hour, highest so far outside the plant as the prefectural government knows.
The result was compiled from the data from March 11 to 31 last year that remained in the 19 monitoring posts installed near the nuclear power plant. In Yamada in Futaba-machi, it was 1,020 microsieverts/hour at 12AM on March 16, 2011, and it was 904 microsieverts/hour at 5PM on March 12 in Shinzan, also in Futaba-machi.
According to Fukushima Prefecture, the monitoring posts in the north of Fukushima I Nuclear Power Plant started to register higher radiation levels in March 12, and the monitoring posts in the south of the plant in Naraha-machi and Hirono-machi in March 15.
In the case of Kamihatori, the maximum level was recorded at 3PM on March 12, before the hydrogen explosion at Reactor 1 at Fukushima I Nuclear Power Plant. According to the prefectural government, it was probably because "radioactive materials had been leaking even before the explosion". The prefectural government says it will conduct more detailed analysis including wind directions and wind speed.
Now, for Fukushima Prefecture to pretend this was new information (that the radiation had been leaking even before the Reactor 1 explosion), that's highly misleading. Fukushima Prefecture started measuring radiation levels in the areas surrounding the two nuclear power plants (Fukushima I and II) as early as 8AM on March 12, 2011. The first measurement that would have shown them that the radiation level was already several times higher than normal (0.04 - 0.06 microsievert/hour) was that of Tomioka-machi (Fukushima II) at 0.18 microsievert/hour at 8:25AM on March 12, 2012. At 8:52AM on the same day, they measured 14 microsieverts/hour in Namie-machi. Reactor 1 had a hydrogen explosion at 3:36PM.
(All of these were disclosed long time ago - June 3, 2011 - by NISA of all people, and no one in the media said a thing. If you read Japanese, see my Japanese blog.)
But what's more interesting about the latest disclosure by the Fukushima prefectural government is that the spikes in air radiation levels coincide not with the explosive events but with the vents that TEPCO did or attempted.
From the data released by the Fukushima prefectural government (I put the English labels):
Kamihatori, Futaba-machi: The first spike of radiation occurred even before the first vent of Reactor 1 on March 12, 2011. The huge spike to 1590 microsieverts/hour occurred at 3PM, after the vent at 10:17AM and after the pressure of the Reactor 1 Containment Vessel dropped at 2:30PM.
Kamiyatori is located northwest of Fukushima I Nuclear Power Plant. On March 12, 2011, the areas that registered high levels of radiation were all located north and northwest of the plant.
Then, after the vent of Reactor 2 on 12AM on March 15, 2011 (which was a dry vent), huge spikes in radiation were recorded in the areas in Okuma-machi, Tomioka-machi, and Naraha-machi, which were located south of the plant.
Mukaihata, Okuma-machi, immediate south of the plant. Spike at 11PM on March 14, 2011:
Yonomori, Tomioka-machi. Spike at 2AM on March 15, 2011:
Yamadaoka, Naraha-machi. Spike at 3AM on March 15, 2011:
The plume that went past Okuma, Tomioka, Naraha reached Kitaibaraki City in Ibaraki at 5:50AM on the same day, registering 5.5 microsieverts/hour. The Japanese media reported it, as possibly caused by the explosion of Reactor 2 (here's Sankei Shinbun on March 15, 2011), and no one understood the significance of the news at that time. Hardly anyone knew what "microsievert" was.
Well, it may not have been the explosion that caused the spikes. It is likely to have been the vent - intentional release of radioactive materials to lower pressure to avoid explosions. Well the explosions or some explosive event (in the case of Reactor 2) took place at Fukushima I Nuclear Power Plant after they did the vent. So what was the vent for?
That the vent, not the explosions, caused the radiation levels to rise has already been stated by none other than TEPCO in its report. Again, when the report was released, the media paid no attention, and people didn't care (other than the familiar refrain of "TEPCO lies").
A Tokyo University researcher stated in his paper accepted by a peer-reviewed magazine that a huge spike of radiation was registered at Fukushima I Nuclear Power Plant after the Reactor 2 dry vent. Again, no one paid attention.