Associated Press has an insightful and disturbing report about how the U.S. Nuclear Regulatory Commission came to do two things in the first week following the events at Fukushima which are still producing backlash in Japan and the U.S.
In those early days of the crisis NRC Chairman Gregory Jaczko told a Congressional committee March 16th that the agency believed all of the water in the spent fuel pool at unit #4 was gone and that it was releasing huge amounts of radioactive particles into the atmosphere.
Based on this assessment, Jaczko issued a statement advising all Americans in Japan within 50 miles of the Fukushima reactor site to evacuate the area. This statement was emphasized in a March 17 White House press briefing.
The Japanese government immediately protested these statements saying that to the best of their knowledge the spent fuel was still covered in water. Even more important, they objected to Jaczko interfering in the domestic affairs of a sovereign nation.
It wasn't until two months later that the NRC revised its views on the condition of the pool based on video evidence and water chemistry samples that showed the fuel was undamaged by a hydrogen explosion at unit 4 and that water was covering the fuel right up to the top of the pool.
Enter a career government official
Charles Casto, an NRC career executive stationed in Japan at the time, who said he made the assessment that the spent fuel pool had lost its water. He blames "the fog of war" because there was no sensor data from the plant and no visual information on the condition of the pool. He added that there were high radiation levels being detected around unit 4 so that led to the assumption it was coming from the spent fuel pool.
This raises the question of what did the NRC really know and when did they know it? For instance, by the time Jaczko delivered his testimony to Congress a week after the tsunami hit the plant, there had been time for remote sensing UAVs and low earth orbiting satellites to provide data about the condition of the spent fuel pool. It was now visible from the air since the hydrogen explosion blew off the top of the building structure that surrounds the plant.
What can IFR sensors see?
|Image: U.S. Army|
Infrared sensors on UAV's can report the approximate temperature of the hood of a car in a parking lot differentiating it from residual heat of the blacktop. See this Aviation Week report on the use of IFR sensors on UAVs.
According to a retired U.S. nuclear utility executive, at Fukushima the Unit 1 & 2 spent fuel pools have surface dimensions of 7 meters by 12 meters.
They have a depth of 14 meters, with 7 meters of water above the tops of the stored fuel bundles when pools are full. Unit 3& 4 spent fuel pools have surface dimensions of 10 meters by 12 meters, with the same depth and above-fuel water levels as units #1 & 2.
These are large objects and their temperature would easily be detected by am infrared sensor on a UAV, helicopter, or satellite. The question is if these data were collected, were they ever sent to the NRC?
History of remote sensing data acquisition at Fukushima
The New York Times reports that aerial sensing of radiation from the Fukushima plants was acquired in the first week following the disaster. The U.S. Department of Energy took extensive aerial air and ground samples. Their report from October 2011 provides a summary of the flights, data acquired, and maps of the extent of radioactive contamination.
What we are left with is that Mr. Castro is explaining the uncertainty he dealt with at the time and how it was translated into congressional testimony and a judgement call by the NRC for the 50 mile evacuation.
Arguments will continue for a long time over these responses. Mr. Castro's forthcoming remarks don't make the agency look very good, and perhaps even appear as though he is falling on his sword, metaphorically speaking, in the Japanese tradition. That's probably too harsh a judgement. He's provided some transparency into the sequence of events. That's helpful and a lesson learned for his successors.
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