This is live coverage of the HNK feed. I'm doing my best to make sense of the translation. Apparently there is an ongoing fire that may be a spent fuel fire. This is very concerning. Evacuation has been ordered up to 30 km (20 miles). A spent fuel fire has the potential of causing far greater radiation release to the environment than a reactor accident.
The number 4 reactor was not operating at the time of the earthquake according to NHK. However, the loss of power that occurred when the tsunami wiped out the diesel generators caused the spent fuel pools to lose water circulation. Heat from the spent fuel would have eventually boiled off the water once circulation was lost. When spent fuel is uncovered it can heat up to such high temperatures that its zirconium alloy cladding catches fire. That appears to have taken place. Moreover these conditions apparently led to hydrogen generation which caused an explosion that destroyed the roof of the reactor 4 building.
Radiation levels of 400 milliseverts (reporting was previously in microseverts, one thousand times less) have been reported between reactors 3 and 4. The live NHK report stated that the hydrogen explosion and fire at reactor 4 may have been caused by burning of the zircalloy cladding of spent fuel rods in the damaged pool. Neutrons have been measured outside of the reactor indicating that water levels are low or the spent fuel has become uncovered. Neutrons are stopped rapidly by hydrogen in water, but will pass through heavier nuclei. Neutrons have a long path length in air.
This is an image of a functioning spent fuel pool. The beautiful blue color is caused by radiation exceeding the speed of light in water (it is less than the speed of light in a vacuum) Nuclear plant workers at Chernobyl who saw this color when they looked at the exposed reactor core there knew that they would soon be dead of radiation poisoning. Uncovered spent fuel will be extremely dangerous to nuclear workers trying to contain the disaster in Japan.
Spent fuel in pools around reactors contains very high levels of radioactivity. If this is a spent fuel cladding fire large amounts of radioactivity could be released to the environment.
I ran a NOAA particle trajectory model to see what it might show us about possible paths particles from the Fukushima vicinity might follow. This model run indicates the possibility of very low levels of particles from the accident vicinity reaching the coastline of the Pacific northwest of the U.S. at mid-levels of the troposphere in 84 hours. Levels over the U.S. would likely be diluted to very low levels by dispersion and mixing. These model runs are not forecasts.
Most radioactive particles will probably end up in the Pacific Ocean.
Same model parameters except that initial height is lowered from 500 meters to 100 meters.
Particle tracking model run starting tomorrow at 100 meters going to 84 hours out. Tracks shift out directly to the east offshore from Japan then curve north towards the Aleutian Islands.
Same parameters starting 2 days from now. Radioactive particles go out over the Pacific then recurve in the direction of the Philippines.
http://ready.arl.noaa.gov/...
Updated by FishOutofWater at Tue Mar 15, 2011, 07:30:43 AM
NHK now reports the fire is out and radiation levels have dropped.
Acknowledgment
The authors gratefully acknowledge the NOAA Air Resources Laboratory (ARL) for the provision of the HYSPLIT transport and dispersion model and/or READY website (http://www.arl.noaa.gov/...) used in this publication.
