Fukushima update: Not yet in the clear
by Andrew Davies
March 18, 2011
Overall, with possible exception of spent fuel pool of reactor #3, the status of all facilities is very similar to yesterday, which is a bad thing. Major uncertainty relates to amount of radiation already being released to air and sea, to risk of a violent fire in the cladding of the fuel rods as the spent fuel pools are exposed for hours, as well as to the behavior of the reactor cores as water levels remain low.
Good news is that the violent release of radioactivity due to fire or explosion feared yesterday has not happened yet. Power is still not restored to the facility, but some progress has made to bring off site power and more equipment. This means more effective cooling could be established in some days. At least until that happens, the situation remains critical and unpredictable.
Important: Our updates are based on the best information we have been able to collect from various sources. There is a lot of confusion in any crisis situation, and in this case several governments and official bodies have already questioned whether all the available information is being provided.
Summary: Status of facilities
Reactors 1-3: water level in reactors low (about half of fuel rods exposed), no grid power, seawater injection apparently ongoing. Fuel rods have certainly damaged and are releasing radioactive substances.
Fire department has brought in 30 more trucks, at least one reported to be a “Super Bomber” able to shoot to a distance of 2 kilometers. Yesterday police trucks were unable to operate close to plant because of high radiation levels, only SDF (Self Defense Force) trucks that can be operated from inside the cabin were used.
Spent fuel pools of units 1&2: Water levels in Unit 1 are decreasing. Steam was reported from unit 2, expected to be boiling.
Spent fuel pool of unit 3: Water in #3 almost depleted, but Tepco hopes some water is left. Fuel rods have certainly damaged, releasing radioactive substances. The reactor buildings are heavily damaged, allowing releases directly to outside air.
Spent fuel pool of unit 4: Water level very unclear.
Spent fuel pools of units 5&6: Temperatures still rising, water left but level unclear.
Worst case scenarios
* The zirconium contained in the fuel rod cladding can react violently with air, if exposed for hours. This fire would release and spread very large amounts of radioactivity high up in the air. Wide disagreement on the probability of this happening.
* A large amount of molten fuel accumulates at the bottom and a nuclear reaction starts. Very low probability and can be prevented if there is any borated water in the pool.
* Reactor boils dry, molten core breaches reactor pressure vessel and comes in contact with the water in the containment, which boils rapidly causing a steam explosion.
* A major risk is an event (e.g. increased release of radioactivity from a spent fuel pool due to overheating) that raises local radiation levels to completely intolerable levels - preventing further work to restore cooling.
Tepco seemed to suggest that encasing the plant in concrete is an option if cooling efforts fail (according to Reuters live feed).
Local wind speed slowed down considerably in the morning but direction remained towards the sea. Winds towards Tokyo are still feared for Sunday.