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Integrity of spent fuel rod pools also vitally important
NHK report that the explosion in No 3. was likely caused by spent fuel
rods being exposed to air.
Once fuel rods are spent, they are removed from the reactor by crane and kept
submerged in a concrete pool filled with water near the top of the reactor vessel.
Since the spent rods take three to four years to cool, it is important that cold
water is continually pumped in and circulated around them.
The pumping system failed due to the power outage and the spent rods became
partially exposed to air and hydrogen was produced which later ignited.
So just as the integrity of the main reactors vessels is paramount, the integrity
of the pools that hold the spent rods is also vitally important.
Unfortunately wind directions around the crippled reactors is westward.
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