Chico Harlan and Steven Mufson, Monday, March 14
TOKYO — A second explosion rocked Japan’s seaside Fukushima Daiichi nuclear complex Monday, this time destroying an outer building at unit 3. A Japanese government official separately said that a third reactor at the six-reactor facility had lost its cooling capacity, adding to the complications facing the engineers who try to limit the damage of a partial meltdown.
Like the Saturday explosion at unit 1, the blast at unit 3 took place after a buildup of hydrogen was vented by the reactor. The hydrogen was produced by the exposure of the reactor’s fuel rods and their zirconium alloy casing to hot steam.
In normal conditions, the fuel rods would be covered and cooled by water.
The explosion occurred as Tokyo Electric entered day four of its battle against a cascade of failures at its two Fukushima nuclear complexes, using fire pumps to inject tens of thousands of gallons of seawater into two reactors to contain partial meltdowns of ultra-hot fuel rods.
The tactic produced high pressures and vapors that the company vented into its containment structures and then into the air, raising concerns about radioactivity levels in the surrounding area where people have already been evacuated. The utility said that at one of the huge, complicated reactors, a safety relief valve was opened manually to lower the pressure levels in a containment vessel.
But the limited vapor emissions were seen as far less dire than the consequences of failure in the fight against a more far-reaching partial or complete meltdown that would occur if the rods blazed their way through the reactor’s layers of steel and concrete walls.
At the 40-year-old Fukushima Daiichi unit 1, where an explosion Saturday destroyed a building housing the reactor, the spent fuel pool, in accordance with General Electric’s design, is placed above the reactor. Tokyo Electric said it was trying to figure out how to maintain water levels in the pools, indicating that the normal safety systems there had failed, too. Failure to keep adequate water levels in a pool would lead to a catastrophic fire, said nuclear experts, some of whom think that unit 1’s pool may now be outside.
“That would be like Chernobyl on steroids,” said Arnie Gundersen, a nuclear engineer at Fairewinds Associates and a member of the public oversight panel for the Vermont Yankee nuclear plant, which is identical to the Fukushima Daiichi unit 1. More...

No comments:
Post a Comment