JAPAN’S M WORD – MELTDOWN

Japan now assumes 'possibility of a meltdown' at troubled reactors; Japanese workers raced against the clock to pump seawater into two damaged nuclear reactors. It’s a last-ditch effort to cool them enough to avert the kind of core meltdowns that happened at Chernobyl and Three Mile Island.
Mark Clayton, March 13, 2011 (Christian Science Monitor)

"Japanese workers and nuclear experts raced against the clock to pump seawater into two damaged nuclear reactors…[in] a last-ditch effort to cool them enough to avert Chernobyl- or Three Mile Island-like core meltdowns even as government officials admitted partial meltdowns are already assumed [in the wake of Friday’s 8.9 earthquake]…

"…[S]ix reactors at two different nuclear power plants – Fukushima I and nearby Fukushima II – [are] in a state of emergency…11 of the nation’s 54 reactors [are] shut down…knocking out about 30 percent of Japan’s power [and short-term blackouts and long-term energy shortages are anticipated]…[T]he decision had been made far sooner to inject seawater directly into the No. 3 reactor…a previously unprecedented step that some US experts described as a desperate measure. Despite that, coolant levels at the No. 3 reactor dropped so that part of the fuel rods became exposed…"

Post-hydrogen explosion containment hall at reactor 1 with the containment building inside still intact. (click to enlarge)

"A nuclear reactor core meltdown occurs when fuel rods in the reactor’s core overheat and begin to melt. The rods are filled with [radioactive substances]…It is possible for that molten material to get so hot that it could melt through the primary steel confinement shell…[and] even through the floor of the reactor building…Underscoring the seriousness of the situation, the Fukushima prefecture government Sunday widened its mandatory evacuation zone to 20 kilometers (12.4 miles) around both nuclear plants…Up to 450,000 residents could be evacuated overall…

"Although all three of the Fukushima I’s then-operating reactors shut down successfully…it takes at least 24-48 hours for them to cool…But diesel emergency generators were knocked out…[and the] battery-powered cooling system backup soon lost power…Tokyo Electric Power Company, which owns the plant, began pumping seawater into the No. 1 reactor…Even so, an enormous explosion…destroyed most of a secondary containment building…[but] left intact a critical steel shell…Efforts to cool that unit with seawater continued…[A] further, similar hydrogen-based explosion could also occur at the No. 3 reactor at Fukushima I. since the fuel rods had been briefly exposed, raising the risk of meltdown and explosion…"

click to enlarge

"Meanwhile, radiation levels well in excess of government standards were reported around the Fukushima I plant with its three troubled reactors – including cesium 137 – corroborating the view that partial meltdowns had occurred…Radiation screening centers have been set up…As many as 160 may have been exposed overall…Japanese efforts to cool the reactors had clearly had at least some effect…[but] worry [continues] about the spent fuel pools near these reactors…If the water leaks from the pools that could also lead to a major release of radioactivity…[A]ny major releases of radioactivity could be especially dangerous because the reactors are so close to masses of people…"

[Ken Bergeron, physicist, Sandia National Laboratories:] “We're in uncharted territory…We're in the land where probability says we shouldn't be. And we're hoping that all of the barriers to release of radioactivity will not fail.”