Nuclear Experts Explain Worst-Case Scenario at Fukushima Power Plant

[tekisui]

Source: Scientific American

(snip)

"Reactor analysts like to categorize potential reactor accidents into groups," said Bergeron, who did research on nuclear reactor accident simulation at Sandia National Laboratory in New Mexico. "And the type of accident that is occurring in Japan is known as a station blackout. It means loss of offsite AC power—power lines are down—and then a subsequent failure of emergency power on site—the diesel generators. It is considered to be extremely unlikely, but the station blackout has been one of the great concerns for decades.

"The probability of this occurring is hard to calculate primarily because of the possibility of what are called common-cause accidents, where the loss of offsite power and of onsite power are caused by the same thing. In this case, it was the earthquake and tsunami. So we're in uncharted territory, we're in a land where probability says we shouldn't be. And we're hoping that all of the barriers to release of radioactivity will not fail."

Bergeron explained the basics of overheating at a nuclear fission plant. "The fuel rods are long uranium rods clad in a . They're held in a cylindrical-shaped array. And the water covers all of that. If the water descends below the level of the fuel, then the temperature starts going up and the cladding bursts, releasing a lot of fission products. And eventually the core just starts slumping and melting. Quite a bit of this happened in TMI , but the pressure vessel did not fail."

(snip)

And just what is that worst-case scenario? "They're venting in order to keep the containment vessel from failing. But if a core melts, it will slump to the bottom of the reactor vessel, probably melt through the reactor vessel onto the containment floor. It's likely to spread as a molten pool—like lava—to the edge of the steel shell, and melt through. That would result in a containment failure in a matter of less than a day. It's good that it's got a better containment system than Chernobyl, but it's not as strong as most of the reactors in this country."

more: http://www.scientificamerican.com/article.cfm?id=fukushima-core

[msongs]

1. Soviet spokesman reporting live from Chernobyl says "nothing to worry about"... nt

[regnaD kciN]

3. At Chernobyl, they never even announced the accident...

The explosion took place on April 26, 1986. The accident didn't even come to light for two days, when scientists in Sweden noticed an increase in radioactivity in the air, and determined that it didn't come from any of their own sources.

Something to keep in mind when you read that the explosion (producing a column of black/dark gray smoke) was merely "steam," etc.

[roguevalley]

4. better start mixing the cement now. I hope.

[Skip_In_Boulder]

2. Hmm, So at this point we need to hope for the best case scenario,

[Rex]

5. Hope for the best, plan for the worst.

[Skip_In_Boulder]

6. Yep