The reporting about the nuclear plants in Japan is really getting confusing.  For a few days, it seemed like every story featured a frightening headline, with the story itself was a lot less terrifying.  Here are highlights from an interview with MIT Professor of Nuclear Science and Engineering Ron Ballinger:

What’s the worst-case scenario?

Well, first off, we can’t have a Chernobyl-like situation. The system is designed so that as long as we keep water in there to keep it cool, nothing will happen.

–What happens if all the water boils off?

Hypothetically, if the water all boils and evaporates, then the fuel will stay molten and eventually melt through the steel vessel. But that’s already beyond a hypothetical worst-case scenario for me. The steel vessel is four inches thick, and they could always put seawater around the vessel, and that would keep it cool, so it can’t melt.

Radiation spiked at 1,015 microsievert per hour before the explosion. Is that dangerous?

No, that’s about 100 milirem. It’s high, but you get about 35 milirems on a trans-Atlantic flight. And if you live in Denver, you get about 50 milirems per year.

–What is the dangerous level, and what happens when that level is reached?

The LD50—that is to say, the point when 50 percent of the people exposed will meet Jesus—is in the order of 250 rem, or maybe 400. A big number. Keep in mind, what they’ve been exposed to is 0.1 rem, and about 50 percent fatality is on the order of 400 rem.

Read the whole thing.  It is completely worth it.  Since then, there have been reports of 0.8rem – much higher than normal – but still about 1/500th of the devastating levels that everyone really fears.  But, then again, according to the New York Times, Japan seems to have passed Ballinger’s worst case scenario from just a couple of days ago.

Japan’s nuclear crisis verged toward catastrophe on Tuesday after an explosion damaged the vessel containing the nuclear core at one reactor and a fire at another spewed large amounts of radioactive material into the air, according to statements from Japanese government and industry officials.

Engineers at the plant, working at tremendous personal risk, on Tuesday continued efforts to cool down the most heavily damaged unit, reactor No. 2, by pumping in seawater. According to government statements, most of the 800 workers at the plant had been withdrawn, leaving 50 or so workers in a desperate effort to keep the cores of three stricken reactors cooled with seawater pumped by firefighting equipment, while crews battled to put out the fire at the No. 4 reactor, which they claimed to have done just after noon on Tuesday.

Yet, Japan’s NHK News is reporting that radiation levels have since fallen.

Japan’s Chief Cabinet Secretary Yukio Edano says the radiation level on the premises of the quake-damaged Fukushima No. 1 nuclear power plant has been falling.
Edano told reporters on Tuesday afternoon that water is being injected steadily into the plant’s No. 1 and No. 3 reactors, but that the injection of water into the No. 2 reactor is not yet stable.

Earlier in the day, radiation levels as high as 8,217 microsieverts per hour were detected around the plant’s main entrance.

Edano said that although the figure is serious, the level has been falling from its momentary peak. He said he’s slightly relieved by this development.

Who knows where this ends up at this point? The reports are truly all over the board.  The majority of opinion seems to indicate that it will end up between Three Mile Island and Chernobyl, regardless of what happens from here.  That’s a huge range though.  While it’s extremely unlikely that any possible death toll from Japan’s nuclear plants will come anywhere close to the toll from the actual quake/tsunami—it’s just another horrible event to worry about, in a place that really, really doesn’t need it right now.