Japanese reactor fallout: Meltdowns are a safety feature, and the U.S. West Coast is NOT at risk from radiation (UPDATE 5)

Update 5: Added Potassium Iodide Pills: Don't do that! to links
We see breathless, worry-inducing news headlines about Japan's nuclear reactor disasters. References to Chernobyl, Three Mile Island, meltdowns, containment breaches.

It's bad, no doubt about it. Japan is certain to experience long-term impacts from these reactor failures. But it's best to avoid getting caught up in the borderline hysteria that seems to have taken hold of most media sources. Remember, when reading news headlines, if it bleeds, it leads. While the headlines are dramatic attention-getters, what are the real risks?

For example, when you hear about a possible meltdown, do you picture a horror scenario where all life on earth is threatened due to radioactive fallout? Will the nuclear reactor core burn its way down into the earth's crust, as in The China Syndrome? Or, is a meltdown actually a safety feature, intended to prevent major catastrophe?

Knowledge is the antidote

Here's information that might help counter the fear-inducing headlines.

First, here's an article (at Pajamas Media, no less) that describes the Japanese reactor designs, and why the reported explosions aren't quite as catastrophic as the headlines make them out to be. It discusses the containment mechanisms and the difference between containment vessels and containment buildings–important to know if you want to pick apart the headlines and avoid misreading the situation.

Winds (shown in red) likely to carry fallout into Pacific ocean. Source: Meteorologist Cliff Mass

It's interesting to note that (according to the article) a core meltdown is a safety feature–if cooling systems fail, and the core is exposed (which has happened in Japan, at least partially) then the core is supposed to "melt down" and spread out on the graphite floor of the containment vessel, where the nuclear reactions will stop and it will begin to cool. That's what the containment vessel is designed to do, and it's one of the main reasons why Chernobyl was such a disaster: it didn't have a containment vessel, so when the core cooling failed and the core started to burn, it did not spread out - it continued to burn and release radioactive particles into the atmosphere.

In order to evaluate the severity of a core meltdown, you need additional information: is the containment vessel floor intact? Are there other factors that make the meltdown event worse than planned?

From my reading of the material, as long as the containment vessel performs as designed, a core meltdown is supposed to stop the reactor core's reactions. That doesn't mean there won't be atmospheric radiation releases (gases vented from the containment vessel), but it should be viewed as a safety feature rather than as an uncontrolled, unplanned outcome. That doesn't make it a Good Thing–it's bad, but it's better than what happened at Chernobyl.

Added: The real problem seems to be the spent fuel pool which does not have a containment vessel, and latest reports say that the spent fuel pool has no water, which means the fuel rods are uncovered, making a fire and explosion possible if not likely–which is probably worse than a core meltdown inside a containment vessel.

Wind patterns and fallout risks for the U.S.

Now, what about radioactive fallout? There have been intentional and unintentional releases of radioactive gases from the Japanese power plants. Where will the winds carry them?

What's the probable risk for people in the U.S. of A.? Are we likely to be hit with dangerous radioactive fallout? The current wind patterns indicate that fallout will probably not reach the mainland U.S.

Meteorologist Cliff Mass points out that the current wind patterns are favorable, and, that most radiation making its way to us should dissipate due to atmospheric mixing and precipitation.

Stop worrying

You Can Stop Worrying About A Radiation Disaster In Japan -- Here's Why (In-depth blog post by Josef Oehmen of MIT)

MIT NSE Nuclear Information Hub - Excellent source of fact-based information