The new, raised assessment of the Fukushima Daiichi nuclear accident puts it on par with Chernobyl in terms of potential consequences, but it is obvious to anyone that there is a difference between Japan’s ongoing crisis and the 1986 explosion in the Ukraine. Summed up in a single word, that difference is “containment.”

Steel and cement vessels surround each of the reactor cores at Fukushima Daiichi, as is the case in all but a few of the 443 atomic power units operating around the world today.

But there are a few remaining nuclear plants still operating, all early Soviet design, that do not have primary containment vessels. And one of them happens to be located in a major seismic hazard zone.

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