Yomiuri Yomiuri / Reuters
There was another explosion at a Japanese nuclear power plant today. Same power plant, same cause, different reactor. (Also, same outcome: The outer layer of the buildings surrounding the reactor was blown apart, but, again, there was no increase in radiation following the blast. The reactor, itself, is still contained.)
This particular reactor—Fukushima Daiichi #3—is a little bit different, though, and the Wall Street Journal does a good job of explaining why.
Nuclear experts are particularly worried about the No. 3 unit, supplied by Toshiba Corp., because it uses an unconventional fuel called MOX fuel, short for mixed oxide.
It is made by mixing low-enriched uranium with plutonium that has been recycled from a global stockpile of defunct nuclear weapons. This recycling is part of an international effort to decrease the number of nuclear weapons and move from "megatons to megawatts."
MOX fuel has greater concentrations of "actinides," or radioactive elements and runs hotter than conventional fuel, so a shut down plant would have to deal with more "decay" or residual heat from fuel rods.
There are at least two dozen MOX-burning nuclear plants globally. But some experts believe that an accident at a nuclear power plant utilizing MOX fuel could be more dangerous than one that uses conventional uranium-based fuel.
It's worth noting that this is one of the reasons why an interdisciplinary faculty group from MIT advised against the United States adopting a nuclear fuel recycling program. Primarily, the group was worried about proliferation—the process of recycling the fuel leaves more opportunities for potentially dangerous materials to fall into the wrong hands.
MIT didn't rule out recycling completely—just advised against it in the near term. But reading their report took me from thinking of nuclear recycling as simply common sense, to having a much more nuanced understanding of both the rewards and the risks.
I'd recommend this report as a relatively readable primer on the nuances of nuclear energy, in general. The full thing is 12 chapters long, but the executive summary is a quick read, and it's all available for free online.