Japan: The Reactor Risk

Updated.

The United States Nuclear Regulatory Commission does not have a listing for “meltdown” in its glossary of terms. The closest you get is “core melt accident,” which the NRC defines as “an event or sequence of events that result in the melting of part of the fuel in the reactor core.” In the case of a “core melt accident,” a reactor’s nuclear fuel rods overheat and, at a temperature of several thousand degrees, quite literally begin to melt.

The Three Mile Island disaster, in 1979, is often described as a “partial core meltdown.” In that case, the reactor vessel, which houses the reactor behind thick walls of steel and concrete, was not breached. The Chernobyl disaster, in 1986, resulted in a rupture of the reactor vessel and the wide dispersal of radioactive particles. However, since Russian reactor design is very different from American (and Japanese), most experts argue that the Chernobyl accident does not offer much information that is useful outside of Russia. (I wrote about another plant, Indian Point, in 2003.)

The disaster in Japan already ranks as worse than Three Mile Island, and the obvious worry now is that it will reach Chernobyl-like proportions. The crises seem to be piling up almost by the hour—yesterday, a third explosion occurred, which quite possibly damaged the reactor vessel of the most severely stricken reactor, No. 2. Also, spent fuel rods at reactor No. 4 seem to have caught fire—these fuel rods, though no longer useful for producing electricity, still produce a tremendous amount of heat, and need to be cooled. The Tokyo Electric Power Company, which owns the Fukushima reactor complex, withdrew all but about fifty workers from this site, which would indicate very serious fear for their safety. If the company were to abandon the complex, it seems that all three of the reactors that were functioning at the time of the earthquake—Nos. 1, 2, and 3 (4 was shut down for refurbishment) would suffer meltdowns—however you define that. (It seems that they have all probably suffered “partial meltdowns.”)

What would happen then is not entirely clear, which in itself is rather terrifying. A great deal would depend on the strength and integrity of the reactor vessels. As many have pointed out, there have been serious safety concerns raised about the design of the reactor vessels of the Fukushima plants, which is more or less identical to the design at about two dozen plants in the U.S.

Read more from our coverage of the earthquake and its aftermath.

Photograph: AP Photo/Wally Santana.