Map of the areas affected by Friday's earthquake, including the Fukushima Daiichi power station. (Image courtesy of USGS)
A nuclear reactor creates power through the process of fission, in which the nucleus of an unstable atom is broken apart. One of the most common isotopes used in fission reactions is uranium 235. The nucleus of a U235 atom is massive, consisting of 92 protons and 143 neutrons. If it absorbs an additional neutron, it becomes too heavy and decays into other, more stable elements. Fission of the U235 nucleus also yields a second neutron, which then causes a chain reaction of fission in other, nearby atoms of U235. In a nuclear reactor, uranium pellets are housed in metal fuel rods that are submerged in highly pressurized water. Fission reactions inside the fuel rods create heat, which causes the surrounding water to boil. The boiling water is then transferred to a turbine, where its heat energy is converted to electricity.
Diagram of a nuclear reactor. (Image courtesy of 45 Nuclear Plants)
Immediately following the earthquake, workers at the Fukushima Daiichi station deployed a control system in the reactors and successfully halted the fission process; but with no electricity, the cooling mechanism failed. Residual heat in the fuel rods is now causing water to boil off, increasing the pressure inside the reactor to dangerous levels and raising concerns of a full meltdown. If the fuel rods are exposed to air for too long, the metal casing could crack, allowing radioactive material and hydrogen to escape and possibly triggering an explosion that would release radiation into the atmosphere. Explosions have already occurred in two out of three damaged reactors. Twenty-two people were diagnosed with radiation poisoning after the first explosion and the roof of one of the secondary containment vessels was blown off in the second.
As Japan continues racing against the clock to keep its nuclear energy contained, the debate over nuclear power rages in the rest of the world. Many are citing the Three Mile Island incident in 1979, the 1986 disaster at Chernobyl, and now the crisis at Fukushima as prohibitive warnings to the growth of nuclear power. Others, like risk assessment scholar David Ropeik, have questioned the relative danger of radiation poisoning when compared with the carcinogenicity of coal and oil burning byproducts.
Either way, the situation in Japan isn't getting any better. Even if operators prevent a full meltdown at the Fukushima plant, it will take years for the people of Japan to recover from this tragedy. According to the New York Times, one senior official is less than optimistic, remarking "under the best scenarios, this isn’t going to end anytime soon."