In the midst of the hysteria concerning the state of Japan’s nuclear reactors, one of the more sober articles written to explain what is really happening at the nuclear power plants affected by the recent earthquake and tsunami comes courtesy of Joshua Keating, who explains to us what a nuclear meltdown is:
. . . It’s an inexact term, but “meltdown” generally refers to the complete melting of a plant’s nuclear fuel rods. These rods are about half an inch in diameter and 12 feet long and are surrounded by a zirconium covering called cladding. To prevent overheating, water is constantly circulated through the reactor. When the cooling system fails, the rods, made of a ceramic material, can melt. The melted nuclear material drips down and accumulates, possibly penetrating the core.
In the case of the Fukushima plant, it is believed that the top 2 to 3 feet of the rods were exposed after the power went out, causing them to overheat. The vessel containing the nuclear core has not been penetrated. Nuclear engineers prefer the term “partial melting” for events of this type.
The good news is that the plant is not currently operating, meaning that the fuel is only producing about 6 percent of the heat normally generated when it’s up and running. During the 1986 Chernobyl disaster, the plant was still running during a power surge that essentially turned the plant’s reactor core into a small nuclear bomb, pushing actual radioactive material — as opposed to gas with trace radioactive elements — out into the air.
The bad news is that without power, the plant’s technicians can’t resume the normal circulation of water through the core to cool down the rods.
The controlled venting of steam from the reactor — while necessary to prevent overheating — is also problematic. Inside the core, the steam reacts with the protective zirconium casing surrounding the rods, creating hydrogen. When this hydrogen is vented out and interacts with oxygen, it can cause explosions like those that occurred at the plant on March 12 and 14. The steam also contains cesium and iodine — radioactive elements that are dangerous to human health. The level of radioactivity around the plant, while relatively modest, is still twice what the Japanese government considers safe. This venting process could potentially continue for several months.
This is not an ideal state of affairs by any stretch of the imagination. But it is also not The China Syndrome. As Keating goes on to point out, “a disaster on the scale of Chernobyl, which left hundreds of square miles uninhabitable for years, is believed to be nearly impossible because of improved containment facilities at modern nuclear plants.”
For these reasons, and for others, James Acton reminds us that “Nuclear Power Is Worth the Risk.” As Acton points out, there are a large number of backup systems that make the possibility that a catastrophe may occur exceedingly small. To be sure, a single disaster may override all of those backups, and no one should be sanguine about the lessons of Japan. But the best way to react to what has happened in Japan is to study how the design behind nuclear reactors can be improved so as to be able to withstand even the worst natural or man-made disasters imaginable. It is not to throw the baby out with the bathwater when it comes to nuclear power, especially given the fact–as Acton points out–that other sources of energy generation carry risks as well.
UPDATE: NPR is reporting that the Japanese prime minister is stating that radiation has reached “dangerous levels,” and is urging people to remain indoors. In fact, people are fleeing from the area around the power plant. Despite this, there remains little to no chance that the situation will devolve into another Chernobyl. There may be radiation that seeps into the ground as a result of melting, and it is clear that people in Japan are taking the threat very seriously. Developing . . .