Wednesday, February 27, 2008

Nuclear Power

A great overview of the current state of nuclear power in the country, in a very readable, first person account of a visit to the Three Mile Island plant, that covers all the bases.

What went wrong with nuclear power? How did the cleanest, cheapest solution to our oil dependence become the stuff of apocalyptic nightmares? Where does the myth end and the truth begin?

…The inside [of the nuclear plant at Three Mile Island] was like nowhere else in the world. It is tempting to say that if you were to wake up inside, without ever having seen a power plant, you would know instantly where you were. Pipes the diameter of a Volkswagen bus and painted in glossy primary colors stretched along the walls and the ceiling, springing into the room at ninety-degree elbows before shooting upward to the floor above or down to the one below. Hoses the size of anacondas coiled their way around corners and over door headers, and stop valves that looked like nautical steering wheels were strapped to the walls with tags to identify them. Everything was polished and reflective under bright lights, and the air seemed to shiver from the pipes’ vibrations. It was like being trapped inside a giant air conditioner.

We climbed an open metal staircase that stretched between the pipes and machinery and followed catwalks to look around. Virtually everything around us related to water: tanks so enormous that the curve of the cylinder was nearly imperceptible, filters capable of purifying thousands of gallons at once. If the Hollywood depiction of a nuclear plant involves zones of exposure and pervasive risk, where workers live in fear of radiation—think The China Syndrome or Silkwood—life inside a real power plant was startling proof of what actually drives a nuclear plant: water. Except for the presence of uranium in a single room, the rest of a nuclear compound is essentially a giant steam engine, with three circuits of water doing virtually all the work.

The first of these water circuits, known as the primary, is the only one that actually touches radioactive fuel. In the earliest stage of the process, this water is channeled through a series of tall, thin tubes of uranium known as fuel rods, which are extremely hot from their natural decay process. It takes only a few seconds for the heat from the uranium to make the water hot, too. Once the water reaches 212 degrees, it must be pressurized to avoid boiling; at 600 degrees, under 2,000 pounds of pressure per square inch, it is ready to be pumped into the next stage of the process, known as the steam generator.

Here, the superheated primary water is brought into contact with a secondary circuit of cooler water. Since the pipes of the two circuits are allowed to touch but the water inside them is not, only the heat can be transferred, and none of the radioactivity. As the secondary circuit absorbs this heat, it boils into steam, which is piped into a series of giant fan blades known as turbines. The force of the steam blowing through those fans causes the blades to spin. If Three Mile Island were a steamboat, this would be the final result—the spinning fans would rotate a paddle wheel and push the boat across the water. Instead, at a power plant, the spinning motion is used to rotate a giant coil of wire inside a magnetic field, creating a current of loose electrons.

Presto: nuclear power.

All that remains is to cool the water and start over. For this, a third circuit of water is pumped into the plant directly from the Susquehanna River, absorbing heat and then flowing back outside to the cooling towers and into the river below. Since, at least in theory, this water never comes into contact with anything inside the plant except its own pipes, the warm water returning to the river should be no more or less polluted than when it was first pumped out. Likewise, the evaporative clouds billowing from the tops of the cooling towers, which appear so grimy in photographs, are actually no different from the clouds forming naturally above the river. In fact, those billowing clouds, which even some nuclear workers casually refer to as “smoke” or “steam,” are actually neither. Like a man’s breath on a cold day, they’re mostly water vapor and tend to fade or even disappear in warm weather. True steam, by comparison, is the more sophisticated substance—entirely gaseous and devoid of humidity—that powers a plant’s turbines, and this almost never stops blowing, especially at TMI. Over the past ten years, the plant has become famous for its constancy, setting records for continuous operation. The latest, among more than 250 similar reactors worldwide, was 689 days without pause or fail.

What all this amounts to, in a typical year, is about 7.2 million megawatt hours of electricity, or enough to satisfy the needs of 800,000 homes. By way of comparison, to produce the same amount of electricity, a coal-fired power plant would have to incinerate more than 3 million metric tons of fuel, producing 500 pounds of carbon dioxide per second, as well as 1,200 pounds of ash per minute and 750 pounds of sulfur dioxide every five minutes. Looking at the cooling towers with that in mind, where a smokestack would be at any of the nation’s 600 coal plants, it is easy to appreciate the lure of nuclear power: The carbon footprint of a nuclear plant is precisely…nothing.