Three Mile Island Anniversary March 28, 2011Posted by Lofty Ambitions in Science.
Tags: Movies & TV, Nuclear Weapons, Physics, Radioactivity
This weekend, we were working on our regular post for Wednesday about radioactivity and how we measure it, because we’re trying to make sense, in small ways, of the nuclear accident currently unfolding in Japan. Suddenly, we remembered that, on March 28, 1979, a valve stuck at Three Mile Island. At that time, we were teenagers not yet very aware of the world’s dangers. This was before the twenty-hour news cycle (which would feel its birth pangs later that year with the Iran hostage crisis), when we spent afternoons listening to the Bee Gees, Rod Stewart, and The Knack.
The accident at Three Mile Island began with a minor problem in a secondary system, but the chain of events continued, as they so often do. A relief valve stuck open in the primary system, and some coolant from the nuclear reactor escaped. That wasn’t good, but it’s what happened next that really accelerated the problem. An engineer in the control room misunderstood what one of the indicators was telling him. An indicator light showed that electric power was not operating the valve, but they interpreted that to mean the valve was closed, not requiring power. If the valve was closed, the coolant level had risen, so they released some steam, further lowering the coolant level. The core was being exposed.
Years later, in 1985, a television camera finally physically accessed the core (read more at National Museum of American History), and we understood that it had partially melted down. The cladding (the first level of uranium containment) on most of the fuel rods had failed, allowing the products that result from fission in the core to be released into the cooling water surrounding the rods. Tons of melted uranium flowed to the bottom of the reactor vessel (the second layer of containment).
Less than two weeks before Three Mile Island, The China Syndrome hit the theaters. Anna, already a fan of Michael Douglas from The Streets of San Francisco, became an even bigger fan of Jack Lemmon, who played Jack Godell, the shift supervisor at the fictional nuclear power plant. During what seems to be a relatively routine SCRAM, or shutdown, Godell discovers that a gauge has given the operators the wrong information. He taps the indicator with his pen, and it unsticks. They thought the water level in the reactor core was too high and released some, but the gauge was wrong and the release has left the water level too low. When the water level cooling the fuel rods gets too low, the rods can overheat. Moviegoers understood the Three Mile Island scenario because The China Syndrome had shown us something similar.
During the incident in the film, Godell feels an unusual vibration that tells him something bigger than a stuck indicator is amiss, and it turns out to be falsified x-rays of pipe welds. When he examines one of the suspicious water pumps himself, he discovers radioactive material has leaked. We won’t spoil the rest of the story, but suffice it to say that the power company wants to hush things up.
In the Three Mile Island accident, radioactive coolant escaped to an auxiliary building, outside the official containment area. And radioactive steam was vented directly into the atmosphere. Still, several studies found no contamination in the area’s water and soil and determined that the releases didn’t raise radioactivity levels enough outside the containment area to cause any additional cancer deaths. The nuclear accident at Three Mile Island remains the worst in United States history, and the cleanup didn’t officially end until 1993.
The nuclear accident at Fukushima Daiichi in Japan seems worse than Three Mile Island, though each of the three damaged reactors (of six reactors at the plant) have been individually rated, like Three Mile Island’s single reactor accident, as a 5 on the International Nuclear Events Scale. Preventing explosions (and the widespread dispersal of radioactive contaminants) and preventing acute radiation sickness (and the near-term deaths that result) are crucial in limiting the severity of the accident.
In Japan, the fission products have contaminated water that is now in some of the plant’s basements and tunnels. Contaminated water has made its way the short distance from the nuclear plant’s buildings to the sea. Traces of radioactive iodine and cesium have been noted in tap water and vegetables even farther away. As we prepare to post this piece, the news reports that trace amounts of plutonium—the most toxic substance that might be released in a nuclear accident—have been found outside the nuclear plant itself. While some plutonium might be left from weapons testing in years gone by, at least two of the samples are believed to be from the one nuclear reactor at the plant that uses both plutonium and uranium as fuel.
On Wednesday, we’ll pick up this conversation again, as we’d planned, with a discussion of how we measure and talk about radiation.