Nuclear Accident Clean-
Up And Contamination
By Amanda Onion
NEW YORK - How do you go about cleaning up an invisible, odorless mess? That's the tricky task of workers who come in to decontaminate a plant following a nuclear accident.
If radiation strikes a person, it can cause damage to tissues and cells
Much of the process requires technology such as instruments to measure radiation levels, lead-protected gear and sometimes even robots to travel into zones with unknown degrees of contamination.
"Once the reaction stops, it's mostly the by-products you have to worry about," explained Peter Parker, a professor at Yale University's Nuclear Structure Laboratory.
Judging from early figures released from the Tokaimura uranium processing plant outside of Tokyo, experts in the U.S. predict the damage may not require extensive cleaning.
On Thursday contamination levels around the plant were reported to have been from 10,000 to 20,000 times the normal levels. By Friday those levels had apparently dropped low enough that Japanese officials lifted an advisory that had ordered 310,000 area residents to stay indoors.
"If radiation levels were high and then went back down, that implies you had a big blast of radiation and less contamination," said Brian Rothman, a radiation clean-up specialist at Rothman Radiological Services in New Mexico. "It's like if someone had turned on a giant x-ray machine and zapped everything around."
A Self-Sustaining Chain Reaction
When a nuclear reaction spins out of control, there are two things that clean-up crews need to worry about: radiation and the by-products of the uncontrolled nuclear reaction.
Radiation and radiated metals are not the only dangers associated with a nuclear accident
A nuclear reaction in a uranium plant produces energy by combining high amounts of reactive uranium. The proximity of the uranium atoms triggers the atoms to release their nuclei, which then become neutrons. Those released neutrons act like tiny cleavers and split other uranium atoms, which, in turn, release even more neutrons in a process known as fission.
If fission is not contained and controlled in a reactor, those atom-splitting neutrons can spread from the reaction in the form of radiation. If radiation strikes a person,it can cause damage to tissues and cells.
If the radiation reaches any metals in the surrounding area, it reacts with the metal and makes it "hot." That means that atoms in the metal absorb an extra neutron and then become unstable. An unstable atom is dangerous because it releases continuous energy in the form of gamma rays or alpha or beta particles. Radioactive metals also remain hot long after the reaction, itself, is extinguished.
"Being near radioactive metal like that is like sitting on an x-ray machine that's always on," said Rothman. The only way to eliminate the hazard, he explained, is to remove any metal in the vicinity of the reaction.
But radiation and radiated metals are not the only dangers associated with a nuclear accident. Even more damaging are the amounts of radioactive materials that spew out from a nuclear reaction. During fission, as uranium atoms are split apart, uranium atoms are converted into a range of radioactive materials such as plutonium, krypton, iodine, xenon, cesium and strontium. All of these elements then escape into the atmosphere and contaminate their surroundings.
"The good news is there was only about 35 pounds of material involved," said David Lochman at the Union of Concerned Scientists. That means, he explained, that radiation from the Japanese reaction probably only reached metals inside the facility. By comparison, nearly 100 tons of uranium reacted out of control at the Chernobyl plant in the Ukraine in 1986.
Less severely contaminated material can simply be wiped down. 'You literally use soap and water'
At Chernobyl the range of contamination was horrifyingly vast. As the massive explosion burned for days, plumes of radioactive gasses and tiny particles rose into the sky and were carried literally around the world by winds. Soils, waters, clothes, and houses were contaminated to an extent that a complete clean up was virtually impossible (it continues today).
Contamination following the explosion in Japan was less severe since the explosion was smaller and because it happened on a rainy day.
"Water helps to dilute those particles," said Rothman. "So at some points you're not even going to be able to measure it."
Even in a diluted state, however, contamination can be dangerous. Lochbaum estimates that if people were exposed to some of the higher contamination levels reported around the Japanese plant for 90 minutes or more, they stand a one in 300 chance of getting radiation-induced cancer.
To reduce that risk, workers will need to take readings of all materials in the vicinity of the plant and then clean infected areas. That work may require a robot to go in first and scout out just how high radiation levels are in certain places and then gauge how long people can safely work in the area. Any severely contaminated material is then removed. According to Rothman, less severely contaminated material can simply be wiped down. "You literally use soap and water," he said.
Although it may sound like a straight-forward job, Lochbaum cautions a proper cleaningtakes time.
"It's not going to be a huge undertaking," he said. "But clean up should be a slow and deliberate process that could take a year or longer."