A new study by University of Rochester researchers shows that byproducts of nuclear activities can remain in the environment longer than previously thought.
A team led by Udo Fehn, professor in the Department of Earth and Environmental Sciences, and graduate student Usha Rao is investigating a new way to trace nuclear emissions as they work their way through the environment. Fehn and Rao are making measurements using accelerator mass spectrometry (AMS), a technique pioneered at the University.
The team measured concentrations of iodine-129 (I-129) in western New York and adjoining areas. I-129 is a long-lived radioactive isotope (an isotope has the same chemical characteristics of an element but has a different mass) produced by the fission of uranium in nuclear reactors.
Fehn and Rao found elevated levels of I-129 more than 125 miles from its source at West Valley, the site of a nuclear reprocessing facility that operated from 1966 to 1972. West Valley is about 30 miles southeast of Buffalo.
The quantities of I-129 they found pose no danger, scientists stress. At its highest level near West Valley, the substance gives off just a tiny fraction of the radiation we all receive everyday simply from being on the earth, where we're exposed to a slight amount of radiation both from space and from earth. But scientists say the distribution of I-129, with the highest concentrations currently in the creeks that drain West Valley, indicate that leaks from the facility are still occurring.
The team measured I-129 in about 200 samples taken from aquatic plants, soil, tree rings, and water from streams, creeks, and lakes as far north and west as Lake Superior and as far east as Nova Scotia. They found that the radio-isotope is nearly 10 times more abundant throughout western New York than in surrounding areas, and was found at elevated levels as far as the eastern edge of the Finger Lakes, more than 125 miles away. Those levels increase steadily closer to West Valley; in the two creeks that drain the land surrounding the facility, Buttermilk and Cattaraugus creeks, I-129 levels are about 10,000 times higher than background levels.
The team found that I-129 levels are not elevated near two nuclear power plants near Lake Ontario in western New York, Nine Mile Point in Oswego and Ginna near Rochester, or near the Davis- Besse nuclear plant in southeastern Ohio. This indicates that those facilities are not leaking nuclear byproducts into the environment, Fehn says, and that the elevated levels found in western New York can be attributed to leakage from West Valley.
"I-129 released to the air from smokestack emissions during the operation of the site has now spread throughout western New York," says Rao, who is doing the study as part of her Ph.D. thesis. "It is surprising to find that the signal is still detectable both around the site and in western New York more than 20 years after reprocessing activities at the facility ended."
The team chose to measure I-129 because it's one of only a few byproducts of nuclear activity that remain in the environment decades later. Since the most dangerous byproducts of nuclear activity, such as other forms of iodine, break down within days, it's impossible to measure them now.
"Since I-129 is not harmful, this in itself is not an alarming study," says Fehn. "Our work shows that we can use I-129 to watch how radioactive releases progress through the environment, and it gives us a highly sensitive method to trace byproducts of nuclear activities."
Results of the study were presented recently at a meeting of the Geological Society of America in Buffalo by Rao, who will also present results next month at the seventh International Conference on Accelerator Mass Spectrometry in Tucson, Ariz. Also working on the ongoing project, which has been partially funded by the National Science Foundation, have been senior technical associate Ray Teng and undergraduates Heather McNeil, Sachiko Tanikawa, Mark Campanelli, Lisa Gabor and Ignacio Murio.
West Valley was home to the nation's only facility set up to reprocess used nuclear fuel exclusively from commercial power reactors. In that process fuel rods are dissolved to separate plutonium and uranium from the fission products. The radioactive remnants of this process now sit in storage tanks, and scientists are developing processes to solidify and encase the waste for long-term, safer storage. West Valley, which is also home to a low-level radioactive waste dump that closed in 1975, is managed by the U.S. Department of Energy and the New York State Energy Research and Development Authority (NYSERDA).
I-129 is produced naturally from the fission of uranium in the earth and from cosmic rays bombarding the atmosphere. Levels around the world have shot up 1,000-fold from bomb testing and the widespread use of nuclear power. The amount spread over Western New York from West Valley -- a little less than one kilogram -- is in addition to these sources. Scientists can detect extremely low concentrations of such isotopes by using AMS, a technique developed at the University's Nuclear Structure Research Laboratory, where most of these measurements were done.
Fehn's team, working with outside collaborators and with Harry Gove, professor emeritus of physics, previously measured the distribution of chlorine-36, another byproduct of reprocessing, at two reprocessing sites operated by the U.S. military: Idaho Falls, Idaho, and Savannah River in South Carolina. The results indicated that contamination from those plants is also more widespread than previously thought.