- EVANSTON, Illinois (ENS) - Breakdown products in enclosed nuclear waste
storage tanks may build up pressure and explode warns a new study by researchers
at Northwestern University and the University of Notre Dame.
-
- In laboratory experiments, the scientists
showed that alumina, an oxide of aluminum that is found in many soils,
can greatly accelerate chemical reactions in which gamma rays break down
toxic chlorinated chemicals. Gamma rays are high energy X-rays given off
by many of the highly radioactive wastes produced in weapons manufacture,
such as cobalt-60.
-
- The good news is that gamma irradiation
may be an effective means of degrading some highly toxic pollutants, such
as dioxin or PCBs, in contaminated soil.
-
- The bad news is that 177 huge underground
tanks on the Hanford Nuclear Reservation in eastern Washington, which hold
54 million gallons of high-level radioactive and chemical waste, may face
an increasing risk of rupture or explosion as volatile gases, including
hydrogen and perhaps methane, are generated as the chemicals are broken
down by minerals in the tanks.
-
- Radioactive waste inside a tank at Hanford
Nuclear Facility (Photo courtesy DOE Hanford) "They're big cauldrons
of radioactive soup," says Kimberly Gray, associate professor of civil
and chemical engineering at Northwestern's Robert R. McCormick School of
Engineering and Applied Science.
-
- Gray conducted the new study with physical
chemist Prashant Kamat of Notre Dame's Radiation Laboratory and Northwestern
graduate student George Zacheis. The results are reported in the April
8 issue of the Journal of Physical Chemistry.
-
- The Hanford tanks, Gray said, contain
radioactive metals and nonradioactive metal oxides and organic chemicals
that were byproducts of nuclear weapons production. Metal oxides are driving
reactions in which the radiation breaks down the chemicals, she said.
-
- "By storing radioactive liquid with
solid material, they are degrading components of the mixture and producing
gases," Gray said. The rate of gas production can not currently be
predicted, she said, so engineers and chemists want to learn how they are
generated.
-
- Radioactive waste in the single-shell
tanks at Hanford is now being pumped into double-shell tanks for storage
until the waste can be stabilized in glass in a process known as vitrification.
-
-
- Kimberly Gray is president-elect, Association
of Environmental Engineering Professors (Photo courtesy Northwestern University)
Last year, Gray and her colleagues were looking for ways to use radiation
to cleanse excavated soil when they observed that some soils were more
easily cleaned than others. "We showed that this is a robust technology
that seems to work on a wide variety of soils," Gray said, "but
we realized that when the soils were high in minerals, the process worked
really, really well."
-
- Gray says the findings suggest radiation-induced
breakdown, or radiolysis, may be useful for detoxification in both environmental
and industrial settings. It has never been employed for either.
-
- In the environment, radiation can penetrate
soil and act at a distance, making it unnecessary to wash pollutants off
the soil for treatment.
-
- In industry, adding minerals to the chemical
waste-stream and zapping the mixture with gamma rays may be an effective
way to detoxify the wastes or even generate useful feedstock chemicals
that could be recovered.
-
- "This research helps us understand
the risks associated with stored radioactive wastes in places like Hanford,"
Gray said. "I think this research also helps us develop treatment
technologies for soil contamination. And I think it shows the potential
for us to develop new kinds of catalysts that we could adapt for either
selectively breaking bonds or making new chemicals in treatment for waste-stream
reduction."
-
- The 560-square-mile Hanford Reservation
is where the government produced plutonium from World War II through the
end of the Cold War. Of the 177 tanks on the site, 70 have already leaked
about one million gallons of waste into the soil and groundwater, threatening
the Columbia River 12 miles away. Hanford, whose only activity now is storage
and cleanup, is administered by the U.S. Department of Energy.
-
- The research reported in the Journal
of Physical Chemistry was funded by the National Science Foundation, the
Department of Energy and the Occidental Petroleum Corporation.
|
