Over four decades in operation, the Hanford Site in eastern Washington state had as many as nine nuclear reactors at a time working with five processing complexes to produce plutonium for America’s nuclear arsenal.
On the other side of the country, the Savannah River Site in South Carolina had as many as five reactors working through the Cold War to produce tritium and plutonium for the weapons program.
This security and nuclear research effort has produced wastes that are now the focus of a massive cleanup effort by DOE across several research and production facilities. Just between these two particular sites, hundreds of tanks now hold 90 million gallons of radioactive waste, enough to fill more than 130 Olympic-size swimming pools. Add to that millions of cubic feet of solid waste and tens of square miles of contaminated groundwater, and you get a feel for the agency’s greatest environmental challenge.
“The needs are just enormous,” said Michelle Buchanan, ORNL’s associate laboratory director for physical science. “The tanks alone represent some of the toughest chemistry on the face of the earth. These wastes are a true witch’s brew of chemicals.”
Nuclear legacy
DOE has worked for decades to clean up its nuclear legacy, and the effort has been largely successful. Starting with more than 100 contaminated sites in 1989, the agency has completed cleanup at all but the 16 most challenging.
The remaining sites—which include some at DOE’s Oak Ridge facilities—are the toughest. In some cases they are prohibitively expensive to address using existing technology; in others, the technology just doesn’t exist. Consider, too, that radioactive waste will need to be isolated for thousands of years, and you can see the need both for new research and for strategies that make use of recent discoveries.
It’s a challenge in need of new solutions, some of which will certainly come from the agency’s largest science lab, ORNL. ORNL hosts unique and powerful research tools, including the world’s second most powerful supercomputer, the world's most intense reactor-based and pulsed neutron beams, and a variety of world-class scanning probe and scanning transmission electron microscopes. It also provides a collaborative environment for talented chemists, environmental scientists, engineers, geologists, biologists, materials scientists, physicists and computational scientists to put their heads together to solve common problems.
State of flux
Of all of DOE’s environmental challenges, the most vexing are the waste tanks, which hold a mishmash of highly radioactive, chemically hazardous and often corrosive substances. Some are liquid, some sludge, and even if you could analyze them completely, they are in a state of constant flux.
“A big need is to characterize those tanks, and to do it on a continuous basis,” Buchanan said. “The tanks are not in equilibrium. Things are always changing. So being able to come up with new sensors and analytical techniques where you can remotely and in situ [in place] monitor concentrations and speciation [chemical form] is very important.”
Ultimately, the tank contents must be treated—meaning the most radioactive materials must be pulled out and put into the most stable form possible (See “Researchers use soybean oil to reduce uranium in groundwater,” page XX)—and disposed of in such a way that they’re unlikely to harm us or our descendants.
There are other problems, too. DOE must grapple with groundwater contamination at a number of sites, as contaminant plumes move toward public water supplies. Groundwater is also a key concern for long-term storage, as investigators face the likelihood that even the best-engineered waste storage is bound to fail over the course of centuries. Converting the wastes to more stable forms and packaging them in highly corrosion-resistant containers represent major challenges for materials and corrosion scientists, but no material will be stable forever.
“The radionuclides eventually will get released—the repositories will collapse, the canisters will be breached, the cladding on spent fuel rods will decompose, and these things will get released into the local environment,” explained ORNL geochemist David Wesolowski.
“Then the next question is, how long is it going to take?” Wesolowski said. “Once you get to the ultimate point to where the radioactive waste is exposed to the groundwater, how long is it going to take for it to migrate to places we care about?”
These and other challenges prompted the Secretary of Energy’s Advisory Board earlier this year to gather scientists from national laboratories and universities around the country. Their task was to consider how scientific progress over the last decade or so can address these long-term problems. The Environmental Management Basic Research Needs Workshop Report now being completed will identify the risks and the science and technology needs and will help chart the roadmap for future federal funding to address these needs.
“The nice thing about the workshop is it brought together people with experience working with environmental management issues and people who are just good scientists who love to solve problems,” Buchanan said.
“It’s some of the most challenging science you can think of. Not only is it a great need; it’s also fascinating science.”
See also:
- Computers and tanks
- Rocks and neutrons
- ORNL process isolates troublesome cesium
- Researchers use soybean oil to reduce uranium in groundwater
