As the nation's nuclear stockpile is reduced, more and more nuclear components will be cleaned and stored at Department of Energy sites across the nation, including the National Nuclear Security Administration's Pantex Plant in Amarillo, which is tasked with the dismantlement and interim storage missions.
To perform their missions in a safe and environmentally-responsible way, Pantex has begun using non-hazardous "green" solvents for some of their weapon parts cleaning activities, according to assistant professor of chemistry Darren Williams.
Williams and a team of Sam Houston State University researchers are working to add to the list of these "green" replacement solvents.
The research, funded by Pantex, tests solvents used to clean such items as nuclear components, tools, dissolving polymers and explosives to make the process non-hazardous for those charged with the task.
“When the Department of Energy disassembles a weapon, they clean every piece to store, and they store everything,” Williams said. “They don’t just give these parts away to the junk dealer when they’re done.
“If they’re going to store these parts indefinitely, say 30 years, they want to clean them well so that they don’t corrode in storage,” he said. “It could be a very bad situation if they corrode.”
For the project, Williams and his team are applying the “Hansen solubility model” created more than 30 years ago for the paints and polymer industry, which made paints safer to use, to find a replacement for hazardous or volatile solvents currently used to clean these materials.
The team works to determine the solubility of adhesives by taking a small tablet of each adhesive and putting it into a vial of different solvents, according to senior chemistry major Bryan Crom.
The research is being performed on aluminum alloys, or “coupons,” sent by Pantex to mimic real parts.
“The idea is similar to removing glue from a surface,” said Trisha O’Bryon, also a senior chemistry major. “You want to be able to make the glue swell so it almost pops off.
“That’s what we’re trying to do, figure out a blend to put on little pieces of metal that already have that adhesive on it, so we can get the adhesive to fall off without hurting the metal,” she said.
Williams compared the work they are doing to the replacement of acetone in fingernail polish remover with the compound methylethylketone.
“That is a situation where chemists have said ‘methylethylketone is less volatile, so let’s substitute that,’” he said. “When people get the fingernail polish off, they’re not exposing themselves to acetone, because to really get it off, you have to soak your finger. We wanted people to do that with a less volatile solvent, so they don’t get headaches.”
Over the summer, the undergraduates spent approximately five hours a day in the lab, testing more than 20 solvents and taking more than 1,500 images in their quest for the right combination of components to make the adhesives “swell.”
“If you have 100 solvents, which are not hard to collect, there are 12 million possibilities. If you think about 12 million choices—and that’s just a blend with four (or fewer) components—that’s too many to test,” Williams said. “It took us three months to take 1,500 pictures, and that’s not even close to 12 million possibilities.”
To narrow the choices, assistant professor of mathematics Brian Loft designed computer software that sorts possible combinations based on the Hansen solubility parameters to come up with the best blends to try.
“The software predicts the interactions between the adhesives and the solvent blends,” Williams said, adding that they graph the results, plotting the different properties of the molecules and solvents.
The solvents that come closest to the adhesive on the three-dimensional graph interact with it more, and the software and graphing technique allows the researchers to see what they can mix together that will get them the closest to their desired outcome.
This process is much safer, and more environmentally-friendly, than the method Pantex was previously using to find their “green solutions.”
“They’ve been using trial and error, and there’s an enormous potential for waste,” Williams said. “If you think about just picking something off the shelf and seeing if it will work, that’s not a good way to do it.”
Because the Department of Energy’s national laboratories at Los Alamos, Livermore, Sandia and production plants like Pantex use millions of gallons of these solvents every year, Williams’ work could impact the lives of those labs’ employees.
“If you have a solvent that’s very volatile, it’ll smell and drive you out of the room,” Williams said, adding that some can cause headaches and even cancer. “We have at Pantex alone over 3,000 workers, so we’re reducing the exposure of their daily lives to these chemicals.”
Williams recently presented this research to scientists from more than 20 countries at the 40th International Conference on Explosives hosted by the Fraunhofer Institute for Chemical Technology in Karlsruhe, Germany. In December, he will present it to the Joint Army Navy NASA Airforce conference on explosives and propellants.
The nearly $100,000 grant is scheduled to be completed by March 2010, but Williams said he will continue to conduct research in the same area.
“It can be applied to military or pharmaceuticals. Any product you’ve ever run across has been through a solvent of some sort some time in its production,” he said. “This applies to paints, pharmaceuticals, military explosives, nuclear explosives, semiconductors; just about anything.
“There are so many materials out there that need this kind of analysis, that I don’t see an endpoint,” he said.