CONTACT: Kevin Roark, 505-665-9202, [email protected]
EMBARGOED UNTIL 8:30 a.m. PDT, Wednesday, April 4
NEW CHEMISTRY OFFERS ALTERNATIVE PLUTONIUM STORAGE PROCESS
LOS ALAMOS, N.M., April 4, 2001 -- Storage of the nation's excess actinide metals, including plutonium and uranium, present a myriad of problems from pollution concerns to proliferation risk. Solid-state chemists at the Department of Energy's Los Alamos National Laboratory have discovered a new reaction process that may prove to be a solution to some of the most serious storage problems.
Kent Abney, of the Chemistry Division's Isotope and Nuclear Chemistry group, along with Anthony Lupinetti, a post-doc with a dual C-Division and Nuclear Materials Technology Division appointment, and Ed Garcia also from NMT Division, have been looking at methods of reacting actinide elements with stable elements. The team presented its findings today at the 221st American Chemical Society national meeting in San Diego. The goal is the creation of uranium, thorium and plutonium compounds that are environmentally friendly and harder to use in weapons.
Plutonium is chemically reactive with water vapor in the air. Plutonium metal powder can catch fire if it's not constantly bathed in an inert gas, such as argon. Plutonium metal can also be easily dissolved in water--a potential for environmental and safety problems in the absence of robust containment.
Plutonium metal can be converted to an oxide, a more stable form but one that still possesses some of the same problems as the pure stuff--it's reactive with water and has a potential proliferation concern.
Plutonium not earmarked for weapons work from seven separate sites across the DOE complex tops 38 metric tons, a sizeable surplus. Most of the material is housed at the Pantex plant outside Amarillo, Texas, and is planned to be used in existing nuclear reactors to generate electricity.
To address plutonium's storage challenges, Abney and Lupinetti are looking at new ways to combine actinides with the element boron.
It has long been known that plutonium and boron, a solid semi-metal or metalloid--meaning it is an intermediary element, sharing some of the properties of metals as well as non-metals--could be combined to create a very stable and insoluble compound, plutonium boride. However, until now this could only be done at extremely high temperatures, over 3,000 degrees centigrade, and the process was a grind--literally.
In order to get the two elements to mix, something they don't do easily, they would have to be melted at very high temperature, cooled, then ground into a powder, then mixed and melted again. Sometimes this process would have to be done over and over to achieve proper mixing. Abney and Lupinetti have developed a reactive process that takes place at more easily attainable temperatures, between 400 and 800 degrees centigrade and doesn't involve the grind.
"We're using reactive compounds to overcome the problems of working these very complex reactions that involve double-decomposition, or the double-breakdown of compounds into simpler compounds or elements," said Lupinetti. "By combining actinide metal halides, like uranium tetra- and tri-chlorides with molecular boron precursors like magnesium diboride or calcium hexaboride, we've been able to do reactions at much lower temperatures, in the 500-800 degrees centigrade range."
The end result of a uranium tetra-chloride reaction with magnesium-diboride yields uranium boride mixed with a magnesium chloride. The latter is easily washed away, leaving behind the uranium-boride, a compound that is stable and insoluble. In addition, actinides mixed with boron, which readily absorbs neutrons, are not easily converted to their pure form, making them harder to use in weapons.
The amounts of material used in the proof of principle research was small, in the 100 milligram range, with the reactions taking place in a small sealed quartz tube. The tube, under vacuum to remove all gasses and water vapor was heated in a small electric furnace over a period of one to five days with a three-day cool down. The resultant compounds were later analyzed through a comparison technique called X-ray-powder diffraction.
"We're interested in synthesizing actinide materials that have well-known properties--and have an important impact on our storage problems--using new methods and new materials," said Abney. "With the goal of finding processes that are easier to do and with end results that provide the country with a better way to store our surplus nuclear materials."
"It's a very young field," said Lupinetti. "We're still discovering what the rules are in combining these things--using the entire periodic chart and wide variations of temperature with unusual materials like high-temperature solvents, there are so many variables, we're all really learning this together, so it's very exciting science."
The bulk of the work is done at the Laboratory's Technical Area 48 Radiochemistry Site, in an actinide lab called the "Alpha Wing." The lab contains both negative pressure and positive pressure glove boxes along with hooded workstations and analytical areas that are perfect for doing small-scale actinide work. Larger scale research is being conducted at the Laboratory's plutonium facility, TA-55.
"The Alpha Wing provides the Laboratory with a unique capability in that it's available to not only staff members but undergraduate, graduate and post-doc students without security clearances," said Abney. "It's a great opportunity for our young up-and-coming chemists and engineers to get experience working with plutonium, uranium and other actinides. We feel like we're training the next generation of scientists."
And the future looks bright. Abney and Lupinetti are exploring ways to use readily available compounds to get the actinide-boron reactive temperatures even lower using unique materials as solvents, like lithium chloride and potassium chloride, which melt at temperatures around 350 degrees centigrade when mixed in equal amounts.
They believe they have solutions to other experimental problems as well and feel as though scale-up of these processes should not pose an insurmountable roadblock to full implementation, once the reactive systems are proven and refined.
Los Alamos National Laboratory is operated by the University of California for the U.S. Department of Energy's National Nuclear Security Administration.
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