Disposing of and storing nuclear by-products is a controversial and problematic issue for governments around the world. Dealing with such volatile substances can be dangerous, and they must be stored where they will not damage the environment. US researchers have developed a new method of dealing with products such as plutonium and other compounds, that will mean storage is a much more certain process.

Chemists at the US 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. The goal of the team is to create uranium, thorium and plutonium compounds that are environmentally friendly and harder to use as weapons.

Plutonium is chemically reactive with water vapour in the air. In fact, 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 which means there is a potential for environmental and safety problems if it is not treated and contained properly.

To address plutonium's storage challenges, scientists Kent Abney and Anthony Lupinetti are looking at new ways to combine actinides with the element boron.

It has long been known that plutonium and boron, 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.The process was also time-consuming.

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 even mixing.

Abney and Lupinetti have short-cutted this laborious task and developed a reactive process that takes place at lower temperatures, between 400 and 800 degrees centigrade and is relatively quick.

Hazard-disposal

"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," says Lupinetti. "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 is uranium boride mixed with a magnesium chloride. The latter salt 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 research was small, with the reactions taking place in a small sealed quartz tube. This tube, under vacuum to remove all gases and water vapour, was heated in a small electric furnace over a period of one to five days with a three-day cool- down process. The resultant compounds were later analysed via X-ray.

"We're interested in synthesising actinide materials that have well-known properties, and have an important impact on our storage problems, using new methods and new materials," says 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," says 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."

Abney and Lupinetti are exploring ways to use readily available compounds to get the actinide-boron reactive temperatures even lower. They're using unique materials as solvents, like lithium chloride and potassium chloride. These melt at temperatures around 350 degrees centigrade when mixed in equal amounts.