Plutonium storage made simple

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 the problems involved with the storage of actinide metals such as plutonium and uranium.

Kent Abney, Anthony Lupinetti and Ed Garcia have been looking at methods of reacting actinide elements with stable elements. The goal is the creation of uranium, thorium and plutonium compounds that are environmentally friendly and harder to use in weapons.

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, 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, however, have developed a reactive process that takes place at more easily attainable temperatures, between 400 and 800 degrees centigrade. What's more, it 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.

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

The researchers believe that a scaling-up of the processes should not pose an insurmountable roadblock to full implementation, once the reactive systems are proven and refined.