FACTSHEET: From DUF6 to DU metal By Lizzy Bloem

DUF6 is readily available and inexpensive as raw material, since storage of the huge stockpiles is costly. For example Starmet, US, obtained DUF4 at one cent per pound (2.2 cents per kilo) from the Department of Energy.

MSC conversion facility, Oak Ridge, USSeveral different companies may be involved in converting DUF6 to depleted uranium weaponry, although in some cases a single company handles the entire process.

One facility may convert DUF6 to DUF4, while another converts DUF4 to depleted uranium metal. Still other companies process, alloy, form and machine the metal and assemble it into weaponry. As a result, facilities with several production lines produce a highly contaminated mixed waste stream.

Process

In the first step, DUF6 is reduced with hydrogen to produce depleted uranium tetrafluoride (DUF4) and hydrogen fluoride (HF). DUF4 is also named 'green salt' because of its characteristic colour.

The second step is the reduction of green salt, usually with magnesium. The chemicals are mixed in a crucible and heated in a furnace. The products of this reaction are a uranium metal mass, referred to as a 'derby', and magnesium fluoride (MgF2).

Large scale processing of DUF6, including uranium powders, liquid and gas, has great potential danger. Uranium powder is pyrophoric; it is susceptible to auto-oxidation in the air and even to self-ignition.

Waste

Particles of uranium and uranium oxide, escaping in the process, contaminate the air inside and outside the plants. Radiation can be measured miles downwind.

Wastewater contaminated by uranium may get physical-chemical treatment before release to city sewers. Sludge from water coming from the thermal treatment has to be handled as radioactive waste.

The conversion processes lead to bulky wastes. Conversion of DUF6 into DUF4 produces the by-product hydrogen fluoride (HF). This gas is extremely corrosive. HF even reacts with the containers holding it. It is possible that contaminated HF is sold for commercial use. Since long-term storage of hydrogen fluoride is dangerous, HF mostly converted to CaF2. For this, HF is captured in a scrubber that mixes HF with water to form hydrofluoric acid, which is then neutralised with lime, and calcium fluoride (CaF2) is formed. This calcium fluoride waste is also contaminated with uranium.

As a result of reduction of DUF4 (green salt) into uranium metal, a large quantity of magnesium fluoride (MgF2) contaminated with uranium is produced. This radioactive waste may be disposed of in a landfill or a disposal facility, depending on its radioactivity and regulations.

Past disposal practices at production sites resulted in contamination of sewers, soil, groundwater, and municipal water supplies with DU and other harmful substances. One of several examples is Starmet Corporation (former Nuclear Metals), in Concord, Massachusetts, US. Starmet was a conversion and production facility, that also made depleted uranium penetrators for anti-tank weapons. From 1958 to 1985, the company disposed of 400,000 pounds of depleted uranium and other radioactive and toxic waste into an unlined holding basin on their property. No environmental measures were taken. It is one of the most dangerous contaminated sites in the country. Groundwater contamination from Starmet is headed towards the Assabet River which runs into the Concord River which is the only source of drinking water for the town of Billerica. A 'temporary' cleanup of the site is estimated at US$500,000. Concord experiences elevated levels of different cancers compared with the state average.