FACTSHEET: Long-term DUF6 storage By Lizzy Bloem

The waste is known as depleted uranium (DU), depleted uranium hexafluoride (DUF6) or depleted hex. Enrichment for commercial reactors generates about seven times more DU than enriched uranium. Enrichment for nuclear weapons or nuclear research reactors produces even more waste. Next to waste rock and tailings it is the largest category of waste in the nuclear industry.

Storage often occurs outside the enrichment plant, in cylinders of carbon steel. Many cylinders are in badly corroded state. Cylinders in the US even date back as far as the 1950?s. They pose significant leaking and breaching dangers. At least ten cylinders have breached during the last 40 years.

Within the occurring range of temperature and pressure in the cylinders, DUF6 can be a solid, liquid, or gas. Solid DUF6 is a white, dense, crystalline material that resembles rock salt. Under low temperature and high pressure in cylinders, DUF6 appears to be solid on the bottom and gas in the top.

DUF6 is convenient for processing, but dangerous for long-term storage or disposal. It is an unstable, toxic chemical. If DUF6 escapes from the cylinder, it reacts with moisture in the air to form hydrogen fluoride (HF) and uranyl fluoride (UO2F2), both poisonous gasses. For this reason, DUF6 has to be handled in leaktight containers. Maintenance and surveillance have to be continued as long as the DUF6 remains in the cylinders. The half-life of U238 is 4.5 billion years, but cylinder use is measured in decades.

During the early years of the nuclear age, 1945-1960, DUF6 was collected, stored and dumped in nature. For decades DUF6 has also been converted into uranium metal. DUF6 becomes raw material for the military and civil industry, despite its radioactivity and toxicity.

There is also another possibility for further use of DUF6 in the nuclear fuel chain. DUF6 is used, after conversion into depleted uranium oxide, in mixed oxide fuel (MOX) for nuclear reactors. In this process new waste streams are generated.

An alternative for long-term storage of DUF6 is storage after conversion into depleted uranium oxide (UO2 or U3O8). Uranium oxide is chemically far more stable. Depleted uranium oxide is stored in buildings, below ground vaults and in mines.

Converting the entire stock of DUF6 of the US would lead to more than 50,000 empty cylinders. The cylinders will increase the already massive problem of how to dispose of slightly contaminated scrap.