Depleted Uranium Stockpiles and Inventories

Reference article · Updated 2026-11-06

Key facts

The US Department of Energy has described its depleted UF6 inventory as roughly 800,000 tonnes in about 67,000 cylinders (DOE Inspector General, 2023).
DOE's inventory sits mainly at Paducah, Kentucky and Portsmouth, Ohio; earlier reports also listed Oak Ridge, Tennessee.
Conversion plants at Paducah and Portsmouth began operating in 2010 and 2011 to turn the hexafluoride into more stable oxide.
Published totals differ between documents and years, so any single number should be tied to its source and date.

Why depleted uranium accumulates

Enrichment makes far more depleted material than product. Producing one tonne of reactor-grade low-enriched uranium requires several times that mass of natural uranium, and most of the difference leaves the plant as tails; the mass-balance calculator shows the proportions for a chosen assay. The tails are stored as uranium hexafluoride, the same chemical form used in the enrichment process.

The only large-scale uses of depleted uranium metal are in shielding, counterweights and munitions (see the DU basics page), and those uses consume a tiny fraction of what enrichment generates. Re-enrichment of older tails, when economics allow, is the other route that reduces stocks. The result is a growing inventory of material that has potential future value as a source of U-235 and U-238, but that has to be managed safely in the meantime.

The United States Department of Energy inventory

The United States holds the best-documented stockpile because DOE and its predecessors operated the government gaseous diffusion plants. An older DOE-era inventory table put the total near 700,000 metric tonnes in about 57,000 cylinders, with the largest shares at Paducah (about 436,000 t), Portsmouth (about 196,000 t) and Oak Ridge (about 54,000 t). Later documents give higher totals: the DOE Office of Inspector General audit DOE-OIG-23-04 and DOE's own Portsmouth/Paducah project office describe roughly 800,000 tonnes in about 67,000 cylinders. Another DOE page cites about 740,000 tonnes. The differences reflect different dates, counting rules and whether cylinder contents or product weights are being reported.

Site	State	Figure reported	Source and date
Paducah	Kentucky	about 523,500 t in about 43,000 cylinders	DOE fact sheet, February 2018
Portsmouth	Ohio	about 227,400 t in about 19,000 cylinders	DOE fact sheet, February 2018
Oak Ridge (ETTP)	Tennessee	about 4,800 cylinders at the time of a 2004 notice	Federal Register, July 2004

These figures are not additive across rows because the sources use different bases and dates; the table is meant to show scale and sources, not to total the stockpile. The 1999 programmatic environmental impact statement that set the DOE policy covered the three sites together.

Deconversion: from hexafluoride to oxide

In 1999 DOE chose to convert its depleted UF6 to a more stable chemical form instead of leaving it in cylinders indefinitely. Two dedicated plants, one at Paducah and one at Portsmouth, were built for this purpose and began operating in 2010 and 2011. They react the UF6 with steam and hydrogen to produce depleted uranium oxide, mostly U3O8, and anhydrous hydrofluoric acid, which has commercial value and can be sold or neutralised. DOE describes the conversion campaigns as lasting decades; it has cited roughly 18 years for Portsmouth and 30 for Paducah in its project information.

Trade press reporting on DOE contractor results states that the Paducah plant converted about 14,000 tonnes of uranium oxides in fiscal year 2019. As with all such operating statistics they are best read in the contractor and DOE reports for the relevant year. Contracts for operating the plants have been re-competed from time to time; DOE issued a request for information about a new conversion project in 2020.

Other countries operate comparable deconversion plants at their own enrichment sites. This page does not give foreign inventory figures because no primary source for them was verified; readers looking for them should consult national regulators, operators' annual reports and the OECD-NEA and IAEA reports on the nuclear fuel cycle.

Cylinder storage and safety

Cylinders of depleted UF6 are steel containers stored in yards. The principal risks documented in DOE and NRC documents are corrosion of the steel over time, which can lead to leaks if not managed; chemical hazards if UF6 meets moisture, forming hydrofluoric acid and uranyl fluoride; and the cost of long-term surveillance. DOE has maintained cylinder inspection and maintenance programmes, including re-stacking and repainting, as part of the management programme.

The radiological hazard from sealed cylinders is low compared with the chemical hazard of a release. Regulatory oversight in the United States is through DOE orders for DOE-owned cylinders and through the NRC for privately-owned material at commercial enrichment plants, where licensees must also provide a plan for deconversion and financial assurance for it. See the US enrichment plants page for licensing at the commercial plants.

Use and disposal options

Studies for DOE and the NRC have evaluated several end points for the oxide. The environmental impact analyses considered continued storage, beneficial use in shielding and other products, and disposal in a near-surface facility or a deep geological facility such as a mine. Technical questions in these analyses include the oxide's long-term behaviour in different disposal environments, the in-growth of decay products over very long periods and the quantities involved, which are large compared with other low-level waste streams.

No final disposal decision is described in this page, because the sources used here do not establish one for the whole inventory. In the meantime the oxide is stored in cylinders at the conversion sites. Whether the material is classed as a resource or a waste is a policy choice that affects reporting. If operators plan to re-enrich it, the stocks are an asset; if not, the cost of disposal is a liability for the licensee or the government.

The related question of what happens to the plants themselves after enrichment ends is covered in the US decommissioning page and the European decommissioning page.

Frequently asked questions

How much depleted uranium does the United States hold?

DOE documents describe about 800,000 tonnes of depleted UF6 in roughly 67,000 cylinders (DOE Inspector General, 2023). Older documents give about 700,000 tonnes, so check the date of any figure.

Where is the US depleted UF6 stored?

Mainly at Paducah, Kentucky and Portsmouth, Ohio. Oak Ridge, Tennessee held cylinders in earlier inventories.

What is deconversion?

It is the chemical conversion of depleted UF6 to a stable oxide, usually U3O8, with hydrofluoric acid as a by-product. DOE plants at Paducah and Portsmouth began operating in 2010 and 2011.

Can depleted uranium be reused?

Yes, in small quantities for shielding and counterweights, and by re-enriching it when economics allow. These uses consume only a small fraction of total stocks.

Is there a final disposal route for the oxide?

Environmental analyses have considered near-surface and mine disposal, but this page does not report a final decision for the whole inventory.