Uranium Industry Incidents Beyond Dams: Spills and Legacy

Reference article · Updated 2026-11-06

Key facts

On 4 January 1986 an overfilled UF6 cylinder ruptured at Sequoyah Fuels, Gore, Oklahoma. One worker died of hydrogen fluoride inhalation (NRC).
On 7 December 2013 a leach tank at the Ranger mine, Australia, failed and released about 1,400 m3 of acidic slurry. The Supervising Scientist found no adverse offsite impact.
EPA describes a legacy of about 520 abandoned uranium mines on the Navajo Nation, mined between 1944 and 1986.
Germany's Wismut remediation covers a legacy of 311 million m3 of waste rock and 160 million m3 of tailings.

Four categories of non-dam incident

Incidents in the uranium industry fall into a few recognisable types. Separating them avoids comparing unlike things.

Process accidents in plants for leaching, conversion or fuel fabrication, where a vessel, tank or cylinder fails.
Spills and leaks of process liquors, solutions or contaminated water to soil or surface water.
Legacy mines and mills, where abandoned workings, waste rock and tailings were left without modern closure.
Remediation challenges, in which large inactive waste piles must be moved, covered or monitored for decades.

Tailings dam failures are a separate, better-documented category. They are covered in the chronology of tailings dam failures and the page on uranium mill tailings dam failures.

Process accident: Sequoyah Fuels, Oklahoma, 1986

The Sequoyah Fuels Corporation plant near Gore, Oklahoma, converted uranium concentrate to uranium hexafluoride (UF₆), the gaseous compound used for enrichment. According to the US Nuclear Regulatory Commission's preliminary report, a cylinder filled with UF₆ ruptured at about 11:30 on 4 January 1986. It was being heated in a steam chest. The cylinder had been overfilled. Once this was recognised, a supervisor directed workers to remove the excess by heating.

UF₆ reacts with moisture to form hydrogen fluoride, a corrosive and toxic gas. The NRC report states that one worker died after inhaling hydrogen fluoride. Published accounts identify the worker by name. The NRC and medical literature agree on the cause of death.

The NRC investigated the accident and issued reports in its NUREG-1179 and NUREG-1198 series, including lessons learned. Counts of hospitalised workers differ between secondary accounts and are not stated here.

The case illustrates that, at the conversion stage, the dominant acute hazard is chemical (fluoride and acids) more than radiological. More detail on the toxicology of uranium compounds appears on the page about uranium toxicity.

Process failure: Ranger mine leach tank, Australia, 2013

The Ranger uranium mine lies in Australia's Northern Territory. Energy Resources of Australia operates it. Leach Tank 1, a vessel used to dissolve uranium from crushed ore in acid, collapsed on 7 December 2013. Northern Territory government sources describe a release of about 1,400 m³ of acidic slurry that stayed within the mine site.

The Supervising Scientist investigated. The investigation was published as Supervising Scientist Report 207, with an interim report as Report 206. It found no adverse offsite environmental or health impact. The federal government suspended processing until regulators were satisfied about the integrity of the site. The operator reported a processing suspension of about six months.

After the event, Aboriginal organisations and environmental groups questioned the independence of the regulatory arrangements. The operator described the containment as having worked as designed. Both positions are statements by interested parties. They are mentioned here as context, not as findings.

The mine is in a landscape of cultural importance to the Mirarr people. The broader context is discussed on the page about uranium mining and Indigenous peoples.

Legacy mines: the Navajo Nation, United States

From 1944 to 1986, mine operators extracted millions of tons of uranium ore from lands of the Navajo Nation. The mines were later abandoned. EPA's cleanup plan for the Navajo Nation refers to more than 500 abandoned uranium mines and four inactive milling sites. An EPA progress report puts the number of mines at 520.

Five federal agencies ran the first coordinated Five-Year Plan from 2008 to 2012. EPA documents record that it exceeded its target of on-site screening of 200 to 250 mines. A Ten-Year Plan for 2020 to 2029 continues the work.

This legacy consists of scattered small sites rather than one dramatic release. The issues include:

exposed waste rock;
contaminated soil;
contaminated groundwater;
use of local materials in structures.

Related impacts on the community are discussed in uranium mining and Indigenous peoples.

Legacy at industrial scale: Wismut, Germany

The Wismut company produced uranium in Saxony and Thuringia until 1990. An evaluation by the German Federal Institute for Geosciences and Natural Resources (BGR) gives production over the whole period as about 231,000 tonnes of uranium. Another source gives more than 232,000 tonnes for 1945 to 1989. A round figure of roughly 230,000 tonnes is therefore safest.

Wismut's own description of the legacy includes:

about 1,400 km of open mine workings;
311 million m³ of waste rock;
160 million m³ of tailings.

The federal government is the sole shareholder. The company states that about 7.3 billion euros had been allocated from the federal budget by the end of 2024. The BGR project description lists the current project phase as 1 January 2012 to 31 December 2026.

The scale and duration of Wismut make it a benchmark for how long large uranium legacy programmes can take.

Inactive mill sites: Moab, Utah

At Moab, Utah, a large pile of uranium mill tailings stood beside the Colorado River. The US Department of Energy (DOE) runs a remedial action project there. It is moving the tailings and other contaminated material by rail to an engineered disposal cell at Crescent Junction, about 30 miles to the north. Some off-site vicinity properties are included. DOE has announced that over 16 million tons have been moved. Different documents state the completion date differently, so check the current DOE schedule.

The site is an example of remediation that is neither an accident nor a dam failure. It is a planned relocation of a hazard. Principles for designing disposal and cover systems are described on the page about uranium mill tailings.

How to judge incident reports

Incident narratives about the uranium industry vary widely in reliability. The strongest sources are regulator investigations (for example NRC reports or the Supervising Scientist's reports), government remediation plans and peer-reviewed studies. Company statements and advocacy publications are useful for context, but they are written from a position.

Numbers about releases, exposures and hospitalisations differ across secondary accounts. Trace them to the original report. For the overall approach to sources, see the page on sources and methodology.

Frequently asked questions

What happened at Sequoyah Fuels in 1986?

A cylinder of uranium hexafluoride that had been overfilled ruptured during heating on 4 January 1986 at Gore, Oklahoma. According to the NRC, one worker died from inhaling hydrogen fluoride.

Was the 2013 Ranger leach tank failure a threat to the environment?

About 1,400 cubic metres of acidic slurry were released but stayed within the mine site. The Supervising Scientist found no adverse offsite environmental or health impact.

How many abandoned uranium mines are on the Navajo Nation?

EPA documents refer to more than 500, and an EPA progress report gives 520, from mining carried out between 1944 and 1986.

What is a legacy site?

A former mine or mill that was left without modern closure. Waste rock, tailings or contaminated ground remain and require remediation, often by a government.

Why are some incidents not listed on this page?

Only events supported by regulator or institutional reports are included. Others were omitted because their figures could not be traced to a reliable source.