The U.S. Nuclear Regulatory Commission has stopped yellowcake shipments from a Pumpkin Buttes mine after uranium dust escaped from a drum and exposed three workers in Canada.
The government is requiring Casper-based Uranium One USA to investigate why yellowcake that originated from the Willow Creek facility was exposed to workers in Blind River, Ontario, on June 23.
“A worker at the Blind River facility loosened the lid clamp of this pressurized drum, and uranium concentrate powder was ejected from the drum into the immediate work area,” according to the government’s letter, sent Thursday. “This resulted in three workers being exposed to airborne uranium.”
About 57.2 pounds of uranium oxide was in the air, according to the government.
The drum had been shipped to the Canadian facility, owned by Cameco Corp., to be converted to uranium hexafluoride for nuclear fuel rods May 29. Other drums were bulging, indicating they were also pressurized.
By July 9, Uranium One must propose a safe way of opening the other drums.
The employees did not get sick, said Donna Wichers, a senior vice president for Uranium One USA, a subsidiary of Toronto-based Uranium One Inc.
“According to Cameco, the affected employee is fine,” Wichers said. “Everything is normal and there is no impact to the employee.”
Willow Creek is made up of two properties, the Christensen Ranch mine, from which uranium is drawn from the ground, and the Irigaray central processing plant, in which the ore becomes yellowcake.
In the United States, yellowcake is processed Metropolis, Ill. at a conversion plant owned by Honeywell. It’s one of five such plants in the world and the only in the United States. Canada, France, United Kingdom, China, and Russia also have conversion plants.
“We have conversion contracts with the converter in Illinois and the converter in Canada,” Wichers said. “Production from Willow Creek is sent to both converters.”
It’s the second time in the past year that the NRC has investigated operations at Willow Creek .
In October, a uranium escaped from a dryer at Irigaray. The government stopped drying operations while the issue was addressed.
The NRC allowed Uranium One to begin operations in February 2011. Willow Creek has functioned on and off as a uranium mine and processing plant since the 1970s with different owners.
A previous uranium mine owner apparently also had problems with pressurized yellowcake drums.
“We are also aware that a similar event occurred with a yellowcake drum at the Wyoming facility you now operate, in April 1998,” the NRC said in the letter. “As a result of the 1998 event, the former licensee implemented corrective action to prevent recurrence.