Environmentalists worry about the Andrews County site, about 365 miles west of Dallas, and how the company keeps wanting to bury additional types of waste.
Commissioners made no comment about the amendment before voting. A call seeking comment from commission Chairman Bryan W. Shaw was not immediately returned Wednesday.
McDonald says the depleted uranium, which is a byproduct of nuclear power plants, is classified as low-level and will come from federal energy facilities
The amendment provides "the U.S. Department of Energy with a much-needed option as it looks for safe, secure disposal of orphaned waste that it has been storing for up to 40 or 50 years," McDonald said, noting that the amendment syncs up the license with the actual disposal operations taking place.
But experts say depleted uranium gets more radioactive as time passes and if disposed of improperly could pose health risks, such as cancer. And environmental groups, including the Sierra Club and Public Citizen, have long worried about the local geology and contamination of underground water sources near the site, which can accept low-level nuclear waste from compact states Texas, Vermont and 36 other states.
To ensure safety, the depleted uranium will be disposed of at the greatest depth possible, commission spokeswoman Andrea Morrow has said.
State Rep. Lon Burnam, a Democrat from Fort Worth who opposed the amendment and has long opposed the dumping site, called the company's ongoing expansion in size and scope "mission creep."
He was distressed that the commission prohibited any public comments at the commissioners meeting in Austin on Wednesday.
"I'm stunned more by the arrogance than the outcome," he said.
McDonald has said the part of the amendment that expands the volume came from concerns about capacity from state legislators and a commission that oversees the low-level waste site.
Most recently, the Waste Control Specialists' facility has become the temporary storage site for about 100 containers from Los Alamos National Laboratory that were originally destined for disposal at the Waste Isolation Pilot Plant in New Mexico, the federal government's only permanent repository for waste from decades of building nuclear bombs.