SALT LAKE CITY (AP) — State regulators denied a Salt Lake City-based nuclear waste processing company an exemption to bury thousands of tons of depleted uranium munitions at its site.

The Utah Waste Management and Radiation Control Board on Thursday voted unanimously to reject the military ordnance after EnergySolutions had petitioned the Department of Environmental Quality for an exemption to Utah's provisional prohibition on burying the radioactive munitions.

Agency staff and outside consultants concluded metallic depleted uranium is more hazardous and unstable than the processing company had characterized in its presentations.

"While disappointed by the Utah regulators' recommendation today," said the firm's marketing vice president, Mark Walker, "EnergySolutions will continue to cooperate with the ongoing regulatory review of the performance assessment that was initially submitted to the Utah Department of Environmental Quality in 2011 and concurs with the (waste) board's request to expeditiously complete their review."

Stephen Marschke, a nuclear engineer with SC&A Consulting, told the board that the company has failed to demonstrate that the "exemption will not result in undue hazard to public health and safety or result in undue hazard to the environment."

Board members said they were uncomfortable authorizing such waste before the Department of Environmental Quality completes its long-running "performance assessment" of the Clive facility, located 80 miles (about 130 kilometers) west of Salt Lake City, where EnergySolutions hopes to bury far more depleted uranium oxide, a granular waste product from the uranium-enrichment process.

EnergySolutions wanted regulatory approval to avoid a lengthy performance assessment so it could competitively bid on a U.S. Department of Defense contract for the munitions disposal.

The 5,000 cubic yards (about 3,800 cubic meters) of 30 mm bullets are at Tooele Army Depot and a military installation in Indiana.

Don Verbica, with the radiation control division, said he didn't believe previous assessments done at the Clive facility addressed the risks posed by depleted uranium metal.

"They have to demonstrate that (disposal of the material) will not result in an undue hazard to public health, safety and the environment," Verbica said.

Verbica added that depleted uranium metal is chemically unstable, relatively mobile and pyrophoric, or able to ignite spontaneously.