U.S. Energy Secretary Rick Perry once again visited a site near Las Vegas where weapons-grade plutonium is stored and low-level radioactive material was mistakenly sent for years.
Perry confirmed his team gave Gov. Steve Sisolak classified and unclassified briefings during Thursday's tour of the Nevada National Security Site.
The facility is at the center of a legal battle over plutonium the department secretly shipped to Nevada last year over the state's objections. Nevada wants a judge to order the Energy Department to remove the waste.
In addition, Perry disclosed last month that the site had been sent low-level radioactive waste for disposal that was mislabeled for as long as six years.
Perry toured the site in May with Nevada's U.S. senators.
Sisolak said Friday he invited Perry to return after the department acknowledged shipping the "improperly characterized" waste from Tennessee to the Nevada site.
"It is unfortunate that the important national security efforts conducted at NNSS have been overshadowed by the DOE's recent shipment missteps," the governor said. "I remain committed to holding them accountable."
Rep. Steven Horsford, D-Nevada, called on Perry to resign, saying the disclosure was further evidence that Nevada has been covertly coerced into illegally receiving nuclear materials "through negligence or outright trickery."
Perry said Thursday's visit was intended to show that his department is committed to working closely with Nevada officials.
None of the materials shipped to Nevada, possibly beginning in 2013, from the Y-12 facility in Oak Ridge, Tennessee, posed any health or safety threats to workers or the public, Energy Department spokeswoman Shaylyn Hynes has said.
But she acknowledged the shipments slated for disposal at the Nevada site were not in compliance with acceptance criteria.
She said the National Nuclear Security Administration has launched an internal investigation "to determine how this went undetected for a six-year period."
Deputy Energy Secretary Dan Brouillette also has ordered a department-wide assessment of its procedures and practices for packaging and shipping radioactive waste.