Associated Press

LAS VEGAS — Nevada’s U.S. senators and Energy Secretary Rick Perry toured a site north of Las Vegas where the federal government is storing weapons-grade plutonium secretly shipped from South Carolina last year.

Aides said the Friday visit to the Device Assembly Facility at the Nevada National Security Site and briefings with Democratic Sens. Catherine Cortez Masto and Jacky Rosen were closed to the media and public. National Nuclear Security Administration head Lisa Gordon-Hagerty also made the trip.

The senators said in a joint statement Friday that they saw the plutonium and discussed safety and security during the tour with Perry.

Perry said in a Department of Energy statement released Saturday that he and Gordon-Hagerty briefed the senators on the timeline to remove “the material” and reiterated “our commitment to begin removal in 2021 and brief them on major milestones related to that removal.”

The Nevada senators in a joint statement said Friday they’d hold federal officials to that commitment.

“While we both appreciate Secretary Perry’s engagement today, we strongly reiterated that we would be ensuring he and his Department honor their agreement to remove the weapons-grade plutonium from Nevada,” they said.

The facility is an angular low-slung structure covered by compacted earth. It marks what officials say is a warren of steel-reinforced concrete cells spanning an area almost the area of a Manhattan city block.

It became the focus of intense interest after Nevada sued the Energy Department and the government disclosed in court filings in January that it had already moved half a metric ton (1,102 pounds) of plutonium to Nevada from the Savannah River Site in South Carolina. Officials said the shipments were kept secret for national security reasons.

The government is under court order from a federal judge in South Carolina to remove a full metric ton (2,204 pounds) of plutonium from the Savannah River nuclear weapons refining complex by 2020, and to remove another 5 metric tons (11,020 pounds) in future years.

Nevada maintains the government failed to conduct proper environmental reviews, and that an accident transporting, handling or storing the material could permanently harm an area home to 2.2 million permanent residents and host to more than 40 million tourists a year.

The Energy Department says critics have incorrectly categorized the material as the kind of nuclear waste that the Trump administration wants to store at a the proposed but mothballed Yucca Mountain national nuclear waste repository. The Device Assembly Facility and Yucca Mountain are about 25 miles (40 kilometers) apart.

In a letter to Cortez Masto, Perry said it is not nuclear waste, but “material essential for the maintenance of the U.S. weapons stockpile.”

The Energy Department has said it plans to eventually move the plutonium to the Waste Isolation Pilot Plant in New Mexico.

Cortez Masto said Perry promised no more of the weapons-grade material would be moved to Nevada.

The state still is seeking a court order from a federal judge in Reno preventing any shipments because it says the Energy Department’s track record shows it cannot be trusted. A related case is pending before the 9th U.S. Circuit Court of Appeals in San Francisco.

Cortez Masto said she told Perry she would drop holds she placed on pending nominations for Energy Department vacancies, and she noted the Energy Department committed to $1 billion in investments before 2025 at the former Nevada Test Site.

The 1,360-square-mile (3,520-square-kilometer) area, now called the Nevada National Security Site, is nearly the size of Rhode Island.

It is best-known as the home to about 100 above-ground and more than 800 underground nuclear tests from 1951 to 1992.

It serves today as a testing, research and training site and for U.S. studies of nuclear, chemical, biological and other weapons.