DOE Headquarters, Forrestal Building, DC (copy) (copy)

The James Forrestal Building, the headquarters of the U.S. Department of Energy, in Washington, D.C.

The federal government, namely the U.S. Department of Energy, and the state of Nevada are close to settling a protracted lawsuit concerning the covert shipment of plutonium from the Savannah River Site to the Nevada National Security Site roughly two years ago.

The two parties this week announced they had reached an agreement in principle, another step toward a final resolution or contract. Earlier this month, the federal government and the Silver State said they were engaged in "substantive and promising" negotiations.

"The parties are currently working diligently to finalize the necessary documents and to obtain final government settlement approvals," a March 31 federal court filing reads. "Any order or decision issuing from the court has the potential to disrupt current negotiations and jeopardize the amicable resolution to the ongoing dispute."

District Judge Miranda M. Du agreed to suspend the related court case until May 29. An update on the prospective settlement is due a day later.

Nevada in late 2018 sued the Energy Department to prevent it from shipping weapons-usable plutonium from the Savannah River Site, south of Aiken, to the Nevada National Security Site, northwest of Las Vegas, as was planned and announced in a July 2018 study.

A half-metric ton of defense plutonium, though, had already been moved to the Nevada reserve. The clandestine relocation campaign was completed prior to November 2018, according to a 2019 court declaration from the National Nuclear Security Administration's general counsel, Bruce Diamond.

Nevada late last year asked the federal court to force the Energy Department to remove the half-metric ton as well as vacate the 2018 review that described and analyzed the shipments.

Both Dan Brouillette, the current secretary of energy, and Rick Perry, the former secretary of energy, have promised Nevada's congressional delegation that the plutonium once kept at the Savannah River Site would be removed from the Silver State by the end of 2026.

Relocation efforts will start in 2021, the two secretaries have said.

South Carolina joined the lawsuit as a defendant, siding with the Energy Department, in January 2019. The state exited months later.

Colin Demarest covers the Savannah River Site, the U.S. Department of Energy, the National Nuclear Security Administration and government in general. Follow him on Twitter: @demarest_colin