South Carolina won an important victory Tuesday in its struggle to avoid becoming a permanent nuclear waste dump for the federal government as the U.S. Court of Appeals ordered the Nuclear Regulatory Commission to restart the Yucca Mountain project.

The ruling, for the District of Columbia Circuit, also was a constitutional victory for the separation of powers, which was abrogated when the Obama administration moved to unilaterally dismantle a congressionally mandated project of nearly 30 years standing in 2010.

In doing so, the administration was willing to leave South Carolina and Washington state holding the bag on huge quantities of high-level nuclear waste slated for disposal at the remote Yucca Mountain site in Nevada. Aiken County, home of Savannah River Site, joined the states in their lawsuit.

And the administration was content to leave a growing volume of commercial nuclear waste at 104 reactor sites across the nation, even though electrical ratepayers have paid billions into the disposal fund for Yucca Mountain through a surcharge in their power bills.

As Chief Judge Brett Kavanaugh wrote for the majority, the NRC “by its own admission ... has no current intention of complying with the law. Rather, the commission has simply shut down its review and consideration of the Department of Energy’s license application.”

Actually, the NRC did far more than that, as the Government Accountability Office detailed in a 2011 review. Under the direction of former NRC chairman Gregory Jaczko, the Yucca project was dismantled to the greatest extent possible, with the removal of data, computers and on-site facilities.

Since then the plan to store high-level waste in a geological repository within Yucca Mountain has languished.

The court ruled that neither the president nor the NRC can simply ignore congressional mandates over policy disputes.

Judge Kavanaugh wrote that “the President may not decline to follow a statutory mandate or prohibition simply because of policy objections.”

And further, “It is no overstatement to say that our constitutional system of separation of powers would be significantly altered if we were to allow executive and independent agencies to disregard federal law in the manner asserted in this case by the Nuclear Regulatory Commission.”

Senior Circuit Judge A. Raymond Randolph, in a concurring opinion, singled out Mr. Jaczko for orchestrating “a systematic campaign of noncompliance” on Yucca. Mr. Jaczko was a former staffer for Senate Majority Leader Harry Reid, D-Nev., one of the president’s most important congressional allies.

The termination of Yucca coincided with a tough re-election campaign for Sen. Reid, and helped bolster his standing with home-state voters.

The ruling requires that the NRC restart the licensing process for the high-level nuclear waste repository. Congress should affirm its long-standing support for Yucca by making the allocations necessary to complete the project.

And South Carolina should stay focused on keeping the administration and the NRC honest.