RENO, Nev. (AP) — The U.S. Energy Department is asking a federal judge in Reno to dismiss the state’s lawsuit challenging plutonium shipments to Nevada while an appeals court considers whether to overturn the judge’s earlier refusal to temporarily block the shipments.

Department officials have also stepped up their explanation of why the site housing the weapons-grade plutonium north of Las Vegas isn’t vulnerable to dangers posed by earthquakes despite concerns raised last month by an independent safety board.

Bruce Hamilton, chairman of the Defense Nuclear Facilities Safety Board, said in a March 21 letter to Secretary Rick Perry that “a seismically induced high explosive violent reaction could result in unmitigated” radiation exposure to the public.

But Hamilton told a House subcommittee last week his warning was directed at a type of testing that no longer occurs at the Nevada site.