Managers at the nation's only underground nuclear waste repository in southeastern New Mexico say monitors have picked up on increasing movement, indicating instability of the walls and ceilings in an area of the facility that has been closed off for more than a year.

Officials at the Waste Isolation Pilot Plant say there's a potential for falling rock inside one of the disposal rooms.

They say rock falls are not uncommon in areas where crews have been unable to perform regular maintenance. A rock fall last November forced a brief evacuation, but there were no injuries or contamination.

The repository began accepting shipments earlier this year after a nearly three-year shutdown that stemmed from a radiation release. The incident was caused by a chemical reaction inside a container of waste shipped from Los Alamos National Laboratory.