Some cleanup efforts at a nuclear waste landfill in eastern Idaho are on hold while workers try to figure out what caused the walls of a dig area to partially collapse, causing an excavator to slide into the pit.

No radiation was released during the incident last Thursday, and no one was injured, said Erik Simpson with Fluor Idaho. Fluor is the contractor hired to clean up the site at the Idaho National Laboratory.

The excavator was digging up transuranic waste - a type of nuclear waste with a longer half-life than uranium - at the 97-acre Subsurface Disposal Area when the side of the pit collapsed. Simpson said the excavator slid partway into the 21-foot-deep pit, and remained in his protective cab for about 90 minutes before he could be safely removed.

Simpson said officials are working on how to safely remove the excavator and trying to determine what caused the collapse.