RICHLAND  (AP) — Radioactive contamination found on a piece of equipment on the Hanford Nuclear Reservation was not the result of a leak in an underground nuclear waste storage tank.

The U.S. Department of Energy said Wednesday that an analysis has ruled out that the contamination came from a leak within double-walled tank AZ-101.

The department and its contractor are now looking at other potential sources, such as historical contamination from previous work at the tank.

The contamination was found last Thursday on a robotic device doing an inspection of the space between the two walls of the underground tank. The contamination was found on the robot when it was removed.

A low level of contamination also appeared on the clothing of a worker, but the department said no skin contamination was found.