Idaho State University was fined last week for losing a small amount of radioactive, weapons-grade plutonium that is too small to make a nuclear bomb, but could be used in a dirty bomb, according to a regulatory commission.

Dr. Cornelis Van der Schyf, vice president for research at the university, blamed partially completed paperwork from 15 years ago as the school tried to dispose of the plutonium.

"Unfortunately, because there was a lack of sufficient historical records to demonstrate the disposal pathway employed in 2003, the source in question had to be listed as missing," he said in a statement to The Associated Press. "The radioactive source in question poses no direct health issue or risk to public safety."

The school, which reported the material missing on Oct. 13, was hit with an $8,500 fine and has 30 days to dispute the measure.

Victor Dricks, a U.S. Nuclear Regulatory Commission spokesman, said the agency “has very rigorous controls for the use and storage of radioactive materials as evidenced by this enforcement action," he said of the proposed fine for failing to keep track of the material.

The agency said a school employee doing a routine inventory discovered the university could only account for 13 of its 14 plutonium sources, each weighing about the same small amount.

Idaho State University has a nuclear engineering program and works with the U.S. Department of Energy's Idaho National Laboratory, considered the nation's primary nuclear research lab and located about 65 miles northwest of the school.

The plutonium was being used to develop ways to ensure nuclear waste containers weren't leaking and to find ways to detect radioactive material being illegally brought into the U.S. following the Sept. 11, 2001, terrorist attacks, the school said in an email to the AP.

The school searched documents and found records from 2003 and 2004 saying the material was on campus and awaiting disposal. However, there were no documents saying the plutonium had been properly disposed.

The last document mentioning the plutonium is dated Nov. 23, 2003. It said the Idaho National Laboratory didn't want the plutonium and the school's technical safety office had it "pending disposal of the next waste shipment."

The school also reviewed documents on waste barrels there and others transferred off campus since 2003, and opened and examined some of them. Finally, officials searched the campus but didn't find the plutonium.

The nuclear commission said senior university officials planned to return the school's remaining plutonium to the Energy Department. It's not clear if that has happened.

Energy Department officials didn't return calls seeking comment Friday.

Dricks, the commission spokesman, said returning the plutonium was part of the school's plan to reduce its inventory of radioactive material.

He said overall it has "a good record with the NRC."

The Associated Press contributed to this report