Two Y-12 security police officers were wounded overnight by the accidental discharge of a firearm, a federal spokesman said today.

The guards received first aid at Y-12 and then were taken to the Oak Ridge Methodist Medical Center, where they were treated and released, Steven Wyatt of the National Nuclear Security Administration said via email. Their injuries were described as minor.

The incident is under investigation, and Wyatt declined to provide additional details.

The accidental discharge of the weapon reportedly occurred sometime after midnight, but the exact time of incident was not immediately available. Wyatt would not say what type of weapon was involved.

The news of the latest security incident comes on the anniversary of the worst security breach in the plant’s history. On July 28, 2012, three Plowshares protesters broke into the high-security installation and defaced structures, including spray-painted messages on the walls of the Highly Enriched Uranium Materials Facility.