KITTERY, Maine (AP) - The Portsmouth Naval Shipyard is investigating what caused a fire outside a nuclear-powered submarine that was severely damaged by another blaze last month.

The Kittery shipyard said Monday a small fire was reported about 7 p.m. Saturday in the dry dock where the USS Miami is located. Officials say a shipyard employee doused it with a portable extinguisher before the shipyard's fire department arrived.

The shipyard says the ship's reactor was never in danger. No one was hurt.

A May 23 fire heavily damaged the submarine while it was in dry dock for an overhaul, but its nuclear propulsion was spared.

Repair costs are estimated at $400 million. The Navy says that fire started when an industrial vacuum cleaner sucked up a heat source that ignited debris inside the vacuum.

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