KITTERY, Maine (AP) — Preliminary findings from Navy investigators suggest a fire aboard a dry-docked submarine started in a vacuum cleaner used by shipyard workers, officials said Wednesday. The Navy also confirmed a preliminary estimate of $400 million for repairs.

A statement from the Portsmouth Naval Shipyard said the vacuum was used by workers to clean up after each shift and was stored in an unoccupied space when the fire started.

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The repair cost estimate allows the Navy to begin lining up funding.

The Navy estimated that an additional 10 percent cost — or $40 million more — would be needed to account for disruption to other planned work across all naval shipyards and for potential assistance from private sector contractors, the shipyard said.

Further details on the fire and the cost of repairs will come in two weeks after the Navy issues initial findings from its investigations.

The nuclear-powered submarine was severely damaged by the fire that broke out May 23 when the submarine was three months into a 20-month overhaul.

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The fire burned for 10 hours, creating intense heat in forward compartments including the torpedo room, crew quarters, and the command and control centers. The rear part of the submarine including its nuclear propulsion escaped damage.

The Navy is seeking to determine whether the hull is still sound.

“Navy engineers are conducting a full technical assessment including internal and external hull surveys and damage assessments to develop a detailed cost estimate,” the shipyard said.

The detailed cost estimate will factor into whether it makes financial sense to repair the 22-year-old Los Angeles-class submarine.

The Los Angeles-class attack submarine cost $900 million when it was built. New Virginia-class subs cost more than $2 billion apiece.

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Copyright 2012 The Associated Press.