The Navy has decided to scrap the submarine USS Miami because of the high cost of repairs after a fire that damaged the vessel at the Portsmouth Naval Shipyard last year. Navy Rear Adm. Rick Breckenridge, director of undersea warfare, said Tuesday that repairing the Groton, Conn.-based sub would have meant canceling work on dozens of other ships because of new budget restraints. He says that would’ve hurt the Navy’s overall readiness. The Navy originally said it planned to repair the submarine but the discovery of new damage would further drive up the cost of repairs, originally estimated at about $450 million. A shipyard worker was sentenced to 17 years in prison after admitting he set fire to the Miami in dry dock at the Kittery shipyard during a 20-month overhaul.