The Vermont Yankee nuclear plant is back in operation after a 26-day outage for refueling and maintenance. The plant, owned by the New Orleans-headquartered Entergy Corp., officially went on line at 12:21 p.m. Friday, company officials said in a statement. About 1,000 extra workers were added temporarily to the plant’s usual contingent of more than 600 to replace about a third of the fuel assemblies in the reactor. Workers also replaced a large electrical transformer and a recirculation pump. The work should set up Vermont Yankee to run for another 18 months before its next refueling outage.