Feb 18 (Reuters) - The U.S. Nuclear Regulatory Commission (NRC) said on Thursday it would increase its oversight on Entergy Corp's 685-megawatt Pilgrim nuclear power plant in Massachusetts after completing a performance review of Pilgrim nuclear power station.

The plant in Plymouth, Massachusetts, was found to have had problems with its safety relief valves.

The NRC said it identified the finding after a security inspection at the plant in September 2015. ---------------------------------------------------------- PLANT BACKGROUND/TIMELINE STATE: Massachusetts COUNTY: Plymouth TOWN: Plymouth OPERATOR: Entergy OWNER(S): Entergy UNIT(S): 685 MW Nuclear FUEL: Nuclear DISPATCH: Baseload COST: $462.25 million in 2007 US dollars TIMELINE: 1972 - Pilgrim enters service 2006 - Entergy files with NRC to renew the original

40-year operating license for an additional

20 years 2012 - NRC renews reactor license 2032 - License expires (Reporting by Kevin Jose in Bengaluru; Editing by Bill Trott)