Opponents of nuclear energy said they will go to court if Sacramento's citizen-owned electric power district tries to transfer its closed nuclear plant to private industry. The Rancho Seco nuclear facility has been shut down since June 7, the day after Sacramento-area residents approved a ballot measure ordering the Sacramento Municipal Utility District to close the plant. The utility's five-member elected board of directors is divided on the legal question of whether the district, known by its initials of SMUD, has the right to sell the plant to private investors. The SMUD board will consider a proposal by an investor group called Golden State Energy Corp. to reopen Rancho Seco and sell its power back to SMUD. The lead group among the investors is Quadrex Corp. of Campbell, Calif., which specializes in repair and retrofitting of nuclear facilities.