Hours after officials at the troubled Rancho Seco nuclear plant resumed tests needed for reopening, they had to halt them again because radioactive water drained onto the reactor building floor. The water was not released outside the site and no one was exposed to it, said Brad Thomas, spokesman for the Sacramento Municipal Utility District. The 1,100 gallons of slightly radioactive water was misrouted from a storage tank to a spray system within the reactor containment building because a valve that was not closed was improperly cleared as closed, Thomas said. The water flowed onto the floor and into a drain system designed to capture and process radioactive liquids, he said. SMUD had been testing the plant's safety systems before restarting the plant, which has been idle since December, 1985. Thomas said SMUD officials are assessing what impact the incident will have on plans to restart the reactor in early March.