Tokyo Electric Power Company Holdings Inc. said Thursday that it will shut down a reactor at the Kashiwazaki-Kariwa nuclear power plant after an alarm was triggered during control rod withdrawal operations following its restart.The reactor is the first to be restarted by TEPCO since the 2011 Fukushima nuclear disaster. The resumption came on Wednesday, a day later than initially planned, after a control rod alarm sounded during a final pre-startup test.Earlier Thursday, the operator said it suspended control rod withdrawal operations at the just-restarted No. 6 unit of the plant in Niigata Prefecture, northwest of Tokyo.TEPCO said it was looking into what happened. The Nuclear Regulation Authority said the reactor is stable, adding that there are no safety problems.Control rods are used t…