A nuclear reactor at one of South Korea\'s nuclear power plants automatically shut down Sunday after its reactor protection system gave warning signals, plant operators said.    The Shin (New) Wolsong 1 reactor, located some 371 kilometers southeast of Seoul, was shut down at 10:53 a.m. due to the malfunction of a system that controls power output, according to an official from the state-run Korea Hydro & Nuclear Power Co., Ltd.    An investigation is currently underway to confirm the exact cause of the malfunctioning of the power supply device.    There is no danger, however, of a radiation leak from the reactor, he added.    The operation of the reactor will resume after the ongoing investigation finds the exact problem and the Nuclear Safety and Security Commission approves its resumption, the official said.    The 1 million kilowatt nuclear reactor went into full operation on July 31 this year.    The stoppage of the nuclear reactor comes as concerns are rising over a possible power supply shortage this week. The government earlier worried that the nation\'s power reserves are forecast to tumble from Aug. 13-24, when the peak vacation season ends at the height of summer.    South Korea came close to suffering nationwide blackouts last September due to unseasonably high temperatures, which pushed up demand to what the government called \"dangerous levels.\"    South Korea currently operates 23 nuclear reactors, which supply about 30 percent of its total electricity consumption.