KIEV, Ukraine (AP) - A nuclear reactor malfunctioned at Ukraine's Khmelnytsky power plant, forcing plant operators to halt it for repairs, officials said Saturday. The only operational reactor at Khmelnytsky was shut down shortly before midnight Friday after a section of its cooling system went out of order, the Nuclear Regulation Administration, Ukraine's nuclear safety body, said. The repairs were expected to last for a week, plant officials said. The Khmelnytsky plant is one of Ukraine's five nuclear power facilities which account for more than 40% of the former Soviet republic's electricity production. Three more reactors at Khmelnytsky are under construction.