Following an unplanned shutdown and repairs three days earlier, unit 2 at Exelon's Byron nuclear plant returned to service Saturday.Operators tripped the reactor manually from full power Wednesday after losing water flow to its generator's stator cooling system, according to a report filed with the Nuclear Regulatory Commission. The plant shut down safely, although the report also noted that, "a digital rod position indication system urgent failure occurred with a general warning on control rod position M12. Indication for the train 'B' reactor trip breaker was lost. All control rods inserted upon reactor trip and the train 'B' reactor trip breaker was locally verified open."The plant reached full power again at about noon, Saturday. After the shutdown, crews made repairs to a motor that drives the main generator's cooling pump, Exelon said in a release Monday. As with the generator, the malfunctioning equipment was located on the non-nuclear side of the plant.According to the NRC, the unit is one of two Westinghouse pressurized water reactors at the site near Rockford, Ill. Both were originally licensed in the mid-1980s.