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Minn. nuclear plant at full power

RED WING - Operators at Prairie Island Nuclear Plant successfully reduced levels of hydrazine, an ammonia-like chemical, in the non-nuclear side of the plant and returned Unit 1 to full power Sunday.

Plant operators had declared a Notification of Unusual Event, the lowest of four emergency classifications established by the U.S. Nuclear Regulatory Commission, at 3:52 a.m. Sunday when elevated levels of hydrazine, an ammonia-like chemical, were detected in the turbine building as Unit 1 was being returned to service. They exited the NUE at 10:20 p.m.

An NUE declaration indicates a potential reduction in the level of safety at the plant but no threat to public safety. The declaration's purpose is to have the plant's operating staff reach a state of readiness for emergency response if necessary.

Hydrazine is added to secondary feedwater at the plant to remove dissolved oxygen, which helps reduce corrosion in the piping. While the levels of hydrazine detected were higher than normal, the concentrations were less than levels that are considered dangerous to life and health. Ventilation in the affected part of the plant was increased to dissipate the chemical. No detectable hydrazine was found outside the plant.

Unit 1 had shut down at 8:17 a.m. Thursday when a component of the unit's control circuitry failed as routine testing was being performed on a redundant circuit. The circuits are part of the plant's instrumentation system that controls and monitors the reactor's operation. Repairs were made and operators commenced reactor startup Saturday afternoon. There were no injuries and no radiological release as the result of the shutdown or of the hydrazine detection. There was no threat to the public.

Prairie Island Unit 2 continued to operate at 100 percent power.

Prairie Island, near Red Wing, generates 1,076 megawatts of electricity, enough electricity to power approximately 750,000 homes. Nuclear Management Co. operates the plant for owner Xcel Energy.