NRC BEGINS SPECIAL INSPECTION AT
PRAIRIE ISLAND NUCLEAR PLANT DUE TO REACTOR TRIP
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The Nuclear Regulatory Commission is conducting a special inspection at the Prairie Island Nuclear Power Station to review the causes of a reactor trip (automatic shutdown) and a subsequent trip of one of two auxiliary feedwater pumps. The two-unit plant operated by Xcel Energy is located near Red Wing, Minn.
                       
On July 31, 2008, at 8:17 a.m. Prairie Island Unit 1 reactor tripped and was shut down safely. Unit 2 was not affected.

“Although public health and safety were not at risk as a result of the event, it is important for us to understand what caused the trip and the problem with the auxiliary feedwater pump,” said Regional Administrator James Caldwell. “Our special inspection team is also tasked with reviewing the utility’s corrective actions and the company’s analysis of the extent of the problem.”

The reactor trip occurred when a component of the reactor trip system failed and provided a trip signal to the reactor. All plant systems responded as expected during the shutdown with the exception of the turbine driven auxiliary feed water pump. The pump started as expected but tripped shortly thereafter. Auxiliary feedwater pumps provide back-up water supply to the reactor.

Region III dispatched a three-person special inspection team to the plant to review the root causes of the reactor trip and the turbine driven auxiliary feedwater pump issue. The special inspection will also review the utility’s response to the situation and the company’s corrective actions.

The duration of a special inspection cannot be determined in advance. The average duration of a special inspection is seven days. The inspection report will be issued about 45 days after the inspection is complete. It will be available through the NRC RIII Office of Public Affairs and at the NRC web site: http://www.nrc.gov/reading-rm/adams/web-based.html

When Unit 1 was being returned to service on August 3, plant operators declared an Unusual Event due to elevated levels of hydrazine, an ammonia-like chemical in the turbine building. An  Unusual Event is the lowest level of emergency in the NRC’s emergency classification system. The company terminated the Unusual Event later on the same day when levels of hydrazine were successfully reduced. The special inspection team will review the circumstances around the Unusual Event.

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Wednesday, August 06, 2008