NRC Begins Special Inspection at Callaway Nuclear Plant

NRC begins special inspection at Callaway nuclear plant

The U.S. Nuclear Regulatory Commission (NRC) started special inspections at the Callaway nuclear power plant following a reactor shutdown in August.
The reactor tripped Aug. 11, and all of the systems performed as expected. However, when workers with Ameren Missouri tried to switch to the motor-driven water pumps, a control valve failed to operate. Internal circuitry in the control valve system had been previously modified in late 2014, which seemed to have introduced a flaw in the design that resulted in the failure.
Another control valve in the system had similar modifications and also experienced a failure in December 2014. The NRC said a third unrelated control valve failed in the same system earlier this year that had already been corrected. The previous affected valves were repaired and tested prior to the plant restarting Aug. 12.
NRC said the special inspection is to better understand the circumstances around the failure, determine if the licensee performed a comprehensive review of the condition and review corrective actions to ensure that the causes were addressed. Staff determined the inspection is warranted because the valves provide an important function in the mitigation of selected plant events. Inspectors will spend about a week on site looking into outstanding questions with respect to Ameren Missouri’s testing, maintenance, design change and corrective action processes specific to these valves and associated system.
Mark McLachlan, senior director of engineering for Ameren Missouri, acknowledges that the control valves were repaired and tested prior to the plant restarting and that Callaway has operated safely t 100 percent power since the incident.
“Currently, the NRC is conducting a special inspection to better understand the circumstances following a reactor shutdown earlier this year,” McLachlan said. “During this inspection, the NRC will review Callaway’s initial response and corrective actions following the control valves failures to ensure appropriate actions were taken.”
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