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The inspectors reviewed a self-revealing f … The inspectors reviewed a self-revealing finding for the failure of AmerenUE engineering personnel to correctly establish the relay settings for the alternate emergency power supply diesel output breakers. On August 21, 2011, Callaway Plant experienced a loss of power to the alternate emergency power supply diesel bus PA05. This resulted in all four alternate emergency power supply diesels starting; however, the number three diesel output breaker immediately tripped open. The licensee determined that the breakers protective relaying was improperly set. Further investigation by AmerenUE discovered that all four of the diesel output breakers had incorrect settings. The incorrect settings occurred due to the limited range of the relay chosen for the application and the engineering recommendations that prioritized protecting the diesel over limiting the margin to unintended breaker trips. Callaway engineering reviews had not identified the low margin to unintended trips. The licensee initiated corrective actions associated with Callaway Action Request 201106701 to change the differential current relay settings. This finding is more than minor because it is associated with the design control attribute of the Mitigating Systems Cornerstone and affects the cornerstone objective to ensure the availability, reliability, and capability of systems that respond to initiating events to prevent undesirable consequences. Using Manual Chapter 0609.04, Phase 1 Initial Screening and Characterization of Findings, the finding is of very low safety significance because it was a design deficiency that did not result in a loss of system safety function, did not represent an actual loss of safety function of one or more non-technical specification trains of equipment designated as risk-significant per 10 CFR 50.65, for greater than 24 hours, and did not screen as potentially risk significant due to a seismic, flooding, or severe weather initiating event. This finding has a crosscutting aspect in the area of problem identification and resolution because the licensee failed to implement a corrective action program with a low threshold for identifying issues commensurate with their safety significanceommensurate with their safety significance
23:59:59, 30 September 2011 +
23:59:59, 30 September 2011 +
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19:04:33, 30 September 2017 +
23:59:59, 30 September 2011 +