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Event Report Forms (ERFs) are filed to the IAEA. Sometimes there are multiple event reports, updating the rating, the event description. Here you only see the latest event report

ERF send date: Fri, 26-07-2002
ERF description: On November 29, 2001, the licensee identified a potential common mode failure of the auxiliaryfeedwater (AFW) system upon a loss of instrument air. Specifically, a loss of instrument air would cause the AFW minimum flow recirculation valves to fail closed. At the time, there were no backup air or nitrogen accumulators associated with these specific valves. If the discharge or flow control valves for the AFW pumps had been throttled or closed while the minimum flow recirculation valves were also closed, the AFW pumps would have been placed in a condition of insufficient flow. This could have resulted in pump damage in a short interval of time. The licensee also identified that early in the post reactor trip emergency operating procedures, the operators were directed to control the AFW system flow without specific written guidance to maintain minimum AFW flow. The plant operators were directed to control flow to the steam generators to maintain desired level and to prevent overcooling of the reactor coolant system. The AFW minimum flow recirculation valves are air-operated. Without the short-term recovery of instrument air (within less than 10 minutes), the AFW minimum flow recirculation valves would fail closed, potentially damaging the AFW pumps and causing the loss of secondary heat removal capability. There was no indication of recirculation flow available to operators in the control room. Heat removal capability through primary system feed and bleed would also be adversely affected since instrument air is required to operate the pressurizer power-operated relief valves and nitrogen backup was not available. A loss of instrument air would cause a loss of normal feedwater and would initiate a dual-unit reactor trip.

In addition, other initiating events, e.g., fire, loss of off-site power, may have a similar vulnerability. The licensee’s corrective actions included prompt operator training, procedural changes to the emergency operating procedures, and the addition of back-up pneumatic supplies for the AFW pump minimum flow recirculation valves.
ERF rating date: 10-07-2002
ERF contact person: Joseph J. Holonich
ERF address: U.S. Nuclear Regulatory Commission, Washington, DC 20555
ERF affiliation: USNRC

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