Online testing of the secondary side pressure relief valves revealed that 3 valves did not open at the required pressure set point on the initial tests. All valves did open on subsequent tests at a higher pressure and have been restored to operable status. These 3 valves and 3 other similar valves were installed during the last refueling outage and it is concluded that all 6 valves have the same set point drift failure mechanism. All 6 valves are assumed to have been inoperable at some time during the last operating cycle. The
steam generator design analysis specifies a minimum pressure relief capability to prevent a failure of the
steam generator and subsequent potential loss of
decay heat removal capability. This condition could have prevented the fulfillment of the safety function needed to remove residual heat. An engineering analysis is in progress to determine the actual impact on the safety function.
Per Technical Specifications 3.4.1.2.3, reactor power was reduced to below 66.3% due to the remaining 3 inoperable relief valves.
The licensee notified the NRC Resident Inspector.
- * * EVENT RETRACTION FROM ADAM MILLER TO DONALD NORWOOD AT 1130 EST ON 12/11/2009 * * *
In addition to the 6 valves discussed in EN 45464, an additional valve was found to be inoperable. Thus, it is assumed that 7 of the 18 secondary side pressure relief valves were inoperable at some time during the last operating cycle. An engineering analysis has determined that the inoperable secondary side pressure relief valves did not result in a condition that could have prevented the fulfillment of the safety function needed to remove residual heat. The impact of the inoperable secondary side pressure relief valves on the steam generators and associated secondary side piping integrity was assessed by comparison to an existing analysis. A qualitative assessment of that analysis indicates that with the reduced steam relief capacity, the pressure in the steam generators and associated secondary side piping would remain below the ASME code allowable. Thus, there would have been no failure of the steam generators and no subsequent potential loss of decay heat removal capability. Therefore, this event does not meet the criteria of 50.72(b)(3)(v)(B) and is being retracted. This event will be reported as a 60 day LER in accordance with 10CFR50.73(a)(2)(i)(B).
The licensee notified the NRC Resident Inspector.
Notified R1DO (Holody).
