05000318/LER-2013-004
| Calvert Cliffs Nuclear Power Plant, Unit 2 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| Initial Reporting | |
| ENS 49054 | 10 CFR 50.72(b)(2)(iv)(B), RPS System Actuation, 10 CFR 50.72(b)(3)(iv)(A), System Actuation |
| 3182013004R00 - NRC Website | |
A. PRE-EVENT PLANT CONDITIONS:
Unit 2 was operating at 99.5 percent of rated thermal power on May 21, 2013.
B. EVENT:
On May 21, 2013 at 0533, Calvert Cliffs Nuclear Power Plant Unit 2 initiated a manual reactor trip from 99.5 percent power in response to a trip of 22 Steam Generator Feed Pump (SGFP).
The cause of the initiating event was the failure of 22 SGFP coupling that connects the pump to its steam turbine driver, such that the pump and steam turbine were effectively disconnected.
All control element assemblies fully inserted as expected.' Containment atmosphere parameters were unaffected by the trip. Radiation levels were not affected by the trip.
C. INOPERABLE STRUCTURES, COMPONENTS, OR SYSTEMS THAT CONTRIBUTED
TO THE EVENT:
There were no inoperable structures, components, or systems at the time of the trip that contributed to the event.
D. DATES AND APPROXIMATE TIMES OF MAJOR OCCURRENCES:
May 21, 2013 At 0520, SGFP status panel alarm received for supervisory instrument alarm.
May 21, 2013 At 0522, Dispatched Operations personnel to local vibration panel. Report was 22 SGFP alert vibration in alarm.
May 21, 2013 At 0533, Plant Operators initiated a manual reactor trip in response to the trip of 22 SGFP. Post-reactor trip actions were completed in accordance with station procedures with no additional complications.
May 21, 2013 Following manual reactor trip, investigation determined 22 SGFP coupling that connects the pump to its steam turbine driver had failed.
May 30, 2013 Completed 22 SGFP repair.
May 30, 2013 At 2255, Unit 2 returned to 99.5 percent power following completion of post- maintenance testing.
E. OTHER SYSTEMS OR SECONDARY FUNCTIONS AFFECTED:
No other systems or secondary functions were affected.
The Calvert Cliffs Unit 2 manual reactor trip was in response to the trip of 22 SGFP. The trip of 22 SGFP occurred due to a failed pump coupling that connects the pump to its steam turbine driver, such that the pump and steam turbine were effectively disconnected. Inspection of the pump end of the coupling assembly revealed mechanical damage and separation along a weld seam. Failure analysis identified areas of incomplete weld fusion on the turbine end of the coupling dating to the original component manufacture. These pre-existing manufacturing flaws combined with stresses induced by high cycle stress and SGFP start/stop cycles over the life of the coupling resulted in fatigue failure.
III. ANALYSIS OF EVENT:
The manual reactor trip resulted in a valid actuation of the Reactor Protective System. The actuation was not part of a pre-planned sequence during testing or reactor operation.
Therefore, this event is reportable in accordance with 10 CFR 50.73(a)(2)(iv)(A). Immediate notification of this event (Event Number 49054) was made on May 21, 2013, in accordance with 10 CFR 50.72(b)(2)(iv)(B) and 10 CFR 50.72(b)(3)(iv)(A).
The Nuclear Regulatory Commission Performance Indicator for Unplanned Scrams per 7,000 Critical Hours is projected to rise to approximately 1.8 and remain green. No other performance indicators were impacted.
There were no actual nuclear safety consequences incurred from this event. The loss of feedwater event is analyzed in Section 14.6 of the Calvert Cliffs' Updated Final Safety Analysis Report. The analyses assumes the closure of the feedwater regulating valves, the loss of condensate or feedwater pumps, or a pipe break in the condensate or feedwater systems during steady-state operation results in a total loss of feedwater flow event. However, in this event, At Calvert Cliffs, there have been no recent similar events involving a reactor trip caused by the failure of the SGFP coupling.