05000244/LER-2011-003
| R.E. Ginna Nuclear Power Plant | |
| Event date: | 10-11-2011 |
|---|---|
| Report date: | 12-02-2011 |
| 2442011003R00 - NRC Website | |
I. DESCRIPTION OF EVENT
A. PRE-EVENT PLANT CONDITIONS:
The reactor was in Operational Mode 1 at 100% power, 2235 psig and 574 degrees F.
B. EVENT:
On October 11, 2011 at 23:28 hours the R.E. Ginna Nuclear Power Plant experienced a Turbine and Reactor Trip. Turbine Lube Oil (TLO) piping internal to the TLO reservoir severed at the 1.5 inch branch line containing the turning gear lube oil pump discharge check valve. This caused a decrease of Auto Stop Trip (AST) oil pressure, which resulted in a turbine and reactor trip when 2 out of 3 AST pressure switches activated on the low oil pressure.
C. INOPERABLE STRUCTURES, COMPONENTS OR SYSTEMS THAT CONTRIBUTED
TO THE EVENT:
None
D. DATES AND APPROXIMATE TIMES OF MAJOR OCCURRENCES:
1966-1969 Original construction 10/1997 Inspection performed on check valves and lube oil tank. No concerns noted.
05/2011 Inspection performed on check valves and lube oil tank. No concerns noted.
06/2011 Plant startup from refueling outage 10/11/2011 Weld failure leads to reactor trip Note: The TLO reservoir is drained, cleaned, and inspected routinely every refueling outage.
E. OTHER SYSTEMS OR SECONDARY FUNCTIONS AFFECTED:
None
F. METHOD OF DISCOVERY:
The turbine and reactor trips were immediately apparent due to plant response, alarms, and indications in the Control Room.
The reactor protection system operated as expected as a result of the turbine trip. Motor driven and turbine driven auxiliary feedwater pumps started on the Anticipated Transient Without Scram (ATWS) mitigation system signal. All systems operated as expected.
II. CAUSE OF EVENT:
The cause of this event is attributed to NUREG-1022 Cause Code B, Design, Manufacturing, Construction/Installation.
This event was entered into the site corrective action program (CR-2011-007076). The cause of the piping failure was determined to be high piping stresses from original construction in combination with substandard welding, normal operating conditions, routine maintenance, and cyclical fatigue.
The poor quality of the weld from initial construction created stress risers that served as the crack initiation site. Cold spring forces introduced during initial construction exerted on this short section of bent small bore piping resulted in stress near the yield strength of the pipe. Routine check valve removal and installation practices initiated a crack in the branch connection. Normal system operating vibration propagated the crack through the pipe until the pipe failed.
III ANALYSIS OF THE EVENT:
This event is reportable in accordance with 10 CFR50.73, Licensee Events Report System under item (a)(2)(iv) based on actuation of the Reactor Protection System and Auxiliary Feedwater System.
An assessment was performed considering both the safety consequences and implications of this event with the following conclusions:
The reactor trip breakers opened as required and the control rods inserted as designed. Heatup and pressurization of the Reactor Coolant System (RCS) presented no significant challenge to RCS pressure control systems and no Power Operated Relief Valve (PORV) or safety valve actuation occurred. Maximum steam generator secondary side pressures were well below the atmospheric relief valve pressure setpoint. Automatic actuation of the Motor Driven and Turbine Driven Auxiliary Feedwater pumps occurred as expected due to the ATWS mitigation system on low feedwater flow signal. All auxiliary feedwater pumps performed as expected and met required flow rates.
The plant transient response is bounded by the Loss of External Electrical Load transient analyzed as part of the licensing basis described in the UFSAR.
Based on the above considerations, the nuclear safety consequences of this event are very low.
This event impacted NRC performance indicatorlE01, Unplanned Scrams per 7000 Critical Hours.
This value changed from 0 to 0.9. The plant returned to Mode 1 on 10/15/2011.
IV CORRECTIVE ACTIONS:
A. ACTION TAKEN TO RETURN AFFECTED SYSTEMS TO PRE-EVENT NORMAL
STATUS:
Following a minor design change, repairs were performed to the piping and the system was restored to service.
B. ACTION TAKEN OR PLANNED TO PREVENT RECURRENCE
An additional set of flanges were installed in the larger connected piping to facilitate removal and reinstallation of the check valves in this location. Preventive Maintenance activities will be revised for the lube oil and seal oil systems to perform visual inspections of the welding following reassembly of piping with a similar configuration.
V. ADDITIONAL INFORMATION:
A. FAILED COMPONENT
1.5 inch branch line piping containing turning gear lube oil pump discharge check valve.
B. PREVIOUS LERS ON SIMILAR EVENTS
A review of recent Ginna events identified one similar event:
C. THE ENERGY INDUSTRY IDENTIFICATION SYSTEM (EllS) COMPONENT
FUNCTION IDENTIFIER AND SYSTEM NAME OF EACH COMPONENT OR
SYSTEM REFERRED TO IN THIS LER:
IEEE 803 FUNCTION IEEE 805 SYSTEM
COMPONENT IDENTIFIER INDENTIFICATION
5479R CKV TD Piping PSP TD
D. SPECIAL COMMENTS
None