05000219/LER-2013-004
| Oyster Creek, Unit 1 | |
| Event date: | 12-14-2013 |
|---|---|
| Report date: | 02-12-2014 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 2192013004R00 - NRC Website | |
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Plant Conditions Prior To Event
Event Date: December 14, 2013 Event Time: 0336 EST Unit 1 Mode: Power Operation Power Level: 95%
Description of Event
On 12/14/13 at approximately 0336 EST, during quarterly turbine valve testing with reactor power at 95% of rated thermal power, the plant experienced reactor pressure control abnormalities. Turbine Control Valves 2 and 3 failed closed due to the Servo Motor Feedback Support Bracket bolts backing out and falling out thereby requiring a scram. Operators initiated a manual reactor scram due to reactor pressure rising to 1042 psig which approached the scram set point.
Turbine Control Valve (TCV) 2 and 3 Servo Motor feedback lever brackets became loose and then detached from their supports. Also identified was that a vertical connection to transmit the required Turbine Bypass Valve (TBV) relay position from the Turbine Front Standard to the Bypass Valve Assembly became detached.
The failure of the TBV control connection was a lack of effective application of vendor maintenance direction. The immediate corrective action was completed as part of 1F33. The TBV clevis and push/pull rod connections were adjusted to meet OEM required minimum thread engagement and the jamb nuts were secured from rotation per OEM vendor recommendation.
Cause of Event
The OEM during manufacture did not follow their assembly drawings and installed inappropriate locking mechanisms (split washers) instead of the assembly drawing required parts (lock plates).
The failure of the TBV control connection was a lack of effective application of vendor maintenance direction.
The resulting investigation determined that the primary failures associated with TCV-2/3 inside the Control Valve Hydraulic Enclosure (CVHE) (General Electric Part number 715E847) were due to a lack of the equipment configuration to meet OEM requirements.
The root cause determined that the manufacturer failed to assemble the Control Valve Hydraulic Enclosure per there design.
Analysis of Event
This issue resulted in a manual reactor SCRAM with the ensuing 1F33 forced outage. Without operator intervention this issue would have further challenged the equipment, operating margin and regulatory margin by driving an automatic SCRAM on high reactor pressure. This event necessitated a reactor cool down to be performed with the Isolation Condensers instead of the Turbine Bypass Valves due to Bypass Valve unavailability.
There were no significant equipment problems noted related to maintaining the reactor in a safe Cold Shutdown Condition.
There were no safety consequences impacting the plant or public safety as a result of this event. All control rods fully inserted and plant response was as expected. This event is being reported pursuant to 10CFR50.73(a)(2)(iv)(A) due to an actuation of the Reactor Protection System (RPS).
Corrective Actions
The immediate corrective actions were completed as part of 1F33 which were to adjust the TBV clevis and push/pull rod connections to meet OEM required minimum thread engagement and secure the jamb nuts from rotation per OEM vendor recommendation. The corrective action was completed as part of 1F33 to implement OEM vendor design and install lock plate securing mechanisms as per vendor documentation.
The root cause determined that the manufacturer failed to assemble the Control Valve Hydraulic Enclosure per there design. Procedures are being revised to inspect for the correct configuration per the GE assembly drawings to ensure any replaced parts will maintain this configuration. PMs, specifications, and procedures that inspect, adjust, or replace the turbine control linkages are being revised to include minimum thread engagement and appropriate torque methods and values.
Previous Occurrences
There have been no similar Licensee Event Reports associated with this component failure submitted at OCNGS in the last two years.
Component Data Component IEEE 805 System ID IEEE 803A Component Control Valve Hydraulic Enclosure TG XC