05000311/LER-2010-002
| Salem Generating Station - Unit 2 | |
| Event date: | |
|---|---|
| Report date: | |
| 3112010002R01 - NRC Website | |
PLANT AND SYSTEM IDENTIFICATION
Westinghouse - Pressurized Water Reactor (PWR/4) Auxiliary Feedwater System {BA/-} Main Feedwater System {SJ/-} * Energy Industry Identification System {EIIS} codes and component function identifier codes appear as {SS/CCC}
IDENTIFICATION OF OCCURRENCE
Event Date: January 21, 2010 Discovery Date: January 21, 2010
CONDITIONS PRIOR TO OCCURRENCE
Salem Unit 2 was in Mode 1 (POWER OPERATION) at approximately 78% reactor power when the automatic trip occurred. Prior to the reactor trip a turbine runback was in progress due to the trip of the 21 Steam Generator Feedwater Pump (SGFP). There was no equipment out of service that impacted this event.
DESCRIPTION OF OCCURRENCE
On January 21, 2010, at 1818 hours0.021 days <br />0.505 hours <br />0.00301 weeks <br />6.91749e-4 months <br />, the 21 Steam Generator Feedwater Pump (SGFP) {SJ/P} tripped.
A turbine runback automatically initiated as expected and steam generator level in all four Steam Generators (SG) continued to lower. The 22 SG reached the SG low level reactor trip setpoint at 1820 hours0.0211 days <br />0.506 hours <br />0.00301 weeks <br />6.9251e-4 months <br /> resulting in an automatic reactor trip. All control rods fully inserted on the trip. All three Auxiliary Feedwater (AFW) pumps {BA/P} started in response to the low SG water level and decay heat was removed by the steam dumps to the main condenser. Operators entered the emergency procedures for the plant trip and stabilized the plant in Mode 3 (HOT STANDBY).
This report is being made in accordance with 10CFR50.73 (a)(2)(iv)(A), "any event or condition that resulted in manual or automatic actuation of any of the systems listed in paragraph (a)(2)(iv)(B).
CAUSE OF OCCURRENCE
The cause of the 21 SGFP trip was an internal wiring short in the SGFP trip circuit that resulted in a false low suction pressure trip signal. The short circuit occurred due to the barrel of the lug for the normally closed contact coming in contact with the terminal screw of the normally open contact resulting in failure of the electrical insulation on the barrel. The cause for the wiring short was the result of poor work practices.
The reactor tripped on low water level in the 22 SG as designed. The low level SG trip setpoint as evaluated in the accident analysis is set at a level to ensure that adequate heat removal is maintained following a loss of normal feedwater. To increase the reliability of plant operations in response to a trip of a single SGFP, Salem installed an automatic plant runback feature in the 1990s. This feature is not credited in the accident analysis. Testing and evaluation following the 22 SG low level reactor trip determined that the systems responding to- the loss of a single SGFP operated as designed but did not prevent the reactor trip from occurring.
PREVIOUS OCCURRENCES
A review for LERs for the past 3 years did not identify any prior similar occurrences related to improper lug installation.0 LER 311/2007-002-00 identified a reactor trip due to a breach in the condensate system which resulted in the trip of the 21 SGFP, a turbine runback and reactor trip as a result of low level in the 22 SG. The corrective actions were specific to the demineralizer vessel sight glass failure which caused the 21 SGFP trip.
SAFETY CONSEQUENCES AND IMPLICATIONS
There were no safety consequences associated with this event. All safety related equipment functioned as designed in response to this event and the plant was stabilized in Mode 3 in accordance with plant operating procedures. The plant runback in response to a SGFP trip is not credited in the accident analysis, the accident analysis evaluates the loss of all feedwater which is mitigated by a reactor trip on low steam generator water level and actuation of the auxiliary feedwater system which functioned appropriately during this event.
A review of this event determined that a Safety System Functional Failure (SSFF) as defined in NEI 99- 02, Regulatory Assessment Performance Indicator Guidelines, did not occur since the ability to remove residual heat and mitigate the consequences of an accident were maintained.
CORRECTIVE ACTIONS
1. Repaired the damaged insulation and wiring in the 21. SGFP trip control circuit.
2. Performed an extent of condition inspection on the remaining Unit 2 SGFP panels for insulation degradation similar to the 21 SGFP and did not identify any deficiencieS.
3. Completed a root cause evaluation and determined that improper lug orientation, not damaged insulation, directly caused the internal wiring short and additional inspections were required to prevent shorting across the terminal screws. The Unit 1 SGFP pressure switches were inspected during the 1R20 refueling outage in April 2010 for proper lug orientation. The Unit 2 SGFP pressure switches will be inspected for proper lug orientation during the next refueling outage in the Spring of 2011.
4. Appropriate documents will be revised to clarify the guidance for lug installation and a training analysis will be performed to determine any necessary changes to the training program.
5. Testing and evaluation have determined that the systems responding to the loss of a single SGFP were operating as designed. An evaluation of the integrated plant response to a SGFP trip from full power will be performed and changes will be implemented as appropriate.
COMMITMENTS
No commitments are made in this LER.