05000334/LER-2014-002
| Beaver Valley Power Station Unit Number 1 | |
| Event date: | 01-06-2014 |
|---|---|
| Report date: | 03-07-2014 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat 10 CFR 50.73(a)(2)(i)(C), 50.54(x) TS Deviation |
| 3342014002R00 - NRC Website | |
Energy Industry Identification System (EllS) codes are identified in the text as [XX].
CONDITIONS PRIOR TO OCCURRENCE
Unit 1: Mode 3, 553 degrees F, 2239 psig There were no systems, structures, or components (SSCs) that were inoperable at the start of the event that contributed to the event.
DESCRIPTION OF EVENT
On January 6, 2014, at 1659 hours0.0192 days <br />0.461 hours <br />0.00274 weeks <br />6.312495e-4 months <br /> the Beaver Valley Power Station (BVPS) Unit 1 tripped from full power due to a main transformer [XMFR] differential protection [87] main unit generator [GEN] trip as a result of a main unit transformer failure (Reference BVPS Unit 1 LER 2014-001-00 Automatic Rector Trip due to Main Unit Transformer Failure). All three Auxiliary Feedwater [BA] (AFW) pumps [P] automatically started, as expected, due to lowering steam generator [SG] levels. The reactor trip response was as expected with no complications. At 1757 hours0.0203 days <br />0.488 hours <br />0.00291 weeks <br />6.685385e-4 months <br /> the plant was stabilized in Mode 3.
At 1848 hours0.0214 days <br />0.513 hours <br />0.00306 weeks <br />7.03164e-4 months <br /> the Control Room received an alarm indicating that the Turbine Driven AFW (TDAFW) pump had stopped. The responding operator reported that the TDAFW pump had tripped and the two Motor Driven (MDAFW) pumps were operating properly. At 1902 hours0.022 days <br />0.528 hours <br />0.00314 weeks <br />7.23711e-4 months <br /> the MDAFW pumps were secured. The TDAFW pump ran for 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and 49 minutes at which time the pump tripped due to governor oscillations.
The TDAFW pump was declared inoperable. On January 7, 2014, the TDAFW pump was run to determine the cause of the pump trip. The pump ran for 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and 21 minutes then tripped due to governor oscillations. Subsequent investigation determined that the governor oscillations were due to a misadjusted governor [65] needle valve [FCV] that was last adjusted during refueling outage 1R22 in October 2013.
Background
During 1R22, maintenance was performed on the turbine governor for the TDAFW pump. On November 1, 2013, at 1006 hours0.0116 days <br />0.279 hours <br />0.00166 weeks <br />3.82783e-4 months <br /> Unit 1 entered Mode 3. At 2320 hours0.0269 days <br />0.644 hours <br />0.00384 weeks <br />8.8276e-4 months <br /> the TDAFW pump was started for surveillance testing. After two minutes of run time, the pump was secured from the Control Room due to the turbine emitting steam and water from the drains more than the local operator thought was normal. The pump casing drains were opened and water was drained from the pump. Based on initial TDAFW pump operation in Mode 3 and the amount of water observed draining out of the turbine, there was not reasonable assurance that the TDAFW pump was operable upon entry into Mode 3.
On November 2, 2013, at 0011 hours1.273148e-4 days <br />0.00306 hours <br />1.818783e-5 weeks <br />4.1855e-6 months <br />, the TDAFW pump was again started for surveillance and post maintenance testing. After 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and 22 minutes the pump was secured from the Control Room due to governor oscillations and declared inoperable. It was thought that the oscillations were caused by water that had accumulated in the steam lines during their heat up process. The main steam lines were drained and the TDAFW pump was run successfully for 18 minutes during a post maintenance test. The TDAFW pump was declared operable at 1323 hours0.0153 days <br />0.368 hours <br />0.00219 weeks <br />5.034015e-4 months <br />.
On November 4, 2013, at 1127 hours0.013 days <br />0.313 hours <br />0.00186 weeks <br />4.288235e-4 months <br />, the "A" train MDAFW pump was declared inoperable due to the discovery of water in its lubricating oil. The "A" train MDAFW pump was repaired, tested then declared operable on November 6, 2013, at 1253 hours0.0145 days <br />0.348 hours <br />0.00207 weeks <br />4.767665e-4 months <br />.
On November 5, 2013 Unit 1 tripped from 47 percent power due to a faulted 4KV cable [CBL5] (Reference BVPS Unit 1 LER 2013-003-00, Beaver Valley Unit 1 Turbine Trip and Subsequent Reactor Trip due to 4KV Cable Fault). During the trip the TDAFW pump automatically started, as expected. The TDAFW pump ran for 33 minutes and was secured from the Control Room when the plant was stable in Mode 3.
There were no problems noted with the pump operation during the thirty three minute run.
On November 26, 2013, the "B" train MDAFW pump was rendered inoperable from 0858 hours0.00993 days <br />0.238 hours <br />0.00142 weeks <br />3.26469e-4 months <br /> until 0933 hours0.0108 days <br />0.259 hours <br />0.00154 weeks <br />3.550065e-4 months <br /> for the performance of a planned quarterly surveillance test.
On December 9, 2013, the "A" train MDAFW pump was rendered inoperable from 0933 hours0.0108 days <br />0.259 hours <br />0.00154 weeks <br />3.550065e-4 months <br /> until 1236 hours0.0143 days <br />0.343 hours <br />0.00204 weeks <br />4.70298e-4 months <br /> for the performance of a planned quarterly surveillance test.
On December 18, 2013, the "B" train MDAFW pump was rendered inoperable from 0934 hours0.0108 days <br />0.259 hours <br />0.00154 weeks <br />3.55387e-4 months <br /> until 0949 hours0.011 days <br />0.264 hours <br />0.00157 weeks <br />3.610945e-4 months <br /> for the performance of planned relay surveillance testing.
As noted above, on January 6, 2014, at 1659 hours0.0192 days <br />0.461 hours <br />0.00274 weeks <br />6.312495e-4 months <br />, Unit 1 tripped from full power due to a main transformer differential protection main unit generator trip. The TDAFW pump ran for 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and 49 minutes at which time the pump tripped due to governor oscillations. The TDAFW pump was declared inoperable.
On January 7, 2014, the TDAFW pump was run to determine the cause of the pump trip. The pump ran for 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and 21 minutes then tripped due to governor oscillations. After further investigation and discussion with the pump vendor, it was determined that the governor oscillations were due to a misadjusted governor compensating needle valve. The governor adjustment was made during the refueling outage when the turbine was run using pressurized air and not steam as the motive force. This resulted in the turbine governor oil running at a lower than normal operating temperature. When the pump was run with steam as the motive force, the oil in the governor control heated up and the flow through the needle valve changed enough to cause the governor control to oscillate. This resulted in divergent governor oscillations that eventually caused the pump to trip on over-speed.
On January 8, 2014, the TDAFW pump was run, with steam as the motive force, and the governor needle valve was properly adjusted. The TDAFW pump surveillance test was then run for 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and 41 minutes without incident. At 1609 hours0.0186 days <br />0.447 hours <br />0.00266 weeks <br />6.122245e-4 months <br /> the pump was declared operable. It has been determined that the TDAFW pump was inoperable due to the misadjusted governor control from the time Mode 3 was entered following the 1R22 refueling outage until the issue was corrected on January 8, 2014.
CAUSE OF EVENT
The TDAFW Pump governor was not adjusted with the governor at stable governor oil operating temperature following maintenance activities during 1R22. This action in conjunction with not re-insulating the turbine trip and throttle valve during 1R22 ultimately resulted in excessive governor oscillations due to oil viscosity changes from heating of the governor oil from near ambient room temperature to near stable governor operating oil temperature. Due to excessive governor oscillations, the turbine trip and throttle valve automatically tripped closed to prevent potential damage to the TDAFW pump.
The significance of temperature change on turbine governor oil viscosity and resulting governor performance was not recognized nor addressed in site procedures and in the TDAFW Pump operability decision making process.
ANALYSIS OF EVENT
BVPS Unit 1 tripped from full power due to a main transformer differential protection main unit generator trip. All three AFW pumps automatically started, as expected, due to lowering steam generator levels. The TDAFW pump ran for 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and 49 minutes at which time the pump tripped due to governor oscillations.
The TDAFW pump was declared inoperable. Subsequent investigation determined that the governor oscillations were due to a misadjusted governor needle valve that was last set during 1R22 in October, 2013. Therefore the pump was unavailable from the time Mode 3 was entered on November 1, 2013. A degraded condition exposure time of 1635.4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />, while the TDAFW pump was unavailable due to the governor needle valve being out of adjustment, was assumed in this analysis.
The plant risk associated with the BVPS Unit 1 TDAFW pump oscillating governor event is considered to be very low. This is based on the delta core damage frequency and delta large early release frequency for the event during the 1635.4 hour4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> period that the degraded condition existed.
This event is being reported under 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by Technical Specifications and under 10 CFR 50.73(a)(2)(v)(B) as a condition that could have prevented the fulfillment of a Safety Function — Remove Residual Heat. Although this event is being reported under 10 CFR 50.73(a)(2)(v)(B) it will not be counted as a Safety System Functional Failure for the performance indicator based on an engineering analysis showing that there was no loss of ability to fulfill the safety function as the pump mission time requirement for the limiting Design Basis Accident was satisfied.
CORRECTIVE ACTIONS
1.) Performed a proper adjustment of the governor control needle valve while at a stable governor operating oil temperature. (Complete) 2.) Revise the appropriate surveillance procedures to ensure a stable governor operating oil temperature is achieved in order to adequately assess governor performance.
3.) Revise the appropriate maintenance procedures to ensure a stable governor operating oil temperature is achieved prior to making final needle valve adjustments.
Completion of the above and other corrective actions is being tracked through the BVPS Corrective Action Program.
PREVIOUS SIMILAR EVENTS
A review of BVPS LERs from the previous three years identified the following BVPS Unit 1 LERs involving Auxiliary Feedwater System.
BVPS LER 2013-001-00 Manual Start of a Motor Driven Auxiliary Feedwater Pump BVPS LER 2011-002-01 Failure to Comply With Technical Specification 3.7.5 due to the Inoperability of Two or More Trains of the Auxiliary Feedwater CR 2014-00177, 2014-00244, 2014-02358 a d'