05000348/LER-2005-001
| Docket Numbersequential Revmonth Day Year Year Month Day Yearnumber No. 05000 | |
| Event date: | 04-28-2005 |
|---|---|
| Report date: | 06-23-2005 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 3482005001R00 - NRC Website | |
Westinghouse -- Pressurized Water Reactor Energy Industry Identification Codes are identified in the text as [XX]
Description of Event
On May 4, 2005, with the unit operating at 100% power, it was determined that Unit 1 had operated in a condition prohibited by TS 3.3.2.0 from 16:22 on April 28, 2005 until 03:41 on April 29, 2005 in that a SSPS[JC] logic circuit for Main Steam Line (MSL) differential pressure Safety Injection actuation logic had failed at 04:22 on April 28, 2005, and the appropriate failed logic train LCO RAS was not applied until 01:34 on April 29, 2005.
At 04:22 on April 28, 2005, Main Control Board Annunciator 1B SG Steam Line High Delta P Alert and associated computer alarm came in and trip status indicating light PB485B2 was lit. Control Room personnel addressed all Annunciator Response Procedure (ARP) actions. TS 3.3.2.D was entered based on a suspected failed channel. Historically, this symptom set has been due to a failed channel. The RAS for TS 3.3.2.D for a failed process instrumentation channel requires the channel to be placed in trip condition within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />. The channel was placed in trip at 08:54 on April 28, 2005. TS 3.3.2.0 for inoperable Engineered Safety Feature Actuation System (ESFAS) logic was not applied at this time.
This TS requires restoration to operability within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> or unit shutdown within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.
Instrumentation and Controls (I&C) personnel subsequently determined that the channel bistable was functioning properly at 10:30 on April 28, 2005 and the channel was taken out of trip, but the annunciator, trip status indicating light, and computer point remained in the alarm condition. The work order was replanned to check the SSPS. A Multiplexer Test Switch was taken to the "A+B" position and the trip status light began flashing, indicating a potential problem either in one train of SSPS, the multiplexer, or an input relay. Operations directed Maintenance to place the channel back in trip at 15:18 on April 28, 2005 per TS 3.3.2.D.
Following additional planning and troubleshooting, the multiplexer and the input relays were verified to be functioning properly. This indicated the problem was in the SSPS logic circuits. At 01:34 on April 29, 2005, the RAS for TS 3.3.2.D was exited and the RAS for TS 3.3.2.0 was entered.
The failed card was identified as a Universal Logic Board (ULB) in A Train SSPS. The failed card was replaced, SSPS surveillance testing was performed satisfactorily, and TS 3.3.2.0 was exited at 03:41 on April 29, 2005.
Cause of Event
The equipment failure described in this event was caused by a failed NAND gate on the affected Universal Logic Board. The degraded logic NAND gate caused the associated multiplexing NAND gate to be low, resulting in the annunciator, trip status indicating light, and computer alarm.
The failed card was a new card that had been installed in October 2004 as part of the plant preventive maintenance program. The card has been returned to the vendor for investigation of the cause of the failure.
An LER is required because of firm evidence that a condition existed for a time longer than permitted by Technical Specification 3.3.2.C, i.e. the A Train SSPS Steam Line Differential Pressure Safety Injection actuation logic had failed at 04:22 on April 28, 2005 and this failure was not identified until 01:34 on April 29, 2005.
The time required to identify the failed actuation logic was extended due to insufficient troubleshooting guidance or preplanned work sequences. Preplanned diagnostic steps, if carried out prior to placing the suspect channel in test, would have permitted earlier diagnosis and repair of the actual problem.
Safety Assessment The health and safety of the public were unaffected by this event.
The B Train of SSPS and all equipment actuated by B Train SSPS remained operable throughout this event. Other than the one failed logic circuit, all actuation functions of A Train SSPS were unaffected by this event.
Since only one actuation signal within only one train of SSPS was affected, this event does not represent a Safety System Functional Failure.
Corrective Action The failed card was replaced and has been returned to the vendor for analysis.
Preplanned systematic diagnostic guidance will be developed and provided to planning personnel that will include lessons learned from this event by August 15, 2005.
Additional Information
The following LERs have been submitted in the past two years on Technical Specification violations:
Met.
Service Water Inoperable Inoperable Pump Inoperable.