05000311/LER-2007-003
| Docket Number Sequential Revmonth Day Year Year Month Day Yearnumber No. | |
| Event date: | 08-06-2007 |
|---|---|
| Report date: | 11-16-2007 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| 3112007003R01 - NRC Website | |
PLANT AND SYSTEM IDENTIFICATION
Westinghouse — Pressurized Water Reactor (PWR/4) Feedwater Steam Generator Level Control {JB/FCV} Solid State Protection System {JG}(SSPS) Solid State Protection System Circuit Card {JG/CBD} * Energy Industry Identification System {El IS} codes and component function identifier codes appear as {SS/CCC}
IDENTIFICATION OF OCCURRENCE
Event Date: August 6, 2007 Discovery Date: August 6, 2007
CONDITIONS PRIOR TO OCCURRENCE
Salem Unit 2 was in Operational Mode 1 at 100% reactor power.
No structures, systems or components were inoperable at the time that contributed to the event.
DESCRIPTION OF OCCURRENCE
On August 6, 2007, Salem Unit 2 was operating at approximately 100% power steady state conditions. At 1311 hours0.0152 days <br />0.364 hours <br />0.00217 weeks <br />4.988355e-4 months <br />, a reactor trip occurred as a result of the 22 Steam Generator (S/G) water level reaching its low low setpoint.
Control room personnel observed the overhead annunciator (OHA) D-24 "Feedwater Interlock" alarming and clearing several times immediately prior to the reactor trip without the associated valid inputs. This spurious Solid State Protection System {JG}(SSPS) feedwater interlock signal closed the feedwater regulating valves {JB/FCV} (21-24 BF19s). Closure of these valves interrupted the main feedwater flow to all steam generators, resulting in the low low steam generator level and subsequent reactor trip.
All safety systems responded as designed and the unit was stabilized in Mode 3. 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).
�NRC FORM 366 (6-2004) PRINTED ON RECYCLED PAPER
PREVIOUS OCCURRENCES
Salem Unit 1 LER 272/2000-005-00 "Reactor Trip Due to a Failed Solid State Protection System (SSPS)" took place in 2000. The cause of this event was a defective SSPS output driver circuit card (A517). The root cause of this event was long-term exposure to an environment that caused corrosion on the leads and case material for the circuit card transistors. Long-term exposure to a corrosive environment was an industry issue that affected Motorola and RCA transistors manufactured prior to 1997. The corrective actions replaced the failed circuit card and established a SSPS circuit board refurbishment program to improve equipment reliability.
The corrective actions taken for the 2000 event were appropriate and would not have prevented this event. The failure of the SSPS circuit card reported in this LER is different than the one reported in 2000, as stated below.
CAUSE OF OCCURRENCE
PSEG established a Root Cause Evaluation team to determine the cause of the reactor trip.
The direct cause of the reactor trip was a failed SSPS Train "A" output driver card A517 due to a defective solder joint. The defective solder joint was made during card refurbishment in September 2006 by PSEG maintenance. The-technician who performed the solder joint was qualified and experienced, and performed the card refurbishment in accordance with established procedures and standards. Because soldering components on these circuit cards is difficult, PSEG relies on post soldering testing and inspection to detect flaws. The defective solder joint was not identified using the PSEG refurbishment test and inspection procedure, which is more stringent than industry standard.
The card is located in cabinets behind the control room in a controlled environment that is not exposed to plant induced vibrations.
The root cause of the failed SSPS Train "A" output driver card A517 circuit card has been attributed to inadequate post soldering test practices in that the post soldering test and inspection was not comprehensive enough to identify the defective soldering.
SAFETY CONSEQUENCES AND IMPLICATIONS
There were no safety consequences associated with this event.
The spurious feedwater interlock signal did not result in any safety related component being unavailable to perform as designed in the event of an accident. All safety related systems functioned as designed in response to the event.
A review of this event determined that a Safety System Functional Failure (SSFF) as defined in NEI 99-02 did not occur.
NRC Fc)R,M 366A(1-2001)
CORRECTIVE ACTIONS
1. The safeguards output driver card A517 was replaced.
2. The Technical Specification required functional surveillance tests on SSPS Train "A" and "B" were satisfactory completed.
3. The SSPS refurbishment test and inspection procedure for SSPS safety related circuit cards will be revised to include the use of soldering standards with inspection of both sides of the circuit card, a manual functional testing with agitation, and component margin testing.
COMMITMENTS
No commitments are made in this LER.