05000293/LER-2001-001
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FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6) PAGE (3) PILGRIM NUCLEAR POWER STATION 05000-293 I � REVISION
BACKGROUND
Emergency AC power is provided to the Pilgrim Station Auxiliary Power Distribution System through the safety-related 4160 VAC buses A5 and A6. � The startup transformer (SUT) is designed to supply these buses if the preferred offsite power (345 kV) is available. � Should preferred offsite power be lost or become seriously degraded, two emergency diesel generators (EDG) are designed to provide onsite power to their respective buses.
The core spray (CS) and residual heat removal (RHR) systems are part of the Core Standby Cooling Systems (CSCS) used to mitigate design basis accidents and are powered by the emergency AC system. � Bus A5 supplies 4160 VAC to CS pump A and RHR pumps A and C. � Bus A6 supplies 4160 VAC to CS pump B and RHR pumps B and D.
Buses A5 and A6 also supply 480 VAC power to safety-related buses B1 and B2.
Safety-related 480 VAC swing bus B6 is designed to be powered by A5 or A6. � The CS train A injection valves are powered from 480 VAC Motor Control Center (MCC) B17 which is powered by bus Bl. � The CS train B injection valves are powered from 480 VAC MCC B18, which is powered by bus B2. � The RHR/low pressure coolant injection (LPCI) valves are powered from MCC B20, which is powered by bus B6.
Bus B6 is a swing type bus that can be powered by bus B1 or B2. � Bus B1 is the normal power source for bus B6 with B1/B6 supply breakers52-102 and 52-601 in the CLOSED position and bus B2/B6 supply breakers52-202 and 52-602 in the OPEN position. � The normal and alternate supply breakers are interlocked to prevent B6 from being simultaneously powered by bus Bl and B2.
Control power for the B6 transfer scheme, and Bl/B6 and B2/B6 supply breakers is provided by the 125 VDC swing bus D6 that is powered from bus D16 or bus D17 through automatic transfer switches Y-10, D32 and D33. � This configuration makes the control power for the circuit breakers highly reliable and independent of the 480 VAC buses.
If bus Bl were to experience a loss of voltage, the design provides an automatic transfer of B6 from B1 to B2 to ensure continuous power to B6. � Moreover, if a loss of offsite power were to occur, buses B1 and B2 would both de-energize and the B6 supply breakers that are closed would open. � The B6 transfer scheme is self-seeking; meaning that the B1/B6 or B2/B6 supply breakers would close, depending upon which bus (Bl or B2) re-energizes first with a 2-second preference for Bl.
As � part � of � the � Pilgrim � Station � Unresolved � Safety � Issue � (USI) � A-46 � seismic upgrade program, � undervoltage relays � (GE type HFA) � in the B6 � transfer scheme (relay 27-B2Z2 in bus B2 and relay 27-B2X2 in bus B6) were replaced with Joslyn Clark � relays � qualified � and � dedicated by � Trentec � Corporation, � an � Appendix � B supplier. � These � relays were � installed and � tested under Plant � Design Change (PDC) � 98-23 � during � the � 1999 � refueling � outage � (RFO-12). � As � part � of � the procurement � for PDC 98-23, � Trentec dedication testing was performed on one of five relays. � After the dedication program at Trentec, � a pre-installation bench test was performed at � Pilgrim Station to verify time-delay operation, � and an integrated post work automatic transfer test was performed. � The post work test used existing procedure 3.M.3-27, � "480 VAC BUS B6 AUTOMATIC TRANSFER TEST" and successfully demonstrated the transfer of bus B6 � from B1 � to B2 � and B2 � to Bl.
FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (61 PAGE (3) PILGRIM NUCLEAR POWER STATION 05000-293 I REVISION The maintenance requests associated with PDC 98-23 were closed out in June 1999 with no i discrepancies i identified. i Acceptable Trentec i qualification data had been received, including seismic qualification.
EVENT DESCRIPTION
The B6 transfer scheme uses 125 VDC control power from DC transfer bus D6 via switch Y-10. i The i SE relay in i transfer i switch Y-10 i had experienced degraded performance i and i increased i surveillance i testing i had i been i instituted. i The degrading i condition i of i the i SE i relay i was i reported i in i problem i reports, i most recently i in i PRO0.9497 i and i in i LER i 2000-003-00, i "125V i DC i Swing i Bus i Automatic Transfer Switch Dearaded Performance." i A decision was made to replace the SR relay in transfer switch Y-10 with two qualified relays available in the Pilgrim Station warehouse. On December 22, 2000, while physically inspecting one of the relays withdrawn from the warehouse to be installed as part of temporary modification TM 00-053 to replace the degraded SE relay, it was observed that the time-delayed contact configuration of the relay was not as ordered from the supplier (Trentec). The relay examined had two instantaneous contacts and two time-delayed contacts (corresponding to Joslyn Clark part number (P/N) X714UPDA- 125) rather than four time-delayed contacts as indicated on the label (Joslyn Clark P/N X714UPDE-125) and required by the purchase specifications. i It was concluded that the relays without time delay contacts could be used in the proposed application.
Trentec, the commercial dedication vendor, obtained 5 relays, P/N X714UPDE, from Joslyn Clark. One of the five was used for seismic testing and the remaining four were dedicated and furnished to Pilgrim Station. A review of plant design change (PDC) 98-23 was initiated to identify where the other two relays with the same part number were installed. This review concluded that two relays had been installed in the B2/B6 transfer scheme during RFO-12 as part of a seismic upgrade.
i On January 2, 2001, an inspection was made of the two installed relays, one in the B2 cabinet located in the switchgear room and one in the B6 cabinet located in the cable spreading room. The physical location of the two relays in their respective cabinets made immediate recognition of the contact configuration difficult. Observations and photographs were communicated with both Trentec and Joslyn Clark, to determine if a configuration discrepancy existed.
After being made aware of the discrepancy, Trentec inspected the relay that had been used for and retained after qualification testing and determined it to be correctly labeled and configured with 4 time-delayed contacts. i When the nonconformance was verified, PRO1.9004 was written to document the condition.
Due to uncertainties of the potential impact of the incorrect configuration, B2/B6 was disabled and a Technical Specification limiting condition for operation (LCO A01-005) was entered, taking low pressure coolant injection (LPCI) out of service.
A detailed evaluation was initiated to determine the impact of the two instantaneous relay contacts on the B2/B6 transfer scheme and its ability to maintain 480 VAC power to B6. i The review concluded that if B2 remains energized, an automatic transfer of bus B6 to bus B2 would occur if bus B1 were to become de-energized. If a loss of offsite power occurred and B1 re-energized FACILITY NAME (1) DOCKET NUMBER (2) � 05000-293 LER NUMBER (6) first, � B6 would energize � from B1. � If, � however, � B2 � re-energized more � than � 2 seconds before Bl, � the B2/B6 transfer breakers would not close and bus B6 would not automatically re-energize as designed.
The � NRC � Operations � Center � was � notified � in � accordance � with � 10 � CFR 50.72(b)(1)(ii)(B), � at � 1737 hours0.0201 days <br />0.483 hours <br />0.00287 weeks <br />6.609285e-4 months <br /> on January 11, � 2001, � due to the belief that a condition was identified to be potentially outside the design basis.
This event occurred at 100 percent reactor power with the reactor mode selector switch in the RUN position. � The reactor vessel pressure was about � 1035 psig with the water temperature at the saturation temperature for that pressure.
CAUSE
The root cause for installation of two nonconforming Joslyn Clark relays under PDC 98-23 � is the failure � to detect � the mismatch between the relay label � and contact configuration by Trentec during commercial dedication activities under Purchase � Order � #STR � 144343. � Missed � opportunities � to � have � identified � this discrepancy � include � PNPS � receipt � inspection, � pre-installation � calibration and bench testing, and post work testing at Pilgrim. � The relay nonconformances were not identified at any of these steps. � A detailed root cause was completed as part of PRO1.9004.
EXTENT OF THE PROBLEM
An extent review was performed to determine whether similar relays had been installed in other safety-related applications. � It was concluded that Pilgrim Station received four incorrectly labeled relays. � Two were � installed in the B2/B6 transfer scheme as part of PDC 98-23. � The remaining two were installed as part of temporary modification TM 00-053 on December 23, � 2000 after concluding the � acceptability � of � using � the � two � instantaneous � contacts. � Trentec � also supplied Square D relays under the same purchase order. � An evaluation concluded that the Square D parts supplied by Trentec were configured as specified.
CORRECTIVE ACTION
Corrective actions taken include the following:
Relay modification kits were obtained from the vendor and time-delayed operating links � were � installed � on � both � relays � in � the � B2/B6 � transfer � scheme. � These modifications were made in accordance with FRN 98-23-03 and post work testing was � initiated � in � accordance with � temporary procedure � TP � 01-001. � The � bench testing � initially � failed � on � relay � 27-B2Z2 � due � to � misalignment � in � the � relay timing head. � A nonconformance report (NCR 00-032) was issued and a modification was made in accordance with FRN 98-23-04 and the relay performed correctly. � The installation and testing of both relays were completed and the LPCI � LCO was exited at � 7:45AM on January 7, � 2001, � within � the allowed out � of � service � time.
The � installation � and � post � work � testing � of � the � two � relays � restored � the � B6 transfer scheme to its design basis.
Entergy � Corporate � Quality � Assurance � has � issued � a � corrective � action � program document (CAR 01-005) request to Trentec to identify the cause of the failure to FACILITY NAME (1) DOCKET NUMBER (1)__ 05000-293 LER NUMBER (6) identify the mismatch between the relay label and contact configuration, t their corrective actions and their completion schedule. t In addition, an extent review was requested of Trentec on previous purchase orders.
ACTION TO PREVENT RECURRENCE
Actions t to prevent t recurrence t include t an assessment t of t the t effectiveness t of:
Trentec's t corrective actions t as t they relate t to t future procurement t activities; Pilgrim's t receipt t inspection; t pre-installation calibration; t bench testing; t and post t work t testing t to t identify t and t implement t necessary t improvements. t These actions are being tracked under the Pilgrim Station corrective action program (PRO1.9004).
SAFETY CONSEQUENCES
The event posed no threat to public health and safety.
The core standby cooling system t (CSCS) t consists of the HPCI t system, t Automatic Depressurization t system t (ADS), t Core t Spray t (CS) t system, t and t the t Residual t Heat Removal t (RHR) t system in the low-pressure coolant injection (LPCI) mode.
The CS and LPCI t systems t function independently to provide t low pressure core cooling. t Of the electrical loads powered by B6, t the most critical loads are the control power for the LPCI injection valves MO-1001-28A/29A and MO-1001-28B/29B.
The t CS t system t consists t of t two t 100% t capacity t trains t for t low-pressure t core cooling. t The CS system, t in conjunction with LPCI function, t results in a total of three low-pressure core cooling trains, t of which only two are necessary for low-pressure core cooling.
The CS pumps are powered from 4160 VAC bus A5 t (train A) t and 4160 VAC bus A6 (train B), t the CS t control t system is powered t from 125V DC A t (train A) t and B (train B), t the CS valves are powered from 480 VAC Bus B1 t (train A) and B2 t (train B). t The nonconforming relays installed in the B6 transfer scheme could result in failure of B6 to be automatically re-energized only if there was a loss-of- offsite power and B2 was restored more than 2 seconds faster than B1. t In this unlikely event, t the relays connecting B2 to B6 would lock out and transfer would not occur. t During the time that the incorrect relays were installed, t Pilgrim Station did not experience a loss of offsite power and therefore the potential loss of both B1 and B2 was not experienced.
REPORTABILITY
This t report t is t submitted t in t accordance t with t 10 t CFR t 50.73(a)(2)(ii)(B) (10CFR50.73 rule prior to January 23, t 2001) because the modification made during RFO-12 installed two relays that had nonconforming instantaneous contacts.
t This condition could have prevented t the t design basis t B1/B2 t transfer t for B6 t under conditions of a LOOP/LOCA, t loss of B1 and restoration of B2 power more than 2 seconds faster than B1.
This t report t also satisfies t the requirements t to submit a report t in accordance with 10 CFR 21 for nonconforming material received from a qualified supplier and installed in safety-related applications.
FACILITY NAME (1) DOCKET NUMBER (2L � 05000-293 LER NUMBER (6)
SIMILARITY TO PREVIOUS EVENTS
A review was conducted of Pilgrim Station Licensee Event Reports � (LERs) � issued since 1995. � The review identified the following reports involving B6. � LER 99- 007-00, � "Bus � B6 � Voltage � Restoration � Not � Consistent � with � Safety � Analysis Assumptions," � and LER 00-003-00, � "125V DC Swing Bus Automatic Transfer Switch Degraded Performance.
ENERGY INDUSTRY IDENTIFICATION SYSTEM (EIIS) CODES The EIIS codes for this report are as follows:
COMPONENTS � CODES Automatic Transfer Switch � 83 Relay � 83
SYSTEMS
Low Pressure Coolant Injection (LPCI) system � BO Low Voltage Power System-Class 1E � ED