05000261/LER-2011-002

LER-2011-002, Reactor Trip Due to a Failed Relay Coil on RCP-3-X(B) and actuation of Auxiliary Feedwater System

H. B. Robinson Steam Electric Plant, Unit No. 2
Event date:	09-26-2011
Report date:	11-15-2011
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(B), System Actuation 10 CFR 50.73(a)(2)(iv)(A), System Actuation
2612011002R00 - NRC Website

10. POWER LEVEL

100%

FACILITY NAME

Pamela Fergen TELEPHONE NUMBER (Include Area Code) 843-857-5314

CAUSE SYSTEM COMPONENT

MANU-

TO EPIX

Y CAUSE SYSTEM COMPONENT MANU- FACTURER

TO EPIX

B JC RLY Westinghouse

14. SUPPLEMENTAL REPORT EXPECTED

• YES (If yes, complete 15. EXPECTED SUBMISSION DATE) 0 NO I

MONTH DAY YEAR

ABSTRACT (Limit to 1400 spaces. i.e.. approximately 15 sinale-soaced typewritten lines) At 1145 hours0.0133 days <br />0.318 hours <br />0.00189 weeks <br />4.356725e-4 months <br /> EDT on September 26, 2011, with H. B. Robinson Steam Electric Plant (HBRSEP), Unit No. 2, while in Mode 1 at approximately 100% power, an automatic reactor trip occurred. At the time of the trip, the control room received a "One Loop Low Flow" alarm indicating that Reactor Coolant Pump (RCP) 'C' had shut down. The Reactor Protection System (RPS) tripped the reactor on an input that breaker 52/14, for RCP `C,' had opened. Verification of plant conditions immediately following the event identified that RCP 'C' was still running and that breaker 52/14 was still closed. The false indication signal, from relay RCP-3-X(B) was the source of the RPS trip signal.

This event has been investigated in accordance with the HBRSEP, Unit No. 2, Corrective Action Program (CAP) and is documented in Nuclear Condition Report (NCR) 490203. The investigation concluded that the reactor trip was due to a defective coil lead wire, as supplied by the vendor, on the RCP-3-X(B) relay. Relay RCP-3-X(B) was replaced and post maintenance testing was performed. Relays at risk for a similar failure were also replaced.

The condition described in this Licensee Event Report is reportable in accordance with 10 CFR 50.73(a)(2)(iv)(A), any event or condition that resulted in manual or automatic actuation of any of the systems listed in 10 CFR 50.73(a)(2)(iv)(B).

I. DESCRIPTION OF EVENT

At 1145 hours0.0133 days <br />0.318 hours <br />0.00189 weeks <br />4.356725e-4 months <br /> EDT on September 26, 2011, with H. B. Robinson Steam Electric Plant (HBRSEP), Unit No. 2, while in Mode 1 at approximately 100% power, an automatic reactor trip occurred. At the time of the trip, the control room received a "One Loop Low Flow" alarm [EDS System:Component IB:FA] indicating that the 'C' Reactor Coolant Pump (RCP) [AB:P] had shut down. The Reactor Protection System (RPS) [JC] tripped the reactor on an input that breaker 52/14 [AB:BKR], for RCP `C,' had opened. Verification of plant conditions immediately following the event identified that RCP `C' was still running and that breaker 52/14 was still closed. The false indication signal, from relay RCP-3-X(B) [JC:RLY] was the source of the RPS trip signal. RCP-3-X(B) is a Westinghouse relay, Model NBFD66S.

The Auxiliary Feedwater System [BA] automatically actuated, as expected, due to low steam generator [SB:SG] water level, and provided feedwater to the steam generators. The steam generator and pressurizer [AB:PZR] Power Operated Relief Valves (PORVs) [AB:RV] and the Main Steam Safety Valves [SB:RV] did not open during the event. All control rods [AB:ROD] fully inserted following the reactor trip.

II. CAUSE OF EVENT

This event has been investigated in accordance with the HBRSEP, Unit No. 2, Corrective Action Program (CAP) and is documented in Nuclear Condition Report (NCR) 490203. The investigation concluded that the reactor trip was due to a defective coil lead wire, as supplied by the vendor, on the RCP-3-X(B) relay.

III. SAFETY SIGNIFICANCE

This event had minor safety significance. It did result in a reactor trip, which challenges safety systems; however, all safety systems responded appropriately to this event.

IV. CORRECTIVE ACTIONS

Completed Corrective Actions:

• Relay RCP-3-X(B) was replaced and post maintenance testing was performed. Relays at risk for a similar failure were also replaced.

Planned Corrective Actions:

• Implement a Single Point Vulnerability Program to reduce plant risk.

2. DOCKET 6. LER NUMBER 3. PAGE 1. FACILITY NAME H. B. Robinson Steam Electric Plant, Unit No. 2 05000261

Previous Similar Events:

Licensee Event Report 2006-001-00 At 0247 hours0.00286 days <br />0.0686 hours <br />4.083995e-4 weeks <br />9.39835e-5 months <br /> EDT on October 25, 2006, with H. B. Robinson Steam Electric Plant (HBRSEP), Unit No. 2, in Mode 1 at 100% power, control room operators responded to alarms received for steam flow greater than feed flow on all three steam generators. The control room operators diagnosed the event as a 100% load rejection and initiated a manual reactor trip at 0248 hours0.00287 days <br />0.0689 hours <br />4.100529e-4 weeks <br />9.4364e-5 months <br />, 68.8 seconds following the start of the event. The root cause of this event was failure of a turbine governor valve electro-hydraulic control system card. While equipment failures were identified as the cause of this event, no similar component failures were identified.

Licensee Event Report 2010-007-01 At 1437 hours0.0166 days <br />0.399 hours <br />0.00238 weeks <br />5.467785e-4 months <br /> EDT on September 9, 2010, with H. B. Robinson Steam Electric Plant (HBRSEP), Unit No. 2, in Mode 1 at 100% power, an automatic reactor trip occurred. The reactor trip signal was based on the Overtemperature AT (OTAT) reactor protection function. The root cause of this event was a degraded connection on a circuit board (1A08H2) in the electro-hydraulic (EH) controls cabinet. This condition caused the loss of the governor valve common signal to the four turbine governor valves. Closure of the governor valves caused pressure and temperature in the Reactor Coolant System (RCS) to change. This resulted in the opening of a pressurizer PORV and the OTAT reactor protection function initiating a reactor trip. While equipment failures were identified as the cause of this event, no similar component failures were identified.