05000298/LER-2016-002

LER-2016-002, De-Energized High Pressure Coolant Injection Auxiliary Lube Oil Pump Caused By Light Bulb Failure Results in Loss of Safety Function

Cooper Nuclear Station
Event date:	04-26-2016
Report date:	06-27-2016
Reporting criterion:	10 CFR 50.73(a)(2)(v), Loss of Safety Function
Initial Reporting
ENS 51886	10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident
2982016002R00 - NRC Website

LER 16-002-00 for Cooper Regarding De-Energized High Pressure Coolant Injection Auxiliary Lube Oil Pump Caused By Light Bulb Failure Results in Loss of Safety Function

ML16190A112
Person / Time
Site:	Cooper
Issue date:	06/27/2016
From:	Limpias O A Nebraska Public Power District (NPPD)
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NLS2016037 LER 16-002-00
Download: ML16190A112 (5)

Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by Internet e- mail to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

PLANT STATUS

Cooper Nuclear Station (CNS) was in Mode 1, Power Operation, at 100 percent, steady-state power at the time the condition was identified. Service Water Pump "B" and Service Water Booster Pump "B" were inoperable when HPCI (High Pressure Coolant Injection) was inoperable. No other emergency core cooling systems were inoperable during the event.

BACKGROUND

The HPCI System (EllS:BJ) provides protection to the core for the case of a small break in the reactor coolant pressure boundary which does not result in rapid depressurization of the reactor vessel, (El IS:RPV). The HPCI System permits the nuclear plant to be shutdown while maintaining sufficient reactor vessel water inventory until the reactor vessel is depressurized. The HPCI System continues to operate until reactor vessel pressure is below the pressure at which Low Pressure Coolant Injection (El IS:BO) operation or Core Spray System (El IS:BM) operation can be used to maintain core cooling.

HPCI consists of a steam turbine assembly (EIIS:TRB) driving a multi-stage booster and main pump assembly (EIIS:P) and system piping, valves, controls and instrumentation. The HPCI turbine is driven by steam from the reactor which is generated by decay and residual heat.

A control governor (EIIS:65) receives a HPCI flow signal and adjusts the turbine steam control'yalve (EIIS:SCV) so that HPCI design pump discharge flow rate is obtained. The flow signal used fdr automatic control of the turbine is derived from a differential pressure measurement across a 'flow element (EIIS:FE) in the HPCI pump discharge pipeline. The governor controls the pressure applied to the hydraulic operator of the turbine control valve, which, in turn, controls the steam flow to the turbine.

Upon receipt of the actuation signal, the auxiliary oil pump starts, providing hydraulic pressure for the turbine stop valve and turbine control valve hydraulic operator. The flow signal will ramp the control governor until rated flow is achieved. As hydraulic oil pressure is developed, the turbine stop valve and the turbine control valve open simultaneously and the turbine accelerates toward the speed setting of the control governor. As HPCI flow increases, the flow signal adjusts the control governor setting so that design flow is maintained.

EVENT DESCRIPTION

On April 26, 2016, while performing a walkdown of Control Room panels, it was noted that the green off light for HPCI auxiliary lube oil pump (ALOP) was not illuminated. The bulb was replaced and the replacement bulb did not illuminate. A non-licensed operator was dispatched to the HPCI ALOP starter and reported the green bulb was broken and appeared to have shattered in the socket. An attempt was made to start the ALOP with the control switch and the pump did not start. The ALOP is required to start in order to open the steam admission valves for the HPCI turbine. The HPCI system was declared inoperable at 1754 Central Daylight Time (CDT) resulting in entry into Technical Specifications (TS) Limiting Condition of Operation 3.5.1, Condition C, HPCI System Inoperable.

Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by intemet e- mail to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

Investigation found the 125 volts direct current (VDC) fuse open circuited and the local indication green light and socket were damaged. The green bulb and socket were replaced as well as the red bulb. The 125 VDC fuses were also replaced. The HPCI system was restored to operable status on April 28, 2016, at 1245 CDT after post work testing had been satisfactorily completed.

Examination of the local green indication bulb and socket, and a review of the circuit schematic found that the light did not have a dropping resistor. In this circuit, a dropping resistor helps prevent the fuse in the HPCI ALOP control circuit from opening by limiting current in the indication bulb side of the circuit if a short circuit in the bulb were to occur.

The original HPCI starter circuit utilized a local indication light with a dropping resistor. The circuit was modified in 1984 by the vendor to accommodate environmental requirements. A direct voltage light and socket were substituted for the dropping resistor and light combination. Consequently, if the indication light were to short it would open circuit the 125 VDC portion of the starter circuit. The commercial grade bulb that failed was a 3 watt bulb with a 120MB base style.

BASIS FOR REPORT

The HPCI System is a single train safety system. This condition is reportable in accordance with 10 CFR 50.73(a)(2)(v) as "any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to...(D) Mitigate the consequences of an accident.

The event was reported as Event Notification 51886.

SAFETY SIGNIFICANCE

This is a Safety System Functional Failure. There were no actual safety consequences associated with this event. The potential safety consequences of this event were minimal due to the limited duration the condition existed and the redundant/diverse core cooling systems which remained operable. The HPCI ALOP performance had been previously tested satisfactory at 1312 CDT on the day of the failure. The HPCI system is an emergency core cooling system designed to inject water into the reactor vessel to provide core cooling. The total duration of inoperability, including the time prior to discovery of the condition was less than the 14 day Technical Specification Completion Time. During the time period of inoperability, other core cooling systems (Automatic Depressurization System, Core Spray, and Low Pressure Coolant Injection) were operable and would have adequately responded to a design basis event. The Reactor Core Isolation Cooling system was also operable during this event.

CAUSE

A lack of engineering knowledge led to a design change in 1984 in the HPCI ALOP starter circuitry that diminished the robustness of the circuit with respect to a specific failure modality; direct short circuiting within the indication bulb itself.

Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by internet e- mail to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regulatory Affairs, NEOB-10202, (3150-0104), Office of Management and Budget, Washington, DC 20503. If a means used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

3. LER NUMBER 2. DOCKET NUMBER 05000- 298 Cooper Nuclear Station 2016 - 002 - 00

CORRECTIVE ACTIONS

Develop and implement training to the engineering population with respect to this failure modality. The training will be given to the engineering population in the next available Engineering Support Program training sessions, and will be incorporated into initial training for new-hire engineers.

PREVIOUS EVENTS

An electrical relay in the starter circuit prematurely failed after only 133 hours0.00154 days <br />0.0369 hours <br />2.199074e-4 weeks <br />5.06065e-5 months <br /> of operation.

remote Direct Current Ammeter Circuits causing a secondary fire due to multiple fire induced faults.