05000298/LER-2016-001

LER-2016-001, De-Energized High Pressure Coolant Injection Auxiliary Lube Oil Pump Caused by Relay Failure Results in Loss of Safety Function and a Condition Prohibited by Technical Specifications

Cooper Nuclear Station
Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v), Loss of Safety Function
Initial Reporting
ENS 51882	10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident
2982016001R00 - NRC Website

LER 16-001-01 for Cooper Nuclear Station Regarding De-Energized High Pressure Coolant Injection Auxiliary Lube Oil Pump Caused by Relay Failure Results in Loss of Safety Function, a Condition Prohibited by Tech Specs, and a 10 CFR Part 21 Report

ML17279A111
Person / Time
Site:	Cooper
Issue date:	09/27/2017
From:	Dent J Nebraska Public Power District (NPPD)
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NLS2017086 LER 16-001-01
Download: ML17279A111 (6)

Reported lessons learned are incorporated into the licensing process and fed back to industry. Send comments regarding burden estimate to the FOR, 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

2016

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 High Pressure Coolant Injection (HPCI) was inoperable. No other emergency core cooling systems were inoperable during the event.

BACKGROUND

The HPCI System (EIIS: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 (EIIS: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 (EIIS: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 valve (EIIS:SCV) so that HPCI design pump discharge flow rate is obtained. The flow signal used for automatic control of the HPCI 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 HPCI 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 25, 2016, while performing a walkdown of Control Room panels, a licensed operator noticed that the green indication light for the HPCI auxiliary lube oil pump (ALOP) was not illuminated. The bulb in the Control Room panel was replaced, but did not illuminate. A non-licensed station operator was subsequently sent to the HPCI ALOP starter to verify local indications and found the local indication lights were not illuminated on the starter rack, indicating that the ALOP starter had lost power. The ALOP is required to start in order to open the steam admission valves for the HPCI turbine. An attempt was made in the Control Room to start the ALOP, but it did not start.

Cooper Nuclear Station 05000- 298 - 001 -00 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

2016 Operations then declared HPCI inoperable at 2117 Central Daylight Time (CDT), resulting in entry into Technical Specifications Limiting Condition of Operation 3.5.1, Condition C, HPCI System Inoperable.

Investigation revealed that the electrical relay (27) [Allen Bradley 700DC Type P relay] for the ALOP had been replaced on April 19, 2016, during the recent three-year required preventive maintenance window.

After various checks were made, it was discovered that the coil within the relay had failed after 133 hours0.00154 days <br />0.0369 hours <br />2.199074e-4 weeks <br />5.06065e-5 months <br /> of service. The relay is expected to provide three years of reliable service between replacements.

As such, it was concluded that the coil had sustained an infant mortality type failure.

The dedication process used by the vendor of the relay, NuTherm, at the time the relay was purchased by CNS, consisted of verifying the pickup and dropout voltages, and verifying contact resistances. After purchase of the relay, but prior to installation, NuTherm revised their dedication process to require additionally cycling the relay 30 times in addition to the previous voltage and resistance checks:

The relay that failed was replaced with a new relay that was purchased in September 2013 from a different lot than the failed relay purchased in March 2011. After satisfactory completion of post work testing of the ALOP, HPCI was declared operable at 1314 CDT on April 26, 2016.

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 condition is also reportable in accordance with 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by TS since, due to HPCI inoperability, the verification of the Reactor Core Isolation Cooling system operability exceeded the 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> required completion time plus the 12 hour1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> completion time to be in Mode 3 if this verification is not completed. The event was reported as Event Notification 51882.

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 throughout the event. 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.

Cooper Nuclear Station 05000- 298 - 001 - 00 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.

CAUSE

The root cause of the event was determined to be that the prior pre-installation checks performed by NuTherm on the relay were inadequate to prevent the infant mortality failure that occurred in this case.

CORRECTIVE ACTIONS

NuTherm revised their dedication process such that this type of failure will be detected. In addition, there are no relays from this lot in storage at CNS; however a check of maintenance records found that some of the relays from this lot are installed in the plant. These installed relays are well beyond the infant mortality period and have performed as expected.

PREVIOUS EVENTS

• There have been no events reported in the last three years related to the HPCI ALOp.

Cooper Nuclear Station 05000- 298 - 001 -00