05000321/LER-2017-002

LER-2017-002, High Pressure Coolant Injection System Declared Inoperable Due to Degraded Inverter

Edwin I. Hatch Nuclear Plant Unit 1
Event date:	02-08-2017
Report date:	4-7-2017
Reporting criterion:	10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident
LER closed by
IR 05000321/2017002 (3 August 2017)
3212017002R00 - NRC Website

LER 17-002-00 for Edwin I. Hatch, Unit 1, Regarding High Pressure Coolant Injection System Declared Inoperable Due to Degraded Inverter

ML17097A333
Person / Time
Site:	Hatch
Issue date:	04/07/2017
From:	Wheat J T Southern Nuclear Operating Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NL-17-0585 LER 17-002-00
Download: ML17097A333 (6)

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 e-mail to Infocollects.Resource@nrc.gov, and to the Desk Officer, Office of Information and Regu atory 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 Edwin I. Hatch Nuclear Plant Unit 1 05000-321

Event Description

On February 8, 2017, at 1151 EST with Unit 1 at approximately 100 percent rated thermal power, the High Pressure Coolant Injection (HPCI) suction and discharge pressure indicators were noted to be downscale during a main control room panel walk down. Upon further investigation, it was discovered that the output voltage of the DC to AC inverter (EIIS Code INVT) was degraded. This inverter provides power to multiple HPCI control room indications as well as to the HPCI flow controller and power supply. HPCI was therefore declared inoperable.

Failed Components Information:

Master Parts List Number: 1E41K603 Manufacturer: Abacus Controls Inc.

Model Number: 452-4-120M9 Type: Inverter Event Cause Analysis The cause of the event is due to degradation of the output voltage of the DC to AC inverter. The HPCI DC to AC inverter supplies power to the HPCI flow controller and power supply. The flow controller maintains constant flow over the pressure range of HPCI system operation and automatically starts if HPCI system initiation is required. The power supply provides DC control power to the HPCI Turbine Speed Control logic.

Without the flow controller and the power supply, the HPCI Turbine would not be able to run if called upon, causing HPCI to be declared inoperable.

Safety Assessment This event is reportable per 10 CFR 50.73(a)(2)(v)(D) due to an event or condition that could have prevented fulfillment of a safety function needed to mitigate the consequences of an accident.

The HPCI system is a single train system designed to permit the unit to be shut down while maintaining sufficient reactor pressure vessel (RPV) water inventory. The system continues to operate until the RPV is below the pressure at which either operation of the Low Pressure Coolant Injection (LPCI) mode of the Residual Heat Removal or the Core Spray (CS) system will maintain core cooling. The HPCI system consists of a steam turbine that drives a constant flow pump, system piping, valves, controls, and instrumentation. Upon receipt of an initiation signal, the HPCI turbine stop valve and turbine control valve open simultaneously. The HPCI turbine then accelerates to a specified speed to provide necessary pump flow.

Upon a "small" or "intermediate" break resulting in a loss of coolant accident (LOCA), HPCI provides sufficient inventory to prevent the core from being uncovered. It performs a dual function by providing makeup water to the reactor pressure vessel (RPV) as well as supplementing the break in depressurizing the RPV. If HPCI is unavailable, the Automatic Depressurization System (ADS) is credited to depressurize 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 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.

05000-321 a LER NUMBER the RPV to enable operation of the low pressure Emergency Core Cooling Systems (ECCS) (i.e., CS and LPCI). The Reactor Core Isolation Cooling (RCIC) system is also available to restore and maintain water level in the event HPCI is inoperable.

Although HPCI was declared inoperable, ADS, CS, LPCI, and RCIC were operable to provide core cooling in the event of a small or immediate break LOCA or a design basis accident (DBA) LOCA. Therefore, based on the ability of the station to mitigate the consequences of a potential loss of the HPCI system combined with a LOCA, this event is considered to have very low safety significance.

Corrective Actions

The degraded inverter was removed and replaced to return HPCI to operable status. As part of an extent of condition review, the internals of the degraded inverter were inspected to determine what caused premature failure of the inverter. Based on the findings of this inspection, the preventative maintenance frequency for inverter replacement and calibration will be adjusted as necessary.

Previous Similar Events

None.