05000366/LER-2016-001

LER-2016-001, 2C EDG Fuel Oil Relief Valve Leakage Caused Train Inoperability

Edwin I. Hatch Nuclear Plant Unit 2
Event date:	04-13-2016
Report date:	06-08-2016
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident
3662016001R00 - NRC Website

LER 16-001-00 for E.I. Hatch, Unit 2, Regarding 2C EDG Fuel Oil Relief Valve Leakage Caused Train Inoperability

ML16160A247
Person / Time
Site:	Hatch
Issue date:	06/08/2016
From:	Pierce C R Southern Co, Southern Nuclear Operating Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NL-16-0811 LER 16-001-00
Download: ML16160A247 (7)

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 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.

2016 - 001 - 00 05000-366

PLANT AND SYSTEM IDENTIFICATION

General Electric- Boiling Water Reactor (BWR) Energy Industry Identification System codes appear in the text as (EIIS Code XX)

DESCRIPTION OF EVENT

On March 17, 2016 with Unit 2 at 100 percent rated thermal power (RTP), a fuel oil leak was observed at the inlet to the fuel oil relief valve during the performance of the 2C Emergency Diesel Generator (EDG) (EIIS Code DG) semi-annual surveillance. During the surveillance, the leak progressed from a constant drip to a steady stream. Investigation revealed that the leak was due to a through-wall crack on the relief valve body inlet thread region. The 2C EDG was initially declared inoperable until the relief valve was fixed on the same day the leak was identified.

Visual inspection of the flaw determined that the failure was consistent with flaws observed in cases of fatigue failures.

Follow-up site Engineering analysis of the failure provided reasonable assurance of historic operability; however a vendor was engaged to perform an independent review with a detailed seismic model of the system.

On April 13, 2016, it was determined, based on vendor analysis, that a seismic event could cause the degraded fuel oil relief valve to adversely affect EDG operation. The analysis concluded that although the 2C EDG could have met its 7-day mission time with the existing leakage rate, a design basis earthquake could reduce the ability of the diesel to maintain the minimum fuel header pressure and sufficient amount of fuel for 7 days. Thus the seismic qualification of the 2C EDG was degraded, but the safety function of the emergency AC system would only be challenged in the event of either a loss of offsite power (LOSP) or loss of coolant accident (LOCA) concurrent with a seismic event.

CAUSE OF EVENT

The cause of the fuel oil leak was due to a through-wall crack on the relief valve body inlet thread region as a result of high-cycle fatigue due to vibration. Causal factors also included a lack of preventative maintenance to proactively replace the valve and degraded pipe hangers.

REPORTABILITY ANALYSIS AND SAFETY ASSESSMENT

This event is reportable under 10 CFR 50.73(a)(2)(i)(B) as an operation or condition prohibited by Technical Specifications due to the inability of the 2C EDG to maintain minimum fuel header pressure and sufficient amount of fuel for 7 days during a seismic event. Vendor analysis showed that based on a seismic event, the degraded fuel oil relief valve would adversely impact EDG operation resulting in the EDG being inoperable for a period of time longer than allowed by Technical Specifications.

This event is also reportable under 10 CFR 50.73(a)(2)(v)(D) as an event or condition that could have prevented fulfillment of a safety function. The 2C EDG fuel oil discharge piping at the relief valve lost its seismic qualification at an indeterminate point in the past. Per NUREG-1022, since the other EDGs which support Unit 2 (2A and 1B EDGs) have been declared inoperable a number of times for maintenance and surveillance testing, these instances provide a potential loss of fulfillment of a safety function such that more than one Unit 2 EDG was inoperable at the same time in the past 3 years.

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 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.

Edwin I. Hatch Nuclear Plant Unit 2 05000-366

NO

This event is not reportable per 10 CFR 50.72(b)(3)(v)(D) since at the time of discovery, the event did not prevent the fulfillment of a safety function that is needed to mitigate the consequences of an accident. When the degraded condition was identified on 2C EDG, neither the 2A nor 1B EDG were inoperable.

Unit 2 requires two associated EDGs to mitigate the consequences of an accident following a LOCA concurrent with a LOSP. Since the 2C EDG was inoperable for an indeterminate amount of time due to the loss of the seismic qualification of the fuel oil discharge piping at the relief valve, the maximum assumed time period used in a reactor oversight process assessment is one year. In the one year time period preceding the failure of the 2C EDG, neither the 1B nor 2A EDG were out of service for a maintenance overhaul. Although the 1B and 2A EDGs were administratively declared inoperable for testing a number of times in the one-year period preceding the 2C fuel oil leak, they were only unavailable to automatically respond to a design basis accident for a short period of time during the actual surveillance interval when the engine control switch was in 'local' control for pre-start operations or system realignment. During the rest of the time period that the associated EDG was declared inoperable for testing, the associated EDG was available to automatically respond to a LOSP or LOCA signal and provide emergency power to the associated Unit. Even if the engine was loaded to the grid for surveillance testing, load shedding would automatically occur to provide emergency AC power to the associated safety- related bus. While in local control, trained system operators were continuously present with procedural guidance to return the EDG to automatic operation if needed.

During the limited time periods when either the 1B or 2A EDG was out of service for minor maintenance or surveillance testing, along with the 2C EDG being inoperable due to the fuel oil relief valve having lost its seismic qualification, there was a loss of safety function for Unit 2 Emergency AC. At no time were all Unit 2 associated EDGs inoperable at the same time.

Even though this condition was contrary to Tech Spec requirements, no loss of standby emergency power occurred.

There was always at least one Unit 2 associated EDG operable, with two associated EDGs operable the majority of the time except for short periods of minor maintenance and surveillance testing. Based on this information this reported condition had low safety consequence.

CORRECTIVE ACTIONS

Upon identification of the fuel oil leak, the 2C EDG was declared inoperable and the 2C fuel oil relief valve was replaced.

As part of an extent of condition, the replacement history of each EDGs fuel oil relief valve was reviewed to determine if the valve needed to be replaced.

Preventive maintenance tasks are also being established for all 5 EDGs to replace each respective fuel pump outlet relief valve every 12 years of service. The PM shall additionally provide for inspection, and if necessary, repair/replacement of piping, unions, and supports/hangers in close vicinity of these relief valves.

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 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.

CONTINUATION SHEET

Edwin I. Hatch Nuclear Plant Unit 2 05000-366

ADDITIONAL INFORMATION

Other Systems Affected: 4.16 kV ESF bus 2G (lost onsite standby power source when EDG 2C declared inoperable) Failed Components Information:

EllS System Code: EK EllS Component Code: DG Manufacturer: Fairbanks Morse Model Number: 3800TD Type: Fuel Oil Relief Valve Manufacturer Code: F010 Commitment Information: This report does not created any new licensing commitments.

Previous Similar Events:

During operation of Emergency Diesel Generator (EDG) 1A for monthly surveillance on June 3, 2010 with the Unit operating at full power, a section of one-quarter-inch tubing in the fuel oil system became disconnected from its fitting rendering EDG 1 A inoperable due to the potential for fire. Applicable requirements of the Technical Specifications were accomplished and plant operations continued. The tubing's function is to route waste fuel oil from the injectors to the fuel oil collection tank. The tubing separation occurred at the fitting to a discharge check valve which prevents backflow of waste oil to the injectors. The apparent cause of both the leakage and subsequent tubing separation was degradation of the tubing connection due to wear and stresses resulting from the repetitive disassembly and re-assembly during scheduled maintenance activities. Subsequent to both the noted leakage and the tubing separation, the corresponding tubing for the other four EDGs was examined for signs of leakage or cracking. None was found and those EDGs were determined to be operable. The separated tubing in the diesel fuel oil system of EDG 1A was repaired and the EDG returned to available status on June 4, 2010. Because the cause of the diesel fuel leak was due to repetitive removal and re-assembly as part of planned diesel generator maintenance, the corrective actions from the 2010 event would not be expected to have prevented the condition reported in this LER.