05000364/LER-2017-001

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LER-2017-001, 2B Emergency Diesel Generator Rendered Inoperable Due to a Jacket Water Leak without Makeup Capability
Joseph M. Farley Nuclear Plant, Unit 2
Event date: 06-23-2017
Report date: 08-21-2017
Reporting criterion: 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
3642017001R00 - NRC Website
LER 17-001-00 for Farley, Unit 2, Regarding 28 Emergency Diesel Generator Rendered Inoperable Due to a Jacket Water Leak without Makeup Capability
ML17233A354
Person / Time
Site: Farley Southern Nuclear icon.png
Issue date: 08/21/2017
From: Wheat J T
Southern Nuclear Operating Co
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
NL-17-1420
Download: ML17233A354 (5)


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EVENT DESCRIPTION:

On April 21. 2017. at approximately 14:30 with Farley Unit 2 operating in Mode 1 and at 100% power, an operator noticed a jacket water (JW) leak [EllS Code LB, PSF] on the 2B Emergency Diesel Generator (EDG) [EllS Code F010] from the keep warm pump 30 minutes into a 60 minute monthly surveillance run. Based upon the volume of water leaking from the connection and available in the JW expansion tank, the 2B EDG would not have met its 7 day mission time. Thus, the 2B EDG was declared INOPERABLE and Technical Specification (TS) 3.8.1 Condition B was entered. The leak was repaired on April 23, 2017, using a new fabricated pipe nipple with threads adjusted for a better fit-up.

Review of documentation from a previous repair on the same leaking joint on March 3, 2017 revealed that Maintenance personnel had noted the repair was less than adequate due to the lack of replacement inventory available at the time.

Maintenance personnel reused the worn threaded connection with added sealant on the discharge of the keep warm pump to repair the leak. Post maintenance testing of the 2B EDG verified that no leaks were present before returning the EDG to Mode 1 at approximately 04:00 on March 4, 2017. The 2B EDG was also run on March 20th in accordance with the surveillance test procedure without recurrence of the JW leak.

Based upon the measured leak rate on April 21, 2017, the 2B EDG would have been unable to meet its 7 day mission time without the use of makeup water to the JW expansion tank. Therefore, the station took credit for the availability of the backup service water (SW) flow path [EIIS Code LB, PSF] to makeup to the JW expansion tank as needed during a design basis accident. It was later discovered that the SW makeup flow path was clogged and unable to pass flow on June 23, 2017.

EVENT CAUSE ANALYSIS:

The water level of the JW expansion tank is controlled manually by operators who under normal operating conditions makeup to the tank via a Demineralized (Demin) Water line. Even though Demin Water is the preferred source of clean water makeup to the tank, it is not classified as a safety-related component and is unavailable during a design basis accident as a source of makeup water to the tank. The safety-related SW line that is utilized to makeup to the JW expansion tank is not the preferred makeup source to the tank due to the poor quality of the water. Until the June 23rd discovery, the station credited the availability of SW to makeup to the JW expansion tank as needed during a design basis accident even though the SW line was neither required per the station's licensing basis nor included in a periodic surveillance program.

While continued operation in a condition prohibited by TS was the result of the station's inability to makeup to the JW expansion tank via the SW line, the root cause of the recurring JW leak was directly attributed to inadequate Maintenance practices and behaviors regarding deficient conditions. Therefore, both inadequate Maintenance practices and behaviors as well as the inability to makeup to the JW expansion tank during a design basis accident contributed to the station's continued operation in a condition prohibited by TS.

REPORTABILITY AND SAFETY ASSESSMENT:

Based upon the measured leak rate from the April 21st JW leak, the 2B EDG may not have been able to meet its 7 day mission time had a demand signal been received after March 3rd. The subsequent discovery of the clogged SW makeup line on June 23rd indicated that the 2B EDG may not have been able to perform its safety function if needed during a design basis accident. As a result of these conditions the station unknowingly operated in a condition prohibited by TS which is reportable under 50.73(a)(2)(i)(B).

Even though SW was not available at the time, the safety significance of the JW leak is considered minimal, as other methods of making up to the JW expansion tank were available.

In reviewing the past operability of the 1-2A and 1C EDGs from March 3rd until April 21st, two instances occurred where the 1C EDG was inoperable and unavailable due to being tagged out for barring the engine. Barring the diesel engine is a short duration activity that is performed after the diesel operates. These two instances of 1C EDG inoperability to bar the engine were concurrent with the 2B EDG being unable to meet its mission time. However, there is reasonable assurance that if a design basis accident had occurred during this time period, the 2B EDG would have started and provided emergency AC power to B train engineered safety feature systems. If the JW leak that was experienced on April 21st had developed during this period of postulated operation, there would have been adequate time to restore 1C EDG to OPERABLE status while the 2B EDG powered B train systems (i.e., the leak on 2B EDG would not have prevented it from performing the function while actions were taken to return 1C EDG to service).

Furthermore, there were alternate means of providing makeup to the JW expansion tank (even though the SW makeup line was clogged) and there was sufficient time to perform those non-complex actions based upon the calculated leak rate (i.e., reinitiating Demin water makeup during a loss of offsite power via electrical bus realignments or makeup to the tank using temporary hose connections in the 2B EDG room). Therefore, the past inoperability of the 1C EDG did not result in a condition that could have prevented fulfillment of a safety function.

CORRECTIVE ACTIONS:

Actions necessary to address inadequate Maintenance practices and behaviors encompass enhanced training activities for Maintenance managers and supervisors targeted at improving conservative decision making and understanding the events surrounding the 2B EDG JW leak. The station will also develop a job aide to enhance the preparation, review, and conduct of Maintenance work. This job aide will highlight work on safety-related components, and the availability of materials and contingency materials.

The station took additional actions to address the inability to makeup to the JW expansion tank from SW. Of the various actions entered into the Corrective Action Program, the most significant incorporated ancillary sources of makeup water to the JW expansion tank into existing procedural guidance. This change provides operators with the guidance necessary to makeup to the tank in the event the primary and backup sources of makeup water are unavailable.

PREVIOUS SIMILAR EVENTS.

None

OTHER SYSTEMS AFFECTED:

No systems other than those mentioned in this report were affected by this event.