05000400/LER-2016-002

LER-2016-002, 'A' Essential Services Chilled Water Chiller Trip due to Oil Leak from Failed Tube Fitting

Shearon Harris Nuclear Power Plant - Unit 1
Event date:	07-22-2016
Report date:	09-20-2016
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
4002016002R00 - NRC Website

LER 16-002-00 for Shearon Harris, Unit 1, Regarding 'A' Essential Services Chilled Water Chiller Trip Due to Oil Leak from Failed Tube Fitting

ML16263A251
Person / Time
Site:	Harris
Issue date:	09/19/2016
From:	Waldrep B C Duke Energy Progress
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
HNP-16-071 LER 16-002-00
Download: ML16263A251 (5)

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 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- Shearon Harris Nuclear Power Plant - Unit 1 400 Note: Energy Industry Identification System (EIIS) codes are identified in the text within brackets [ ].

A. Background

Event Date: July 22, 2016 Mode: 1 Reactor Power: 100 percent No Structures, Systems or Components (SSCs) were inoperable at the start of this event that contributed to the event. No change in plant mode or in reactor power occurred as a result of this event.

On July 15, 2016, the 'A' train Essential Services Chilled Water (ESCW) [KM] chiller [CHU] tripped due to low oil pressure.

An oil leak was identified at a brass tube fitting [PSF] connecting the high-pressure side of an oil pressure differential sensing line to the lubrication system, and the chiller was declared inoperable. The leaking fitting had been in service for over 10 years, and was replaced with a like-for-like component. The chiller was declared operable on July 16, 2016.

The failed component was the 'A' train Essential Services Chilled Water chiller, oil pressure differential sensing line tube fitting, high pressure side, manufactured by Swagelok, Part Number B-600-1-4.

B. Event Description

On July 22, 2016, the 'A' ESCW chiller tripped a second time due to low oil pressure, with the cause being additional oil leakage from the replaced tube fitting. The 'A' ESCW chiller was again declared inoperable. Vibrations were identified on the oil pressure differential sensing line. An equivalent stainless steel fitting was installed in place of the brass. The 'A' ESCW chiller was then declared operable.

Metallurgical analysis of both failed fittings was conducted. Stress corrosion cracking was identified in the first fitting, which contributed significantly to the overall failure and was the initiation site of the fatigue failure. However, the failure of the second fitting was dominated by fatigue, with possible signs of stress corrosion cracking in some locations. Thus, cyclic stress-driven fatigue is considered the primary cause of failure, with stress corrosion cracking having a secondary role. After the second failure, a notable vibration was discovered in the oil pressure differential sensing line, likely driving the fatigue.

This condition is reportable as a condition prohibited by Technical Specification (TS) per 10 CFR 50.73(a)(2)(i)(B). The second fitting failed short of the 30-day mission time of the ESCW system and after the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> action statement time for the applicable ESCW TS Limiting Condition for Operability. The vibrations in the sensing line were likely present when the second fitting was installed after the July 15 failure, as demonstrated by the failure of the first fitting. Thus, the ESCW system was inoperable for longer than permitted by TS, making the July 22, 2016, event reportable.

C. Causal Factor The cause of the failed tube fitting was fatigue crack growth resulting from vibration, with stress corrosion cracking having a secondary role.

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, 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- Shearon Harris Nuclear Power Plant - Unit 1 400

D. Safety Analysis

No loss of safety function occurred during the event. The `B' ESCW chiller was available throughout the specified period to perform the credited safety function. Thus, the failure of the 'A' ESCW chiller has very low safety significance. At no point during the impacted period was the ESCW system required to mitigate the effects of a Design Basis Accident. Thus, there is no consequence to the health and safety of site personnel or to the public.

E. Corrective Actions

Corrective Actions Completed:

The failed tube fitting was replaced with an equivalent stainless steel fitting. This stainless steel fitting is not as susceptible to stress corrosion cracking in this environment and has higher endurance limits/fatigue strength.

Corrective Actions Planned:

Additional analysis is underway to address the vibrations present on the oil pressure differential sensing line of the 'A' ESCW Chiller.

F. Additional Information:

There have been no previous Licensee Event Reports at Harris due to a tripped ESCW Chiller from oil leakage through a tube fitting due to fatigue failure.