05000278/LER-2016-001

LER-2016-001, Leak in High Pressure Coolant Injection Drain Pipe Results in a Loss of Safety Function

Peach Bottom Atomic Power Station Unit 3
Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident
Initial Reporting
ENS 52264	10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident
2782016001R00 - NRC Website

LER 16-001-00 for Peach Bottom, Unit 3, Regarding Leak in High Pressure Coolant Injection Drain Pipe Results in a Loss of Safety Function

ML16327A051
Person / Time
Site:	Peach Bottom
Issue date:	11/22/2016
From:	Navin P D Exelon Generation Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
CCN: 16-103 LER 16-001-00
Download: ML16327A051 (4)

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 collecfion.

3. LER NUMBER

001 0 2016 Unit Conditions Prior to the Event Unit 3 was operating in Mode 1 at approximately 100% rated thermal power. There were no structures, systems or components out of service that contributed to this event.

Description of Event

The High Pressure Coolant Injection (HPCI) system (El IS: BJ) is part of the emergency core cooling system that assures that the reactor is adequately cooled in the event of a small break loss of coolant accident. The system permits the reactor to be shut down while maintaining sufficient water inventory until the reactor vessel is depressurized and the low pressure coolant injection system maintains core cooling. The system uses a steam-driven pump with suction from the condensate storage tank or the suppression pool, and injects water into the reactor vessel via one of the two main feedwater lines. The turbine is driven by steam from a main steam line and exhaust steam is discharged to the suppression pool. To remove condensation that forms in the turbine, drain lines are in place that send water to a drain pot. Restricting orifices are located on the 3/4" diameter drain lines to reduce pressure prior to the water entering the drain pot. The drain lines are classified as ASME Code Class 2 exempt and operate above 200 degrees F when the HPCI pump is operating.

On 9/26/16, investigation of a water leak on one of the 3/4" diameter drain lines for the HPCI turbine determined there was a through-wall flaw resulting in a leak of approximately 2 drops per minute.

Pressure boundary integrity is required for system operability. As a result, the HPCI system was declared inoperable at approximately 1845 hours0.0214 days <br />0.513 hours <br />0.00305 weeks <br />7.020225e-4 months <br /> in accordance with Technical Specification 3.5.1.C. The pipe section was replaced and the HPCI system was declared operable on 9/28/16 at approximately 2102 hours0.0243 days <br />0.584 hours <br />0.00348 weeks <br />7.99811e-4 months <br />. The elapsed time from the discovery of the failure to when the equipment was returned to service was approximately 50 hours5.787037e-4 days <br />0.0139 hours <br />8.267196e-5 weeks <br />1.9025e-5 months <br /> and 17 minutes.

Cause and Analysis of the Event The affected section of the pipe was removed. Inspection identified pitting on the interior surface of the pipe, just upstream of the pressure reducing orifice. The flaw was the result of a liquid drop impingement erosion process caused by the flow characteristics upstream of the orifice. A review of maintenance records dating back to the 1980s identified no previous replacements of this pipe; it is likely it was installed as part of original construction. The pump was last operated the previous day (9/25/16) and no leaks were noted. However, the failure mechanism (erosion) requires a significant period of time to develop into a through-wall flaw.

HPCI is a single train system. Therefore, this event is being reported in accordance with 10CFR 50.73(a)(2)(v)(D) as a condition that could have prevented the fulfillment of the safety function of a system needed to mitigate the consequences of an accident. This issue was also reported to the NRC in accordance with 10CFR 50.72(b)(3)(v)(D) on 9/27/16 at 0020 hours2.314815e-4 days <br />0.00556 hours <br />3.306878e-5 weeks <br />7.61e-6 months <br /> by EN 52264.

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 Intocollects 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

3. LER NUMBER

001 0 2016 There were no actual consequences as a result of the leak. If a design basis event had occurred, the HPCI system would have been able to perform its design function. If a failure were to occur that would have prevented HPCI from performing its design function, the Automatic Depressurization System would have reduced reactor pressure to allow the low pressure cooling systems to maintain reactor vessel level and provide core cooling.

Corrective Actions

The affected section of pipe and the orifice were replaced. The second HPCI turbine drain line was inspected, along with the two drain lines on the Unit 2 HPCI turbine, and no leaks were identified.

Additional actions are planned to perform inspections of similar drain piping that contain orifices.

Previous Similar Occurrences Based on a review of maintenance records, no previous similar occurrences of through-wall flaws of this piping have occurred.