05000339/LER-2016-001

LER-2016-001, Technical Specification Required Shutdown Due to Reactor Coolant System Leak

North Anna Power Station, Unit 2
Event date:	07-30-2016
Report date:	09-21-2016
3392016001R00 - NRC Website

LER 16-001-00 for North Anna Power Station, Unit 2 Regarding Technical Specification Required Shutdown Due to Reactor Coolant System Leak

ML16271A408
Person / Time
Site:	North Anna
Issue date:	09/21/2016
From:	Bischof G T Virginia Electric & Power Co (VEPCO)
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
LER 16-001-00
Download: ML16271A408 (5)

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1.0 DESCRIPTION OF THE EVENT On July 29, 2016 Reactor Coolant System (RCS) (EIIS System - AB) unidentified leakage was identified to take a 0.05 gallons per minute step increase coincident with similar increase in Unit 2 containment sump in-leakage. Containment entries were initiated to determine the source of the leakage. On July 30, 2016, at 1152 hours0.0133 days <br />0.32 hours <br />0.0019 weeks <br />4.38336e-4 months <br />, it was determined that there was an un-isolatable through wall leak in the controlled bleed-off piping (EIIS System — AB, Component — PSX) associated with the Reactor Coolant Pump (RCP) (EIIS System — AB, Component — P) seal for 2-RC-P-1C. At that time, the limiting action of Technical Specification (TS) 3.4.13, RCS Operational Leakage, Condition B was entered which required placing the unit in Mode 3 within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and Mode 5 within 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br />, and the power ramp to remove the Unit 2 from service commenced. At 1702 on July 30, 2016, the unit was placed in Mode 3 and the unit was placed in Mode 5 at 0538 on July 31, 2016.

Due to the pressure boundary leakage, this event was reported at 1517 hours0.0176 days <br />0.421 hours <br />0.00251 weeks <br />5.772185e-4 months <br /> on July 30, 2016, in accordance with 10 CFR 50.72(b)(2)(i), for "Initiation of plant shutdown required by Technical Specifications" and 10 CFR. 50.72(b)(3)(ii)(A) for "Any event or condition that results in the condition of the nuclear power plant including its principle safety barriers, being seriously degraded.

2.0 SIGNIFICANT SAFETY CONSEQUENCES AND IMPLICATIONS No significant safety consequences resulted from this event because Unit 2 was promptly removed from service and the affected controlled bleed-off piping associated with the RCP seal for 2-RC-P-1C was replaced. The health and safety of the public were not affected by this event.

3.0 CAUSE The direct cause of the RCS unidentified leakage was determined to be a large mean stress placed on the socket weld due to the controlled bleed-off line not being properly aligned in the downstream pipe support, and therefore not allowing for the thermal growth of the RCS. As a result of the large mean stress, a crack initiated at a small defect (lack of fusion) in the toe of the socket weld and propagated through the weld due to normal cyclic vibration from the. Reactor Coolant Pump.