05000387/LER-2016-011

LER-2016-001, Valve inoperability for a period longer than allowed by Technical Specifications

Susquehanna Steam Electric Station Unit 1
Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
3872016001R01 - NRC Website

LER 16-011-00 for Susquehanna, Unit 1, Regarding Valve Inoperability for a Period Longer Than Allowed by Technical Specifications

ML16137A021
Person / Time
Site:	Susquehanna
Issue date:	05/16/2016
From:	Franke J A Susquehanna, Talen Energy
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
PLA-7476 LER 16-011-00
Download: ML16137A021 (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 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.

CONDITIONS PRIOR TO EVENT

Unit 1 — Mode 5, 0 percent Rated Thermal Power Unit 2 — Mode 1, 100 percent Rated Thermal Power Unit 1 was in Mode 5 for a planned 24 month refueling cycle outage.

There were no structures, systems, or components inoperable at the start of the event that contributed to the event, except as described below.

EVENT DESCRIPTION

On March 17 and 19, 2016, two (2) safety related check valves would not properly close during surveillance testing. The valves subject of this LER (141F039A, 141F039B; EIIS code ISV) provide a boundary between water in the Reactor Water Clean Up (RWCU) and Feedwater (FW) Systems. They are both swing check valves designed to close and isolate the reactor vessel and primary containment from the RWCU system.

Additionally, the 'A' valve functions to prevent diversion of RCIC injection flow away from the reactor vessel; the 'B' valve performs the same function for HPCI.

During the 2016 performance of the surveillance to verify Local Leak Rate Test (Appendix J requirements) values were within required limits, the valves were discovered to be open when expected to be closed.

Despite this, the As-Found Minimum Path Criteria to meet Appendix J requirements were not exceeded.

Correction of this condition was required to meet As-Left test requirements.

These valves were newly installed during the 2014 refueling outage. During initial post installation surveillance testing, the test volume(s) would not pressurize, indicating the valves were not seated. Rapid pressuization and depressurization was used to simulate dynamic flow to close the valves by normal means.

The valves were tested following the exercising and met As-Left criteria.

Investigation of the valve internals by maintenance personnel following testing in 2016 revealed interference between the hinge arm and internal seat ring was causing the valves to stick open.

This event is being reported in accordance with 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by Technical Specifications based on evidence that the valves were not in the fully closed position prior to discovery of the condition. Specifically, the need for the valves to be closed is a requirement deliniated in TS 3.6.1.3, Primary Containment Isolation Valves (PCIVs).

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.

Susquehanna Steam Electric Station, Unit 1 05000387

CAUSE OF EVENT

The direct cause of the event was determined to be interference between the hinge arm and internal seat ring. The apparent cause of this event was determined to be a material deficiency introduced at the time of manufacture. A causal factor of less than adequate receipt inspection was identified. Investigation of the valve internals by maintenance personnel revealed the valves were sticking due to interference between the hinge arm and internal seat ring. The condition was resolved by the removal of the excess valve body material causing the interference.

The casting batch which produced the swing arms for the affected valves allowed for excess material on the hinge arm about the hinge pin area. The excess material reduced the expected gap between the hinge arm and the valve seat ring at the 12 o'clock location so that when the disc was at rest the hinge arm came in contact with the top of the seat ring. Similarly, when the disc was fully open, another portion of the hinge arm came in contact with the seat ring.

The same valves on Unit 2 were examined for this cause and were determined to not be affected by this manufacturing defect based upon differences in manufacture batch numbers and LLRT test results.

ANALYSIS/SAFETY SIGNIFICANCE

Each of these valves act as 1 of the 2 required isolation valves in lines that penetrate the primary containment. If both valves were to fail open during an accident, the calculated site boundary exposure under 10 CFR 100 and/or anticipated dose to the Control Room Envelope could be exceeded. Additionally, these valves ensure coolant remains in the vessel when needed. Sufficient closure of the valves ensures the vessel does not lose coolant unexpectedly during an accident.

A review of surveillance test results obtained from the redundant valves each in series with 141F039A and 141F039B revealed no issues. The quantified leakage from these redundant valves (141818A and 141818B; El IS code ISV) obtained during testing in both 2014 and 2016 was well below administrative and TS limits. Therefore, the safety function of these valves was maintained during the period in question.

The actual consequences of this event did not adversely affect the health and safety of the public or station personnel.

CORRECTIVE ACTIONS

The valves were disassembled, inspected, and reworked. Leak Rate Testing (which confirms valve closure) was performed following the maintenance to ensure the valves functioned properly. No additional actions were required to correct the condition.

PREVIOUS SIMILAR EVENTS

No previous similar events at the station involving these valves were identified.