05000352/LER-2017-001

LER-2017-001, Condition Prohibited by TS due to Parts Quality Issue

Limerick Generating Station, Units 1 And 2
Event date:
Report date:
3522017001R00 - NRC Website

LER 17-001-00 for Limerick Generating Station, Units 1 and 2 Regarding Condition Prohibited by TS due to Parts Quality Issue

ML17027A107
Person / Time
Site:	Limerick
Issue date:	01/27/2017
From:	Libra R W Exelon Generation Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
LG-17-009 LER 17-001-00
Download: ML17027A107 (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 collection.

Limerick Generating Station, Units 1 and 2 05000352 & 05000353

3. LER NUMBER

2017 - 00 001 I. Unit Conditions Prior to the Event Limerick Generating Station (LGS) Units 1 and 2 were both operating in Operational Condition (OPCON) 1 at 100 percent power at the time of the event. There were no other structures, systems, or components inoperable at the time of the event that contributed to the event.

II. Description of the Event

Over a period of approximately one month, the Main Control Room (MCR) Heating, Ventilating and Air Conditioning (HVAC) system experienced four failures. Three of the failures were caused by an intermittent dropout, or chattering of the LOOP start relay for two fans (0B-V116 MCR Supply and OB-V121 MCR Return Fans). The fourth failure was due to a contactor in the MCC for the OB-V116 MCR Supply Fan. Each of these events caused an unplanned Limiting Condition for Operation (LCO) entry and inoperability of the Control Room Emergency Fresh Air Supply (CREFAS) system. A timeline of events is as follows:

10/19/16 - KS-078-326B and KS-078-359B relays replaced for Preventative Maintenance (PM).

Post Maintenance Testing (PMT) was performed by running the OB MCR HVAC train.

11/13/2016 - To support chiller swaps the OA MCR HVAC train was secured and Operations attempted to start the OB train. This was the first start attempt since the PMT performance on 10/19/16. When the supply fan handswitch was placed in RUN, the fan did not start. Relay replacements were performed for KS-078-026B, which was found failed, and KS-078-326B, which was found chattering. Following replacements, the supply fan was started successfully.

When Operations attempted to start the OB return fan by placing the handswitch in RUN, it did not start. The KS-078-359B relay was found chattering, thereby preventing the return fan from starting.

11/20/16 - After running the OB train of MCR HVAC for a period of one week, the supply fan tripped. The contactor was observed to be chattering. Breaker maintenance was performed and the contactors were replaced. Additionally, new wiring was installed internal to the breaker cubicle. During troubleshooting, the KS-078-326B and KS-078-026B relays were removed from the field and bench tested satisfactorily.

11/29/16 - To support a MCR chiller swap, the OA MCR fans were secured and Operations attempted to start the OB train. When the supply fan handswitch was placed in RUN, the fan did not start. The cause was determined to be a failed KS-078-326B relay.

12/5/16 - The 'B' MCR Return fan tripped and the 'A' MCR return fan auto-started.

Troubleshooting efforts identified a chattering KS-078-359B relay in the field.

On 11/29/16, the site believed that the relay failure was not an infantile failure and that there may be a common condition that was causing these failures. The relay was sent for testing and evaluation, and on 12/15/16, the station received the analysis which identified a manufacturing issue had caused the relay failures.

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.

Limerick Generating Station, Units 1 and 2 05000352 & 05000353

3. LER NUMBER

2017 - 00 001

III. Analysis of the Event

The identified relay failures were all determined to be attributed to intermittent drop out, or chattering of the installed Agastat/Tyco model ETR1413D004 (ETR TDPU series) relay coil.

These relays were all installed as normally energized, power monitoring/ Loss of Offsite Power (LOOP) start relays. They are installed to allow a 35-second time delay before the fan restarts on re-energization of the associated load center during a LOOP.

The testing determined that the relays were not reliable and failure of the relays could not be predicted. The OB MCR HVAC train was determined to be unreliable since the initial relay replacement on 10/19/16 until when the relays were replaced with relays from a different lot on 12/05/16. The B train of MCR HVAC was conservatively determined to be inoperable for a period of 47 days, which is greater than the allowable LCO action window of 7 days (per TS 3.7.2.a.1) for an inoperable CREFAS train, and therefore was deemed to be a condition prohibited by TS.

IV. Cause of the Event

Bench tests were performed on-site on the removed relays in addition to failure analysis by an offsite testing facility. This testing determined the cause of the relay chattering to be an incorrectly installed capacitor on the internal timing circuit board.

V. Corrective Actions Completed/Planned Extent of condition actions were taken to replace all of the Agastat 2016 ETR relays installed at Limerick. A total of two additional relays, from the same lot, were identified to be installed in the plant and both these relays were proactively replaced.

A Part 21 was generated by TE Connectivity for the manufacturing issue. (ML17006A011) VI. Previous Similar Occurrences There were no previous similar occurrences in the last five years of MCR Supply fan and Return fan trips due to defective relays.

VII. Component data:

System: V Central Control Complex Env. Ctrl. Sys.

Component: RLY Relay, Time- Delay Starting or Closing Component number: KS-078-326B & KS-078-359B Manufacturer: T351 Tyco Instrument DIV Model number: ETR1413D004