05000220/LER-2021-002, Isolation of Both Emergency Condensers Due to Loss of UPS 162A

Isolation of Both Emergency Condensers Due to Loss of UPS 162A

ML21327A024
Person / Time
Site:	Nine Mile Point
Issue date:	11/19/2021
From:	Schuerman A Exelon Generation Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
NMP1L3436 LER 2021-002-00
Download: ML21327A024 (7)

LER-2021-002, Isolation of Both Emergency Condensers Due to Loss of UPS 162A

Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat
2202021002R00 - NRC Website

text

Exelon Generation NMP1L3436 November 19, 2021 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Nine Mile Point Nuclear Station, Unit 1 Renewed Facility Operating License No. DPR-63 Docket No. 50-220 10 CFR 50.73

Subject:

NMP1 Licensee Event Report 2021-002, Revision 0, Isolation of both Emergency Condensers due to loss of UPS 162A In accordance with the reporting requirements contained in 1 O CFR 50. 73(a)(2)(v)(B), please find enclosed NMP1 Licensee Event Report (LER) 2021-002, Revision 0, Isolation of both Emergency Condensers due to loss of UPS 162A.

There are no regulatory commitments contained in this letter.

Should you have any questions regarding the information in this submittal, please contact Brandon Shultz, Site Regulatory Assurance Manager, at (315) 349-7012.

Respectfully, Schuerman, AdamG Adam Schuerman Digitally signed by Schuerman, AdamG DN: cn=Schuerman, Adam G Date: 2021.11.17 12:09:38 -05'00' Plant Manager, Nine Mile Point Nuclear Station Exelon Generation Company, LLC AS/JRA

Enclosure:

NMP1 Licensee Event Report 2021-002, Revision 0, Isolation of both Emergency Condensers due to loss of UPS 162A cc:

NRC Regional Administrator, Region I NRC Resident Inspector NRC Project Manager

Enclosure NMP1 Licensee Event 2021-002, Revision 0 Isolation of both Emergency Condensers due to loss of UPS 162A Nine Mile Point Nuclear Station, Unit 1 Renewed Facility Operating License No. DPR-63

Abstract

On Saturday September 25, 2021, at approximately 0341 hours0.00395 days <br />0.0947 hours <br />5.638227e-4 weeks <br />1.297505e-4 months <br /> with power level at approximately 100 percent, Nine Mile Point Unit 1 (NMP1) experienced a loss of Uninterruptible Power Supply (UPS) 162Awhich resulted in the loss of Reactor Protection System (RPS) Bus 11. The loss of RPS Bus #11 resulted in a half scram, Reactor Water Cleanup isolation, and isolation of both

1. 11 and #12 Emergency Condensers. The cause of this event was the premature failure of the oscillator board (X2) and/or the sync board (X5) in UPS 162A. Corrective actions include replacement of faulted sync and oscillator boards.

This event is reportable under 1 0CFR50.73(a)(2)(v)(B).

I.

DESCRIPTION OF EVENT

A. PRE-EVENT PLANT CONDITIONS:

Unit 1 was in Run, operating at approximately 100% rated thermal power when the event occurred. There were no structures, systems, or components out of service that contributed to this event.

B. EVENT:

On September 25, 2021, at approximately 0341 hours0.00395 days <br />0.0947 hours <br />5.638227e-4 weeks <br />1.297505e-4 months <br />, the NMP Unit 1 control room received multiple annunciators concurrent with a loss and subsequent restoration of RPS Bus #11 on UPS 162A. This resulted in a half scram, Reactor Water Cleanup isolation, and isolation of both #11 and #12 Emergency Condensers. The Emergency Condenser System was declared inoperable, and the appropriate Technical Specification Action was entered.

The condition was reported to the NRC on September 25, 2021 at approximately 0916 hours0.0106 days <br />0.254 hours <br />0.00151 weeks <br />3.48538e-4 months <br /> pursuant to the requirements of 10 CFR 50.72(b)(3)(v)(B) (Event Notification#55492).

After consultation with the vendor Ametek, the oscillator board (X2) and the sync board (X5) were replaced simultaneously. This was done based on advisement from Ametek that these cards should be replaced in pairs. Following replacement of these circuit boards, UPS-162A was restarted and exhibited no signs of frequency or voltage oscillations.

Additionally, the UPS-162A was energized and the output monitored for several days to ensure consistent output performance while unloaded with no anomalies noted.

Nine Mile Point Unit 2 (NMP2) was unaffected.

The event has been entered into the plant's corrective action program as IR 04448532.

C. INOPERABLE STRUCTURES, COMPONENTS, OR SYSTEMS THAT CONTRIBUTED TO THE EVENT:

No other systems, structures, or components contributed to this event.

D. DATES AND APPROXIMATE TIMES OF MAJOR OCCURRENCES AND OPERATOR ACTIONS:

The dates, times, major occurrences, and operator actions for this event are as follows.

September 25, 2021 :

0341 Received multiple Control Room alarms due to loss and subsequent restoration of RPS Bus #11 on UPS 162A.

Both Emergency Condensers #11 and #12 isolate. Reactor Water Cleanup isolate.

0403 RPS Bus #11 de-energized by operators to prepare for dead bus transfer to l&C Bus 130A.

0405 RPS Bus #11 power was restored by operators via l&C Bus 130A 0420 Restored #11 Emergency Condenser to standby 0429 Restored #12 Emergency Condenser to standby 1031 RPS Bus #11 de-energized by operators to prepare for dead bus transfer to UPS 1628 1033 RPS Bus #11 power was restored by operators via UPS 1628 Both Emergency Condensers were inoperable for a total of 48 minutes from event initiation to restoration.

During the time Emergency Condensers were isolated, NMP1 Limiting Condition of Operation (LCO) 3.1.3.a was not met.

Subsequently, the station entered LCO 3.1.3.e but normal orderly shutdown was not initiated since the first condenser restored in approximately 39 minutes, driving the station to LCO 3.1.3.b. Full compliance with LCO 3.1.3 was restored at 0429.

E. METHOD OF DISCOVERY

This event was self-revealing as identified by multiple Control Room alarms.

F. SAFETY SYSTEM RESPONSES:

Upon loss of the RPS #11 Instrument Bus, the Emergency Condensers and Reactor Water Cleanup isolated as expected due to the voltage transient. Also, the momentary loss of power resulted in Reactor Building Emergency Ventilation initiation.

II. CAUSE OF EVENT

The cause of this event was determined to be the premature failure of the UPS 162A oscillator board (X2) and/or the sync board (XS).

Ill. ANALYSIS OF THE EVENT There were no actual nuclear safety consequences associated with this event. No initiating transient was present.

Although the Emergency Condenser loops were automatically isolated, the conditions requiring automatic initiation of the system were not present. The event was caused by an equipment failure creating a voltage transient that led to the spurious isolation.

Although the Emergency Condensers isolated, the isolation signals are designed to be bypassed should they be required to operate. The ability to manually initiate the system is recognized in the Probabilistic Risk Assessment model supported by procedural guidance that directs restoration. It is concluded that the safety significance of this event is low and the event did not pose a threat to the health and safety of the public or plant personnel.

Isolation of both the Emergency Condensers is reportable under 10 CFR 50. 72(b )(3)(v)(B) and 10 CFR 50. 73(a)(2)(v)(B) as any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to control the removal of residual heat.

IV. CORRECTIVE ACTIONS

A. ACTION TAKEN TO RETURN AFFECTED SYSTEMS TO PRE-EVENT NORMAL STATUS:

Operators took immediate actions and transferred the RPS Bus #11 to l&C Bus 130A.The Emergency Condensers #11 and #12 were returned to full standby service September 25, 2021 at 0420 and 0429 respectively. Subsequentially, RPS Bus #11 was then restored to power by operators via UPS 1628.

B. ACTION TAKEN OR PLANNED TO PREVENT RECURRENCE:

The faulted sync and oscillator boards were replaced.

V. ADDITIONAL INFORMATION

A. FAILED COMPONENTS:

Uninterruptible Power Supply I 05000-1 220 B. PREVIOUS LERs ON SIMILAR EVENTS:

D NUMBER NO.

I YEAR SEQUENTIAL REV

~-I 002 1-~

NMP LER 2016-002-00 reported the Isolation of both Emergency Condensers due to loss of UPS 1628. The cause of the LER 2016-002-00 were determined to be the failure of a UPS capacitor and the bypass power transfer set point being set too low for the type of transient.

C. THE ENERGY INDUSTRY IDENTIFICATION SYSTEM (EIIS) COMPONENT FUNCTION IDENTIFIER AND SYSTEM NAME OF EACH COMPONENT OR SYSTEM REFERRED TO IN THIS LER:

COMPONENT Uninterruptible Power Supply Reactor Protection System Emergency Condenser System D. SPECIAL COMMENTS None IEEE 803 FUNCTION IDENTIFIER UJX N/A BN IEEE 805 SYSTEM IDENTIFICATION EF JC BL Page 5

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