05000220/LER-2016-002

LER-2016-002, Isolation of both Emergency Condensers due to loss of UPS 162B

Nine Mile Point Unit 1
Event date:	07-28-2016
Report date:	09-26-2016
Reporting criterion:	10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat
Initial Reporting
ENS 52133	10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat
2202016002R00 - NRC Website

LER 16-002-00 for Nine Mile Point, Unit 1, Regarding Isolation of Both Emergency Condensers due to Loss of UPS 1628

ML16277A145
Person / Time
Site:	Nine Mile Point
Issue date:	09/26/2016
From:	Kreider R E Exelon Generation Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
LER 16-002-00
Download: ML16277A145 (7)

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 internet 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.

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 July 28, 2016, at approximately 2357 hours0.0273 days <br />0.655 hours <br />0.0039 weeks <br />8.968385e-4 months <br />, UPS 162B unexpectedly transferred to its bypass power supply. Contrary to the expectation that the output loads remain energized during a transfer, the RPS Channel 11 Instrument Bus de-energized resulting in numerous half scram and half isolation signals. In addition, both # 11 and # 12 ECs isolated. The EC System was declared inoperable and the appropriate Technical Specification Action was entered.

This condition was reported to the NRC on July 29, 2016 at approximately 0651 hours0.00753 days <br />0.181 hours <br />0.00108 weeks <br />2.477055e-4 months <br /> pursuant to the requirements of 10 CFR 50.72(b)(3)(v)(B) (Event Notification#52133).

Subsequent troubleshooting of UPS 162B determined that a capacitor in the UPS Constant Voltage Transformer shorted. When the capacitor initially shorted, UPS voltage dropped but remained higher than the 60 VAC bypass power supply transfer set point. The UPS's protective relaying logic tripped the UPS loads prior to reaching the 60 VAC setpoint, resulting in de-energization of RPS Channel 11 Instrument Bus before the transfer could occur. Upon the trip of the Instrument Bus, the low voltage setpoint was reached and the UPS transferred to bypass power supply thereby re-engerizing the loads. The voltage transient on the Bus afffected the pressure transmiters for the EC high steam flow isolation signal resulting in the isolation of both EC trains.

Nine Mile Point Unit 2 (NMP2) was unaffected.

The event has been entered into the plant's corrective action program as IR 2698136.

TO THE EVENT:

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

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 internet 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.

05000-220

ACTIONS:

The dates, times, and major occurrences and operator actions for this event are as follows. All dates are 2016.

July 28 2357 Received multiple Control Room alarms due to loss of bus RPS 11. Both Emergency Condensers # 11 and 12 isolate.

July 29 0005 UPS 162B confirmed transferred to its bypass power supply 0041 Restored # 12 Emergency Condenser to standby 0045 Restored #,11 Emergency Condenser to standby During the time the Emergency Condensers were isolated, NMP1 Limiting Condition of Operation 3.1.3.a was not met.

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 isolated as expected due to the voltage transient. Also the momentary loss of power resulted in Reactor Building Emergency Ventilation initiation. Both systems responded to their initiating signals successfully

II. CAUSE OF EVENT:

The causes of this event were determined to be (1) failure of the capacitor due to higher than expected environmental temperatures and (2) the UPS 162B bypass power transfer set point was set too low to allow the expected transfer for the transient.

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 internet 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.

05000-220

3. LER NUMBER

2016 - 00

III. ANALYSIS OF THE EVENT:

There was no actual nuclear safety consequences associated with this event. No initiating transient was present. Although the EC 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:

Operations took immediate actions and verified that RPS Instrument Bus 11 re-enegized when the Instrument Bus automatically transferred to its bypass power supply. The ECs were returned to full standby service at 0045 hours5.208333e-4 days <br />0.0125 hours <br />7.440476e-5 weeks <br />1.71225e-5 months <br />. The RPS 11 Instrument Bus was placed on its redundant UPS power supply UPS 162A, at 0435 hours0.00503 days <br />0.121 hours <br />7.19246e-4 weeks <br />1.655175e-4 months <br />.

B. ACTION TAKEN OR PLANNED TO PREVENT RECURRENCE:

The UPS 162B capacitor and blown fuses were replaced. A new higher temperature capacitor will be selected and installed. The set point for the low voltage transfer will be adjusted to the optimum setting for low voltage transfer.

A. FAILED COMPONENTS:

Uninterruptible Power Supply 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 Int ocollects.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.

05000-220

3. LER NUMBER

2016 - 00

B. PREVIOUS LERs ON SIMILAR EVENTS:

None C. THE ENERGY INDUSTRY IDENTIFICATION SYSTEM (EIIS) COMPONENT FUNCTION

COMPONENT

IEEE 803 IEEE 805

IDENTIFIER IDENTIFICATION

Uninterruptible Power Supply UJX EF Reactor Protection System N/A JC Emergency Condenser System BN BL

D. SPECIAL COMMENTS:

None