05000410/LER-2014-001

LER-2014-001, Emergency Diesel Generator Actuation Due to Loss of Offsite Power Source Line 5

Nine Mile Point Unit 2
Event date:	02-16-2014
Report date:	08-14-2014
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(B), System Actuation 10 CFR 50.73(a)(2)(iv)(A), System Actuation
4102014001R01 - NRC Website

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A. PRE-EVENT PLANT CONDITIONS:

Prior to the event, Nine Mile Point Unit 2 (NMP2) was operating at rated reactor power.

B. EVENT:

On February 16, 2014, at 1216, Offsite Power Line 5 was lost due to a fault and fire on a National Grid Current Transformer (CT) related to Breaker R210. This occurrence resulted in the actuation of the Division I and Division III EDGs, 2EGS*EG1 and 2EGS*EG2. In response, Operations personnel entered the action statements for TS 3.8.1, Condition A, for Line 5 inoperability.

The fault resulted in a voltage transient for both station service and offsite power loads. It caused Feed Water level control valves (2FWS-LV10A and 2FWS-LV10B) actuator controls to lock up and go into manual operation. It resulted in the loss of 'C' and `D' Reactor Water Cleanup (WCS) filter strings. The fault of Breaker R210 also resulted in the loss of Service Water Radwaste Monitor 2SWP*RE146A and Radwaste/Reactor Building Vent Gaseous Effluent Monitoring Systems and a loss of spent fuel pool cooling.

Immediate actions in plant procedure N2- SOP-3, Loss of AC Power, were taken to stabilize the plant. Actions were taken in N2-SOP-38, Loss of Spent Fuel Pool Cooling, to start the Division II Spent Fuel Pool Cooling and Cleanup pump in cooling only mode. Operations personnel took further action per N2-SOP-6, Feed Water Failures, and restored control to automatic with a slight rise in reactor water level. Review of feed water level control drawings and condition reports validated that a momentary loss of control voltage or a large dip can cause the controls for these valves to lock up. Compensatory measures were also established for Service Water Radiation Monitor, 2SWP*RE146A and the Radwaste/Reactor Building Vent Gaseous Effluent Monitoring Systems in accordance with plant procedures and the Offsite Dose Calculation Manual.

The loss of Power Line 5 event which resulted in the EDG actuation has been entered into the corrective action program as CR-2014-001352.

Nine Mile Point Unit 1 (NMP1) was unaffected by the condition associated with the loss of Power Line 5.

Nine Mile Point Unit 2 05000410

TO THE EVENT:

The fault and fire on a National Grid CT related to Breaker R210 resulted in the loss of power to Power Line 5 and resulted in the automatic actuation of the EDGs.

D. DATES AND APPROXIMATE TIMES OF MAJOR OCCURRENCES:

The dates, times and major occurrences for this event are as follows:

February 16 February 17 1216 Received multiple annunciations due to loss of Line 5 1216 Division I and Division III EDGs energized 1216 Entered TS 3.8.1 1216 Entered N2-SOP-3 and 6 1235 Operator dispatched to Scriba switchyard due to report of smoke 1253 N2-SOP-38 is entered 1327 N2-SOP-6 is exited 1430 N2-SOP-38 is exited 1450 Service Water Radiation Monitor restored 0240 Radwaste/Reactor Building Vent Gaseous Monitoring restored 1449 N2-SOP-3 is exited 1628 Line 5 restored to OPERABLE

E. OTHER SYSTEMS OR SECONDARY FUNCTIONS AFFECTED:

No other systems or secondary functions were affected beyond systems discussed in Section I.B.

F. METHOD OF DISCOVERY:

Operations received multiple annunciations in the Control Room due to a loss of Power Line 5. A plant operator was dispatched to investigate report of smoke coming from the Scriba switchyard. The investigation confirmed that a current transformer related to Breaker R210 had failed and was on fire.

G. MAJOR OPERATOR ACTION:

Operations personnel made entries into the Action Statements for TS 3.8.1, Condition A, for Line 5 inoperability. Operations personnel also entered procedures N2-SOP-3, N2- SOP-6, N2-SOP-38 and took compensatory measures as required by station procedures and the Offsite Dose Calculation Manual (ODCM).

H. SAFETY SYSTEM RESPONSES:

Following the loss of Power Line 5, Division I and Division III EDGs were automatically actuated.

II. CAUSE OF EVENT:

The loss of offsite Power Line 5 was due to a fault and fire on a National Grid CT associated with Breaker R210. The causal analysis identified the failure mechanism of the CT as an insulation breakdown internal to the CT.

III. ANALYSIS OF THE EVENT:

This event is reportable in accordance with 10 CFR 50.72(b)(3)(iv)(A), and 10 CFR 50.73(a)(2)(iv)(A).The event caused a valid actuation of the Division I and Division III EDGs, a safety system named in 10 CFR 50.73(a)(2)(iv)(B). The actuation was not part of a preplanned sequence during testing or reactor operation.

Offsite power source Line 5 was lost due to a fault and fire on National Grid Current Transformer (CT) R210. This condition resulted in the actuation of protective relays and the isolation of Bus A which powers Line 5. On February 16, 2014 the (CT) in Phase A of a power line connected to Bus A, Line 21 catastrophically failed causing extensive damage to primary equipment and secondary AC circuitry. The causal analysis identified the failure mechanism of the CT as an insulation breakdown internal to the CT. Bus A was subsequently restored, after isolating the failed CT on both the primary side and the secondary side. All protective systems operated as designed.

The onsite emergency (safety-related) AC power system includes the standby diesel generators that feed the safety-related loads in case of a loss of offsite power (LOOP). The onsite emergency AC power system is divided into three physically separate and electrically independent divisions, any two out of three divisions being capable of bringing the plant to safe shutdown in case of a loss-of-coolant accident (LOCA) or any other Design Basis Accident (DBA). The emergency AC power system is normally energized from offsite power sources. In case of a LOOP, this system is energized by the standby diesel generators. When the loss of Line 5 occurred, the diesel generators actuated automatically, as designed, to energize the safety-related loads. NMP2 was operating at steady-state 100 percent power prior to, during, and following the event.

There were no actual nuclear safety consequences associated with this event.

Based on the above discussion, 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.

This event does not affect the NRC Regulatory Oversight Process Indicators.

IV. CORRECTIVE ACTIONS:

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

STATUS:

Operations personnel took action per N2-SOP-3, N2-SOP-6 and N2-SOP-38 to restore the plant to pre-event conditions.

B. ACTION TAKEN OR PLANNED TO PREVENT RECURRENCE:

Replaced damaged CTs Purchase spare CTs Perform follow up repairs and testing on damaged equipment

A. FAILED COMPONENTS:

There were no other failed components that contributed to this event.

B, PREVIOUS LERs ON SIMILAR EVENTS:

NMP2 LER 2012-005 reported that on October 29, 2012 at 21:00, NMP2 was operating at 100 percent power when an automatic actuation of the Division I EDG occurred due to the loss of a 115 kV off-site power source (Line 5) due to remnant winds of Hurricane Sandy.

NMP1 LER 2008-001 reported that emergency diesel generators actuated when the plant experienced a loss of offsite power. A power line shared with the James A. FitzPatrick was lost.

C. THE ENERGY INDUSTRY IDENTIFICATION SYSTEM (EIIS) COMPONENT FUNCTION

COMPONENT

IEEE 803 FUNCTION IEEE 805 SYSTEM

IDENTIFIER IDENTIFICATION

Current Transformer XCT FK Emergency Diesel Generator DG EK Spent Fuel Pool Cooling Pump P DA Service Water Radiation Monitor N/A IL Reactor Water Cleanup Filter FDM CE

D. SPECIAL COMMENTS:

None