05000410/LER-2012-005

LER-2012-005, Automatic Diesel Actuation Due to the Loss of a 115 kV Offsite Power Source

Docket Number
Event date:	10-29-2012
Report date:	12-21-2012
Reporting criterion:	10 CFR 50.73(a)(2)(iv)(A), System Actuation
Initial Reporting
ENS 48456	10 CFR 50.72(b)(3)(iv)(A), System Actuation
4102012005R00 - NRC Website

A. PRE-EVENT PLANT CONDITIONS:

Prior to the event, Nine Mile Point Unit 2 (NMP2) was operating at 100 percent rated thermal power, with no inoperable systems affecting this event.

B. EVENT:

At approximately 21:00 on Monday October 29, 2012, with Nine Mile Point Unit 2 (NMP2) in Mode 1 Run, the unit experienced an automatic actuation of the Division I Emergency Diesel Generator (EDG) due to the loss of a 115 kV off-site power source (Line 5) associated with the Division I onsite emergency power distribution system.

The loss of Line 5 occurred due to the 'A' 345 kV offsite power source located in the Scriba substation being de-energized. High winds from the remnants of Hurricane Sandy caused a lightning mast maintained by grid operator National Grid to fall in the Scriba substation in close proximity to the 'A' bus, causing a fault which actuated protective relaying and isolated the 'A' bus. Line 5, the 115 kV offsite power source for Division I, is fed by the 'A' bus and was de-energized when the breaker opened to isolate the fault on the 'A' bus, leading to the automatic actuation of the Division I EDG. Following the event, the unit continued to operate at 100 percent power and Line 5 was restored at 03:26 on October 30, 2012. The Diesel generator was secured and placed in standby at 04:47 on October 30, 2012.

This event also affected Nine Mile Point Unit 1 (NMP1). The event was sensed by NMP1, NMP2, and James A. Fitzpatrick, as the output of all three units is routed through the Scriba switchyard.

This event is reportable in accordance with 10 CFR 50.73 (a)(2)(iv)(A), as an automatic actuation of an Emergency Diesel Generator (EDG). The NRC was notified in accordance with 10 CFR 50.72(b)(3)(iv)(A) on October 30, 2012 at 03:35 (Event Number 48456).

EVENT:

At the time of the event, there were no inoperable Systems, structures, or components (SSCs) that contributed to the event.

D. DATES AND APPROXIMATE TIMES OF MAJOR OCCURRENCES:

October 29, 2012 21:00 Loss of Line 5, diesel generator automatically initiates and energizes its bus.

`A' 345kV bus in the Scriba switchyard is de-energized.

Entered Technical Specification (TS) 3.8.1 Condition A for one offsite circuit inoperable.

Feedwater level control valves 2FWS-LV10A, B, and C actuators locked up.

21:08 2FWS-LV10A is reset. Level Control is in manual.

21:35�2FWS-LV10B placed in automatic control.

October 30, 2012 01:09�Notified by power control that the 'A' 345 kV bus in Scriba switchyard has been re- energized.

03:26�Line 5 is restored and is connected in parallel with the Division I diesel generator. Line 5 is operable. Exited TS 3.8.1 condition A.

04:47�Division I Diesel is secured and is in standby.

E. OTHER SYSTEMS OR SECONDARY FUNCTIONS AFFECTED:

The fault in the 'A' 345 kV offsite power source also caused a voltage transient and NMP2 experienced a feedwater level control lockup due to the electrical transient, requiring operators to take manual control.

Reactor pressure vessel level rose slightly, however no Emergency Core Cooling Systems actuated and operators returned feedwater level control to automatic.

F. METHOD OF DISCOVERY:

On October 29, 2012, at 21:00, Operators noted that the 'A' 345 kV Bus was de-energized, leading to a trip of the 115 kV supply line and a loss of offsite power (Line 5).

G. MAJOR OPERATOR ACTION:

■ Entered Special Operating Procedure (SOP) for Loss of offsite power and stabilized the service water system.

■ Entered TS 3.8.1 condition A for one offsite circuit inoperable.

■ Entered SOP for Feedwater Failure and Feedwater Level Control placed in manual mode.

H. SAFETY SYSTEM RESPONSES:

The Division I Emergency Diesel Generator automatically actuated due to the loss of Line 5 and energized its bus.

II. CAUSE OF THE EVENT:

The cause of this event was the failure of the lightning mast which fell in close proximity to the 'A' 345 kV bus.

This caused a fault in the 'A' bus and the subsequent trip of the 115 kV offsite power source (Line 5) and the Division I diesel actuation.

The cause of lightning mast failure was a horizontal crack above the weld between the base plate and the bottom of the mast. The crack propagated around the circumference of the pole just above the base, leading to the lightning mast's failure during the high winds experienced on October 29, 2012.

This event was entered into the Nine Mile Point (NMP) corrective action program as condition report CR-2012- 009832.

III. ANALYSIS OF THE EVENT:

The event is reportable in accordance with 10 CFR 50.73 (a)(2)(iv)(A), as an automatic actuation of an Emergency Diesel Generator (EDG).

There were no systems inoperable and no system failures related to this event. There were no actual safety consequences from this event. The onsite emergency or safety-related ac power system includes the standby ac power system consisting of the standby diesel generators that feed the safety-related loads in case of 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.

During the event, the normal power source for one division of the onsite emergency power distribution system was tripped when a lighting mast fell in the Scriba switchyard. A fault in the 'A' offsite power source led to the loss of Line 5 and as a result, the diesel generator actuated automatically as designed and accelerated to rated speed, voltage, and frequency to energize the safety-related loads. The unit was operating at steady-state 100 percent power prior to and following the event. The event did not occur concurrently with a LOCA or DBA, and did not require the actuation of any safety related equipment required to mitigate an accident. Had the high winds also de-energized the remaining 115 kV offsite power source, the Division II and Division III diesel generators would have been available to power their associated safety-related loads.

During the event, NMP2 also experienced a feedwater level control lockup that required operators to take manual control. No Emergency Core Cooling Systems actuated, and operators returned feedwater level control to automatic.

Based on the above considerations, it has been 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 NRC Reactor Oversight Process (ROP) Performance Indicators.

IV. CORRECTIVE ACTIONS:

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

1. The failed lightning mast has been removed from service by National Grid and will be replaced.

B. ACTION TAKEN OR PLANNED TO PREVENT RECURRENCE:

1. All remaining lightning masts in the Scriba switchyard were visually inspected by National Grid. No other defective masts were found.

2. Interior inspections of the lightning masts in the Scriba switchyard were performed with a digital inspection camera by National Grid.

3. All lightning masts in the NMP1 and NMP2 switchyards were visually inspected. No defective masts were found.

A. FAILED COMPONENTS:

There were no failed components that contributed to this event.

B. PREVIOUS LERs ON SIMILAR EVENTS:

NMP1 LER 2008-001, Loss of offsite Power due to an equipment malfunction. On May 13, 2008, at 08:06, with Nine Mile Point Unit 1 (NMP1) operating at 100% steady state reactor power and one of two 115 kV offsite power lines (Line 1) out of service for planned maintenance, a loss of the second 115 kV offsite power line (Line 4) occurred. Line 4 is a shared line with the James A. Fitzpatrick Nuclear Power Plant. As a result of the loss of Line 4, both emergency diesel generators auto-started and commenced carrying emergency loads as designed. The cause for the loss of Line 4 was external to Nine Mile Point (NMP) and was determined to be a switchyard equipment malfunction at the James A. Fitzpatrick Nuclear Power Plant switchyard.

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

LER:

COMPONENT� IEEE 803� IEEE 805

COMPONENT IDENTIFIER SYSTEM IDENTIFICATION

Lightning Mast� LAR� FK Diesel Generator DG NA Emergency AC Power System� NA� EK Feedwater Level Control System NA JB Reactor Pressure Vessel� RPV� NA

D. SPECIAL COMMENTS:

None