05000220/LER-2012-004, Regarding Automatic Reactor Scram Due to a Generator Load Reject

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Regarding Automatic Reactor Scram Due to a Generator Load Reject
ML13007A090
Person / Time
Site: Nine Mile Point Constellation icon.png
Issue date: 12/21/2012
From: Philippon M
Constellation Energy Nuclear Group, EDF Group, Nine Mile Point
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
LER 12-004-00
Download: ML13007A090 (9)


LER-2012-004, Regarding Automatic Reactor Scram Due to a Generator Load Reject
Event date:
Report date:
Reporting criterion: 10 CFR 50.73(a)(2)(iv)(A), System Actuation

10 CFR 50.73(a)(2)(i)

10 CFR 50.73(a)(2)(vii), Common Cause Inoperability

10 CFR 50.73(a)(2)(ii)(A), Seriously Degraded

10 CFR 50.73(a)(2)(viii)(A)

10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition

10 CFR 50.73(a)(2)(viii)(B)

10 CFR 50.73(a)(2)(iii)

10 CFR 50.73(a)(2)(ix)(A)

10 CFR 50.73(a)(2)(x)

10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor

10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat

10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown

10 CFR 50.73(a)(2)(v), Loss of Safety Function

10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
2202012004R00 - NRC Website

text

Michel A. Philippon P.O. Box 63 Plant General Manager Lycoming, New York 13093 315.349.5205 315.349.1321 Fax CENG.

a joint venture of 0

CorWIlation eff NINE MILE POINT NUCLEAR STATION December 21, 2012 U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 ATTENTION:

Document Control Desk

SUBJECT:

Nine Mile Point Nuclear Station Unit No. 1; Docket No. 50-220 Licensee Event Report 2012-004, Automatic Reactor Scram Due to a Generator Load Reject In accordance with 10 CFR 50.73(a)(2)(iv)(A), please find attached Licensee Event Report 2012-004, Automatic Reactor Scram due to a Generator Load Reject.

There are no regulatory commitments in this submittal.

Should you have questions regarding the information in this submittal, please contact John J. Dosa, Director Licensing, at (315) 349-5219.

ry truly y MAP/GvN

Attachment:

Licensee Event Report 2012-004, Automatic Reactor Scram Due to a Generator Load Reject cc:

NRC Regional Administrator NRC Project Manager NRC Resident Inspector

ATTACHMENT LICENSEE EVENT REPORT 2012-004 AUTOMATIC REACTOR SCRAM DUE TO A GENERATOR LOAD REJECT Nine Mile Point Nuclear Station, LLC December 21, 2012

NRC FORM 366 U.S. NUCLEAR REGULATORY COMMISSION APPROVED BY OMB: NO. 3150-0104 EXPIRES: 10/31/2013 (10-2010)

, the NRC may not conduct or sponsor, and a person is not required to respond to, the information collection.

3. PAGE Nine Mile Point Unit I 05000Z 1 OF 7
4. TITLE Automatic Reactor Scram Due to a Generator Load Reject
5. EVENT DATE
6. LER NUMBER
7. REPORT DATE
8. OTHER FACILITIES INVOLVED JFACILITY NAME DOCKET NUMBER MONTH DAY YEAR YEAR SEQUENTIAL REV MONTH DAY YEAR NUMBER NO.

10 29 2012 2012 004 00 12 21 2012 FACILITY NAME DOCKET NUMBER 1

l

9. OPERATING MODE
11. THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR§: (Check all that apply)

El 20.2201(b)

El 20.2203(a)(3)(i)

El 50.73(a)(2)(i)(C)

El 50.73(a)(2)(vii)

N El 20.2201(d)

El 20.2203(a)(3)(ii)

El 50.73(a)(2)(ii)(A)

El 50.73(a)(2)(viii)(A)

El 20.2203(a)(1)

El 20.2203(a)(4)

[I 50.73(a)(2)(ii)(B)

E-50.73(a)(2)(viii)(B)

10. POWER LEVEL

[] 20.2203(a)(2)(i)

E] 50.36(c)(1)(i)(A)

El 50.73(a)(2)(iii)

E] 50.73(a)(2)(ix)(A)

El 20.2203(a)(2)(ii)

El 50.36(c)(1)(ii)(A) 0 50.73(a)(2)(iv)(A)

El 50.73(a)(2)(x)

[I 20.2203(a)(2)(iii)

[E 50.36(c)(2)

[3 50.73(a)(2)(v)(A)

El 73.71(a)(4) 100 El 20.2203(a)(2)(iv)

El 50.46(a)(3)(ii)

El 50.73(a)(2)(v)(B)

El 73.71(a)(5)

El 20.2203(a)(2)(v)

El 50.73(a)(2)(i)(A)

E] 50.73(a)(2)(v)(C)

El OTHER El 20.2203(a)(2)(vi)

El 50.73(a)(2)(i)(B)

[E 50.73(a)(2)(v)(D)

Specify in Abstract below or in

D. DATES AND APPROXIMATE TIMES OF MAJOR OCCURRENCES

October 29, 2012 21:00:00 21:00:57 21:01:04 21:01:51 Lightning arrestor mast S12-105, in the Scriba switchyard, fell and came in close proximity to a phase of the 345 kV 'A' bus causing a short to ground.

Line 8 and line 9 instantaneous ground directional overcurrent relays (67N-1 and 67N-2) actuated resulting in a generator trip signal to the generator lockout relay, 86G-2. This relay caused a turbine trip and reactor scram from 100% power.

The High Pressure Coolant Injection (HPCI) system automatically initiated on low Reactor Pressure Vessel (RPV) water level as expected due to RPV level shrink following the scram.

RPV level was restored above the HPCI system low level actuation setpoint and the HPCI system initiation signal was reset.

E. OTHER SYSTEMS OR SECONDARY FUNCTIONS AFFECTED

Three Electromatic Relief Valves (ERVs) opened momentarily, as expected, due to the resulting reactor pressure transient following the scram and re-closed automatically.

F. METHOD OF DISCOVERY

This event was discovered by the operators when turbine trip and reactor scram from 100% power was observed in the control room.

G. MAJOR OPERATOR ACTION:

The HPCI system initiation signal was reset after the RPV level was restored above 53 inches. Pressure control was established on the Turbine Bypass Valves, which is the preferred system.

H. SAFETY SYSTEM RESPONSES:

Following initiation of the automatic scram, all control rods fully inserted. The HPCI system automatically initiated on low RPV level as expected due to RPV level shrink following the scram. Three ERVs actuated, as expected, due to the resulting reactor pressure transient following the scram. No other operational conditions requiring the response of safety systems occurred as a result of this event.

NRC FORM 366 (10-2010)

II. CAUSE OF EVENT

At approximately 21:00 on Monday October 29, 2012, high winds from the remnants of Hurricane Sandy caused a lightning arrestor mast maintained by grid operator National Grid to fall in the Scriba switchyard in close proximity to the 345 kV 'A' bus, causing a fault which actuated protective relaying and isolated the 'A' bus. The loss of Line 5, the offsite power source for NMP2 Division 1 resulted in the automatic actuation of the NMP2 Division 1 emergency diesel generator. This event was sensed by NMPI, NMP2., and the Fitzpatrick stations as the Scriba switchyard is a common output for all three stations.

The protective relaying for the switchyard is designed to isolate a fault on the 'A' bus by opening one of the breakers on each of the four tie busses, and the breaker to the 115 kV 'C' bus. The relaying scheme operated as designed by isolating the 'A' bus, while the 'B' bus remained energized.

Prior to the fault being isolated in the transmission switchyard, the fault was detected by both NMP1 station output instantaneous ground directional overcurrent relays (67N-1 and 67N-2), resulting in a generator trip and subsequent reactor scram. The logic for the instantaneous ground directional overcurrent relays is one-out-of-two to actuate the generator trip protective circuitry. During this event, both the 67N-1 and 67N-2 relays actuated which caused the trip signal to the generator lockout relay. This relay caused a turbine trip and reactor scram.

The actuation of the 67N-1 and 67N-2 relays was confirmed by a walk-down performed immediately following the event, which revealed both relays were flagged.

The design of the 67N-1 and 67N-2 relay scheme is to detect a fault condition between the main generator and the station output breakers, and not to detect a fault on the grid. Troubleshooting discovered that the polarity of the primary side of both neutral current transformers (CT-I 1 and CT-12) on the main generator step-up transformer was reversed from the design drawings. Incorrect polarity of the neutral current transformers caused the current polarization portion of the relay to actuate on the fault in the switchyard. The wiring error occurred when the transformer was replaced in 2011.

Nine Mile Point Nuclear Station, LLC (NMPNS) Engineering Procurement Specification E192 identifies the requirement for the design, manufacture, inspection, test, preparation and shipment of the new ABB non-safety related generator step-up transformer (XF-TB01) for NMP1. Within this specification, the requirements for the neutral bushing current transformers are included for the XF-TB01 transformer at NMPI. The testing requirements in the procurement specification state that the vendor shall perform point-to-point continuity tests and electrical insulation tests to verify electrical integrity of the system.

Documentation was provided by ABB stating that this had been completed when it had not.

While Specification E192 detailed many engineering and technical requirements for the new NMPI transformer XF-TB01, the roles and responsibilities for ensuring that the vendor complied with these requirements were not provided. NMPNS Procedure NEP-DES-09 does not define or discuss this subject.

For critical, non-safety related items such as the XF-TB01 transformer, procedure CNG-SC-1.01-3000, Enhanced Procurement for Critical Material, should have been utilized to ensure that adequate oversight and control of the vendor supplied equipment was provided. This procedure requires a Critical Spare Acceptance Plan that details specific attributes, acceptable values or ranges, verification methods, and responsible groups, as well as a documented signature and date for each identified criteria.

Based on the above discussion, the cause for this event was due to unclear specificity of requirements for vendor performed testing and inadequate methods of verification for ensuring vendor compliance with NRC FORM 366 (10-201 0)

engineering specifications. This event was entered into the NMPNS corrective action program as condition report number CR-2012-009820.

III. ANALYSIS OF THE EVENT

This event involved a valid actuation of the Reactor Protection System which resulted in a reactor scram, and a valid actuation of the HPCI system, and is reportable in accordance with 10 CFR 50.73(a)(2)(iv)(A).

There were no actual nuclear safety consequences associated with this event. All control rods fully inserted following the automatic reactor scram. The HPCI system automatically initiated on low RPV level, as expected, due to RPV level shrink following the scram. Three ERVs actuated, as expected, due to the resulting reactor pressure transient following the scram. There were no other automatic initiations of safety systems, and immediate actions performed by the operators were adequate and appropriate in placing and maintaining the reactor in a safe shutdown condition. The reactor scram was without complications and was not risk significant.

The closest related transient described in the NMP1 Updated Final Safety Analysis Report (UFSAR) is the Loss of Electrical Load (Generator Trip) event described in UFSAR Section XV-B.3.19. The maximum reactor pressure and peak neutron flux reached during the October 29, 2012 event were both less than the calculated values presented in the UFSAR analysis for a Loss of Electrical Load. In addition, this transient event does not challenge the Minimum Critical Power Ratio (MCPR) safety limit and, therefore, is not evaluated on a reload cycle basis.

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.

The NRC performance indicator for Unplanned Scrams per 7,000 Critical Hours is projected to rise to approximately 2.47 and remains green. No other NRC performance indicators were impacted by this event.

IV. CORRECTIVE ACTIONS

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

1. The wiring for the neutral current transformers (CT-Il and CT-12) was revised to obtain the correct polarity.
2.

The electrical drawings for the XF-TBO 1 transformer were revised to reflect the correct configuration of the neutral bus bar connections.

3. 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. Procedure NEP-DES-09 will be revised to require the listing of critical attributes for equipment/components and to define testing criteria/verification methods to be performed when factory acceptance testing or modification functional testing cannot be performed to verify the functionality of equipment/components. The revised procedure will add a reference to use procedure NRC FORM 366 (10-2010)

CNG-SC-1.01-3000, Enhanced Procurement for Critical Material, for defining critical attributes, acceptance criteria, verification methods, and responsible individuals to ensure vendor compliance with requirements within engineering specifications.

2.

The requirements in Specification E-192 for the XF-TB01 transformer will be verified to have been met or technically resolved/accepted.

3. Electrical drawings and the transformer vendor manual will be revised to document field wiring of the neutral current transformers and secondary circuits.
4.

Procedure S-RCMP-GEN-005 will be revised to include direction to either electrically test the primary circuit of the neutral current transformer or visually inspect the primary circuit wiring.

5. All remaining lightning masts in the Scriba switchyard were visually inspected by National Grid. No other defective masts were found.
6. Interior inspections of the lightning masts in the Scriba switchyard were performed with a digital inspection camera by National Grid.
7. All lightning masts in the NMP1 and NMP2 switchyards were visually inspected. No defective masts were found.

V. ADDITIONAL INFORMATION

A. FAILED COMPONENTS:

There were no failed components that contributed to this event.

B. PREVIOUS LERs ON SIMILAR EVENTS:

LER 2009-003, Manual Scram and High Pressure Coolant Injection Following a Loss of Feedwater Level Control Due to Firmware Deficiency, submitted on December 4, 2009, describes an event in which NMPI manually scrammed from 100 percent power. The scram was caused by a loss of control of the shaft-driven feedwater pump flow control valve (FCV), which resulted in an increasing feedwater flow rate and rising reactor pressure vessel water level. The cause of the event was a programming error in the vendor-supplied firmware logic that prevented the proper operation of the transfer function of the FCV positioner when the operating positioner became mechanically bound. Instead, the FCV continued to open and raise reactor water level despite operator attempts to manually control the FCV. The actions taken following this event would not have prevented the October 29, 2012 event from occurring.

NRC FORM 366 (10-2010)

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

COMPONENT Reactor Protection System High Pressure Coolant Injection System Main Generator Lockout Relay Main Generator Output Power System Neutral Grounding Bus Bars Electromatic Relief Valve Directional Overcurrent Relays Current Transformers Main Transformer Tie Busses Supply Breakers Lightning Mast Reactor Pressure Vessel D. SPECIAL COMMENTS:

None IEEE 803 FUNCTION IDENTIFIER N/A N/A 86 TG BU RV 67 XFMR XFMR SSBU BKR LAR RPV IEEE 805 SYSTEM IDENTIFICATION JC BJ EL EL EL JC EL EL EL FK FK FK NA NRC FORM 366 (10-2010)