LIC-07-0001, Response to Request for Additional Information Regarding Resolution of Generic Letter 2006-02, Grid Reliability and the Impact on Plant Risk and the Operability of Offsite Power.

Response to Request for Additional Information Regarding Resolution of Generic Letter 2006-02, Grid Reliability and the Impact on Plant Risk and the Operability of Offsite Power.

ML070240203
Person / Time
Site:	Fort Calhoun
Issue date:	01/16/2007
From:	Faulhaber H Omaha Public Power District
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
GL-06-002, LIC-07-0001
Download: ML070240203 (5)

Text

Fort Calhoun Station PO. Box 550 Fort Calhoun, NE 68023 January 16,2007

, LIC-07-000 1 U. S. Nuclear Regulatory Commission Attn: Document Control Desk 1 Washington, DC 20555-0001 1

References:

1. Docket No. 50-285 i 2. NRC Generic Letter 2006-02, "Grid Reliability and the Impact on Plant Risk and the Operability of Offsite Power" (NRC-06-0013)

I I

3. Letter from OPPD (H. J. Faulhaber) to NRC (Document Control Desk), "60 Day Response to Generic Letter 2006-02" dated April 3, 2006 (LIC-06-0025)

4. Letter from NRC (C. Haney) to OPPD (R. T. Ridenoure), "Request for Additional 1I Information Regarding Resolution of Generic Letter 2006-02, Grid Reliability and the Impact on Plant Risk and the Operability of Offsite Power," dated December j 5,2006 (NRC-06-0168) 1 5. Letter from NRC (C. Haney) to OPPD (R. T. Ridenoure), "Revised Response Date 1 For Request For Additional Information Regarding Resolution Of Generic Letter I

i 1 2006-02, Grid Reliability And The Impact On Plant Risk And The Operability Of Offsite Power," dated December 13,2006 (NRC-06-0 176)

SUBJECT:

Response to Request for Additional Information Regarding Resolution of Generic Letter 2006-02, "Grid Reliability and the Impact on Plant Risk and the Operability of Offsite Power" Attached is the Omaha Public Power District (OPPD) response to Reference 4, which is an NRC request for additional information (RAI) regarding resolution of Generic Letter (GL) 2006-02 (Reference 2). In Reference 5, the NRC extended the due date of the required response to January 3 1,2007. Reference 3 is OPPD's initial response to GL 2006-02.

No commitments to the NRC are made in this letter.

I declare under penalty of perjury that the foregoing is true and correct. (Executed on January 16, 2007.)

U. S. Nuclear Regulatory Commission LIC-07-0001 Page 2 If you have additional questions, or require further information, please contact Mr. Thomas C.

Matthews at (402) 533-6938.

Sincerely, Division Manager Nuclear Engineering

Attachment:

Response to RAI Regarding Resolution of Generic Letter 2006-02

LIC-07-0001 Attachment Page 1 ATTACHMENT Response to Request for Additional Information Regarding Resolution of Generic Letter 2006-02, "Grid Reliability and the Impact on Plant Risk and the Operability of Offsite Power"

LIC-07-000 1 Attachment Page 2 REQUESTED INFORMATION (only Question 4 was applicable to Fort Calhoun Station)

NRC Question

4. Identification of Applicable Single Contingencies In response to question 3(a) you did not identify the loss of other critical transmission elements that may cause the offsite power system (OSP) to degrade, other than the loss of the nuclear unit.

If it is possible for specific critical transmission elements (such as other generators, critical transmission line, transformers, capacitor banks, voltage regulators, etc.) to degrade the OSP such that inadequate post-trip voltage could result, have these elements been included in your N-1 contingency analysis? When these elements are included in your GO'S contingency analysis model and failure of one of these transmission elements could result in actuation of your degraded voltage grid relay, is the offsite power declared inoperable? If not, what is your basis for not declaring the offsite power inoperable?

OPPD Answer As stated in OPPD's response (Reference 3) to Item 2(e) of Generic Letter (GL) 2006-02, alarms are generated on the OPPD energy management system (EMS) to notify both Fort Calhoun Station (FCS) and the control area operator (CAO) when the predicted post-plant-trip voltages at Substation 1251 drop below 16l.OkV, 160.8kV, and 158.8kV. These post-plant-trip voltages are specified in Quality Procedure NOD-QP-36, "Grid Operations and Control of Switchyard at FCS" to maintain FCS stability.

The calculation of post-plant-trip voltage is done only for the real-time system configuration.

The grid steady-state analysis considered the following six worst-case contingencies to determine the grid's capability to supply plant loads following a plant trip:

1. Outage of the 345kV line from OPPD Substation 3451 to MidAmerican (MEC) Raun Substation.

2. Outage of MEC Council Bluffs Unit 3.

3. Simultaneous outage of MEC Council Bluffs Unit 3, the 345kV line fiom OPPD Substation 3451 to OPPD Substation 3459 and the 345kV line from OPPD Substation 3451 to OPPD Substation 3454.

4. Outage of the 345kV line from MEC Council Bluffs Substation to OPPD Substation 3456.

5. Simultaneous outage of both 161kV lines from OPPD Substation 1211 to OPPD Substation 1250.

6. Simultaneous outage of the 345kV line fiom OPPD Substation 3451 to OPPD Substation 3459 and the 345kV line from OPPD Substation 3451 to OPPD Substation 3454.

As stated in OPPD's response (Reference 3) to Item 3(a) of GL 2006-02, at an actual or post-trip calculated value of 160.8kV, FCS will enter Technical Specification 2.7(2)c due to inoperability of house transformers T1A-3 and TlA-4. The NRC Operations Center will be notified within four hours.

If at the same time either emergency diesel generator is inoperable, the reactor will be placed in hot shutdown within six hours. At an actual or post-trip calculated value of 158.8kV for more than eight hours, the reactor will be placed in hot shutdown within twelve hours. The house transformers are

LIC-07-000 1 Attachment Page 3 considered inoperable due to the increased likelihood of activating the degraded voltage circuitry in the event of a design basis accident coincident with loss of the offsite power supply.

Text

Fort Calhoun Station PO. Box 550 Fort Calhoun, NE 68023 January 16,2007

, LIC-07-000 1 U. S. Nuclear Regulatory Commission Attn: Document Control Desk 1 Washington, DC 20555-0001 1

References:

1. Docket No. 50-285 i 2. NRC Generic Letter 2006-02, "Grid Reliability and the Impact on Plant Risk and the Operability of Offsite Power" (NRC-06-0013)

I I

3. Letter from OPPD (H. J. Faulhaber) to NRC (Document Control Desk), "60 Day Response to Generic Letter 2006-02" dated April 3, 2006 (LIC-06-0025)

4. Letter from NRC (C. Haney) to OPPD (R. T. Ridenoure), "Request for Additional 1I Information Regarding Resolution of Generic Letter 2006-02, Grid Reliability and the Impact on Plant Risk and the Operability of Offsite Power," dated December j 5,2006 (NRC-06-0168) 1 5. Letter from NRC (C. Haney) to OPPD (R. T. Ridenoure), "Revised Response Date 1 For Request For Additional Information Regarding Resolution Of Generic Letter I

i 1 2006-02, Grid Reliability And The Impact On Plant Risk And The Operability Of Offsite Power," dated December 13,2006 (NRC-06-0 176)

SUBJECT:

Response to Request for Additional Information Regarding Resolution of Generic Letter 2006-02, "Grid Reliability and the Impact on Plant Risk and the Operability of Offsite Power" Attached is the Omaha Public Power District (OPPD) response to Reference 4, which is an NRC request for additional information (RAI) regarding resolution of Generic Letter (GL) 2006-02 (Reference 2). In Reference 5, the NRC extended the due date of the required response to January 3 1,2007. Reference 3 is OPPD's initial response to GL 2006-02.

No commitments to the NRC are made in this letter.

I declare under penalty of perjury that the foregoing is true and correct. (Executed on January 16, 2007.)

U. S. Nuclear Regulatory Commission LIC-07-0001 Page 2 If you have additional questions, or require further information, please contact Mr. Thomas C.

Matthews at (402) 533-6938.

Sincerely, Division Manager Nuclear Engineering

Attachment:

Response to RAI Regarding Resolution of Generic Letter 2006-02

LIC-07-0001 Attachment Page 1 ATTACHMENT Response to Request for Additional Information Regarding Resolution of Generic Letter 2006-02, "Grid Reliability and the Impact on Plant Risk and the Operability of Offsite Power"

LIC-07-000 1 Attachment Page 2 REQUESTED INFORMATION (only Question 4 was applicable to Fort Calhoun Station)

NRC Question

4. Identification of Applicable Single Contingencies In response to question 3(a) you did not identify the loss of other critical transmission elements that may cause the offsite power system (OSP) to degrade, other than the loss of the nuclear unit.

If it is possible for specific critical transmission elements (such as other generators, critical transmission line, transformers, capacitor banks, voltage regulators, etc.) to degrade the OSP such that inadequate post-trip voltage could result, have these elements been included in your N-1 contingency analysis? When these elements are included in your GO'S contingency analysis model and failure of one of these transmission elements could result in actuation of your degraded voltage grid relay, is the offsite power declared inoperable? If not, what is your basis for not declaring the offsite power inoperable?

OPPD Answer As stated in OPPD's response (Reference 3) to Item 2(e) of Generic Letter (GL) 2006-02, alarms are generated on the OPPD energy management system (EMS) to notify both Fort Calhoun Station (FCS) and the control area operator (CAO) when the predicted post-plant-trip voltages at Substation 1251 drop below 16l.OkV, 160.8kV, and 158.8kV. These post-plant-trip voltages are specified in Quality Procedure NOD-QP-36, "Grid Operations and Control of Switchyard at FCS" to maintain FCS stability.

The calculation of post-plant-trip voltage is done only for the real-time system configuration.

The grid steady-state analysis considered the following six worst-case contingencies to determine the grid's capability to supply plant loads following a plant trip:

1. Outage of the 345kV line from OPPD Substation 3451 to MidAmerican (MEC) Raun Substation.

2. Outage of MEC Council Bluffs Unit 3.

3. Simultaneous outage of MEC Council Bluffs Unit 3, the 345kV line fiom OPPD Substation 3451 to OPPD Substation 3459 and the 345kV line from OPPD Substation 3451 to OPPD Substation 3454.

4. Outage of the 345kV line from MEC Council Bluffs Substation to OPPD Substation 3456.

5. Simultaneous outage of both 161kV lines from OPPD Substation 1211 to OPPD Substation 1250.

6. Simultaneous outage of the 345kV line fiom OPPD Substation 3451 to OPPD Substation 3459 and the 345kV line from OPPD Substation 3451 to OPPD Substation 3454.

As stated in OPPD's response (Reference 3) to Item 3(a) of GL 2006-02, at an actual or post-trip calculated value of 160.8kV, FCS will enter Technical Specification 2.7(2)c due to inoperability of house transformers T1A-3 and TlA-4. The NRC Operations Center will be notified within four hours.

If at the same time either emergency diesel generator is inoperable, the reactor will be placed in hot shutdown within six hours. At an actual or post-trip calculated value of 158.8kV for more than eight hours, the reactor will be placed in hot shutdown within twelve hours. The house transformers are

LIC-07-000 1 Attachment Page 3 considered inoperable due to the increased likelihood of activating the degraded voltage circuitry in the event of a design basis accident coincident with loss of the offsite power supply.