Text

Responds to 10CFR50.63, Loss of All AC Power & Provides Summary of Evaluations & Info Requested
	ML18153B693
Person / Time
Site:	Surry, North Anna, 05000000
Issue date:	04/17/1989
From:	Cartwright W; VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	; NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
	88-414, NUDOCS 8904250214
	Download: ML18153B693 (16)
	v • d • e

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VIRGINIA ELECTRIC AND POWER COMPANY RICHMOND, VIRGINIA 23261 W. R, CARTWRIGHT VxcE PR.ESXDENT NUCLEAR April 17, 1989 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D. C. 20555 Gentlemen:

VIRGINIA ELECTRIC AND POWER COMPANY SURRY POWER STATION UNITS 1 AND 2 NORTH ANNA POWER STATION UNITS 1 AND 2 Serial No.

NO/HWB:vlh.

Docket Nos.

License Nos.88-414 R2 50-338 50-339 50-280 50-281 DPR-32 DPR-37 NPF-4 NPF-7 RESPONSE TO 10CFRS0.63: LOSS OF ALL AL TERNA TING CURRENT POWER On July 21, 1988, 10CFR50.63, "Loss of All Alternating Current Power" was promulgated requiring all light-water-cooled nuclear power plants to be capable of withstanding a total loss of alternating current (AC) electric power (i.e. station blackout) for a specified duration and be capable of maintaining reactor cooling for that period. The station specific duration is based on:

(a) the redundancy of the onsite emergency AC power sources (b) the reliability of the onsite emergency AC power sources (c) the expected frequency of loss of offsite power (d) the probable time needed to restore offsite power 8904250214 890417 PDR ADOCK 05000280 P

PNU

e 10CFR50.63 also requires each light-water-cooled nuclear power plant licensed to operate on or before July 21, 1988 to submit by April 17, 1989:

(a) a proposed station blackout duration to be used in determining compliance including a justification for the duration selected, (b) a description of the procedures that will be implemented for station blackout events for the specified duration, and (c) a list of modifications to equipment and procedures to meet requirements of the specified duration In order to respond to these requirements, we have performed Station Blackout coping evaluations for the Surry and North Anna Power Stations. Based on these evaluations, we intend to pursue, for both Surry and North Anna Power Stations, the Alternate AC Power method for coping with a station blackout event.

A summary of these evaluations and the information requested by 10CFR50.63 is provided in Attachment 1 for Surry Power Station and Attachment 2 for North Anna Power Station.

Should you have any questions concerning this response please contact us.

W.R. Cartwright Attachments cc:

U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, N.W.

Suite 2900 Atlanta, GA 30323 Mr. W. E. Holland NRC Senior Resident Inspector Surry Power Station Mr. J. L. Caldwell NRC Senior Resident Inspector North Anna Power Station

.e ATTACHMENT 1 RESPONSE TO STATION BLACKOUT RULE SURRY POWER ST A TION On July 21, 1988, the Nuclear Regulatory Commission (NRC) amended its regulations in 10 CFR Part 50. A new section, 50.63, was added which requires that each light-water-cooled nuclear power plant be able to withstand and recover from a station blackout (SBO) of a specified duration. Utilities are expected to have the baseline assumptions, analyses and related information used in their coping evaluation available for NRC review. It also-identifies the factors that must be considered in specifying the station blackout duration. Section 50.63 requires that, for the station blackout duration, the plant be capable of maintaining core cooling and appropriate containment integrity. Section 50.63 further requires that each licensee submit the following information:

1.

A proposed station blackout duration including a justification for the selection based on the redundancy and reliability of the onsite emergency AC power sources, the expected frequency of loss of offsite power, and the probable time needed to restore offsite power;

2.

A description of the procedures that will be implemented for station blackout events for the duration (as determined in 1 above) and for recovery therefrom; and

3.

A list and proposed schedule for any needed modifications to equipment and associated procedures necessary for the specified SBO duration.

The NRC has issued Regulatory Guide 1.155 "Station Blackout" which describes a means acceptable to the NRC Staff for meeting the requirements of 10 CFR 50.63.

Regulatory Guide (RG) 1.155 states that the NRC Staff has determined that NUMARC 87-00 "Guidelines and Technical Bases for NUMARC Initiatives Addressing Station Blackout at Light Water Reactors" also provides guidance that is in large part identical to the RG 1.155 guidance and is acceptable to the NRC Staff for meeting these requirements.

Table 1 to RG 1.155 provides a cross-reference between RG 1.155 and NUMARC 87-00 and notes where the RG takes precedence.

L TR 88-414 - Attachment 1 - Page 1 of 7

e Virginia Power has evaluated Surry Power Station against the requirements of the SBO rule using guidance from NUMARC 87-00 except where RG 1.155 takes precedence. Based on this evaluation, an AAC power source will be utilized at Surry which meets the criteria specified in Appendix B to NUMARC 87-00. The AAC source will be an Emergency AC (EAC) power source which meets the assumptions in Section 2.3.1 of NUMARC 87-00.

The results of this evaluation are detailed below.

A.

Proposed Station Blackout Duration The information provided in this section is based on our proposal to change the existing "shared" configuration of EDG 3 between Units 1 and 2 with the addition of an EDG such that Emergency Bus 1J and 2J each have a dedicated EDG.

NUMARC 87-00, Section 3 was used to determine a proposed SBO duration of 4 hours4.62963e-5 days 0.00111 hours 6.613757e-6 weeks 1.522e-6 months .

The following plant factors were identified in determining the proposed station blackout duration: The applicable NUMARC 87-00 reference is in parenthesis.

1.

AC Power Design Characteristic Group is "P2*" based on:

a.

Expected frequency of grid-related Loss of Offsite Power (LOOP) -

does not exceed once per 20 years. (Section 3.2.1, Part 1A, P. 3-3)

b.

Estimated frequency of LOOPs due to extremely severe weather places the plant in Extreme Severe Weather (ESW) Group "4".

(Section 3.2.1, Part 1B, P. 3-4)

c.

Estimated frequency of LOOPs due to severe weather places the plant in Severe Weather (SW) Group "1". (Section 3.2.1, Part 1C, P. 3-7)

d.

The offsite power system is in the "I 1/2" group. (Section 3.2.1, Part 1D, P.-3-10) -

e.

Plant - specific pre-hurricane shutdown requirements and procedures which meet the guidelines of section 4.2.3 of NUMARC 87-00 will be implemented.

L TR 88-414 - Attachment 1 - Page 2 of 7

e

2.

The emergency AC power configuration group is "C" based on categorization as a multi-unit site with normally dedicated power supplies.

a.

There are two emergency AC power supplies not credited as alternate AC power sources on the blacked-out unit. (Section 3.2.2, Part 2A, P. 3-15)

b.

One emergency AC power supply per unit is necessary to operate safe shutdown equipment following a loss of offsite power.

(Section 3.2.2, Part 2B, P. 3-15)

3.

The target EDG reliability is 0.950. This reliability was selected based on having a nuclear unit average EDG reliability for the last 100 demands greater than 0.95, consistent with NUMARC 87-00, Section 3.2.4.

Additionally, Surry is a P2* categorized station which allows a 0.95 EDG reliability with a 4 hour4.62963e-5 days 0.00111 hours 6.613757e-6 weeks 1.522e-6 months coping capability.

4.

An AAC power source will be utilized at Surry which meets the criteria specified in Appendix B to NUMARC 87-00. The AAC source will be an EAC power source which meets the assumptions in Section Z.3.1 of NUMARC 87-00.

The AAC power source is immediately available to the nonblacked-out unit and is available to the blacked out unit within one hour of the onset of the station blackout event. The AAC source has sufficient capacity and capability to operate systems necessary for coping with a station blackout for the required SBO duration of 4 hours4.62963e-5 days 0.00111 hours 6.613757e-6 weeks 1.522e-6 months to bring and maintain both units in safe shutdown. An AC independent coping analysis was performed for the one-hour required to connect the AAC power source to the blacked-out unit. The results of this analysis indicate that reactor core uncovery will not occur within one-hour.

The proposed AAC configuration is shown in Figure 1.

The four existing Emergency Buses are connected to the station's offsite power sources through three Reserve Station Service Transformers and associated Transfer Buses D, E, and F. Bus F has two Emergency Buses (lH and 2J) connected to it.

A new class lE EDG (EDG 4) will be connected to either Emergency Bus lJ or 2J (2J shown in Figure 1). After this modification, each Emergency Bus will have a dedicated EDG.

Therefore, if either Emergency Diesel Generator 1 or 4 should start, power would be provided in a "backfeed" arrangement to the opposite unit through Transfer Bus F.

LTR 88-414 - Attachment 1 - Page 3 of 7

B.

C.

e If either EDG 2 or 3 were to start, power would be provided to the opposite unit through the existing Emergency Bus administrative tie breakers and Transfer Bus F. The Emergency Bus with the EDG would be connected to its redundant Emergency Bus with the administrative tie breaker, then transfer power to the other unit through Bus F.

Procedure Description Plant procedures have been reviewed and the necessary procedures will pe prepared or modified by July 17, 1989 to meet the guidelines in NUMARC 87-00, Section 4 in the following areas:

1.

AC power restoration per NUMARC 87-00, Section 4.2.2.

These procedures include the Virginia Power Transmission System Restoration Plan.

2.

Severe weather per NUMARC 87-00, Section 4.2.3. These will include procedures for shutdown of both units in the event of a hurricane. This includes Station Procedure AP-37.0, "Abnormal Environmental Conditions.".

Plant procedures have been reviewed and changes necessary to meet NUMARC 87-00 will be implemented in the following areas:

1.

Station Blackout response per NUMARC 87-00, Section 4.2.1. These include implementation of the AAC source to achieve safe shutdown on both units.

2.

Procedure changes associated with any modifications required after assessing coping capability per NUMARC 87-00, Section 7.

Proposed Modifications and Schedule A new Emergency Diesel Generator will be installed at Surry, dedicated to one Emergency Bus (either lJ or 2J, with EDG 3 dedicated to the other). Surry will now have a dedicated EDG for each Emergency Bus. Any one of the EDGs will have the capacity to serve as the AAC source.

Per NUMARC 87-00, one EDG would be available for the blackout event. Both EDGs on one unit are assumed unavailable. Units 1 and 2 are connected electrically by 4.16KV Transfer Bus F, which normally supplies preferred offsite power to Emergency Bus 1H and 2J. There are also administratively controlled Emergency Bus tie breakers between Buses Hand Jon both units. This existing arrangement would allow power to be transferred between units for the start of any EDG.

L TR 88-414 - Attachment 1 - Page 4 of 7

e Additionally,** breaker control and *protective relay modifications will be implemented to allow interconnection of the buses in this manner.

The Emergency Bus tie breakers will be in the racked-out position during normal plant operation; therefore, local action in the Emergency Switchgear Room is required. Since this action is outside the Control Room, a one-hour coping analysis was required. Additional emergency lighting will be provided as required to perform all operations.

Procedures are in place that address many of the SBO coping requirements.

These procedures will be revised to address the alternate AC method for coping with a Station Blackout. The Station's ECA-1 Series (Emergency Contingency Action) of procedures are based on Westinghouse generic procedures, and address a total loss of power to one unit. These procedures address an SBO with an "AC-Independent" approach in that charging and other fluid system mechanical cross-ties are used during the event. These procedures will be modified in accordance with NUMARC 87-00 guidelines and will provide additional "defense in depth.". There are also procedures that address power restoration to any de-energized Emergency Bus. These must be revised to comply with the NUMARC criteria, including the load "stripping" (from the Control Room) required to control EDG loading.

The AAC source has the capacity and capability to power the equipment necessary to cope with an SBO in accordance with NUMARC 87-00, Section 7 for the required coping duration (4-hours) determined in accordance with NUMARC 87-00, Section 3.2.5. The Virginia Power assessment evaluated using one EDG to achieve safe shutdown on both units.

1.

Condensate Inventory For Decay Heat Removal It has been determined from Section 7.2.1 of NUMARC 87-00 that 56,495 gallons of condensate water are required for decay heat removal for 4 hours4.62963e-5 days 0.00111 hours 6.613757e-6 weeks 1.522e-6 months . The minimum permissible Emergency Condensate Storage Tank level per Technical Specifications provides 110,000 gallons of water, which exceeds the required quantity for coping with a 4 hour4.62963e-5 days 0.00111 hours 6.613757e-6 weeks 1.522e-6 months station blackout.

No plant modifications and minimal procedure revisions are necessary for condensate inventory.

2.

Class lE Battery Capacity A battery capacity calculation has been performed pursuant to NUMARC 87-00, Section 7.2.2 to verify that the Class lE batteries have sufficient capacity to meet station blackout loads for one hour.

L TR 88-414 - Attachment 1 - Page 5 of 7

e Surry has two Class lE batteries per unit. Each battery supplies two instrument channels that provide various low-voltage indication, control, and protection functions. Using. AAC, battery chargers will be available on at least one train per unit. Therefore, two channels of instrumentation will be available for the entire 4-hour period. The voltage of the batteries on the train without AC power will be monitored. Loads will be procedurally stripped, as required, in an attempt to maintain additional channels of instrumentation. No battery will be allowed to degrade to such an extent that polarity reversal is possible.

3.

Compressed Air Air-operated valves relied upon to cope with a station blackout for one hour can either be operated manually or have sufficient backup sources independent of the preferred and blacked-out unit's class lE power supply. Valves requiring manual operation or that need backup sources for operation are identified in plant procedures.

The Surry compressed air system is such that Unit 1 and 2 operate on a common air system. There is one instrument air compressor per unit powered from an Emergency Bus. There are also separate air bottles on critical valves to allow control without a compressor. A modification will be performed to add air bottles to the Steam Generator Atmospheric Dump Valves (PORVs) to achieve one hour coping capability. In the event a compressor is not immediately available, one will be available within one hour (after the appropriate buses are tied together).

4.

Effects Of Loss Of Ventilation The calculated steady state ambient air temperature for the steam-driven AFW pump room during a station blackout induced loss of ventilation is approximately 187°F. Existing ventilation will be utilized to reduce the temperature to below 120°F.

The assumption in NUMARC 87-00, Section 2.7.1 that the Control Room will not exceed 120°F during a station blackout has been assessed. The Control Room at Surry has been calculated to reach a steady state ambient air temperature of 187°F during a SBO.

The Emergency Switchgear Rooms contain the Westinghouse process racks for instrumentation signal processing.

By calculation, the temperature would reach 179°F in this area without ventilation.

Westinghouse recommended that their process equipment operate in an ambient not to exceed 120°F. Therefore, the Control Room and Emergency Switchgear Rooms are dominant areas of concern. Existing ventilation (chiller and air handler) will be provided to the Control Room and Emergency L TR 88-414 - Attachment 1 - Page 6 of 7

5.

6.

e Switchgear Rooms to ensure their temperatures do not exceed 120°F.

This ventilation will be provided within one-hour.

Additionally, the charging pump cubicles are estimated to reach 366°F within 4-hours without ventilation. Existing ventilation will be used to maintain these areas less than 120°F.

Reasonable assurance of operability of station blackout response equipment in the above dominant areas has been assessed using Appendix F to NUMARC 87-00 and/or the Topical Report. Procedure changes necessary in order to provide reasonable assurance for equipment operability will ensure ventilation is provided to the Control/Emergency Switchgear Rooms the charging pump cubicles, and the steam-driven AFW pump room within one hour of an SBO condition.

Containment Isolation The list of containment isolation valves has been reviewed to verify that valves which must be capable of being closed or that must be operated (cycled) under station blackout conditions can be positioned (with indication) independent of the preferred and blacked out unit's Class lE power supplies. No plant modifications and/or associated procedure changes were determined to be required to ensure that appropriate containment integrity can be provided under SBO conditions.

Reactor Coolant Inventory The AAC Source powers the necessary make-up system (charging) to maintain adequate reactor coolant system inventory to ensure that the core is cooled for 4 hours4.62963e-5 days 0.00111 hours 6.613757e-6 weeks 1.522e-6 months .

The ability to maintain adequate reactor coolant system inventory to ensure that the core is cooled independent of AC power has been assessed for one hour. A plant specific analysis was used for this assessment. The expected rates of reactor coolant inventory loss under SBO conditions do not result in core uncovery in one-hour. Therefore, make-up systems to the RCS are not required to maintain core cooling under natural circulation (including reflux boiling) for the initial one-hour period.

The modifications and associated procedure changes identified in Parts A, B, and C above will be completed within two years after the notification provided by the Director, Office of Nuclear Reactor Regulation in accordance with 10 CFR 50.63(C)(3).

L TR 88-414 - Attachment 1 - Page 7 of 7

e ATTACHMENT 2 RESPONSE TO STATION BLACKOUT RULE NORTH ANNA POWER STATION On July 21, 1988, the Nuclear Regulatory Commission (NRC) amended its regulations in 10 CFR Part 50. A new Section, 50.63, was added which requires that each light-water-cooled nuclear power plant be able to withstand and recover from a station blackout (SBO) of a specified duration. Utilities are expected to have the baseline assumptions, analyses and related information used in their coping evaluation available for NRC review. It also identifies the factors that must be considered in specifying the station blackout duration. Section 50.63 requires that, for the station blackout duration, the plant be capable of maintaining core cooling and appropriate containment integrity. Section 50.63 further requires that each licensee submit the following information:

1.

A proposed station blackout duration including a justification for the selection based on the redundancy and reliability of the onsite emergency AC power sources, the expected frequency of loss of offsite power, and the probable time needed to restore offsite power.

2.

A description of the procedures that will be implemented for station blackout events for the duration (as determined in 1 above) and for recovery therefrom; and

3.

A list and proposed schedule for any needed modifications to equipment and associated procedures necessary for the specified SBO duration.

The NRC has issued Regulatory Guide 1.155 "Station Blackout" which describes a means acceptable to the NRC Staff for meeting the requirements of 10 CFR 50.63.

Regulatory Guide (RG) 1.155 states that the NRC Staff has determined that NUMARC 87-00 "Guidelines and Technical Bases for NUMARC Initiatives Addressing Station Blackout at Light Water Reactors" also provides guidance that is in large part identical to the RG 1.155 guidance and is acceptable to the NRC Staff for meeting these requirements.

Table 1 to RG 1.155 provides a cross-reference between RG 1.155 and NUMARC 87-00 and notes where RG 1.155 takes precedence.

Virginia Power has evaluated North Anna Power Station against the requirements of the SBO rule using guidance from NUMARC 87-00 except where RG 1.155 takes L TR 88-414 - Attachment 2 - Page 1 of 7

e precedence. Based on this evaluation, an Alternate AC (AAC) power source will be utilized at North Anna which meets the criteria specified in Appendix B to NUMARC 87-00. The results of this evaluation are detailed below.

A.

Proposed Station Blackout Duration NUMARC 87-00, Section 3 was used to determine a proposed SBO duration of 8 hours9.259259e-5 days 0.00222 hours 1.322751e-5 weeks 3.044e-6 months .

The following plant factors were identified in determining the proposed station blackout duration. The applicable NUMARC 87-00 reference is in parentheses.

1.

AC Power Design Characteristic Group is "P2" based on:

a.

Expected frequency of grid-related Loss of Offsite Power (LOOP) -

does not exceed once per 20 years. (Section 3.2.1, Part lA, p.3-3)

b.

Estimated frequency of LOOPs due to extremely severe weather places the plant in Extreme Severe Weather (ESW) Group "4".

(Section 3.2.1, Part lB, p.3-4)

c.

Estimated frequency of LOOPs due to severe weather places the plant in Severe Weather (SW) Group "2". (Section 3.2.1, Part lC, p.3-7)

d.

The offsite power system is in the "I 1/2" group, (Section 3.2.1, Part lD, p.3-10)

2.

The emergency AC power configuration group is "C" based on categorization as a multi-unit site with normally dedicated power supplies.

a.

There are two emergency AC power supplies not credited as Alternate AC power sources on the blacked-out unit. (Section 3.2.2, Part 2A, p.3-15)

b.

One emergency AC power supply per unit is necessary to operate safe shutdown equipment following a loss of offsite power.

(Section 3.2.2, Part 2B, p.3-15)

3.

The target EDG reliability is 0.950. This reliability was selected based on having a nuclear unit average EDG reliability for the last 100 demands greater than 0.95, consistent with NUMARC 87-00, Section 3.2.4.

4.

An Alternate AC (AAC) power source will be utilized at North Anna which meets the criteria specified in Appendix B to NUMARC 87-00.

L TR 88-414 - Attachment 2 - Page 2 of 7

B.

The AAC source is an Emergency AC (EAC) power source which meets the assumptions in Section 2.3.1 of NUMARC 87-00.

The AAC power source is immediately available to the nonblacked-out unit and is available to the blacked-out unit within one hour of the onset of the station blackout event. The AAC source has sufficient capacity and capability to operate systems necessary for coping with a station blackout for the required SBO duration of 8 hours9.259259e-5 days 0.00222 hours 1.322751e-5 weeks 3.044e-6 months to bring and maintain both units in safe shutdown. An AC independent coping analysis was performed for the one hour required to connect the AAC power source to the blacked-out unit.

The results of this analysis indicate that reactor core uncovery will not occur within one hour.

The proposed AAC configuration is shown in Figure 1.

The four existing Emergency Buses are connected to the station's offsite power sources through three Reserve Station Service Transformers, and associated Transfer Buses D, E, and F. Bus F has two Emergency Buses (1H and 2J) connected to it.

Each Emergency Bus has a dedicated Emergency Diesel Generator.

Therefore, if either Emergency Diesel Generator lH or 2J should start, power would be provided in a "backfeed" arrangement to the opposite unit through Transfer Bus F. If EDG lJ or 2H should start, power would be provided to the opposite unit through either a new Emergency Bus tie breaker (Unit 1) or an existing Emergency Bus tie breaker (Unit 2), in conjunction with Transfer Bus F.

Procedure Description Plant procedures have been reviewed and the necessary procedures will be prepared or modified by July 17, 1989 to meet the guidelines in NUMARC 87-00, Section 4 in the following areas.

1.

AC power restoration per NUMARC 87-00, Section 4.2.2; Procedures include the Virginia Power Transmission System Restoration Plan and Station Procedure AP-10.2, "Restoration of Switch yard."

2.

Severe weather per NUMARC 87-00, Section 4.2.3. This includes Station Procedure AP-41, "Severe Weather Conditions."

Plant procedures have been reviewed and changes necessary to meet NUMARC 87-00 will be implemented in the following areas:

1.

Station Blackout response per NUMARC 87-00, Section 4.2.1.

These include implementation of the AAC source to achieve safe shutdown on both units.

L TR 88-414 - Attachment 2 - Page 3 of 7

2.

Procedure* changes associated with any modifications required after assessing coping capability per NUMARC 87-00, Section 7.

C.

Proposed Modifications and Schedule North Anna will utilize one of its existing class lE Emergency Diesel Generators (EDG) as the AAC source. As discussed earlier, North Anna has a dedicated EDG for each of its four (two per unit) Emergency Buses.

Any one of the EDGs will have the capability to serve as the AAC source.

Per NUMARC 87-00, one EDG would be available for the blackout event.

Both EDGs on the blacked out unit are assumed unavailable.

Units 1 and 2 are connected electrically by 4.16KV Transfer Bus F, which

normally supplies preferred offsite power to Emergency Bus 1H and 2J.

There is also presently an administratively controlled Emergency Bus tie breaker between Unit 2 buses 2H and 2J. This existing arrangement would allow power to be transferred between units should any of EDGs 1H, 2H, or 2J start.

Since this bus tie breaker does not exist between Unit 1 buses 1H and 1J, a modification is necessary to transfer power from Emergency Bus 1J to Unit 2 in the event EDG 1J starts. The proposed modification is to add an administratively controlled Emergency Bus tie breaker to Unit 1, similar to that of Unit 2, which will connect Bus 1J to 1H.

With this modification, all Emergency Buses can be administratively connected together.

This provides maximum operator flexibility to bring and maintain both units into safe shutdown. Note that addition of this 1H-1J administrative tie re-installs a feature originally in the North Anna design but removed in 1981 when the Emergency Bus to Station Service Bus ties were installed.

Breaker control and protective relay modifications will be required to allow interconnection of the buses in this manner. The Emergency Bus tie breakers will be in the racked-out position during normal plant operation; therefore, local action in the Emergency Switchgear Room is required. Since this action is outside the Control Room, a one hour coping analysis was required.

Additional emergency lighting will be supplied as required to perform all actions.

Procedures are in place that address many of the SBO coping requirements. These procedures will be revised to address the Alternate AC method for coping with a Station Blackout. The Station's ECA-0 Procedure Series (Emergency Contingency Action) for loss of all AC power are based on Westinghouse generic procedures, and address a total loss of power to one Unit. These procedures address an SBO with an "AC-Independent" approach in that charging system mechanical cross-L TR 88-414 - Attachment 2 - Page 4 of 7

e ties are used during the event. These procedures will be modified in accordance with NUMARC 87-00 guidelines and will provide additional "defense in depth." There are also procedures (AP-10 Series) that address power restoration to any deenergized Emergency Bus. Again, these procedures must be revised to comply with the NUMARC criteria, including the extensive load "stripping" (from the Control Room) required to control EDG loading.

The AAC source has the capacity and capability to power the equipment necessary to cope with an SBO in accordance with NUMARC 87-00, Section 7 for the required coping duration (8 hours9.259259e-5 days 0.00222 hours 1.322751e-5 weeks 3.044e-6 months ) determined in accordance with NUMARC 87-00, Section 3.2.5.

Our assessment evaluated using one EDG to safely achieve safe shutdown on two units.

1.

2.

Condensate Inventory For Decay Heat Removal It has been determined from Section 7.2.1 of NUMARC 87-00 that 103,024 gallons of condensate water are required for decay heat removal for 8 hours9.259259e-5 days 0.00222 hours 1.322751e-5 weeks 3.044e-6 months .

The minimum permissible Emergency Condensate Storage Tank level for Technical Specifications provides 110,000 gallons of water which exceeds the required quantity for coping with an 8 hour9.259259e-5 days 0.00222 hours 1.322751e-5 weeks 3.044e-6 months station blackout.

No plant modifications and only minor procedure revisions are necessary for condensate inventory.

Class 1E Battery Capacity A battery capacity calculation has been performed pursuant to NUMARC 87-00, Section 7.2.2 to verify that the Class 1E batteries have sufficient capacity to meet station blackout loads for one hour.

North Anna has four batteries per unit, two batteries per safety train. Each battery provides power through an inverter to a vital bus. Each vital bus supplies one instrument channel that provide various low-voltage indication, control, and protection functions.

Using AAC, battery chargers will be available on at least one train per Unit. Therefore, two channels of instrumentation per unit will be available for the entire 8 hour9.259259e-5 days 0.00222 hours 1.322751e-5 weeks 3.044e-6 months period. The voltage of the batteries on the train without AC power will be monitored. Loads will be procedurally stripped, as required, in an attempt to maintain additional channels of instrumentation during the event. No battery will be allowed to degrade to such an extent that polarity reversal is possible.

L TR 88-414 - Attachment 2 - Page 5 of 7

e

3.

Compressed Air Air-operated valves relied upon to cope with a station blackout for one hour can either be operated manually or have sufficient backup compressed air supply independent of the preferred and blacked-out Unit's class 1E power supply.

Valves requiring manual operation or that need backup sources for operation are identified in plant procedures.

The North Anna compressed air system is such that Unit 1 and 2 operate on a common air system. There is one instrument air compressor per unit powered from an Emergency Bus. There are also separate air bottles or a nitrogen supply on critical valves to allow control without a compressor. In the event a compressor is not immediately available due to loss of AC, one will be available within one hour (after the appropriate buses are tied together).

4.

Effects of Loss of Ventilation The calculated steady state ambient air temperature for the steam-driven AFW pump room during a station blackout induced loss of ventilation is approximately 175°F.

In order to provide reasonable assurrance of operability for 8 hours9.259259e-5 days 0.00222 hours 1.322751e-5 weeks 3.044e-6 months , existing ventilation in this space will be utilized, which will lower the temperature to an acceptable 120°F.

The assumption in NUMARC 87-00, Section 2.7.1 that the Control Room will not exceed 120°F during a station blackout has been assessed. The Control Room at North Anna has been calculated to reach a steady-state ambient air temperature of approximately 181 °F during an SBO. The Emergency Switchgear Rooms contain the Westinghouse process racks for instrumentation signal processing and this area is calculated to reach approximately 153°F without ventilation.

Westinghouse recommends that their process equipment operate in an ambient environment not to exceed 120°F.

Therefore, the Control Room and Emergency Switchgear Rooms are dominant areas of concern.

Existing ventilation (chiller, air handler, and associated pumps) will be provided to the Control Room and Emergency Switchgear Rooms to ensure their temperatures do not exceed 120°F.

This ventilation will be provided within one hour.

Additionally, the charging pump cubicles are estimated to reach approximately 300°F without ventilation. Ventilation fans and flexible ducting installed for Appendix "R" will be used to L TR 88-414 - Attachment 2 - Page 6 of 7

e e

maintain these areas less than 120°F. This ventilation will be provided within one hour.

Reasonable assurance of the operability of station blackout response equipment in the above dominant areas has been assessed using Appendix F to NUMARC 87-00 and/or the Topical Report.

Procedure changes will be made to ensure that ventilation is provided to the Control Room, Emergency Switchgear Rooms, the charging pump cubicles, and the steam-driven AFW pump room within one hour of an SBO condition.

5.

Containment Isolation The list of containment isolation valves has been reviewed to verify that those valves which must be capable of being closed or that must be operated (cycled) under station blackout conditions can be positioned (with indication) independent of the preferred and blacked out unit's Class 1E power supplies.

No plant modifications and/ or associated procedure changes were determined to be required to ensure that appropriate containment integrity can be provided under SBO conditions.

6.

Reactor Coolant Inventory The AAC Source powers the necessary RCS make-up system (charging) to maintain adequate reactor coolant system inventory to ensure that the core is cooled for 8 hours9.259259e-5 days 0.00222 hours 1.322751e-5 weeks 3.044e-6 months .

The ability to maintain adequate reactor coolant system inventory to ensure that the core is cooled independent of AC power has been assessed for one hour.

A plant specific analysis was performed for Surry, which bounds the North Anna RCS. The expected rates of reactor coolant inventory loss under SBO conditions do not result in core uncovery in one hour. Therefore, make-up systems are not required to maintain core cooling under natural circulation (including reflux boiling) for the initial one hour period.

The modifications and associated procedure changes identified in Parts A, B, and C above will be completed within two years after notification is provided by the Director, Office of Nuclear Reactor Regulation in accordance with 10 CFR 50.63 (C)(3).

L TR 88-414 - Attachment 2 - Page 7 of 7

ML18153B693

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