ML18152A028
| ML18152A028 | |
| Person / Time | |
|---|---|
| Site: | Surry, North Anna  |
| Issue date: | 04/30/1991 |
| From: | Stewart W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 91-242, NUDOCS 9105070287 | |
| Download: ML18152A028 (34) | |
Text
i e
VIRGINIA ELECTRIC AND POWER COMPANY RICHMOND, VIRGINIA 23261 April 30, 1991 U.S. Nuclear Regulatory Commission Attention: 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.91-242 NL&P/RMN: R6 Docket Nos.
50-280 50-281 50-338 50-339 License Nos. DPR-32 DPR-37 NPF-4 NPF-7 SUPPLEMENTAL
RESPONSE
TO STATION BLACKOUT SAFETY EVALUATION REPORTS Additional information on our plans for compliance with 1 O CFR 50.63 is provided in for Surry Power Station and Attachment 2 for North Anna Power Station.
These plans are based on your rejection of our original April 17, 1989 submittal (as modified for Surry by our August 1, 1990 letter). This action was documented in the Safety Evaluation Reports for Surry and North Anna issued October 15, 1990 and October 18, 1990 respectively.
Based on the preliminary results of our study, which is still ongoing, we currently plan to install two non-safety grade diesel generators at Surry and one non-safety grade diesel generator at North Anna as alternate AC sources. Our proposed blackout durations are four hours with a target diesel reliability of 95%. Existing automatic load sequencing systems will be used to connect loads to the emergency bus. We are considering using automatic connection of the alternate AC diesels at Surry. We are also assessing the need for Surry Technical Specification relief so the proposed system can be installed without a two unit outage. If relief is needed, we will submit a formal Technical Specification change request to address installation at Surry after the final SER is issued.
We will continue to provide additional information at least quarterly in accordance with our November 29, 1990 letter.
However, the detailed design required for implementing these modifications will not be completed until after the SER is issued.
As discussed in the attachments, due to the complexity of the design changes, we
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e estimate implementation of these modifications will require approximately five years after receipt of a favorable SER.
In addition, should the NRG position on how to comply with 1 O CFR 50.63 change, further revisions to our plans may be required.
If you have any questions or require additional information, please contact us.
Very truly yours, l?.1-~~,~
W. L. Stewart Senior Vice President - Nuclear Attachments
- 1.
Response to Station Blackout Rule for Surry Power Station
- 2.
Response to Station Blackout Rule for North Anna Power Station cc:
U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, N.W.
Suite 2900 Atlanta, Georgia 30323 Mr. M. S. Lesser NRC Senior Resident Inspector North Anna Power Station Mr. W. E. Holland NRC Senior Resident Inspector Surry Power Station Response to Station Blackout Rule Surry Power Station
.Virginia Electric and Power Company
RESPONSE TO STATION BLACKOUT RULE SURRY 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 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 ~eeting 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.
In previous Virginia Power letters, serial number 88-414 dated April 17, 1989, 88-414A dated April 20, 1989, 88-414B dated March 30, 1990 and 90-410 dated August 1, 1990, we proposed to install a fourth emergency diesel generator at Surry and then use an emergency diesel generator on the non-blacked out unit as an Alternate AC (AAC) source for the blacked out unit.
This approach was found unacceptable by the NRC as detailed in an October 15, 1990 letter and attached Safety Evaluation Report (SER) and Technical Evaluation Report (TER).
Following this rejection, Virginia Power issued letter 90-661 dated November 29, RKS/kwd:001105 -
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1990 which informed the NRC of our intention to review the feasibility of installing non-safety grade diesels at Surry to act as AAC sources.
Virginia Power agreed to provide supplemental information by April 30, 1991 and report quarterly thereafter on this review.
Accordingly, Virginia Power has further 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, we currently plan to install two non-safety grade diesel generators as AAC power sources which meet 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 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />.
- 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 114."
(Section 3.2.1, Part lB,
- p. 3-4)
- c.
Estimated frequency o{ LOOPs due to severe weather places the plant in Severe Weather (SW) Group 11 1. 11 (Section 3.2.1, Part lC, p3-7)
- d.
The offsite power system is in the "I 1/2" group.
(Section 3.2.1, Part lD, p3-10)
The TER issued with the NRC letter and SER on October 15, 1990, on page 8 stated:
"We do not agree with the licensee's statement... that the two switchyards are electrically independent.
A review of Figure 8.3-1 of the Surry UFSAR indicates that the emergency busses in both units are normally powered from auto-transformers 1 and 2.
These auto transformers connect the two switchyards.
Therefore, the switchyards are electrically connected and can not be considered as independent."
This statement formed the main basis for not accepting our conclusion that Surry is an I 1/2 (NUMARC) or I 1 RKS/kwd:001105 -
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e (Reg. Guide 1.155) plant.
However, the UFSAR figure (8.3-1) that was used to review our conclusion had not yet been updated to reflect recent switchyard modifications.
Our evaluation is based on these recent modifications which removed the auto-transformers that connected the 500KV and 230KV switchyards.
These transformers have each been replaced with a two-winding transformer (500KV to 34.5 KV bus No. 5 and 230KV to 34.5KV bus No. 6).
There are currently no electrical ties between the 500KV and 230 KV switchyards, therefore they can be considered electrically independent. UFSAR change requests were developed during the course of these modifications and are currently being processed.
- e.
Plant specific pre-hurricane shutdown requirements and procedures which meet the guidelines of section 4.2.3 of NUMARC 87-00 have been implemented.
- 2.
The emergency AC power configuration group is "D" based on categorization as a multi-unit site with normally shared power supplies.
- a.
There are three emergency AC power supplies (two dedicated and one shared) which will not be used as AAC power sources.
(Section 3.2.2, Part 2A, p3-15)
- b.
Two emergency AC power supplies (one per unit) are necessary to operate safe shutdown equipment during a station blackout of all units at the site.
(Section 3.2.2, Part 2B, p3-15)
- 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.
A review of the SER issued for Commonwealth Edison's Dresden Units 2 and 3 and Quad Cities Units 1 and 2 indicates that it is acceptable to reduce the required EDG reliability from.975 to.95 provided that conditions are similar to the Dresden design and contingent upon the following:
- a.
"The AAC power source is sized to power the complete contingent of safety-related and nonsafety-related loads associated with one safety division of each unit simultaneously that are normally expected to be available for the loss of offsite power (LOOP) condition."
RKS/kwd:001105 -
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e
- b.
"The AAC power source is connectible to all EDG buses of all the units."
- c.
"The AAC source should be diverse from existing EDG's.
Lack of diversity must be justified by addressing how common mode failures are minimized."
Since the Dresden site is an EAC Group D design, a station blackout must be postulated to affect both units (NUMARC 87-00, section 2.3.1(2)).
Accordingly, an AAC power source will be installed with sufficient capacity to power one safety division of each unit in the event of a LOOP.
Similarly, at Surry two non-safety grade diesels will be installed as an AAC source which will have sufficient capacity to power the LOOP loads associated with one safety division of each Unit.
This is consistent with the above criterion since a station blackout at Surry (as it is at Dresden) is postulated to occur on both units simultaneously (NUMARC 87-00, section 2.3.1(2) and 10CFR50.2).
This arrangement provides reliability equivalent to that afforded by the proposed Dresden design.
At Dresden, the AAC source connects to a single bus from which ties are made to the safety-related buses of each unit.
This provides AAC access to all EDG buses at the site.
The proposed Surry design would permit the connection of the AAC source to the three transfer buses that supply power to the safety-related buses at the station.
This design similarly permits the AAC source to access all EDG buses of each unit consistent with the above criteria.
The proposed Surry design provides both diversity and independence (Reg. Guide 1.155, section 3.2.5) among the AAC and EDGs as follows:
The AAC diesel will be a more recent design than the existing EDGs.
The EDGs and AAC diesel will not share common structures.
The EDGs and AAC diesel will not share common support systems (e.g. fuel oil day tanks, cooling, control power, etc.)
Power and control cables for the EDGs and AAC diesel will be separated.
RKS/kwd:001105 -
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B.
C.
e The EDGs and AAC diesels will not share electrical and mechanical protective devices.
The AAC diesel will not normally be connected to the EDG buses or the transfer buses.
- 4.
An Alternate AC (AAC) power source will be utilized at Surry which meets the criteria specified in Appendix B to NUMARC 87-00.
The AAC power source will be available to the blacked-out unit within one hour following the onset of a station blackout event.
This AAC source will have sufficient capacity to operate all systems (one safety division) on each unit necessary for coping with a station blackout for the required SBO duration of 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />.
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.
Procedure Description 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 of the blacked out unit.
- 2.
Procedure changes associated with any modifications required after assessing coping capability per NUMARC 87-00, Section 7.
Proposed Modifications Addition of an AAC Power Source and Bus Tie Preliminary plans for two AAC diesels are discussed as follows.
These are not finalized, but provide information on our intentions relative to this installation.
Two non-safety related diesel generators will be added to provide a fully capable AAC power source (as characterized by the NRC) to each of the blacked-out units.
They will be sized similar to the existing EDGs and each will have a net output of approximately 3000KW.
The generators will be RKS/kwd:001105 -
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capable of being electrically connected to any of the station's four (two per unit) emergency buses.
They will be controlled from the Control Room and will be available to accept loads within one hour from initiation of an SBO event.
Specifically, one AAC diesel will normally align to transfer bus F (emergency bus lH or 2J) and the second AAC diesel will normally align to either transfer bus Dor E (emergency bus lJ or 2H).
The attached one-line diagram should be referenced.
Parallel operation of the two AAC diesels is not currently planned.
The AAC diesels will be located in their own building.
The diesel building will be designed to meet or exceed the requirements of the Uniform Building Code and the Building Officials and Code Administrators (BOCA) Code.
The building will be designed to limit ambient temperature to 120°F, and will also have space heaters to maintain an acceptable temperature when the diesels are not running.
Fuel oil for the each diesel will be stored in a separate day tank in the diesel building.
Each tank will be sized to allow the diesel to run for the SBO duration.
The diesel building will include Motor Control Centers (MCCs) to power loads required for diesel operation and for normal building loads.
Loads required for diesel operation will be powered from the diesel when off site power is lost.
Currently, analyses have been prepared to demonstrate the ability of the blacked out unit to cope for one hour prior to availability of the AAC source.
This analysis has determined that there is one function that must be performed within the first hour for which AC power is required.
This is the closing of one of the condenser inlet or outlet valves on each of the four water boxes on each unit, eight valves in total.
By energizing one bus on each unit and closing one valve for each water box within thirty minutes, adequate canal inventory will be maintained for the SBO duration.
All actions to restore power and close these valves will be performed from the control room.
In order to ensure timely availability of the AAC power source as required by the above condition, and due to the limited space available in the Surry control room, automatic connection of the AAC diesels to a pre-selected emergency bus may be desired.
In addition, the existing automatic load sequencing for an emergency bus may be used in connecting loads to the bus once it is powered by the AAC machine.
Based on appendix B of NUMARC 87-00, section B.7, NRC approval may be needed to allow automatic connection of the AAC source to the bus and automatic loading of the bus.
Therefore, it is requested that the NRC approve the use of RKS/kwd:001105 -
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such a design or inform Virginia Power of additional information needed to support such an approval.
The time required to procedurally determine that the station is experiencing a station black out, start the diesels, close the various breakers necessary to power the emergency buses and close the condenser valves without automation has not been determined.
However, it could exceed the time available if automation is not allowed.
In addition to the new generators, the conditional ability to electrically tie transfer buses D and E together will be provided.
The tie between the buses will be sized to carry worst case loading of one emergency bus.
The purpose of this tie will be to provide additional system flexibility during a scheduled or forced outage of Reserve station Service Transformer "A" or "B. 11 Virginia Power is continuing to review the installation of the AAC diesels and SBO coping requirements.
Open items from this review will be addressed as the study progresses.
Completion of this review may determine that additional modifications are needed.
Major changes or additions to the approach previously described are not expected.
D.
Review of system Adequacies
- 1.
- 2.
Condensate Inventory For Decay Heat Removal It has been determined that the minimum permissible Emergency Condensate Storage Tank level as required by Technical Specifications exceeds the required quantity for coping with a 4 or 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> station blackout.
No plant modifications and only minor procedure revisions are necessary for condensate inventory.
Class lE Battery Capacity A battery capacity analysis 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.
Surry has two Class lE batteries per unit, one battery per safety train.
Each battery provides two instrument channels that provide various low-voltage indication, control and protection functions.
Using the proposed AAC sources, one battery charger (one train) will be available within one hour on each blacked out unit.
RKS/kwd:001105 -
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3 *
- 4.
Therefore, two channels of instrumentation will be available for the entire 4 hour4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> period.
Compressed Air Compressed air capabilities are presently under review.
Based on the different combinations of emergency buses that may be available from the AAC sources, several options exist for resolution of this issue.
The results of our continuing review of this item will be provided in a later letter.
Effects of Loss of Ventilation The environmental conditions for those areas which are vital for core cooling and decay heat removal were
.examined with respect to loss of ventilation following an SBO.
In general, those areas that have no safety-related ventilation or only one safety-related train of ventilation were analyzed for the resulting temperature profile for the entire SBO duration (4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />).
For those areas which have or will have multiple (Auxiliary Building) or redundant (Control Room, Emergency switchgear Room, Containment, etc.)
ventilation, the loss of ventilation transient was only examined for the period of time until the AAC power source is started and one emergency bus is re-energized (one hour).
Specific areas examined were:
Control Room Emergency Switchgear Room Charging Pump Cubici.es Turbine Driven Auxiliary Feedwater Pump Room (incomplete)
Emergency Service Water Pump House Containment For all areas except Containment and the Emergency Service Water Pump house, a computer code titled "Three-D" was employed in lieu of the NUMARC methodology.
The numerical differences between the two methodologies are minor.
Three-D was employed in order to provide time temperature curves for each compartment and to provide additional analysis capabilities.
In addition, more rigorous reviews of heat loads and heat RKS/kwd:001105 -
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sinks were conducted to support these new analysis.
These reviews resulted in reductions of the overall temperatures expected during a blackout (as compared to our previous submittal).
The following describes the loss of ventilation scenario for each area, the resulting temperatures and the high temperature consequence on personnel and equipment (if any).
- a.
Control Room The Control Room complex consists of an open area which contains the Unit 1 and 2 control boards and individual rooms for each unit's air conditioning equipment, computer equipment and logic equipment.
The HVAC system for the Control Room and Emergency Switchgear Room at Surry is presently being modified in accordance with plans that have been previously reviewed with the NRC.
The analyses performed for SBO are based on the HVAC system as it will exist upon completion of these modifications.
The initial temperature of the area is its normal operating temperature of 75°F.
The nature of the loads in the control room complex are electrical which energize control type equipment rather than power type equipment.
During the SBO, heat loads to the area result from the cooling off of this previously energized, warm electrical equipment plus the emergency DC loads and lighting.
Also considered are area temperatures which are adjacent to the complex but at a higher normal operating temperature, such as the turbine building and cable vault.
Considering these loads, during the first hour after SBO initiation, the maximum temperatures are predicted to reach 98.4°F in the main control room and 99.5°F in the computer room.
These temperatures are not considered detrimental to equipment or personnel in the area.
Restoration:
Following completion of the modifications discussed above, the required air handling and chilled water equipment can be powered from a single emergency bus (i.e., safety train) on each unit.
Therefore, when AAC power becomes available (within one hour), the control room complex will return to normal temperature conditions.
RKS/kwd:001105 -
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- b.
Emergency switchgear Room The emergency switchgear room (ESGR) complex consists of individual areas for the switchgear and support equipment, separated by concrete walls with an open passageway in the wall between the areas. Separate areas are provided for switchgear and relay equipment, instrument racks and battery equipment.
The loss of ventilation scenario for the ESGR is similar to that of the control room due to the two areas being served by the same chilled water system.
The normal maximum temperature of ao°F is assumed as the initial temperature.
The nature of the loads in the switchgear area are electrical and includes such items as: 480 volt load centers, motor control centers, 4 KV switchgear, battery chargers, 4160 volt transformers and power cable.
Although this equipment is de-energized during the SBO, just prior to the event it was operational, and the heat load to the area results from the residual heat given off as these items cool down.
In addition, heat to the SBO unit ESGR given off from the components powered from the emergency DC power system, such as computer inverters, load shedding equipment and emergency lighting was included. Also considered are area temperatures which are adjacent to the complex but at a higher normal operating temperature such as the turbine building and cable vault.
The following summarizes the maximum temperatures experienced during the SBO:
Switchgear Rooms Instrument Rack Room 109.7°F 108.5°F In comparing these temperatures to those limits listed in NUMARC 87-00 Appendix F, neither of the above results are considered to be detrimental from an operability or occupational standpoint.
Restoration:
Following completion of the modifications discussed in section "a" above, the required air handling and chilled water equipment can be powered from a single emergency bus (i.e.,
safety train) on each unit. Therefore, when AAC power becomes available (within one hour), the switchgear area will return to normal temperature conditions.
RKS/kwd:001105 -
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- c.
- d.
Charging Pump Cubicle The only equipment within the charging pump cubicles are the charging pumps and associated valves. There are three pumps for each unit, each in its own separate concrete cubicle.
The cubicle's exhaust ventilation system is handled by the auxiliary building central exhaust fans.
These fans also take exhaust air from other auxiliary building areas.
The central exhaust fans are powered from the lH and lJ emergency buses.
An analysis was performed for one hour assuming no charging pump motor was operating without the Auxiliary building exhaust fan in operation.
The maximum temperature in the cubicle is predicted to be only 135.6°F.
Restoration:
Once the AAC diesels are started and restore power to the emergency buses, a minimum of one of the two building exhaust fans can be energized.
With one fan in operation, temperatures will return to about 120°F or less.
Auxiliary Feedwater Pump House The temperature profile analysis for the Auxiliary Feedwater pump house is incomplete at the present time.
Further analysis of this area is being performed.
The results will be provided in a later letter.
- e.
Emergency Service Water Pump House The emergency service water pump house contains three diesel driven emergency service water pumps.
The ventilation system for this room is a gravity system which contains four intake dampers (mounted in the wall) and one exhaust damper (mounted in the ceiling).
These dampers are manually operated and fail as-is on a loss of AC power.
During normal operation, an operator is directed to the ESWPH to start an ESW Pump and manually open.the dampers.
- f.
Containment The SBO will result in some increased temperature in the containment due to normal RCS heat load and RCP seal leakage.
Westinghouse has performed RKS/kwd:001105 -
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analysis on large dry atmospheric containments for 2, 3 and 4 loop configurations. Two of the cases examined in their analysis shbws that in the first 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> even the larger leak rate results only in a pressure rise on the order of 3 psi and an increase in containment temperature of less than 40°F.
The Westinghouse calculations were done assuming large RCP seal leakage rates and that heat was removed from the atmosphere only by passive containment heat sinks.
Ultimately, should the seal leak situation not be terminated, the heat sinks will saturate and containment conditions could again increase; however, the times required for this to occur are beyond the times when core cooling problems would occur due to lost RCS inventory.
Surry is a small subatmospheric containment whose free volume is approximately 60 percent of a typical large containment.
This difference coupled with the lower assumed leakage rate (23 gpm/seal vs. 300 gpm/seal) would combine to produce temperatures and pressures much less than those Westinghouse reported.
Cooling may be restored when AAC power becomes available.
- 5.
Containment Isolation
- 6.
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 availability of the blacked-out unit's Class lE power supply.
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 sources power the necessary RCS make-up system (charging) to maintain adequate reactor coolant inventory to ensure that the core is cooled for 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />.
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 for reactor coolant inventory loss under SBO conditions do not result in core uncovery in one hour.
Therefore, make-up systems RKS/kwd:001105 -
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- 7.
to the RCS are not required to maintain core cooling under natural circulation (including reflux boiling) for the initial hour period.
Canal Inventory The circulating water system provides cooling water for the main condensers and service water system for both units.
In order to conserve canal inventory one condenser isolation valve for each water box must be closed within thirty minutes.
Additionally, any open component cooling water and bearing cooling water valves that have not been re-powered by the AAC sources must be manually closed after one hour.
By performing these actions, canal inventory will be maintained at a level which is adequate to provide net positive suction head for the heat sinks required for SBO.
E.
Schedule Virginia Power is continuing to review the effort required to install and make operational the facilities needed to bring Surry into compliance with 10CFR50.63.
This is a major effort which will require significant resources and detailed coordination to allow implementation.
It is anticipated that all presently identified SBO modifications and procedure changes will be completed within about 5 years following receipt of favorable notification by the Director, Office of Nuclear Regulation in accordance with 10CFR50.63 (c) (3), regarding Virginia Power's approach to compliance with 10CFR50.63 as documented herein or in further correspondence.
Efforts to proceed with the implementation of these modifications and procedure changes will not begin until such notification is provided.
An installation time exceeding two years is necessary due to the following:
- 1.
The high complexity of the proposed modification.
- 2.
Equipment ordering and fabrication lead times.
- 3.
The number of refueling outages required to make the necessary equipment modifications and tie ins.
- 4.
The amount of procedure changes and training that will be necessary to ensure proper operation of the new AAC power source.
RKS/kwd:001105 -
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Response to Station Blackout Rule North Anna Power Station Virginia Electric and Power Company
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 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.
In previous Virginia Power letters, serial number 88-414 dated April 17, 1989, 88-414A dated April 20, 1989 and 88-414B dated March 30, 1990, we proposed to use an existing North Anna emergency diesel generator on the non-blacked out unit as an Alternate AC (AAC) source for the blacked out unit.
This approach was found unacceptable by the NRC as detailed in an October 18, 1990 letter and attached Safety Evaluation Report (SER) and Technical Evaluation Report (TER).
Following this rejection, Virginia Power issued letter 90-661 dated November 29, 1990 which informed the NRC of our intention to review the RKS/kwd:001105 -
1
feasibility of installing a non-safety grade diesel at North Anna to act as an AAC source.
Virginia Power agreed to provide supplemental information by April 30, 1991 and report quarterly thereafter on this review.
Accordingly, Virginia Power has further evaluated North Anna 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, we currently plan to install a non-safety grade diesel generator as AAC power source 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 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />.
- 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 11 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 112. 11 (Section 3.2.1, Part lC, p3-7)
- d.
The offsite power system is in the "I 1/2 11 group.
(Section 3.2.1, Part lD, p3-10)
The TER issued with the NRC letter and SER on October 18, 1990, on page 7 indicated that:
"Upon the loss of RSST "A," "B," or "C," (loss of the preferred source), the connected emergency bus(es), i.e. lH, 2H, lJ or 2J, can only be powered through manual closure of circuit breakers which tie independent trains together."
With the proposed addition of a bus tie between transfer buses "D" and "E" (reference section C), an alternate offsite source will be manually available to each emergency bus should a RSST be lost.
RKS/kwd:001105 -
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Upon the loss of RSST "A," emergency bus lJ can either be fed from station service bus 2B, or from transfer bus E (RSST "B") through the proposed D to E bus tie.
Upon the loss of RSST "B," emergency bus 2H can be fed from transfer bus D (RSST "A") using the proposed D to E bus tie.
Upon the loss of RSST "C, 11 emergency buses lH and 2J can be fed from bus lB.
Bus 2J would be fed via transfer bus F which in turn would be backfed from bus lH (and ultimately bus lB).
It should be noted that at North Anna, the emergency buses are normally fed from their preferred sources and do not realign upon a unit trip.
This is not the case at many stations where the emergency buses are normally fed from the unit and transfer to the start up transformers upon a unit trip.
For this reason, I3 of NUMARC 87-00 and Reg. Guide 1.155 is not considered applicable for North Anna.
The presently installed capabilities and those proposed for compliance with the SBO rule reinforce the Virginia Power position that the plant should be an I 1/2.
However, it should be noted that there is no adverse impact to the overall site evaluation if the plant is classified I3.
- 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, p3-15)
- 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, p3-15)
- 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.
A review of the SERs issued for Commonwealth Edison's Dresden Units 2 and 3 and Quad Cities Units 1 and 2 indicate that it is acceptable to reduce the required EDG reliability from.975 to.95 provided that RKS/kwd:001105 -
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l conditions are similar to the Dresden design and contingent upon the following:
- a.
"The AAC power source is sized to power the complete contingent of safety-related and nonsafety-related loads associated with one safety division of each unit simultaneously that are normally expected to be available for the loss of offsite power (LOOP) condition."
- b.
"The AAC power source is connectible to all EDG buses of all the units."
- c.
"The AAC source should be diverse from existing EDG's.
Lack of diversity must be justified by addressing how common mode failures are minimized."
Since the Dresden site is an EAC Group D design, a station blackout must be postulated to affect both units (NUMARC 87-00, section 2.3.1(2)).
Accordingly, an AAC power source will be installed with sufficient capacity to power one safety division of each unit in the event of a LOOP.
At North Anna, an AAC will be installed which will have sufficient capacity to power the LOOP loads associated with one safety division of either Unit.
This is consistent with the above criterion since a station blackout at North Anna is postulated to occur on only one unit (NUMARC 87-00, section 2.3.1(2) and 10CFR50.2).
This arrangement provides reliability equivalent to that afforded by the proposed Dresden design.
At Dresden, the AAC source connects to a single bus from which ties are made to the safety-related buses of each unit.
This provides AAC access to all EDG buses at the site.
The proposed North Anna design would permit the connection of the AAC source to the three transfer buses that supply power to the safety-related buses at the station.
This design similarly permits the AAC source to access all EDG buses of each unit consistent with the above criteria.
The proposed North Anna design provides both diversity and independence (Reg. Guide 1.155, section 3.2.5) among the AAC and EDGs as follows:
The AAC diesel will be a more recent design than the existing EDGs.
The EDGs and AAC diesel will not share common structures.
RKS/kwd:001105 -
4
I J
B.
e e
The EDGs and AAC diesel will not share common support systems (e.g. fuel oil day tank, cooling, control power, etc.)
Power and control cables for the EDGs and AAC diesel will be separated.
The EDGs and AAC diesel will not share mechanical and electrical protective devices.
The AAC diesel will not normally be connected to the EOG buses or the transfer buses.
- 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.
The AAC power source will be available to the blacked-out unit within one hour following the onset of a station blackout event.
This AAC source will have sufficient capacity to operate all systems (one safety division) necessary for coping with a station blackout for the required SBO duration of 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />.
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.
Procedure Description 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 of the blacked out unit.
- 2.
Procedure changes associated with any modifications required after assessing coping capability per NUMARC 87-00, Section 7.
RKS/kwd:001105 -
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C.
Proposed Modifications Addition of an AAC Power Source and Bus Tie Preliminary plans for an AAC diesel are discussed as follows.
These are not finalized, but provide information on our intentions relative to this installation.
A non-safety related diesel generator will be added to provide a fully capable AAC power source (as characterized by the NRC) to the blacked-out unit.
It will be sized similar to the existing EDGs and will have a net output of approximately 3000KW.
The generator will be capable of being electrically connected to any of the station's four (two per unit) emergency buses.
It will be controlled from the Control Room and will be available to accept loads within one hour from initiation of an SBO event.
Specifically, the output of the new AAC diesel will be connected to the station's three, 4KV transfer buses (D, E &
F) which in turn will enable it to be connected to any emergency bus (reference the attached one-line).
The AAC diesel will be located in its own building.
The diesel building will be designed to meet or exceed the requirements of the Uniform Building Code and the Building Officials and Code Administrators (BOCA) Code.
The building will be designed to limit ambient temperature to 120°F, and will also have space heaters to maintain an acceptable temperature when the diesel is not running.
Fuel oil for the diesel will be stored in a day tank in the diesel building.
The tank will be sized to allow the diesel to run for the SBO duration.
The diesel building will include Motor Control Centers (MCCs) to power loads required for diesel operation and for normal building loads.
Loads required for diesel operation will be powered from the diesel when off site power is lost.
Currently, analyses have been prepared to demonstrate the ability of the blacked out unit to cope for one hour prior to availability of the AAC source.
However, based on further review, Virginia Power may determine that North Anna can be classified as a 10 minute AAC plant.
In any case, the existing automatic load sequencing for an emergency bus may be used in connecting loads to the bus once it is powered by the AAC machine.
Based on appendix B of NUMARC 87-00, section B.7, NRC approval may be needed to allow automatic loading of the bus.
Therefore, it is requested that the NRC approve the use of such sequencing or inform Virginia Power of additional information or design requirements needed to support such an approval.
RKS/kwd:001105 -
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e In addition to the new generator, the conditional ability to electrically tie transfer buses D and E together will be provided.
The tie between the buses will be sized to carry worst case loading of one emergency bus.
The purpose of this tie will be to provide additional system flexibility during a scheduled or forced outage of Reserve Station Service Transformer "A" or "B. 11 Virginia Power is continuing to review the installation of the AAC diesel and SBO coping requirements.
Open items from this review will be addressed as the study progresses.
Completion of this review may determine that additional modifications are needed.
Major changes or additions to the approach previously described are not expected.
D.
Review of System Adequacies
- 1.
2
- Condensate Inventory For Decay Heat Removal It has been determined that the minimum permissible Emergency Condensate Storage Tank level as required by Technical Specifications exceeds the required quantity for coping with a 4 or 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> station blackout.
No plant modifications and only minor procedure revisions are necessary for condensate inventory.
Class lE Battery Capacity A battery capacity analysis 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.
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 provides various low-voltage indication, control and protection functions.
Using the proposed AAC source, two battery chargers (one train) will be available within one hour on the blacked out unit.
Therefore, two channels of instrumentation will be available for the entire 4 hour4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> period.
RKS/kwd:001105 -
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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 lE 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.
- 4.
Effects of Loss of Ventilation The environmental conditions for those areas which are vital for core cooling and decay heat removal were examined with respect to loss of ventilation following an SBO.
In general, those areas that have no safety-related ventilation or only one safety-related train of ventilation were analyzed for the resulting temperature profile for the entire SBO duration (4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />).
For those areas which have multiple (Auxiliary Building) or redundant (Control Room, Emergency Switchgear Room, Containment, etc.) ventilation, the loss of ventilation transient was only examined for the period of time until the AAC power source is started and one emergency bus is re-energized (one hour).
Specific areas examined were:
Control Room (one unit side only)
Emergency Switchgear Room(one unit side only)
Turbine Driven Auxiliary Feedwater Pump Room Charging Pump Cubicles Service Water Pump House Service Water Valve House Containment For all areas except the Service Water Valve House and Containment, a computer code titled "Three-D" was employed in lieu of the NUMARC methodology.
The numerical _differences between the two methodologies is RKS/kwd:001105 -
8
,l.
e e
minor.
Three-D was employed in order to provide time temperature curves for each compartment and to provide additional analysis capabilities.
In addition, more rigorous reviews of heat loads and heat sinks were conducted to support these new analyses.
These reviews resulted in reductions of the overall temperatures expected during a black out (as compared to our previous submittal).
The following describes the loss of ventilation scenario for each area, the resulting temperatures and the high temperature consequence on personnel and equipment (if any).
- a.
Control Room The Control Room complex consists of an open area which contains the Unit 1 and 2 control boards and individual rooms for each unit's air conditioning equipment, computer equipment and logic equipment.
Two independent air cooling systems and chilled water systems are provided for each unit's portion of the control room plus its computer and logic equipment areas.
Each unit also has a spare chiller.
The initial temperature of the area is its normal operating temperature of 75°F.
The nature of the loads in the control room complex are electrical which energize control type equipment rather than power type equipment.
During the SBO, heat loads to the area result from the cooling off of this previously energized, warm electrical equipment plus the emergency DC loads and lighting.
Also considered are area temperatures which are adjacent to the complex but at a higher normal operating temperature, such as the turbine room and cable vault.
Considering these loads, during the first hour after SBO initiation, the maximum temperatures are predicted to reach 95.2°F in the main control room and 98.3°F in the computer room.
These temperatures are not considered detrimental to equipment or personnel in the area. It is noted that both units nave a shared control room and that the non-blacked-out unit air conditioning units are still functioning.
No credit for this cooling effect has been considered in this analysis.
Restoration:
The required air handling and chilled water equipment can be powered from a RKS/kwd:001105 -
9
- b.
single emergency bus (i.e., safety train).
Therefore, when AAC power becomes available (within one hour), the control room complex will return to normal temperature conditions.
Emergency Switchgear Room The emergency switchgear room (ESGR) complex consists of individual areas for the switchgear and support equipment, separated by concrete walls with an open passageway in the wall between the areas. Separate areas are provided for each unit's air conditioning chillers, switchgear and relay equipment, instrument racks and battery equipment.
Two independent air handling and cooling systems and chilled water systems are provided for each unit's ESGR.
Each unit also has a spare chiller.
The loss of ventilation scenario for the ESGR is similar to that of the control room due to the two areas being served by the same chilled water system.
The normal maximum temperature of so°F is assumed as the initial temperature.
The nature of the loads in the switchgear area are electrical and includes such items as: 480 volt load centers, motor control centers, 4 KV switchgear, battery chargers, 4160 volt transformers and power cable.
Although this equipment is de-energized during the SBO, just prior to the event it was operational, and the heat load to the area results from the residual heat given off as these items cool down.
In addition, heat to the SBO unit ESGR given off from the components powered from the emergency DC power system such as computer inverters, load shedding equipment and emergency lighting was included. Also considered are area temperatures which are adjacent to the complex but at a higher normal operating temperature such as the turbine room and cable vault.
The following summarizes the maximum temperatures experienced during the SBO:
Switchgear and Relay Rooms Instrument Rack Room 100.1°F 93.6°F In comparing these temperatures to those limits listed in NUMARC 87-00 Appendix F, neither of the RKS/kwd:001105 -
10
~
- c.
e above results are considered to be detrimental from an operability or occupational standpoint.
Restoration:
The required air handling and chilled water equipment can be powered from a single emergency bus (i.e., safety train).
Therefore, when AAC power becomes available (within one hour), the switchgear area will return to normal temperature conditions.
Charging Pump Cubicle The only equipment within the charging pump cubicles are the charging pumps and associated valves. There are three pumps for each unit, each in its own separate concrete cubicle.
The cubicle's exhaust ventilation system is handled by the auxiliary building central exhaust fans.
These fans also take exhaust air from other auxiliary building areas.
The central exhaust fans are powered from the lH, lJ and 2J emergency buses.
Therefore, it is possible that the charging pump powered from the 2H bus could operate without having an Auxiliary Building Central Exhaust Fan operating.
For this condition credit was taken for the 2H charging pump motor's internal fan providing cooling to the motor windings.
By itself this mode of operation could result in overheating the motor, however, the relatively short duration of this operation (one hour until at least one exhaust fan is restored and four hours until end of event) coupled with the presence of some air flow is not expected to adversely affect the operation of the motor.
As a result of the operation of the fan on the motor, the heat from the motor is directed into the ductwork and not into the cubicle.
Therefore, cubicle temperature does not increase significantly.
When the central exhaust fans are not running, their associated motor operated dampers are closed (they are fail closed dampers).
In this situation, the charging pump fans pressurize the ductwork and distribute the air into the other cubicles serviced by the central exhaust system. A review of the ductwork system layout indicates this hot air would be fairly evenly distributed and its effects on those areas would be negligible.
RKS/kwd:001105 -
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Restoration:
Once the AAC diesel is started and restores power to an emergency bus, a minimum of one of the three building exhaust fans can be energized.
Although one fan supplies less than the design flow rate, it is still greater than the air flow rate that existed with just the motor fan running and as such does not adversely affect the pump cubicles temperature.
- d.
Auxiliary Feedwater Pump House The Auxiliary Feedwater Pump House (AFPH) contains two motor driven auxiliary feedwater pumps.
The turbine driven pump room is the only room analyzed in the AFPH.
The area of the motor driven pumps is ventilated by two redundant fans each connected to an independent emergency power source.
If during SBO, emergency power is available to operate one of the motor driven pumps, that pump's respective ventilation fan will also be powered keeping the resulting room temperature within the acceptable range.
The area of the turbine driven pump is ventilated by one fan connected to one emergency bus (H) with no provisions to transfer its power source to the other emergency bus (J).
Typically the auxiliary feedwater pumps only operate following a unit trip, therefore just prior to an SBO event none of the equipment would have been in operation and the area temperatures would be approximately the same as the outdoor air temperature.
During an SBO, there is no guarantee that the ventilation fan for the turbine driven Auxiliary Feedwater pump operates as it is only powered from an H bus. Therefore, a four hour analysis was performed based on a conservative maximum starting temperature of 104°F.
While this pump operates, heat is given off to the room due to steam supply, drain, exhaust piping and the turbine pump casing.
The maximum calculated area temperature is 127°F after four hours.
This temperature is not detrimental to the operation of the turbine driven pump, however it does exceed the NUMARC limit of 120°F for habitability of personnel required to perform additional emergency functions. In this case, the personnel door may be opened to reduce area temperature and allow any required operator actions.
RKS/kwd:001105 -
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- e.
Service water Pump House General e
The service water pump house (SWPH) is a common building which contains four service water pumps, a diesel driven fire pump, screenwash pumps, four travelling screen motors, and two air compressors.
The ventilation system for this area is designed to limit the room temperature to 120°F.
Two fans are installed, one powered from emergency bus lH, the other powered from bus lJ.
Conditions During SBO Assuming Unit 1 is blacked out and no ventilation is available for the first hour, an analysis of the SBO effects on the SWPH was performed.
The maximum expected room temperature is 152.9°F.
A review of NUMARC 87-00 Appendix F reveals that this temperature would not be detrimental to the operation of the SWPs and since no operator action is required in this area, this temperature is acceptable.
Once power is restored to a Unit 1 emergency bus, cooling will be available and temperatures will be reduced.
- f.
Service Water Valve House General The service water valve house encloses piping and valving for eight 18 inch service water pipes.
It does not contain any operating equipment except motor operated valves.
There are two major areas within the building.
Each area has redundant fans.
Conditions During SBO The eight 18 inch pipes passing through the service water pump house contain reservoir water at maximum design temperature of 95°F and at SBO the room temperature could be slightly above this or 97°F.
There will be no increase in heat load conditions for this area when passing into the SBO mode from normal operating conditions; therefore, during the first hour of SEO, the room temperature will remain the same as during normal conditions (97°F).
This temperature is well below the upper normal environment temperature of 120°F.
RKS/kwd:001105 -
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- 5.
6 *
- g.
Containment The SBO will result in some increased temperature in the containment due normal RCS heat load and RCP seal leakage.
Westinghouse has performed analysis on large dry atmospheric containments for 2, 3 and 4 loop configurations. Two of the cases examined in their analysis show that in the first ten hours even the larger leak rate results in a pressure rise on the order of 3 psi and an increase in containment temperature of less than 40°F.
The Westinghouse calculations were done assuming large RCP seal leakage rates and that heat was removed from the atmosphere only by passive containment heat sinks.
Ultimately, should the seal leak situation not be terminated, the heat sinks will saturate and containment conditions could again increase; however, the times required for this to occur are beyond the times when core cooling problems would occur due to lost RCS inventory.
North Anna is a small subatmospheric containment whose free volume is approximately 60 percent of a typical large containment.
This difference coupled with the lower assumed leakage rate (23 gpm/seal vs. 300 gpm/seal) would combine to produce temperatures and pressures much less than those Westinghouse reported.
Cooling may be restored when AAC power becomes available.
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 availability of the blacked-out unit's Class lE power supply.
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 <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />.
RKS/kwd:001105 -
14
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.
E.
Schedule Virginia Power is continuing to review the effort required to install and make operational the facilities needed to bring North Anna into compliance with 10CFR50.63.
This is a major effort which will require significant resources and detailed coordination to allow implementation.
It is anticipated that all presently identified SBO modifications and procedure changes can be completed within 5 years following receipt of favorable notification by the Director, Office of Nuclear Regulation in accordance with 10CFR50.63 (c) (3), regarding Virginia Power's approach to compliance with 10CFR50.63 as documented herein or in further correspondence.
Efforts to proceed with the implementation of these modifications will not begin until such notification is provided.
An installation time exceeding two years is necessary due to the following:
- 1.
The high complexity of the proposed modification.
- 2.
Equipment ordering and fabrication lead times.
- 3.
The number of refueling outages required to make the necessary equipment modifications and tie ins.
- 4.
The amount of procedures changes and training that will be necessary to ensure proper operation of the new AAC power source.
RKS/kwd:001105 -
15
~: _-__ c,.,:__ ~ ------------. ----~~- ~~ ;;~~ -;~~~ ------------------ --------------------------------------------------.. -----T-~ -~~;;~~ -~i- ~~---- -1
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REF. 11715-FE - 188.
NEW AAC EQUIPMENT WILL BE NON-SAFETY RELATED VIRGINIA POWER NUCLEAR EIGINEERUli SERYICES tlJRTH CAROLINA POWER RICtMN>.VIRGINIA ONE LINE DIAGRAM STATION BLACKOUT AAC NORTH ANNA POWER STATION DRAWi
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