ML18153D331
| ML18153D331 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 05/10/1993 |
| From: | Stewart W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 93-292, NUDOCS 9305140190 | |
| Download: ML18153D331 (8) | |
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VIRGINIA ELECTRIC AND POWER COMPANY RICHMOND, VIRGINIA 23261
- May 10, 1993 United States Nuclear Regulatory Commission Attention: Document Control Desk Washington, D. C. 20555 Gentlemen:
VIRGINIA ELECTRIC AND POWER COMPANY SURRY POWER STATION UNITS 1 AND 2 STATION BLACKOUT (SBO) ALTERNATIVE DESIGN Serial No.
NL&P/GDM Docket Nos.
License Nos.93-292 R2' 50-280 50-281 DPR-32 DPR-37 As discussed at the station blackout technical meeting between the NRC and Virginia Electric and Power Company on April 21, 1993, we are proposing an alternative approach for responding to a station blackout event from that previously approved by the NRC. Our submittals of April 30 and July 31, 1991 and February 1 O, 1992 (Serial Numbers91-242, 91-402, and 91-738A, respectively) provided our previous plan for mitigating a station blackout. This plan involved the installation of two non-safety related, alternate AC (AAC) diesel generators that would be available to power the loss of offsite power (LOOP) loads for both units in the event of a SBO. Our SBO design was approved in your supplemental safety evaluation report (SSER) dated May 12, 1992.
Subsequent to the issuance of the NRC SSER, we have performed a reevaluation of our planned SBO modifications. This reassessment was prompted by the following considerations:
- 1. Larger-than-expected capacity diesel generators were available for procurement at a cost effective price (3640 KW actual vs. 3000 KW conceptual).
- 2. Connection of the 'F' transfer bus in the current SBO design would be very complex since this bus is shared by both units.
Additionally, removing the 'F' transfer bus from service to facilitate the tie-in of the AAC source would require regulatory relief to avoid a two-unit outage. This relief would be necessary to permit the emergency bus loads normally carried by the 'F' transfer bus to be carried by an emergency diesel generator for an extended period of time.
- 3. Comparison of LOOP loads vs. SBO loads was performed and a determination was made to power only SBO loads.
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- 4. Comparison of SBO loads vs. AAC capacity revealed that one AAC diesel generator can carry the required SBO loads for both units for the required duration.
As a result of our reevaluation, we are proposing to revise our SBO design to use only one AAC diesel generator instead of the two diesels previously planned.
This alternative design meets the requirements of 1 O CFR 50.63 and the criteria specified in NUMARC 87-00, Appendix 8, Alternate AC Power Criteria, including those cases where Regulatory Guide (RG) 1.155, Station Blackout, takes precedence.
The alternative design results in only limited changes to our previous submittals. These changes are discussed in the attachment. The alternative SBO design also permits the use of the North Anna AAC diesel building design at Surry, and the cancellation of the order for one AAC diesel generator and its auxiliary equipment. Furthermore, with the alternative design, the 'F' transfer bus tie-in is no longer required thus eliminating the complexity and need for regulatory relief associated with implementation.
In our letter dated March 17, 1992 (Serial Number 91-7388), we requested a completion schedule that allowed implementation of the SBO modifications by the end of the 1996 Unit 2 refueling outage.
This schedule was approved in the SSER discussed above.
The completion schedule for implementation of the SBO modifications will not be affected by implementation of the alternative design and may be improved. We will advise you if we anticipate completing the modifications during an earlier outage.
We currently plan to install the AAC source in a new building to be located outside the protected area. However, we are also evaluating the potential to install the AAC source in the station's existing spare fourth Emergency Diesel Generator Room.
Due to the engineering and procurement efforts presently underway, a timely response is requested to realize the benefits of the alternative approach and continue on the current completion schedule.
If you have any questions or require additional information, please contact us.
Very truly yours,
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W. L. S ewart Senior Vice President - Nuclear
cc:
U. S. Nuclear Regulatory Commission Region II 101 Marietta Street, N. W.
Suite 2900 Atlanta, Georgia 30323 Mr. M. W. Branch NRC Senior Resident Inspector Surry Power Station
e ATTACHMENT STATION BLACKOUT DESIGN ALTERNATIVE SURRY POWER STATION
A.
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STATION BLACKOUT DESIGN ALTERNATIVE SURRY POWER STATION Station Blackout Duration (SSER Section 2.1)
The NRC Staff Evaluation included in the Supplemental SER dated May 12, 1992 concurred with Virginia Electric and Power Company's selection of the independence of offsite power group as I 1 /2, and that Surry was an offsite power group P2* plant with a coping duration of 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />. These determinations are not affected by the installation of one AAC diesel generator rather than two.
However, the selected EOG reliability target for the Surry Units has been changed from 0.95 to 0.975 due to the revised design.
Proposed AAC Power Source (SSER Section 2.2)
One non-safety related diesel generator will be added to provide an AAC power source to both blacked-out units. It will be sized larger than the existing EDGs and will have a 2000 hour0.0231 days <br />0.556 hours <br />0.00331 weeks <br />7.61e-4 months <br /> output rating of 3640 KW. The generator will be capable of being electrically connected to station emergency buses "2H" and "1 J" (Ref. Fig. 1 ). Also, the interrupting ratings of the existing 4KV emergency bus and the new 4KV AAC system breakers are adequate for AAC configurations.
Control power for the new AAC system breakers will be provided by separate batteries to be located in the AAC building.
The diesel generator will auto-start on loss of reserve power, and will auto-load to station transfer buses "D" and "E" as needed. Operators will then use existing breaker controls within the control room to restore ac power to station emergency buses "1 J" and "2H." The generator will be available to accept loads within 1 O minutes of the operator's determination that an SBO condition exists.
Manual control of the AAC diesel generator is available in the AAC building.
However, due to the starting and loading scheme described above, operator actions within the control room will be sufficient to restore power to one emergency bus in each unit. Operators will then operate selected SBO loads that are required to bring and maintain each unit in safe shutdown (non-Design Basis Accident) as defined in 1 O CFR 50.2.
The AAC source proposed for Surry will meet the applicable criteria specified in NUMARC 87-00, Appendix B. The single AAC source will meet the guidance provided in items B.8, B.9, B.10, 8.11, B.12, and 8.13, and R.G. 1.155 position 3.3.5.5 by utilizing the same design features which were outlined in our prior submittal dated February 10, 1992, with the following exceptions:
B.8 The AAC building will be relocated as discussed below.
e B.9 The AAC source is now sized to carry only the loads required for coping with a station blackout for the required duration. A list of these loads is provided as Table 1.
As noted above, the AAC diesel generator will be located in its own building.
The diesel building design and functional characteristics remain as they were except for two items:
- 1.
Only one diesel generator and its auxiliaries need to be housed, so the building layout is altered. The building will very closely resemble a similar building currently being designed for the North Anna SBO project.
- 2.
The building will be located outside, but adjacent to, the station's Protected Area, just south of Surry's Radwaste Facility.
The AAC Diesel Generator Building design will meet or exceed the requirements of the Virginia Building Code that is based on the Building Officials and Code Administrators (BOCA) Code. This should provide sufficient protection against the effects of likely weather related events but will not provide tornado missile protection or protection against a seismic event.
Station interface for AAC diesel support systems and power will be by enclosed ductway that will provide adequate protection from severe weather. Adequate electrical protection will also be provided for the generator portion of the AAC source and its associated equipment and cables.
This protection should prevent any single failure from simultaneously affecting any emergency AC source or preferred power source and the AAC source.
C.
Compressed Air (SSER Section 2.5)
D.
The method of providing compressed air has changed. Our previous intent was to provide a dedicated feeder from the AAC source to one of the station's service air compressors. Since we are now planning to power emergency bus "1 J" with the AAC source, and since an existing instrument air compressor is supplied by that bus, compressed air can be restored without the need for a dedicated feeder.
This instrument air compressor can be made available during SBO with operator actions outside the control room to align compressor cooling water from the (diesel-backed) fire main.
Proposed Modifications and Schedule Virginia Electric and Power Company has previously requested, and the NRC has approved, completion of the SBO modifications at Surry Power Station during the 1996 Unit 2 refueling outage. The scheduled completion of the SBO modifications is unaffected by implementation of the alternative design and may be improved upon. We will advise you if we anticipate completion of the SBO modifications during an earlier outage.
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F NOTES:
- 1. STATION SERVICE (SSl BUSES.
NORMALLY FED FROM THE STAT!
SERVICE TRANSFORMERS (SSTsl-WHICH ARE NOT SHOWN.
NEW AAC EQUIPMENT WILL BE NON-SAFETY RELATED VIRGINIA POWER NORTH CAROLINA POWER NUCLEAR ENGINEERING SERVICES RICHMOND,VIRGINIA DRWN DJJ ONE LINE DIAGRAM FIGURE 1 STATION BLACKOUT AAC SURRY POWER STATION CHKD ENGR APPD DATE DRAWING NO, S-6295A E- 0300 REV sHloFl A
e TABLE 1 - SURRY STATION BLACKOUT LOADING BO UNIT 1 - BUS 1J KW 4KV MDAFWPUMP 308 CHARGING PUMP 400 CCWPUMP 410 RIIRPUMP 217 480V PRF.sS HEAIBRS 200 AUX BIDG FL1REXHFAN 121 CONTAINMENT AIR FAN 102 MCCLOADING 702 XFMR LOSSES (1J) 8 XFMR LOSSES (1J-1) 19 10TAL UNIT 1 SBO LOADING BO UNIT 2 - BUS 2H 4KV MDAFWPUMP 308 CHARGING PUMP 400 CCWPUMP 410 RIIRPUMP 217 480V PRF.sS HEA1ERS 250 AUXBIDG FL1REXHFAN 121 CONTAINMENT AIR FAN 102 MCCLOADING 588 XFMR LOSSES (2H) 8 XFMR LOSSES (2H-1) 19 10TAL UNIT2 SBO LOADING COMMON LOADS MC BI.DG. LOADS TOTALAAC LOADING CAPACITY (2000 hr)
MARGIN,KW MARGIN,%
300 3640
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400 0
0 200 0
0 702 8
19 1329 0
400 0
0 250 121 0
588 8
19 1386 300 3015 3640 625 17.17 COMMENTS/NOTES Steam driven Aux. feed pump will operate SBO load is estimated to be 400KW Not required for coping Not required for coping 125 KW needed to maintain natural circ conditions per tech specs Only one is required (Shown on Unit 2)
Not required for coping MCC LOOP loads Press. Htrs. ( 400 KV A)
Based on 800 KVA loading (MCC)
Steam driven Aux. feed pump will operate SBO load is estimated to be 400KW Not required for coping Not required for coping 125 KW needed to maintain natural circ conditions per tech specs Not required for coping MCC LOOP loads Press. Htrs. ( 400 KV A)
Based on 800 KV A loading (MCC and Atr. Exh. Fan)
Current estimate NOTE: NRC has previously agreed to the use of only one Charging pump for both units during SBO (10/15/90 SER, para. 2.3.6}. Two charging pumps are included to reduce required operator actions.