ML18153C316

Provides Supplemental Response to NRC 900629 Ltr Re Electrical Crossties,Load Shedding on Nonblackout Unit & Emergency Diesel Generator Reliability.Emergency Diesel Generator Reliability Program in Place,Per Reg Guide 1.155

ML18153C316
Person / Time
Site:	Surry
Issue date:	08/01/1990
From:	Stewart W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
RTR-REGGD-01.155, RTR-REGGD-1.155 90-410, NUDOCS 9008060293
Download: ML18153C316 (9)

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' . e e VIRGINIA ELECTRIC AND POWER COMPANY RICHMOND, VIRGINIA 23261 August 1, 1990 U.S. Nuclear Regulatory Commission Serial No.90-410 Attention: Document Control Desk NL&P/RMN Washington, D.C. 20555 Docket Nos. 50-280 50-281 License Nos. DPR-32 DPR-37 Gentlemen:

VIRGINIA ELECTRIC AND POWER COMPANY SURRY POWER STATION UNITS 1 AND 2 STATION BLACKOUT SUPPLEMENTAL RESPONSE We have received your June 29, 1990 letter which asked us to supplement or modify our previous station blackout submittal concerning three areas: electrical crossties, load shedding on the non-blackout (NBO) unit, and EDG reliability. This letter provides our response.

We understand that the electrical crosstie described in our April 17, 1989 letter is considered unacceptable because, under some circumstances, it may be necessary to interconnect both trains of the emergency busses in the NBO unit. To address this concern, we intend to install a non-safety grade, manually operated crosstie between transfer busses D and E. This new crosstie would enable us to connect emergency busses 1J and 2H. Transfer bus F could be used to connect emergency busses 1H and 2J, as described in our original submittal. Therefore, no matter which bus is energized in the NBO unit, power can be transferred to the blackout (BO) unit without interconnecting the redundant trains of emergency power in the NBO unit.

Our original submittal used a load management scheme to reduce non-essential loads in the NBO unit. The additional diesel capacity was then used to power certain loads in the blackout unit which we considered desirable, but not essential. We now understand that the NRC staff's position is that loads in the NBO unit that would normally be available during a loss of offsite power must be capable of being powered from the alternate AC supply. Accordingly, we have revised our loading scheme. We now propose to use a charging pump mechanical cross connect that will allow one charging pump to supply both units. This eliminates the need for powering a charging pump in the blackout unit. We have also eliminated non-essential loads in the blackout unit. These actions result in a diesel generator loading scheme that complies with NRC staff position and is within the generator's capacity. The Attachment provides additional details of our diesel loading scheme and also addresses other concerns discussed in our July 3, 1990 conference call.

e We have in place an Emergency Diesel Generator Reliability Program to ensure that our target reliabilities are maintained. This program is consistent with Regulatory Guide 1.155, dated August 1988, Section C.1.2.

Our engineering and procurement efforts had been temporarily suspended while we sought clarification of the NRC policy on use of emergency AC generators as alternate AC power supplies. Although we now have a better understanding of NRC interpretation of the rule, it is deemed prudent to obtain NRC concurrence with our modified submittal prior to proceeding with modifications. Further, as a result of our recent communications with the NRC concerning station blackout, we are also considering other alternate AC options, including possible use of combustion turbines located at the site or installation of a non safety related diesel. A final decision on the selected alternate AC option can not be made until after we have received your response to this modified submittal.

Substantial resources must be committed in order to complete any of the modifications, regardless of the selected alternate AC source. Because refueling outages will be required to implement the necessary modifications, the schedule for completion of these modifications will be dependent on NRC approval and subsequent refueling outage dates.

If you have any questions or require additional information, please contact us.

Very truly yours,

~l~~

W. L. Stewart Senior Vice President - Nuclear Attachment cc: U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, N.W.

Suite 2900 Atlanta, Georgia 30323 Mr. W. E. Holland NRC Senior Resident Inspector Surry Power Station

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e ATTACHMENT STATION BLACKOUT SURRY POWER STATION PROPOSED EDG LOADING SCHEME The attached Table 1 provides estimated worst-case steady-state loading for one EDG shutting down both units under Station Blackout (SBO) conditions. This Attachment provides a discussion of the loading provided in Table 1. This "scheme" assumes that a fourth EDG has been installed; as such, one EDG would be available for SBO coping. Power would be transferred to the Blackout (BO) Unit either via a new tie between the existing D and E 4.16 KV transfer buses to connect Emergency Buses lJ and 2H, or via the existing F transfer bus to connect Emergency Buses lH and 2J.

The existing plant procedures were reviewed to determine the normal Operator response to this event, including equipment utilization.

The existing procedures are unit specific; as such, procedure changes would be required to incorporate the use of the cross-tie and the loading restrictions required in the BO unit. Although our analysis is for worst-case EDG loading, the procedures will be developed to allow Operator flexibility in selecting loads to be used for this event, consistent with plant conditions and within the 2000-hr rating of the EDGs.

At the onset of the SBO event, the NBO unit experiences a loss of offsite power and failure of one of the two EDGs. One Emergency Bus and associated loads will not have a 4.16 KV supply. This is an existing design basis condition. In the NBO unit, the operating Component Cooling Water (CCW) Pump will trip and lockout on Emergency Bus undervol tage. By procedure, this pump would be restarted. The Pressurizer Heaters will also trip, and re-energize in 3-minutes. Both the Motor Driven (MD) and Turbine Driven Aux Feedwater Pumps will start on various bus undervoltage relaying schemes; this EDG loading analysis assumes the MD AFW pump is operating. One Charging Pump would remain operating, or would receive an auto-start signal. This loading scenario results in 1981 KW automatically loaded onto the EDG, including MCC load, and 531 KW, including the auxiliary building filter exhaust fan, loaded under administrative control. The BO unit also experiences a loss of offsite power, along with failure of both EDGs.

• Surry has an inter-unit Charging System piping cross-tie, such that one Charging Pump can supply charging (seal injection and primary system makeup) to both units. This cross-tie would be utilized for the SBO event, and would be established within the first hour. Only one Charging Pump is required for the needs of both units. Once the Page 1 of 5

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CCW Pump is started, and if Instrument Air is available, Containment cooling could be re-established in the NBO unit for the remainder of the event. The remainder of this discussion involves the NBO unit, except where noted.

The 480 V MCC loading varies significantly between buses; the loading shown in Table 1 is for the heaviest loaded EDG. Motor operated valves (MOVs) are not included on this list. MOVs are small (normally fractional horsepower), intermittent loads that would be manually controlled for this event. MOV loading is bounded by the margin remaining on the EDG.

The "miscellaneous" loading includes small loads that would be available, including Radiation Monitors, the Semi-Vital Bus, small ventilation fans, the EDG control cabinet, Charging Pump auxiliaries, etc. The Tab;l.e 1 loading has no intentional load shedding on the NBO unit to create EDG capacity for the BO unit.

The design basis for the Station Batteries is a two-hour duty cycle. Operation beyond two-hours is outside the design basis, and adequate voltage cannot be ensured. Two-hours following the SBO, or after battery voltage begins to degrade, certain loads, including Vital Bus inverters, will be removed from the battery that has no charger. This is consistent with the existing loss of offsite power response. One battery and two associated Vital Bus inverters will remain charged and operational for the duration of the event. Preventing the battery from degrading below the design basis final voltage of 105 V will ensure operation of necessary breakers and availability of system protection (relaying) and control to restore additional power sources (onsite and offsite) at the end of the event.

The 4.16 KV bus ties will require actions outside the Control Room, and will therefore be assumed to be made one-hour into the event.

Once the electrical cross-tie is made and an Emergency Bus is powered in the BO unit, DC power would be provided to two Vital Bus inverters for the duration of the event. (As in the NBO unit, two Vital Bus inverters will be removed from the battery without a charger.) The other required load in the BO unit for this event is HVAC for the Emergency Switchgear Room of the BO unit, which includes one air handling . unit. (The NBO unit chiller has sufficient capacity for both units.) An Instrument Air compressor could also be started if deemed necessary by the Operator. This load is shown on the BO unit load list. The BO unit will be managed in accordance with NUMARC 87-00.

The transformer losses shown for the NBO unit are for two completely loaded 1000/1333 KVA, 480 V load center transformers.

Most of these losses are load losses, which are proportional to transformer loading. Though the transformerf? are not loaded to their rating for this scenario, full losses are assumed so that, for analysis purposes, a fixed load can be used. The losses in the Page 2 of 5

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e e BO unit are assumed approximately half of that in the NBO unit, although loading in the BO unit is much less than that.

Table 1 also shows the NBO unit transition to the Residual Heat Removal (RHR) system if required after power has been restored to the BO unit. Prior to the end of the four-hour SBO event, the NBO unit is kept in a hot shutdown condition (licensing basis). The EDG loading incorporates the RHR pump, and removes the BO unit loading.

Sufficient EDG capacity exists for this scenario.

SHARED SYSTEMS The Surry Power Station design incorporates several systems that are shared between units 1 and 2. Of these, the Auxiliary Ventilation and Instrument Air systems are of interest for SBO.

The Charging Pump cubicles will be ventilated by an Auxiliary Building Filter Exhaust Fan. There are two fans, one powered from each unit. Depending on which EDG starts, a fan may be available immediately, or after the electrical cross-tie is made to the other unit. For the loading shown in Table 1, the fan is assumed operating in the NBO unit. The fan is shown on Table 1 operating one-hour into the event. The fan does not normally operate; operator action is required to place the system in service.

The Instrument Air compressors are powered from Emergency Buses lJ and 2J. Only one compressor is required to support both units.

For the postulated event a compressor may not be available until the electrical cross-tie is made. At that time, either Bus lJ or 2J will be energized, and the available compressor would be started. For SBO coping, loss of Instrument Air affects primarily Containment cooling; the Containment isolation valves that supply ccw to the air coolers fail closed on loss of air, which is addressed in the next section. The remaining components (with the exception of the Steam Generator PORVs) fail in their safe position. Compressed air bottles will be provided for the Steam Generator PORVs to ensure an air supply exists at all times.

HVAC CONSIDERATIONS FOR STATION BLACKOUT Several areas in the plant require forced ventilation: the Control Room ( common to uni ts 1 and 2) ; the Emergency switchgear Room (separate rooms for units 1 and 2); and the Charging Pump cubicles (common to units 1 and 2). The Auxiliary Feedwater Pump Rooms (separate rooms for units 1 and 2) do not require forced ventilation; the calculated four-hour steady-state temperature (187 F) in these spaces can be reduced to less than 120 F by opening doors and dampers. With Instrument Air available, forced cooling can be provided for these spaces. Equipment operability in the 187 F ambient is not a concern, based on NUMARC 87-00 Appendix F and the short-term operation (less than four-hours) in Page 3 of 5

e e that environment. Operator habitability is also not a concern, since the stay-times required for necessary operator actions (e.g.,

throttling AFW flow manually) is of short duration.

Modifications to the CR and ESR HVAC systems will be required in order to ensure a chiller and appropriate air handling units are available with any EOG operating. This will ensure both Operator habitability and equipment operability for these areas.

The Charging Pump cubicles will be ventilated using one Aux Buiiding Filter Exhaust Fan. This fan is not normally operated; normal ventilation for this space is provided by a smaller fan, which is also included in the loading in Table 1. Depending on the EOG available, ventilation for this space could be lost for one~

hour. Based on NUMARC 87-00 Appendix F, and the short-time of operation without ventilation, reasonable assurance of operability exists for the equipment in the Charging Pump cubicles.

Containment cooling in the NBO unit will be provided once Instrument Air and ccw are restored (potentially one-hour). Loss of Containment cooling for this period of time will not materially degrade equipment inside Containment. NUMARC 87-00 states that, based on Westinghouse analysis for three-loop plants, the total Containment temperature rise resulting from a Station Blackout event would be 15 F. Based on NUMARC 87-00 Appendix F and previous Equipment Qualification, the correspond_ing equipment degradation resulting from a loss of cooling for one-hour would be minimal.

Containment cooling would continue to be available after the SBO event to provide cooling for the RHR pump motor.

OFFSITE POWER CATEGORIZATION The April 17, 1989, submittal classified Surry in the I 1/2 offsite power group. This classification was based on NUMARC 87-00 section 3.2.1 part l.D. The Surry switchyard has a 500 KV section and a 230 KV section which are not electrically connected. The normal source of AC power to the emergency buses is not from the unit main generator. Each emergency bus is supplied from a separate, independent source of offsite power such that a loss of one offsite source affects only one emergency bus per unit. This is a more reliable arrangement than normally supplying both emergency buses for a unit from the same source and subjecting both buses to the same transients and required transfers to obtain a suitable source of power. On each unit, an administrative tie breaker is available to connect emergency buses from the unit together during shutdown conditions or extr*eme emergency conditions under strict administrative control. Because surry's design does not conform to the described B(l) or B(2) characteristics Surry was classified as I 1/2.

Although R.G. 1. 155 Table 1 did not list NUMARC 87-00 Section 3.2.1, Part 1.D. as a section for which R.G. 1.155 takes Page 4 of 5

e e precedence, we reviewed R.G. 1.155 Table 5 to assist in our categorization. Consideration of the administrative tie breakers allows an I1 (2.b.) categorization (noting that the independence of off site power sources* would require an I2 categorization)

• Without considering the administrative tie breakers, Surry' s design is superior to I2 (2 .b.) because the loss of a single offsite source does not affect both emergency buses of one unit. Operation without both offsite sources is allowed by and limited by Technical Specification LCOs. Limitation of this operation increases the reliability of Surry's offsite power supply during unit operation.

The results of this evaluation concurred with the I 1/2 classification from NUMARC 87-00.

Scaled line maps of the Surry transmission lines were reviewed to ensure the NUMARC 87-00 criteria of at least one-quarter mile of separation between right-of-ways at one-mile from the switchyard exists for Surry. This review confirmed our original classification that Surry has multiple right-of-ways, and the Severe Weather category for Surry remains 11 1 11 , per the NUMARC 87-00 criteria.

CONTAINMENT PENETRATION ISOLATION Table 2 provide*s a list of the Containment penetrations from the UFSAR, along with their applicable isolation valve status on a loss of power, and their motive force. Only valves 3-inches and larger are provided in the Table; valves smaller than 3-inches are exempt from consideration for Station Blackout, per NUMARC 87-00 Section

7. 2. 5. Both NBO and BO uni ts have the capability to achieve Containment isolation if required.

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e TABLE 1 VIRGINIA POWER SBO EDG LOADING SURRY lA NBO UNIT KW +10 MIN +1 HR +2-4 HR +4 HR COMMENTS/NOTES MD AFW PP 308 308 308 308 308 Based on accident flow; SBO flow is lower CHARGING 515 515 515 515 515 Based on accident flow; SBO flow is lower PRESS HTRS 200 200 200 200 200 AB FLTR EXH FAN 121 121 121 121 CCWPP 410 410 410 410 CONT AIR FAN 102 102 102 102 102 RES HEAT REMOVAL 215 215 MCC LOADING 856 856 856 811 811 TOTAL NBO LOADING 1981 2512 2467 2682 BATT CHGRS 23 23 23 23 23 BATT CHGRS 23 23 23 23 23 A/C CHILLERS 180 180 180 180 180 CHILLER PUMP 18 18 18 18 18 CHILLER SW PUMP 18 18 18 18 18 BAT XFR PUMP 9 9 9 9 9 HEAT TRACE 90 90 90 90 90 ESR A/C UNIT 35 35 35 35 35 TRANSF LOSSES 55 55 55 55 55 Assumed fully loaded CRDM FAN 65 65 65 65 65 CRDM FAN 65 65 65 65 65 TG OIL PUMP 45 45 45 0 0 Turbine stops @ 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />; no Turning Gear.

BAT HEATERS 15 15 15 15 15 MISC 215 215 215 215 215 TOTAL NBO MCC 856 856 811 811 1B BO UNIT BATT CHGR 23 75 75 Loading while charging battery BATT CHGR 23 75 75 Loading while charging battery A/C UNIT - ESR 15 15 15 TRANS LOSSES 25 25 25 INST AIR COMP 15 15 15 TOTAL BO UNIT 205 205 0 TOTAL 1981 - 2717 2672 2682 CAPACITY (2000 hr) 2750 2750 2750 2750 2750 MARGIN, KW 2750 769 33 78 68 MARGIN,% 100.00 27.96 1.2 2.84 2.47 NOTE: LOAD VALUES ARE PRELIMINARY AND BASED ON LOAD VALUES USED FOR EXISING EDG LOADING CALCULATIONS KSB/kwd:000391 - 1

~-' ,* '"", e e TABLE 2 SURRY POWER STATION CONTAINMENT ISOLATION MOTIVE FORCE/

SERVICE STATUS ON LOOP VALVE COMMENTS PG WATER to PRT fail closed !OJ Also has check RCP SEAL RETURN closed manual + check CHARGING closed check Also has a NO MOV RHRto RWST normally closed MOV Also has a NC manual RCP-CCW IN closed check Also has a manual RCP-CCW-OUT fail closed !OJ Also has a manual CCW to RHR + CARFs closed check Also has a manual CCW from CARFs fail closed !OJ Also has a manual RSSWIN normally closed MOV RSSWOUT normally closed MOV CCWfrom RHR fail closed !OJ Also has a manual HHSI to RCS COLD LEGs normally closed MOV Also has check LHSI to RCS COLD LEGs normally closed MOV Also has check LHSI to RCS HOT LEGs normally closed MOV Also has check LHSI SUCTION FROM SUMP normally closed MOV RECIRC SPRAY DISCHARGE closed MOV Also has check RECIRC SPRAY SUCTION normally open MOV Previously approved by NRC-UFSAR Section 5.2.1 MAIN STEAM LINE fail closed AOVandNRV AUX FEEDWATER CROSS-TIE closed MOV (

MAIN FEEDWATER LINE closed check S/G RECIRC & XFR closed manual S/G SLOWDOWN fail closed !OJ Also has a manual CONTAINMENT SPRAY DISCH normally closed MOV VENTILATION DUCTS normally closed MOV FUEL XFR TUBE normally closed blind flange COND AIR EJECTOR VENT fail closed !OJ Also has check CONT VAC EJECT SUCTION normally closed !OJ Also has manual