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Forwards Results of Safety Analysis,Confirming That in Event of Hurricane,Concurrent W/Loss of Offsite Power to Both Units,Sufficient Svc Water Flow Provided to Equipment to Ensure Safe Hot Shutdown
	ML18153B715
Person / Time
Site:	Surry
Issue date:	05/05/1989
From:	Stewart W; VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	; NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
	88-790B, NUDOCS 8905180171
	Download: ML18153B715 (15)
	v • d • e

-* e e VIRGINIA ELECTRIC AND POWER COMPANY RICHMOND, VIRGINIA 23261 May 5, 1989

. U. S. Nuclear Regulatory Commission Serial No. 88-7908 Attn: Document Control Desk NO/HWB:vlh R3 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 GDC-2 REANALYSIS: SERVICE WATER SYSTEM During the Safety System Functional Inspection of the Surry Service Water System the NRC Staff identified a concern with regard to the ability of the Service Water System to perform its safety function during a hurricane as required by General Design Criterion 2 (GDC-2). For this reason, the NRC requested the results of the safety analysis which

** _.confirms that in the event of a hurricane concurrent with the loss of offsite power (LOOP) to both units, sufficient service water flow is provided to equipment necessary to ensure a safe hot shutdown.

We have completed our reanalysis that demonstrates the adequacy of the service water system with respect to compliance with GDC-2. Attachment 1 provides the results of this reanalysis. Also provided in this report is the necessary operator actions and the times to achieve and maintain cold shutdown in the event of a hurricane. We are revising the applicable station procedures to address the results of the analysis and will complete this effort by June 30, 1989.

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

W. L. Stewart Senior Vice President-Power Attachment 89051aA00017c! ~;ggg~ao PDR PNU p

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

e ATTACHMENT 1

SUMMARY

REPORT HURRICANE SHUTDOWN ANALYSIS SURRY POWER STATION LTR 88-7909 - ATTACHMENT 1 - PAGE 1 OF 12

e*

BACKGROUND As a result of the recent Safety System Functional Inspection at the Surry Station, the NRC requested additional information on system performance in the event of a hurricane. The NRC request is as follows:

"During the Safety System Functional Inspection of the Surry Units 1 and 2 service water system conducted in September 1988, the staff identified a concern with regard to the ability of the service water system to perform its safety function during a hurricane as required by General Design Criterion 2.

Specifically, following a hurricane, Section 2.3 of the UFSAR indicates that the level in the service water discharge canal will be 24 ft-4 in. and the inlet canal level will be 26 feet. With the resulting differential head of approximately 1-1/2 feet, sufficient driving head to ensure adequate service water system flow to required components may not be available.

Therefore, please provide the results of your analysis which confirms that in the event of a hurricane and a loss of offsite power to both units, sufficient service water flow is provided to equipment necessary to ensure a safe hot shutdown. A concurrent design basis event (LOCA) need not be postulated.

Further, please identify the necessary actions and times to achieve and maintain cold shutdown under these conditions."

This report provides the results of analysis performed to demonstrate that in the event of a hurricane and associated loss of offsite power to both units, sufficient service water flow is provided to equipment necessary to ensure a safe hot shutdown. In addition to the analysis results, necessary actions and times to achieve and maintain cold shutdown in the event of a hurricane are provided.

LTR 88-7908 - ATTACHMENT 1 - PAGE 2 OF 12

e PROBABLE MAXIMUM HURRICANE In order to determine the maximum river surge during the probable maximum hurricane (PMH), the following analysis of water surface levels during the hu'rricane was performed:

1) Calculation of the open coast surge level and resultant surge level at the site as a function of time.

2) Calculation of the wave height and run-up at the site and at the low level intake structure.

3) Calculation of the wave run-up within the intake canal.

Open coast surge during the probable maximum hurricane was calculated at the entrance to the Chesapeake Bay using methods based on the Bathystropic Storm Tide theory. The highest open coast stillwater level consists of the following components:

The highest astronomical tide.

An initial rise to account for short period anomalies.

The rise due to atmospheric pressure reduction.

The surge generated by the wind component acting perpendicular to the ocean bottom contours.

The surge generated by the wind component acting parallel to the ocean bottom contours.

Once the open coast stillwater level was determined, the storm surge was routed through the Chesapeake Bay and up the James River to the power station.

The mathematical model used for storm surge routing consisted of the one-dimensional continuity and momentum equations applicable to variable area estuaries, embayments, or sea-level canals. The equations are solved simultaneously by means of an explicit finite-difference scheme to yield values of tidal elevation and flow along the longitudinal axis of the waterway. The model LTR 88-7908 - ATTACHMENT 1 - PAGE 3 OF 12

e takes i-nto account the effects of wind stress, river inflow, ocean tidal hydrograph and nonconveyance river water storage.

The entire James River from the river mouth at Chesapeake Bay to Richmond, Virginia, the head of tide, was considered in the mathematical model. The first 75 miles of the river reach from the river mouth was divided into 25 three-mile segments. An adequate storage area was provided in the model to account for the total tidal area of the remaining upstream river reach.

The model was used for storm surge routing by applying the open coast PMH storm surge hydrograph at the river mouth. In addition, an average wind of 91 mph along the PMH maximum wind axis covering the entire river reach was used to account for wind setup along the river. A constant coefficient of 2.8 x 10-6 was used to compute the surface wind stress. The mean monthly fresh water flow of 10,000 cfs was used as the river inflow during the PMH storm surge routing.

The storm surge hydrograph based on the mean sea level datum (MSL) at the Surry station and calculated in the manner described above, is shown in Figure 1. The maximum stillwater level at the Surry station river intake is 22.6 MSL.

HURRICANE SHUTDOWN ANALYSIS In order to demonstrate the safe shutdown of the units in the event of the hurricane surge calculated above, the analyses described in the following paragraphs were performed.

The overall approach of the analysis is to bring the operating unit(s) to a hot shutdown based on sufficient hurricane warning. Hot shutdown units are maintained at hot shutdown (RCS temperature above 350°F) until the storm surge recedes below the level required to obtain sufficient service water flow to allow further cooldown. Unit(s) at cold shutdown or in refueling mode would be maintained at cold shutdown (RCS temperature below 200°F). Refueling activities would be suspended prior to the arrival of the hurricane.

The total amount of condensate that can be stored in missile-protected tankage and be made available to the auxiliary feedwater (AFW) system to provide for hot shutdown unit cooling is described in the UFSAR Section 10.3.5.2. The volume LTR 88-7908 - ATTACHMENT 1 - PAGE 4 OF 12

e e i~cludes the minimum required by Technical Specification limits for the emergency condensate storage tanks plus the contents of the underground emergency condensate makeup tanks. Based on the relationship between AFW volume and energy removal calculation, the heat energy removal capability of the available AFW was determined. Total integrated decay heat and cooldown limitations were examined to determine the length of stay allowed at hot shutdown before cooldown must start. The calculations take no credit for the use of the firewater system which can be used to extend this staytime.

Several intake canal profiles were developed to examine the effect of service water flow as the discharge intake elevation rose with the storm surge and then receded.

The time sequence and levels of the storm surge came from the storm surge analysis described earlier. These values reflect the most severe storm expected to occur (design basis hurricane-PMH). Profiles were developed for 1, 2, and 3 component cooling water (CCW) heat exchangers with an initial canal height of 23 and 26 feet.

During the development of the profiles, variables such as emergency service water makeup and canal outleakage were examined.

Reduced service water flows to the component cooling water heat exchangers were calculated based on the intake canal profiles. The effect of the reduced flow on plant thermal relationships was evaluated using the Heat Exchanger Effectiveness Method using conservative values for fouling factors and tube plugging for the CCW heat exchanger. Heat transfer capabilities were calculated providing the resultant service water, component cooling water, letdown, and residual heat removal system temperatures.

Additionally, a calculation of the resultant drop of the water level in the intake canal was performed based on a starting elevation of 23 feet. The analysis determined that sufficient service water inventory was available during a storm which causes low river levels such that the emergency service water pumps are not available.

SUMMARY

OF CALCULATION RESULTS

1. River surge elevations with respect to time are presented in Figure 1.

LTR 88-7908 - ATTACHMENT 1 - PAGE 5 OF 12

e

2. The available intake canal inventory at elevation 23 ft reduces to 18 ft with no makeup to the canal and required service water flows are provided to the station to maintain units at hot or cold shutdown.

3. 196,000 gallons of condensate are available per unit to maintain hot shutdown.

An additional 60,000 gallons are also available to the hot shutdown unit when the other unit is in cold shutdown or refueling via a unit cross-connect.

4. The available condensate of 196,000 gallons will maintain hot shutdown for 27 hours3.125e-4 days 0.0075 hours 4.464286e-5 weeks 1.02735e-5 months including RCS cooldown to 350°F. With one unit at cold shutdown, the available condensate of 256,000 gallons will maintain the hot shutdown unit for 38 hours4.398148e-4 days 0.0106 hours 6.283069e-5 weeks 1.4459e-5 months including RCS cooldown to 350°F.

5. With two (2) units at hot shutdown and an intake canal elevaHon initially at 23 feet (proposed Technical Specification minimum), the units can be maintained at hot shutdown conditions throughout the hurricane event.

6. With one (1) unit at hot shutdown and one (1) unit at cold shutdown and an initial intake canal elevation of 26 feet, the units can be maintained at hot shutdown and cold shutdown, respectively throughout the design basis hurricane event.

7. With two (2) units at cold shutdown and an initial intake canal elevation of 26 feet, the units can be maintained at cold shutdown throughout the design basis hurricane event.

8. With one or two units at cold shutdown, two (2) emergency service water pumps, three (3) component cooling water (CCW) heat exchangers and two (2)

CCW pumps are required during the design basis hurricane event.

9. For hot shutdown units during the design basis hurricane event, one (1) CCW heat exchanger, one (1) CCW pump, and one (1) auxiliary feedwater train is required per unit.

10. Table 1 provides the resulting system temperatures for the hot shutdown and cold shutdown units.

LTR 88-7909 - ATTACHMENT 1 - PAGE 6 OF 12

11. The hot shutdown units can proceed to cold shutdown approximately 11 hours1.273148e-4 days 0.00306 hours 1.818783e-5 weeks 4.1855e-6 months after the hurricane hits the site using existing equipment and procedures for loss of offsite power. The 11 hours1.273148e-4 days 0.00306 hours 1.818783e-5 weeks 4.1855e-6 months corresponds to the time when the river surge recedes to below an elevation of 8 ft which is the minimum discharge tunnel elevation with loss of tunnel vacuum priming. Cooldown may actually begin earlier, however, the rate of cooldown will be limited by the available service water flow and/ or increase in RCS and CCW temperatures.

DESCRIPTION OF HURRICANE SHUTDOWN ACTIONS Hurricane watches and warnings are provided by the National Weather Service (NWS). Hurricane watches are issued for an area 36 hours4.166667e-4 days 0.01 hours 5.952381e-5 weeks 1.3698e-5 months prior to the expectation of hurricane conditions. Hurricane warnings are issued for an area 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months prior to the expectation. of wind speeds in excess of 73 mph. With the institution of a hurricane warning, station personnel will have sufficient time to take action prior to* arrival of the hurricane.

During the 36 hour4.166667e-4 days 0.01 hours 5.952381e-5 weeks 1.3698e-5 months period prior to the hurricane, the site will start hurricane preparations such as closing missile doors, putting flood protection barriers in place, and preparing equipment required for shutdown. This will require installation of the emergency service water (ESW) pump house door watertight seal plates and ventilation louver opening covers. Also, preparation will be required to ensure three (3) CCW heat exchangers are operable when one or two units are at cold shutdown.

With the NWS 24-hour hurricane warning, procedures for extreme weather conditions will be invoked. These procedures will require placing the operating units in hot shutdown and maintaining the cold units at cold shutdown as follows:

For two units operating prior to the hurricane warning, the units will be shut down 2 hours2.314815e-5 days 5.555556e-4 hours 3.306878e-6 weeks 7.61e-7 months before the hurricane is anticipated to reach the site (i.e., this is defined as when sustained wind speeds exceeds 70 mph onsite). Decay heat removal will be performed using the circulating water system until a loss of power occurs at which time the auxiliary feedwater system will be used. For analysis basis, this is assumed that the loss of power occurs coincident with the LTR 88-7908 - ATTACHMENT 1 - PAGE 7 OF 12

arrival of hurricane winds on site. This criteria is consistent with guidelines provided in NUMARC 87-00 (Section 2.11 "Hurricane Preparations") used for Station Blackout analysis.

With one or both units in cold shutdown or refueling mode at the time of the warning, the water elevation in the Intake Canal must be raised to above 26 feet to ensure that sufficient driving head is available to provide heat removal capability for the Component Cooling System during the expected storm surge.

Reanalysis of the wave run-up within the intake canal identifies a required freeboard of only 4 feet from the top of the canal (elevation 36 feet).

Accordingly, the canal water level will be procedurally required to be 28 feet prior to the arrival of the hurricane to ensure adequate head during the storm surge.

Due to the potential for the intake canal siphoning back through the circulating water pump discharge lines, the circulating water pumps will be shut down prior to the hurricane reaching the site. The plant has been modified to passively break the siphon at elevation 23 ft, however, the hurricane analysis requires an elevation of 26 ft to ensure adequate service water flows with peak river surge. Therefore, the circulating water pumps will be shut down and siphon broken after raising the canal elevation to 28 feet.

To ensure adequate decay heat removal of the shutdown unit(s) at the peak river surge (el 22.6 ft), the CCW heat exchangers and pumps will be cross-connected to allow the flow of the CCW pumps to be equally distributed to the three operable CCW heat exchangers. Also, to minimize the CCW heat loads, nonessential heat loads will be isolated. The analysis is based on using CCW to the Residual Heat Removal (RHR) heat exchangers for decay heat removal for cold shutdown units, and CCW for heat removal for letdown and auxiliary feedwater for decay heat removal for the hot shutdown units.

For the case where one unit was initially operating and one unit was at cold shutdown, an additional 60,000 gallons of condensate is available for the operating unit by cross-connecting to the cold shutdown unit. This additional 60,000 gallons will allow AFW operation for a total of 38 hours4.398148e-4 days 0.0106 hours 6.283069e-5 weeks 1.4459e-5 months after shutdown of the circulating water system. The decay heat load analysis is based on the operating unit(s) being LTR 88-7908 - ATTACHMENT 1 - PAGE 8 OF 12

shut down two (2) hours prior to the hurricane reaching the site and a loss of power o*ccuring. However, in order to ensure that a canal level of 28 ft is established and isolation of the circulating water system occurs without siphoning the canal, the operating unit will be shut down while sustained wind speeds are lower than 35 mph. This will enable operators to visually observe the operation of the circulating water pump discharge piping active vacuum breakers as each pump is shut down, thus ensuring that a reverse siphon is not established.

Upon the hurricane warning, operators will be required to:

1) Start two emergency service water (ESW) pumps after the circulating water pumps are isolated or loss of power occurs.

2) Close or verify closed service water and circulating water isolation valves except in the flowpaths for the following equipment:

CCW heat exchangers

Charging pump service water pumps

Control room and Emergency Switchgear Room Chiller service water pumps.

3) Align and cross-connect the CCW system such that all of the operating CCW pumps feed all of the three operating CCW heat exchangers.

4) Isolate CCW loads except for:

RHR heat exchangers (cold shutdown unit(s))

Letdown (nonregenerative) heat exchangers (hot shutdown unit(s))

Penetration cooling coils

Neutron shield tank cooler

Loads assumed in analysis; but not essential to maintain hot or cold shutdown.

5) Monitor CCW outlet temperatures and adjust the service water outlet valves as necessary to maintain normal system temperatures as the surge reduces the driving head for the heat exchangers. As the driving head diminishes, and with the outlet valves wide open, CCW temperatures LTR 88-7908 - ATTACHMENT 1 - PAGE 9 OF 12

will rise to the values identified in Table 1. As the river recedes and the driving head increases, the outlet valves will again be throttled to maintain normal CCW temperatures.

. 6) Align the hot shutdown unit(s) for RHR decay heat removal after the river recedes* to below an elevation of 8 feet and cool down units to cold shutdown.

CONCLUSIONS

1) In the event of a design base hurricane which causes a blowout of the river, resulting in the loss-of-suction of the ESW pumps, there is sufficient intake canal inventory at the proposed Technical Specification minimum level of 23 feet to maintain the units at hot or cold shutdown for a 24 hour2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months period without makeup to the canal.

2) With both units at hot shutdown and decay heat being removed by the AFW system, the Technical Specification intake canal level of 23 feet provides sufficient inventory to maintain the units at hot shutdown throughout the design base hurricane.

3) With one or two units at cold shutdown, a minimum canal elevation of 26 feet is needed in order to ensure that sufficient heat removal capability is maintained.

4) With both units at hot shutdown, the units can be maintained at hot shutdown utilizing the AFW system for decay heat removal for 27 hours3.125e-4 days 0.0075 hours 4.464286e-5 weeks 1.02735e-5 months . With one unit at hot shutdown and one unit at cold shutdown, the hot shutdown unit can be maintained at hot shutdown for 38 hours4.398148e-4 days 0.0106 hours 6.283069e-5 weeks 1.4459e-5 months on the AFW system. The above times are based on using Technical Specification condensate volumes of the emergency condensate storage tanks plus 100,000 gallons from the emergency condensate makeup tanks. Other sources of condensate are available (the condensate tanks (300,000 gallons) and the fire protection system) but were not considered for the analysis.

LTR 88-7908 - ATIACHMENT 1 - PAGE 10 OF 12

5) The cold shutdown units can be maintained at cold shutdown (RCS < 200°F) throughout the storm surge.

6) . The hot shutdown units can proceed to cold shutdown, if needed, when the river recedes below an elevation of 8 ft. This is approximately 11 hours1.273148e-4 days 0.00306 hours 1.818783e-5 weeks 4.1855e-6 months after the design base hurricane reaches the site. The cooldown will be performed using normal loss of power procedures and system capacities.

LTR 88-7908 - ATIACHMENT 1 - PAGE 11 OF 12

e TABLE1 RESULTANT SYSTEM TEMPERATURE HURRICANE SHUTDOWN ANALYSIS I. Two (2) plants at cold shutdown.

RHR hot 190°F CCW cold 119°F CCW hot 130°F

. SW hot 109°F

2. For one (1) unit at hot shutdown and one (1) unit at cold shutdown.

Cold Plant RHR hot 190°F CCW cold 115°F CCW hot 127°F SW hot 106°F Hot Plant CCW (non-reg. hx) out 113°F ccw cold 102°F CCW hot 111°F SW hot 105°F

3. For two (2) units at hot shutdown.

Same as for hot plant above.

LTR 88-7908 - ATIACHMENT 1 - PAGE 12 OF 12

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ML18153B715

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