ML20217H924

Spent Fuel Pool Boron Dilution Assessment

ML20217H924
Person / Time
Site:	Vogtle
Issue date:	08/08/1997
From:	SOUTHERN NUCLEAR OPERATING CO.
To:
Shared Package
ML20217H901	List: ML20217H898 ML20217H905 ML20217H912 ML20217H924
References
NUDOCS 9708130348
Download: ML20217H924 (26)

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ENCLOSURR6 VOOTL11 ELECTRIC GENERATING PLANT RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REVISED REQUEST TO REVISE TECllNICAL SPECIFICATIONS CREDITf0R BORON AND EN1(JCllMENT INCRFAS]! FOR FUEldIORAGE FUEL STORAGE POOL DILUTION ASSESSMENT l

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VOGTLE SPENT FUEL POOL BORON DILUTION ANALYSIS Table of Contents Section Page

1.0 INTRODUCTION

2 2.0 SPENT FUEL POOL AND RELATED SYSTEM FEATURES 3

2,1 Spent Fuel Pool 3

2.2 Spent Fuel Storage Racks 4

. 2.3 Spent Fuel Pool Cooling System 4

2.4 Spent Fuel Pool Cleanup System 4

2.5 Dilution Sources 5

2.6 Boration Sources 10 2.7 Spent Fuel PoolInstrumentation 11 2.8 Administrative Controls 12 2.9 Piping 13 2.10 Loss Of Offsite Power impact 13

'3.0 SPENT FUEL POOL DlLUTION EVALUATION -

14 3.1 Boron Dilution Times and Volumes 14 3.2 Evaluation Of Boron Dilution Events 15 3.3 Evaluation of Infrequent Spent Fuel Pool Configurations 20 3.4 Summary of Dilution Events 21

4.0 CONCLUSION

S 24

5.0 REFERENCES

25 1

VOOTLE BORON DILUTION ANALYSIS

1.0 INTRODUCTION

A boron dilution analysis has been performed for crediting boron in the Vogtle spent fuel pool (SFP) rack enticality analysis. The boron dilution analysis includes an evaluation of the following plant specific features:

Dilution Sources and Flowrotes Boration Sources Instrumentation Administrative Procedures Piping Loss of Offsite Power impact Boron Dilution Initiating Events Boron Dilution Times and Volumes The boron dilution analysis was performed to ensure that sufficient time is available to detect and mitigate the dilution before the spent fuel rack criticality analysis 0.95 k.n design basis is exceeded.

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2 VOGTLE boron DILUTION ANALYSIS s

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2.0 SPENT FUEL POOL AND RELATED SYSTEM FEATURES This section provides background information on the SFP and its related systems and features.

2.1 Spent Fuel Pool The design purpose of the SFP is to provide for safe storage of irradiated fuel assemblies. The poolis filled with borated water. The water functions to remove decay heat, provide shielding for personnel handling the fuel, and to reduce the amount of radioactive gases released during a fuel handling accident. Pool water evaporation takes place on a continuous basis, requiring periodic makeup. The makeup source can be unborated water, since the evaporation process does not remove boron. Evaporation actually increases the boron concentration in the pool.

There are two spent fuel pools (one per unit). The SFPs are normally connected and contain a combined volume of approximately 772,000 gallons. This value for SFP volume conservatively disregards the Cask Loading P t which is located between the pools and is part of the total water volume when the pools are connected. When the pools are separated, the volume of each individual poolis approximately 386,000 gallons. The SFP is a reinforced concrete structure with a welded steelliner. The concrete structure has formed leak chases that can be drained by opening sample valves that are located in the Auxiliary building. The pool structure is designed to meet seismic requirements. Each poolis approximately 41.5 feet deep.

The transfer canalis located adjacent to each SFP. The transfer canal connects the SFPs with the transfer tubes. The cask loading area is located between the SFPs and provides communication between the pools.

3 VOGTLE BORON olLUTION ANALYSIS

i l

l 2.2 Spent Fuel Storage Racks The spent fuel racks are designed to support and protect the spent fuel assemblies under normal and credible accident conditions.

Their structural strength ensures the ability to withstand l

l combinations of dead loads, live loads (fuel assemblies), and safe shutdown earthquake loads.

l 2.3 Spent Fuel Pool Cooling System There are two trains of spent 1M pu coling. Each of the two trains of the cooling system consists of a pump, a heat exchange', vens, piping and instrumentation. The pump takes suction I

from the fuel pool at an inlet located below tt's pool water level, transfers the pool water through a heat exchanger and returns it to the pool. The return line is designed to prevent siphoning. The heat exchangers are cooled by component cooling water.

The system is designed to remove an amount of decay heat in excess of that produced by the number of spent fuel assemblies that are stored in the pool following a normal refueling, maximum normal refueling, and maximum emergency core unloading cases plus ary fuel assemblies that may remain in the pool from previous refuelings. System piping is arranged so that failure of any pipeline cannot drain the SFP below the water level required for radiation shielding.

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l 2.4 Spent Fuel Pool Cleanup System The SFP cleanup system is designed to maintain water clarity and purity. The cleanup system is connected to the SFP cooling system. A portion of the SFP cooling pump (s) discharge flow, approximately 100 gpm, can be diverted to the cleanup loop, which includes the SFP domineralizer and filter. The filter removes particulates from the SFP water and the SFP demineralizer removes

- ionic impurities.

4 VOGTLE BORON DILUTION ANALYSIS

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The refueling water cleanup loop also uses the SFP demineralizer and filters to clean up the refueling water storage tank after refueling operations.

To assist further in maintaining spent fuel pool water clarity, the water surface is cleaned by a skimmer loop. The system consists of one strainer, pump and filter. The skimmer pump is a centrifugal pump with a 100 gpm design flow rate. The pump discharge flow passes through the filter to remove particulates, then returns to the SFP at three locations remote from the skimmars.

2.5 Dilution Sources 2.5.1 Chemical and Volume Control 9ystem (CVCS) [1.etdown Divert to SFP Transfer Canal)

A potential dilution path exists if a valve interfacing with the spent fuel poot transfer canal (SFPTC) and the CVCS letdown system is left open after makeup has been provided from the Recycle-Holdup Tanks (RHT) to the SFP for evaporative losses. Vogtle SFPTC makeup from the RHTs is performed by closing the inlet to the RHT that is to be transferred to the SFPTC. The flowpath would exist if the CVCS letdown divert valve were to divert after the procedurr, for transfer was complete (with error of not opening the RHT inlet and not closing two valves ic the SFP inlet from the Recycle Evaporator feed demineralizers). This could result in a flowrate of up to 120 gpm to the Spent Fuel Pool Transfer Canal. The transfer canal would fill and spillinto the SFP.

2.5.2 Reactor Makeup Water System Vogtle SFP makeup is performed normally through a 2 inch connection to the SFP cooling loop using the RMWST. Makeup is provided approximately weekly from the RMWST. The capacity of a RMWST pump is 200 gpm at 123 psi. Therefore, an estimated 200 gpm dilution rate of unborated water is used.

5 VOGTLE boron olluTION ANALYSIS

l I

j The reactor makeup water (RMW) system connects to the SFPTC indirectly as a result of CVCS letdown (Section 2.5.1).

In addition, there is a 1 inch connection to the SFP domineralizer used for flushing and sluicing. A l

conservative 150 ppm flowrate is used for this connection.

l There is also a 3/8 inch line in the SFPTC used to supply w:ter as the hydraulle fluid to raise and lower the upender. Because of the size of this line and because it is normally isolated, this line will j

not be considered as a potential dilution flow path.

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j 2.5.3 Dominerallred Water System 1

There is a 2 inch Domineralized Water connection to the SFP cooling loop for makeup. A conservative dilution flow rate of 500 gpm is estimated; l

l The domineralized water system consists of a 250,000 gallon tank for both units with 3 pumps each delivering a design flow of 275 gpm at a head of 150 feet. One or two of these pumps normally 3

run. The non running pumps are placed in automatic and start at a low system pressure. The tank is automatically filled from the water treatment plant.

2.5.4 Component Cooling.

Component cooling water is the cooling medium for the SFP cooling system heat exchangers.

There is no direct connection between the component cooling system and the SFP cooling system.

However, if a leak were to develop in's heat exchanger that is in service, the connection would be made; In case of a leak, the CCW water would be expected to leak into the SFP cooling system because the CCW system normally operates at a slightly higher pressure than the SFP cooling system.

6 VOGTLE boron DILUTION ANALYSIS

It would be expected that the flow rate of any leakage of component cooling water into the SFP cooling system would be low due to the small difference in operating pressures between the two systems. Therefore, a conservative 110 gpm flowrate is estimated.

2.5.5 SFP Domineralizer Rosin Fill Connection The SFP domineralizer has a resin fill line in which demineralized water is used to assist in resin addition. This is a blind flanged connection, Only a small amount of water is used during resin addition. Resin addition and sluicing are procedurally controlled, infrequently performed evolutions.

Misalignment of multiple valves would have to occur to start a dilution. Since neither of these paths can provide a significant dilution rate, they are not considered further in this analysis.

2.5,6 Fire Protection System The spent fuel pool area has two 6 inch fire protection water supply headers that reduce to 4 inch lines and ultimately 2.5 inch lines providing 4 hose stations. The fire protection system consists of two 300,000 gsllcn tanks with 1 engine driven fire pump and 2 diesel driven fire pumps. The design flowrate for each pump is 2500 gpm at 289 feet of head, Any planned addition of fire system water to the SFP would be under the control of an approved 1

procedure and the effect of the addition of the non borated water from the fire system on the SFP boron concentration would be addressed.

The fire protection system contains instrumentation which would alarm in the control room should unplanned flow develop in the fire protection system.

2.5.7 Recycle Holdup Tank Discharge to SFP Transfer Canal 7

VOoTLE boron olluTioN ANALYSIS

i l

l A line runs from the outlet of the Recycle Holdup Tanks (RHT) to the SFP transfer canal (SFPTC) to allow for filling of the transfer canal from the RHTs There are 2 RHTs (shared between units) each with a volume of approximately 112,000 gallons. Each tank is sampled for appropriate boron concentration prior to transferring its contents to the SFPTC. If both RHTs were full of dilute water and transferred to the SFPTC, the total amount of water transferred would be approximately 224,000 gallons. If this evolution was to occur with the transfer canal full, a maximum of 224,000 gallons of water could enter the SFP. A dilution of approximately 500 ppm would occur resulting in a final boron concentration of 1500 ppm from an initial concentration of 2000 ppm (see section 3.1 for calculation of boron dilution times and volumes). An addition of both RHTs cannot result in any significant dilution of sne SFP and is not considered further in this analysis.

2.5.8 Normal Chilled Water A 3 inch Normal Chilled Water line runs in the SFP room. This system by itself does not contain enough water to cause a dilution event should the pipe break. The system can, however, provide l

dilute water to the pool, it is estimated that the system contains approximately 9000 gallons of I

water. Therefore, this water will be used only as an addition to other systems during a seismic event.

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'I 8

VOGTLE boron DILUTION ANALYSIS

2.5.9 Dilution Source and Flow Rate Summary Based on the evaluation of potential SFP dilution sources summarized above, the following dilution sources where determined to be capable of providing a significant arnount of non borated water to the SFP. The potential for these sources to dilute the SFP boron concentration down to the design basis boron concentration (500 ppm) will be evaluated in Section 3.0.

l SOURCE APPROXIMATE FLOW RATE SECTION Chemical and Volume Control System Letdown Divert to SFP Transfer Canal 120 gpm 3.2.2 Reactor Makeup Water System

. SFP Cooling connection 200 gpm 3.2.1

- SFP Demineralizer flush connection 150 gpm 3.2.1 Domineralized Water System

. SFP Cooling connection 500 gpm 3.2.3 600 gpm (pipe break) 3.2.6 Component Cooling Water 110 gpm 3.2.4 Fire Protection Supply Lines 2500 gpm (pipe break)

5. 2.6 4800 gpm (seismic event) 3.2.6 Utility Water 45 gpm (pipe break)

-3,2.6 9

VOGTLE BORON olluTION ANALYSIS

l I

2.6 Boration Sources l

The normal source of borated water to the SFP is from the RWST through the Refueling Water Purification pump or gravity fill. It is also possible to borate the SFP by the addition of dry boric acid directly to the SFP water.

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2.6.1 Refueling Water Storage Tank The refueling water storage tank connects to the SFP through separate inlet and outlet lines.

These connections are normally used to purify the RWST water when the purification loop is isolated from the SFP cooling system. If necessary, this connection can supply approximately 200 gpm of borated water to the SFP via the refueling water purification pump to the inlet to the SFP cooling system purification loop. Gravity fill to the SFP from the RWST can also be used as a boron addition path if offsite power is lost. This line is seismically qualified. The RWST is required by Technical Specifications to be kept at a minimum boron concentration of 2400 ppm and volume of 631,478 gallons during modes 1 through 4 and the Technical Requirements Manual requires a minimum boron concentration of 2400 ppm and a volume of greater than 99,404 gallons in modes 5 and 6.

i 2.6.2 Direct Addition of Boric Acid if necessary, the boron concentration of the SFP can be increased by depositing dry boric acid directly into the SFP. The dry boric acid will dissolve into the SFP water and will be mixed throughout the pool by the SFP cooling system flow and by the thermal convection created by the spent fuel decay heat.

10 VOGTLE BORON DiluTloN ANALYSIS

2.7 Spent Fuel PoolInstrumentation Instrumentation is available to monitor SFP water level and temperature, and the radiation levels in the SFP enclosure. Additional instrumentation is provided to monitor the pressure, flow and temperature of the SFP cooling and cleanup system.

The instrumentation provided to monitor the temperature of the water in the SFP is locally indicated as well as annunciated in the control room, The water level instrumentation alarms, high and low.

level, are annunciated in the control room. The instrumentation which monitors radiation levels in the SFP area, provides high radiation alarms locally in the SFP area and in the control room.

A change of 1 inch in SFP level requires approximately 1060 gallons of water. If a dilution event caused the pool level to rise from the low level alarm point to the high level alarm (2 foot span), a dilution of approxima%iy 23,500 gallons could occur before an alarm would be received in the control room. If the SFP boron concentration were at 2000 ppm initially, such a dilution would only result in a' reduction of the pool boron concentration of approximately 70 ppm.

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r 11 VOGTLE boron Dilution ANALYSIS

2.8 Administrative Controls The following administrative controls are in place to control the SFP boron concentration and water inventory:

1. Procedures are available to aid in the identification and termination of dilution events.

2. The procedures for loss of inventory (other than evaporation) specify that borated rnakeup sources be used as makeup sources. The procedures specify that nonborated sources only be used as a last resort.

3. In accordance with procedures, plant personnel perform rounds in the SFP enclosure once every twelve hours. The personnel making rounds to the SFP are trained to be aware of the change in the status of the SFP They are Instructed to check the temperature and levelin the pool and conditions around the pool during plant rounds.

4. Administrative controls are placed on some of the potential dilution paths.

S. The proposed Technical Specifications associated with the use of soluble boren credit will require the SFP boron concentration to be verified every seven days.

Prior to implementation of the License Amendment allowing credit for soluble boron in the SFP criticality analysis, current administrative controls on the SFP boron concentration and water inventory will be evaluated and procedures will be upgraded as necessary to ensure that the boron concentration is formally controlled during both normal and accident situations. The procedures will ensure that the proper provisions, precautions and instructions will be in place to control the pool boron concentration and water inventory.

12 VoGTLE BORON olluTION ANALYSIS I

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2.9 Piping s

The piping located inside the SFP room consists of 6 inch,4 inch and 2.5 inch fire protection lines, a 3 inch domineralized water line, a 3 inch normal chilled water line and a 1 inch utility water line.

None of the lines are seismically qualified.

t 2.10 Loss of offsite Power impact l

Of the dilution sources listed in Section 2.5.9, only the fire protection system is capable of providing non borated water to the SFP during a loss of offsite power.

l The SFP level instrumentation control room annunciator has backup power from plant batteries, The loss of offsite power would affect the ability to respond to a dilution. The normal source of borated water to the SFP would not be available upon a loss of offsite power. The RWST gravity fill could be established as well as manual addition of dry boric acid to the SFP if it became necessary to increase the SFP boron concentration during a loss of offsite power.

- The SFP cooling pumps are not automatically restarted following a loss of offsite power but are supplied from power supplies backed by the emergency diesel generators These pumps can be manually loaded on the emergency diesel. generators following a loss of offsite power.

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1 13 VOGTLE BORON Dilution ANALYSIS

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3.0 SPENT FUEL POOL DILUTION EVALUATION 3.1 Calculation of Boron Dilution Times and Volumes For the purposes of evaluating SFP dilution times and volumes, the total pool volume available for 1

dilution is conservatively estimated to be 772,000 gallons. This is the total volume of the SFP when l

it is filled to the elevation associated with the pool low level alarm and taking into account the volume displaced by SFP racks and fuel.

The transfer canal is normally isolated from the SFP. Therefore, the dilution analysis will only concern the SFP. For Vogtle, the boron concentration currently maintained in the SFP is greater than 2000 ppm.

Based on the Vogtle criticality analysis (Reference 1), the soluble boron concentration required to maintain the spent fuel boron concentration at K.n s 0.95, including uncertainties and burnup, with a 95% probability at a 95% confidence level (95/95)is 500 ppm.

For the purposes of the evaluating dilution times and volumes, the initial SFP boron concentration is assumed to be at the proposed Technical Specification limit of 2000 ppm. The evaluations are based on the SFP boron concentration being diluted from 2000 ppm to 500 ppm. To dilute the pool volume of 772,000 gallons from 2000 ppm to 500 ppm would conservatively require 1,070,000 gallons of non borated water.

I This analysis assumes thorough mixing of all the non borated water added to the SFP. It is likely, with cooling flow and convection from the spent fuel decay heat, that thorough mixing would occur.

However, if mixing was not adequate, a localized pocket of non borated water could form somewhere in the SFP. This possibility is addressed by the calculation in Reference 1 which shows that the spent fuel rack K n will be less than 1.0 on a 95/95 basis with the SFP filled with non borated water. Thus, even if a pocket of non borated water formed in the SFP, K n would not be expected to equal or exceed 1.0 anywhere in the pool.

14 VoGTLE BORON olluTION ANALYSIS

The time to dilute depends on the initial volume of the pool and the postulated rate of dilution. The dilution volumes and times for the Vogtle dilution scenarios discussed in Sections 3.2 and 3.3 are calculated based on the following equation:

t.% = In (Co / C %)V/Q (Equation 1)

Where:

t,w = time to dilute Co = the boron concentration of the pool volume at the beginning of the event Cw = the boron endpoint concentration Q = dilution rate (gallons of water / minute)

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V = volume (gallons) of SFP 3.2 Evaluation of Boron Dilution Events The potential SFP dilution events that could occur at Vogtle are evaluated below:

3.2.1 Dilution From Reactor Makeup Water Tank The following events assume that the RMW tank is automatically replenished since the normal l

configuration of the reactor makeup water system allows for the contents of the reactor makeup water tank to be automatically replenished from the water treatment system.

Vogtle SFP makeup is performed normally through a 2 inch connection to the SFP cooling loop using the RMWST, Makeup is provided approximately weekly from the RMWST The capacity of a RMWST pump is 200 gpm at 123 psl. Therefore, an estimated 200 gpm dilution rate of unborated water is used. In order to reach the dilution endpoint of 500 ppm, the RMW tank would have to be automatically replenished to allow for over 6 tank volumes (1,070,000 gallons) of dilute reactor makeup water to enter the pool area. At an estimated flowrate of 200 gpm, the dilution would take over 89 hours0.00103 days <br />0.0247 hours <br />1.471561e-4 weeks <br />3.38645e-5 months <br /> to reach the di!utioit endpoint.

15 VoGTLE DoRoN DILUTloN ANALYSIS

l The reactor makeup water (RMW) system connects to the SFPTC indirectly through the boric acid blender to the letdown line (Section 2.5.8). The dilution event is described in section 3.2.2.

There is a i inch connection to the SFP domineralizer used for flushing and sluicing.

A l

conservative 150 gpm flowrate is used for this connection. As above, in order to reach the dilution endpoint of 500 ppm, the RMW tank would have to be automatically replenished to allow for over 6 l

tank volumes (1,070,000 gallons) of dilute reactor makeup water to enter the pool area. At an estimated flowrate of 150 gpm, the dilution would take approximately iig hours to reach the dilution endpoint.

3.2.2 Dilution From CVCS Letdown l

Vogtle Spent Fuel Pool Transfer Canal (SFPTC) filling from the RHTs is performed by closing the inlet to the RHT that is to be transferred to the SFPTC. The potential dilution flowpath would exist if the CVCS letdown divert valve were to divert after the procedure for transfer was complete (with error of not opening the RHT inlet and not closing two valves to the SFPTC inlet from the Recycle Evaporator feed domineralizers). This would result in a flowrate of approximately 120 gpm to the SFPTC. The transfer canal would fill and spillinto the SFP.

Assuming the CVCS blender controls were set to provide unlimited non borated water and the reactor makeup water tank was repeatedly replenished, the 120 gpm flow from the CVCS letdown line to the SFP would take over 148 hours0.00171 days <br />0.0411 hours <br />2.44709e-4 weeks <br />5.6314e-5 months <br /> to reduce the pool boron concentration from 2000 ppm to 500 ppm.

This scenario assumes that the water supplied by the CVCS blender to the RCS is non borated. If the blender controls are set to provide borated water or the RCS contained greater than zero ppm boron, the SFP dilution rate would be reduced. The controls which supply the non borated water to the blender utilize an integrator to limit the amount of water that can be supplied to the blender. If the blender controls were set to provide only a limited amount of water, the amount of dilution of the 16 VOGTLE DORON DILUTION ANALYSIS P

SFP would be reduced because the Pressurizer level would continue to decrease and the Pressurizer low level alarm would alert the operator to the condition.

3.2.3 Dilution From Domineralized Water System There are 3 Demineralized Water Transfer Pumps, One or two of these pumps normally run. The non running pump (s) are placed in automatic to start at a low system pressure. Each pump provides 275 gpm at 65 psi.

Non borated water can be provided from the demineralized water system directly to the SFP cooling system through a 2 inch line that is isolated by a locked closed manual valve. If the valve was be left open following a SFP makeup evolution, it is possible that a dilution event could take place. Assuming a conservative makeup flowrate of 500 gpm, the dilution event would take over l

35 hours4.050926e-4 days <br />0.00972 hours <br />5.787037e-5 weeks <br />1.33175e-5 months <br />. The demineralized water storage tank contains approximately 250,000 gallons. In order to achieve the dilution, the tank would have to be replenished by the water treatment facility over 4 times, in addition to SFP makeup, the domineralized water makeup system provides makeup water to each unit's Condensate Storage tank (automatically) as well as each unit's RMW storage tank (automatically).

3.2.4 Dilution Resulting From SFP Heat Exchanger CCW Leak If a leak were to occur, the low level alarm on the CCW surge tank would alert the operators to a potential malfunction in the component cooling water system, if the level alarm failed, then the level in the tank would decrease until a valve automatically opens to allow refilling the tank with domineralized water. This valve could continue to cycle open, if the surge tank alarm in the CCW

- system fails, the level alarms in the spent fuel pool (SFP) could alert the operators that the level in the spent fuel poolls increasing. If the alarms failed to alert the operators to a malfunction and the leak rate is within the makeup capabilities to the surge tank so that the suction to the CCW pumps 17 VOGTLE BORON olluTioN ANALYSIS

l is not lost, then the plant personnel on rounds in the fuel handling building would identify that the levelin the pool was increasing.

The demineralized water storage tank contains approximately 250,000 gallons. In order to achieve the dilution, the tank would have to be replonished by the water treatment facility over 4 times.

Assuming e conservative makeup flowrate of 110 gpm, the dilution event would take over 162 hours0.00188 days <br />0.045 hours <br />2.678571e-4 weeks <br />6.1641e-5 months <br />.

3.2.6 Dilution From Spent Fuel Pool Domineralizer When the SFP demineralizer is first placed in service after being recharged with fresh resin it can initially remove boron from the water passing through it. The demineralizer normally utilizes a mixed bed of anion and cation resin which would remove a small amount of boron before caturating.

Because of the small amount of boron removed by the demineralizer, it is not considered a credible dilution source for the purposes of this evaluation.

3.2.6 Dilution Resulting From Random Pipe Breaks or Seismic Events Random Pipe Breaks This accident scenario is that a pipe randomly breaks in the vicinity of the spent fuel pool. The maximum flow expected from these lines is 2500 gpm (6' Fire Protection), 600 gpm (3' Demineralized Water), and 45 gpm (1* Utility Water) piping.

The fire protection system consists of 1 engine driven fire pump and 2 diesel driven fire pumps.

The pumps start on low system pressure and each provides 2500 gpm at 289 feet of head. The flowrate from a broken 6 inch fire protection line is estimated to be 2500 gpm. At this flowrate, it would take approximately 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br /> to dilute the pool to the 500 ppm concentration. Each fire 18-VoGTLE BORON olLUTioN ANALYSIS

protection tank contains 3 000 gallons. The tanks are connected so that the total amount of water available would be 600,000 gallons. The fire protection tanks have automatic fill capability from the well water system. Since 1,070.000 gallons of dilute water is necessary to dilute to the 500 ppm concentration, makeup would be required for a dilution event to take place.

The demineralized water system consists of a 250,000 gallon tank for both units with 3 pumps each delivenng a design flow of 275 gpm at a head of 150 feet. One or two of these pumps normally run. The non running pumps are placed in automatic to start at a low system pressure. The tank is automatically filled from the water treatment plant. It is estimated that the flowrate from a ruptured l

3 inch demineralized water pipe it 600 gpm. Assuming that the demineralized water storage tank is full (250,000 gallons) and the water treatment plant (the demineralized water tank's makeup source)is making up to the tank at its maximum flowrate of 480 gpm, the 600 gpm flowrate could last for approximately 35 hours4.050926e-4 days <br />0.00972 hours <br />5.787037e-5 weeks <br />1.33175e-5 months <br /> prior to emptying the tank and deliver approximately 1,260,000 gallons to the spent fuel pool. This amount of water above the 1,070,000 gallons required to achieve a dilution to the 500 ppm concentration and is therefore a potential dilution source.

A 1 inch utility water pipe break in the spent fuel pool area would result in a flowrate of approximately 45 gpm. The utility water system obtains its water from the

, well water storage tank. This storage tank is automatically replenished. A 45 gpm dilution rate would take approximately 396 hours0.00458 days <br />0.11 hours <br />6.547619e-4 weeks <br />1.50678e-4 months <br /> to achieve a dilution to the 500 ppm concentration.

Seismic Event A seismic event could cause piping ruptures in the vicinity of the SFP in piping that is not seismicaliy qualified. Piping within the immediate vicinity of the SFP that could result in dilution of the SFP if it ruptures during a seismic event are the fire protection, demineralized water, normal chilled water, and utility water lines discussed above, For this scenario, it is conservatively assumed that all of the nonseismic piping in the SFP area breaks and that piping that feeds the piping in the SFP area remains intact such that the maximum flowrate is delivered to the SFP area.

19 VOGTLE boron DILUTION ANALYSIS

The most limiting case for a seismic event would occur if the flowrate of the fire protection pumps l

was such that the fire protection tanks would not empty prior to reaching the dilution endpoint (2300 gpm). The total flowrate of systems other than Fire Protection (Demineralized Water, Utility Water, and Normal Chilled Water is 1245 gpm for 15 minutes, then 645 for the remainder of the event.

Using fire protection flowrates that range from 2100 gem (single 6 inch line break) to 4800 gpm (multiple 6 inch line breaks), the most limiting seismic case would be the fire protection pumps at a flowrate of 2300 gpm for 361 minutes. At this time and flowrate, the SFP would have received approximately 1,072,145 gallons of water (enough to reach the dilution endpoint). The fire protection tanks would still contain 4350 gallons. No additional water would have to be added. The total time for this event would be 361 minutes or approximately 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, if offsite power is not available, it would take approximately 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> to reach the dilution endpoint.

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3.3 Evaluation of infrequent Spent Fuel Pool Configurations I

The most limiting SFP configuration at Vogtle for the boron dilution analysis is when the spent fuel pools are separated.

When this case exists, the spent fuel pool volume for each pool is 1

approximately 386,000 gallons at the low level alarm. For the worst case dilution rate, if offsite power is available following a seismic event, it would take approximately 1.6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> reach the boron dilution endpoint. If offsite power is not available, it would be reached in approximately 1.8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />.

The amount of dilute water required for the dilution event decreases from 1,070,000 gallons to 535,000 gallons.

20 VOGTLE BORON OtluTION ANALYSIS

3.4 Summary of Ddution Events SCENARIO FLOWRATE TIME TO DOLUTION COMMENTS (GPM)

(HRS)

Reactor Makeup Water to SFP 200 89 Requeres RMW tank repleneshment for everat to occur Coohng Loop Reactor Makeup Water to SFP 150 119 Requres RMW tank replernshment for event to occur Demi.neralizer CVCS Letdown Divert to SFPTC 120 148 Requres RMW tank.@.4-~.a for event to occur Deminerakzed Water to SFP 500 35.7 Requres dermnerakzed water tank replenrshment for event to occur cooling loop (normal makeup)

CunpOnent Coohng Water 110 162 Requres deminerahzed water tank repleneshment tor event to cccur Interface With SFP Coohng HX -

Random Normal Challed Water 600 N/A Maxunum of 9000 gallons of water detrwered due to system see pipebreak (or Seismic Event) -

Random Utahty Water prpebreak.

45 396 Requres uhirty water tank repleneshment Scr event to occur (or Seismic Event)

Random Fire Protection supply 2500 7.1 Requres fire protechon water tanks repleneshment for event to occur hne pipebreak (3.6 for sogle SFP)

Random Demenerakzed Water 600 29.7 Requres demr'erahred water tank replemshment for event to occur prpebreak (or Seismc Event)

Seismic Event (AII nonseismec 3545 gom for 6

Assumes all nonsersmic ppng ruptures only an the SFP toom pipes break) MOST LIMITING (15 min) then (1.6 for single SFP) 2945 gpm 21 VOGTLE BORON DIUmON ANALYSIS

The evaluation of SFP dilution events in Sections 3.2 and 3.3 eliminated from consideration all but nine of the of the dilution scenarios evaluated.

l Three dilution scenarios involve the transfer of non borated water from the reactor makeup water system to the SFP cooling system, cleanup systems or the transfer canal at a maximum rate of approximately 200 gpm. The reactor makeup water system is not capable of supplying the approximately 1,070,000 gallons of water necessary to dilute the SFP from 2000 ppm to 500 ppm unless the reactor makeup water tank is replenished from the water treatment system. Based on the analysis in Section 3.2 the least amount of time for response allowed by any of these scenarios is 8g hours.

Two dilution scenarios involve the transfer of non borated water from the demineralized water system to the SFP cooling system or pool area itself. The flowrates vary from 500 gpm to a 3

maximum rate of approximately 600 gpm. The demlneralized water system is capable of supplying the approximately 480,000 gallons of water necessary to dilute the SFP from 2000 ppm to 500 ppm if the domineralized water tank la repeated replenished from the water treatment system. Based on l

the analysis in Section 3.2 the least amount of time for response allowed by these scenarios is 2g.7 f

hours.

The Component Cooling Water leak and Utility Water pipebreak scenarios consider flowrates of 110 and 45 gpm. At these flowrates, it would take over 160 hours0.00185 days <br />0.0444 hours <br />2.645503e-4 weeks <br />6.088e-5 months <br /> and 350 hours0.00405 days <br />0.0972 hours <br />5.787037e-4 weeks <br />1.33175e-4 months <br />, respectively, to dilute the SFP, Personnel rounds as well as alarms and flooding indications would allow for termination of the event prior to reaching the dilution endpoint.

A seismic event which breaks all of the larCest nonselsmic piping in the spent fuel pool area would produce an estimated flowrate of 6045 gpm for 15 minutes then 5445 for the remaining time of the event. This flowrate is not the most limiting case for a seismic event. The most limiting case for a seismic event exists where the fire protection system delivers 2300 gpm for the entire event and the other systems deliver 1245 gpm for 15 minutes then 645 for the remainder of the event. The event would take approximately 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> to reach the dilution endpoint. Under conditions where the SFP is in a single pool configuration, the event could take place in approximately 1.6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />. The 22 VOGTLE boron olLUTioN ANALYSIS

heightened awareness of the operating crew due to a seismic event as well as the large quantity of water delivered to the spent fuel pool area should allow for early detection and termination of the event.

The remaining event is the transfer of non borated water from the fire protection tanks to the SFP area as a result of a random pipe rupture. The maximum flowrate is estimated to be 2500 gpm resulting in a c,ution from 2000 ppm to 500 ppm in approximately 7 hours8.101852e-5 days <br />0.00194 hours <br />1.157407e-5 weeks <br />2.6635e-6 months <br />. Under conditions where the SFP is in a single pool configuration, the event could take place in approximately 3.6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.

For any one of these scenarios to successfully result in the dilution of the SFP from 2000 ppm to

)

500 ppm, the addition of 1,070,000 gallons of water to the SFP would have to go unnoticed. The first indication of such an event would be high level alarms in the control room from the spent fuel poollevelinstrumentation. If the high level alarms fall, it is reasonable to expect that the significant increase in coollevel and eventual pool overflow that would result from a pool dilution event will be readily detected by plant operators in time to take mitigative actions. In the random fire protection line break case, alarms for a fire pump running and fire protection tank low level would alert operators of this condition, in cases where tanks require makeup from the water treatment plant, the personnel would be expected to investigate the continuous supply of large quantities of water to plant systems. In addition, because the time required to reach a boron concentration of 500 ppm from 2000 ppm is significantly longer than twelve hours in all but two cases, it can be assumed that 1

the operator rounds through the SFP area that occur once per twelve hours will detect the increase in the pool level even if alarms other than the high level alarm fall and the flooding isn't detected.

For any one of these dilution scenarios to successfully add 1,070,000 gallons of water to the SFP, plant operators would have to fail to question or investigate the continuous makeup of water to the reactor makeup water tank or demineralized water tank, and fail to recognize that the need for 1,070,000 gallons of makeup was unusual.

23 VOGTLE boron Dilution ANALYSIS

4.0 CONCLUsloNS l

A boron dilution analysis has been completed for the Vogtle SFP As a result of this SFP boron dilution analysis, it is concluded that an event which would result in the dilution of the SFP boron concentration from 2000 ppm to 500 ppm is not a credible event. This conclusion is based on the following:

1. In order to dilute the SFP to the design K,n f 0.95, a substantial amount of water (greater than o

1,000,000 gallons)is needed.

2. Since such a large water volume turnover is required, a SFP dilution event would be readily detected by plant personnel via alarms, flooding in the auxiliary building or by normal operator i

rounds through the SFP area.

3. Evaluations indicate that, based on the flow rates of non borated water normally available to the

-SFP, even when significantly higher flow rates are assumed, sufficient time is available to detect and respond to such an event.

It should be noted that this boron dilution evaluation was conducted by evaluating the time and water volumes required to dilute the SFP from 2000 ppm to 500 ppm. The 500 ppm end point was utilized to ensure that K,n for the spent fuel racks would remain less than or equal to 0.95. As part of the criticality analysis for the Vogtle Spent fuel racks (Reference 1), a calculation has been performed on a 95/95 basis to show that the spent fuel rack K,n remains less than 1.0 with non-borated water in the pool. Thus, even if the SFP were diluted to zero ppm, which would take significantly more water than evaluated above, the fuel in the racks would be expected to remain suberitical and the health and safety of the public would be protected.

24 VOOTLE boron DILUTION ANALYSIS

5,0 REFERENCES

1. WCAP 14720. Rev.1 Vogtle Units 1 and 2 Spent Fuel Rack Criticality Analysis With Credit For Soluble Boron, Westinghouse Commercial Nuclear Fuel Division. March 1997.

l l

25 VOGTLE DORON olLUTION ANALYSIS

l ENCLOSURE 7 VOGTLE ELECTRIC GENERATINO PLANT i

RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION l

REVISED REQUEST TO REVISE TECilNICAL SPECIFICATIONS l

CREDIT FOR BORON AND ENRICllMENT INCBEASE FOR FUliL STORAQIl l

RESPONSES TO REQUESTS FOR ADDITIONALINFORMATION l

-71

ENCLOSURE 7 VOGTLE ELECTRIC GENERATING PLANT RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REVISED REQUEST TO REVISE TECHNICAL SPECIFICATIONS CR.15QlT FOR 110RON AND ENRICllMENT INCREASE FOR FUEL STORAGE Question 1.

The stafi does not concur with the proposed placement of the burnup vs. initial enrichment i

tables and figures, or the cell storage configuration in the Core Operating Limits Report (COLR). These are not COLR type item since they do not appear to be items that will change from cycle-to-cycle in the future. Also, the NRC should review any changes to i

these items. T herefore, they should l'e retained in the TS.

l

Response

The proposed Technical Specification change has been revised to incorporate the information in the Technical Specifications.

Question 2.

Proposed TS 3.7.17 should refer to the normal fuel pool boron concentration (2J00 ppm),

l which could be placed in the COLR.

l

Response

The fuel storage pool dilution has been assessed and is included as enclosure 6 to letter LCV-0849 E. The assessment conservatively assumed an initial concentration of 2000 ppm although normally it is maintained at about 2400 ppm. The assumed value of 2000 I

ppm is being incorporated into Specification 3.7.17, Question 3.

Proposed TS 4.3.1.1.c should refer to Knlos than 1.0 with unborated water that includes an allowance for uncertairc es as described in the revised methodology of WCAP-14416-NP-A, rev.1, which are now 95/95 values.

Response

The criticality analyses have been revised in accordance with the revised methodology of WCAP-14416-NP-A, rev.1. The revised analyses are described in enclosure 5.

Specification 4.3.1.1.c is being revised to refer to the 95/95 requirement for the no soluble boron criticality analysis.

Question 4.

Proposed TS 4.3.1.1.b should also refer to the minimum boron concentration required to maintain the Enless than er equal to the 0.95 limit (1250 ppm). For example, "Kar 5 0.95 if fully flooded with water borated ;a 1250 ppm.. "

7-1

_________._j

ENCLOSURE 7 VOGTLE ELECTRIC GENERATING PLANT RESPONSE TO REQUEST FOR ADDITIONAL INFORhiATION REVISED REQUEST TO REVISE TECliNICAL SPECIFICATIONS CREDIT FOR DORON AND ENRICHh1ENT INCREASE FOR FUEL STORAGE

Response

The revised calculated boron concentratinn for Km s 0.95 is 500 ppm for Unit 2 and 450 ppm for Unit 1. The additional boron to account for accidents including a misplaced fuel assembly or loss of cooling raises the concentration to 1250 ppm. Both of these values are less than the specified minimum concentration of 2000 ppm or the normal nominal concentration of about 2400 ppm. In accordance with the request section 4.3.1.1.b is being resised to include a reference to the 450 ppm (Unit 1) and 500 ppm (Unit 2) requirement.

Question 5.

The burnup requirements for 3x3 cheucaboard configuration approaches a burnup limit of over 43,000 hiWD/hiTU. Since WCAP 14416-NP (Table 6) indicates a positive bias above 40,000 htWD/h1TU, axial burnup distribution effects should be included in the burnup credit limit.

Response

The ef1'ects of axial burnup have been considered in the criticality analysis of the VEGP fuel storage racks as stated in section 9.3 of enclosure 5. The axial burnup and enrichment combination determines the point at which a positive bias occurs. The enrichment-burnup combinations for the VEGP analyses are below the combinations in WCAP-14416-NP-A, rev. I that indicate the need to consider a positive bias.

Question 6.

Discuss any changes in plant procedures, if necessary, to control pool boron concentrations and water inventory during both normal and accident conditions.

Response

Prior to the implementation of the license amendment allowing credit for soluble boron in the fuel stor age pool criticality analysis, current admininstrative controls on the fuel storage pool boron concentration and water inventory will be evaluated and procedures will be upgraded as necessary, to ensure that the fuel stocage pool boron concentration is formally controlled during both normal and accident situations. The procedures will ensure that the proper provisions, precautions, and instructions to control the fuel storage pool boron concentration and water inventory are in place, 72

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