ML20198P696

Revised Spent Fuel Pool Boron Dilution Analysis

ML20198P696
Person / Time
Site:	Vogtle
Issue date:	01/16/1998
From:	SOUTHERN NUCLEAR OPERATING CO.
To:
Shared Package
ML20198P685	List: ML20198P680 ML20198P696
References
NUDOCS 9801220214
Download: ML20198P696 (26)

Text

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ATTACHMENT _2 SPENT FUEL POOL BQRON DlLUTION ANALYSIS i

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VOGTLE BORON 0tLUTION ANALYSIC E A K 24 Y PDR .

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 Pool Instrumentation 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 l 3.4 Summary of Dilution Events 21

4.0 CONCLUSION

S 24

5.0 REFERENCES

25 1

.VoGTLE BORON DILUTION ANALYSIS

l

1.0 INTRODUCTION

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

- Dilution Sources and Flowrates 1 Boration Sources i

- Instrumentation ,

- Administrative Procedures

- Piping

- Loss of Offsite Power impact

- Boron Dilution initiating Events

- Boron Dilution Times and Volumes i

The boron dilution analysis was performed to ensure that sufficient time is available to detect and I mitigate the dilution before the spent fuel rack criticality analysis 0.95 k,n design basis is exceeded.

2 VOGTLE boron DILUTION ANALYS'S l

2.0 ' BPENT FUEL POOL AND RELATkD SYSTEM FEATURES This section provides background information on the SFP and its related systems and features. f 2.1 - Spent Fuel Pool The design purpose of the SFP is to provide for safe storage of irradiated fuel assemblies. The pool is 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 Pat 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 water volume of each individual pool is approximately 386,000 gallons. The SFP is a reinforced concrete structure with a welded steel liner. The concrete structure has formed leak chases that can be drained by opening

• sample valves that are located in the Fuel Handling building. The pool structure is ' designed to meet seismic requirements. Each poo!is approximately 41.5 feet deep.

A transfer canal is located adjacent to each SFP. Each transfer canal connects the SFP to its  ;

respective - transfer tube. - The cask loading area is located between the SFPs and provides communication between the pools.

3 VoGTLE boron DILUTION ANALYSIS

. , ___ ._. . . _ . . ~ _

-. .- . . - - - . - - . = _ . . . - . _ - . - - - . -

. l 2.2 Spent Fuel Storage Racks l l

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

2.3 Spent Fuel Pool Cooling System There are two trains of spent fuel pool cooling for each pool. Each of the two trains of the cooling system consists of a pump, a heat exchanger, valves, piping and instrumentation. The pump takes suction from the fuel pool at an inlet located below the pool water level, transfers the pool water

- through a heat exchanger NJ returns it to the pool. The supply and return lines are 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 any 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.

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 GFP demineralizer and filter. The filter removes particulates from the SFP water and the SFP demineralizer removes ionic impurities.

4 VoGTLE boron DILUT1oN ANALYSIS

_-. _--_- -- -. . - - _ - - . . -- - - - . ~ . . . .. - -.-

The refueling water cleanup loop also uses the SFP domineralizer and filters to clean up the refueling water storags 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 centrifugni 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 skimmers.

i 1

2.5 Dilution Sources ,

2.5.1 Chemical and Volume Control System (CVCS) [ Letdown Divert to SFP Transfer Canal]

A potential dilution path exists if a valv9 interfacing with the spent fuel pool 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 intet 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 procedure for transfer was complete (with error of not opening the RHT inlet and not closing two valves to the SFP inlet from the Recycle Evaporator feed demineralizers). Thl. could result in a flowrate of up to 120 gpm to the Spent Fuel Pool Transfer Canal. The transfer canal would fill and spill into 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 thc RMWST. Makeup is provided approximately weekly from the RMWST. The capacity of a RMWS1 pump is 200 gpm at 123 psl. Therefore, an estimated 200 gpm dilution rate of unborated

- water is used.

5 l VOGrLE BORON DILUTION ANALYSIS e , , , , - - e

The reactor makeup water (RMW) system connects to the SFPTC indirectly as a result of CVCS ,

letdown (Sect!on 2.5.1).

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

conservative 150 gpm flowrPte is used for this connection.

There is also a 3/8 inch line in the SFPTC used to supply water as the hydraulic fluid to raise and lower the upender. Because of the size of this line and because it is normally isolated, this line will not be considered as a potential dilution flow path.

2.5.3 Domineralized Water System There is a 2 inch Demineralized Water connection to the SFP cooling loop for makeup. A .

conservative dilution flow rate of 500 gpm is estimated.

The domineralized water system consists of a 250,000 ga!!on 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 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.

2.6.4 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 a 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 t ,

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It would be expected that the flow rate of any leakege of component cooling wa or into the SFP cooling system would be low due to the small difference in operating pressures 5twe3n the two  !

systems. Therefore, a conservative 110 gpm flowrote is estimated. ,

2.5.5 SFP Domineralizer Resin Fill Connection .

The SFP domineralizer has a resin fill line in which domineralized water is used to assist in res5 addition. This is a blind flanged connection. Only a small amount of water is used during resin addition. Rosin addition and sluicing are procedurally controlled, infrequently performed evolutions.

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

2.5.5 Fire Protection System The spent fuel pool area has six 0 inch fire protection water supply headers. Two of these lines reduce to 4 inch lines and ultimately 2.5 inch lines providing 4 hose stations. The other four 6' lines pass through the SFP room, The fire protection system consists of two 300,000 gallon 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 wculd be under the control of an approved

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.

t 7

VOGTLE boron DILUTION ANALYSIS

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. o 2.5J Recycle Holdup Tank Discharge to SFP Transfer Canal 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 transferr6d 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 the 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 dilute water to the pool. It is estimated that the system contains approximately 9000 gallons of water. Therefore, this water will be used only as an addition to other systems during a seismic event.

i l

I E

l VOGTLE BORON olluTION ANALYRIS

d a d 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 amount of non borated water to  ;

I the SFP. The potential for these sources to dilute the SFP boron concentration down to the design basis boron concentration (600 ppm) will be evaluated in Sectiors 3.0.  :

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 Dominerallred 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) 3.2.6 168 gpm (MEB 31 crack) 3.2.6 Utility Water 45 gpm (pipe break) 3.2.6 s

9 VoGTLE boron DILUTloN ANALYSIS

i 2.6 Boration Sources The normal source of borated water to the SFP is from the RWST through the Refueling Water l 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.

i 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 j

.lsolated from the SFP cooling system. If necessary, this connection can supply approximately 200 4 gpm of borated water to the SFP via the refueling water purification pump to the inlet to the SFP q cooling > stem 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 la 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.

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 i- VoGTLE boron DILUTION ANALYSIS l

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2.7 Spent Fuel Poolinsirumentation I

instrumentation is available to monitor SFP water level and temperature, arid the radiation levels in t 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 entrol room.

A change of 1 inch in a single 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 approximately 25,500 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 raduction of the pool boron concentration of approximately 128 ppm.

e t

VoGTLE boron DILUTION ANALYSIS i

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

1. Procedures to aid in the identification and temiination of dilution events.

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

3. Plant personnel will perform rounds in the SFP enclosure once every twelve hours. The personnel making rounds to the SFP will be trained to be aware of the change in the status of the SFP. They will bo instructed to check the temperature and level in the pool and conditions around the pool during plant rounds.

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

5. The proposed Technical Specifications associated with the use of soluble boron 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 ti a 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 ' ace to control the pool boron concentration and water inventory.

12 VOGTLE DORON olLUTION ANALYSIS I

2.9 Piping

~

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, however, they are seismically analyzed and supported.

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

The SFP levelinstrumentation 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 availab'e 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.

1 l-l 13 VoGTLE boron olluTioN ANALYSIS

. - . - . . - - - - - . - - - - - - - . . . - - . . - . - . . ~ - . - - -

i 3.0 SPENT FUEL POOL DILUTION EVALUATION ,

i I - 3.1 - Calculation of Boron Dilution Times and Volumes l

f For the purposes of evaluating SFP dilution times and volumes, the total pool volume available for j l

dilution is conservatively estimated to be 386,000 gallons. ' This is the total volume of the SFP when

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

. 1 The transfer canal is normally isolated from the SFP. Therefore, the dilution analysis will only j concem the SFP. For Vogtle, the boron concentration currently maintained in the SFP is greater j than 2000 ppm; Based'on the Vogtle criticality analysis (Reference 2), the soluble boron j concentration required to maintain the spent fuel at 4 s; 0.95, including uncertainties and bumup, j with a 95% probability at a 95% confidence level (95/95) is 600 pprn. j i

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 beton concentration being diluted from 2000 ppm to 600 ppm. To dilute the pool j volume of 386,000 gallons from 2000 ppm to 600 ppm would conservatively require 465,000 gallons of non-borated water, i

L This analysis assumes thorough mixing of all the non-borated water added to the SFP. It is likely, j

-with cooling flow and convection from the spent fuel decay heat, that thorough mixing would occur. I However, if mixing was not adequate, a localized pocket of non-borated ws**

could form j L somewhere in the bFP. This possibility'is addressed by the calculation in Reference 1 which  ;

'shows that the spent fuel rack 4 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, 4 would not l 1be expected to equal or exceed 1.0 anywhere in the pool, i i

i 14 I P voGTLE boron DILUTION ANALYSIS 5

..  : .-- =- . - . --

e .e f The time to dilute depends on the initial volume of the pool and the postulated rate of dilution. The I 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.no = In (Co / C.na)V/Q (Equation 1)

Where:

}

t.no = time to dilute {

Co a the boron concentration of the pool volume at the beginning of the event }

C.no = the boron endpoint concentration j Q = dilution rate (gallons of water / minute)  !

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: }

r r

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.

i Vogtle SFP makeup , erformed.normally through a 2 Irich connection to the SFP cooling loop using the RMWSY. Makeup is provided approximately weekly from the RMWST. The capacity of a RMWST pump is 200 gpm at 123 pol Therefore, an estimated 200 gpm dilution rate of unborated  ;

~

water is used. -In order to reach the dilution endpoint of 600 ppm, the RMW tank would have to be

automatically replenished to allow for almost 3 tank volumes (465,000 gations) of dilute reactor _ i makeup water to enter the pool area. At an estimated flowrote of 200 gpm, the dilution would take over 38 hours4.398148e-4 days <br />0.0106 hours <br />6.283069e-5 weeks <br />1.4459e-5 months <br /> to reach the dilution endpoint, 15 VoGTLE BORON olluTioN ANALYSIS t

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e The reactor makeup water (RMW) system connects to the SFPTC indirectly through the boric acid blender to the letdown line (Section 2.S.8). The dilution event is described in section 3.2.2.

i There is a 1 inch connection to the SFP demineralizer used for flushing and sluicing. A conservative 150 gpm flowrate is used for this connection. As above, in order to reach the dilution  ;

endpoint of 600 ppm, the RMW tank would have to be automatically replenished to allow for almost

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3 tank volumes (465,000 gallons) of dilute reactor makeup water to enter the pool area. At an estimated flowrate of 150 gpm, the dilution would take approximately 52 hours6.018519e-4 days <br />0.0144 hours <br />8.597884e-5 weeks <br />1.9786e-5 months <br /> to reach the dilution i

endpoint.

I 3.2.2 Dilution From CVCS Letdown 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 SFFTC. The potential dilution flowpath would exist if the CVCS letdown divert valve were to divert after the procedure for transfer was compleie (with error of not opening the RHT inlet and not clnsing two valves to the SFPTC inlet from the Recycle Evaporator feed demineralizers). This would result in a flowrate of approximately 120 gpm to the ,

SFPTC. The transfer canal would fill and spill into 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 64 hours7.407407e-4 days <br />0.0178 hours <br />1.058201e-4 weeks <br />2.4352e-5 months <br /> to reduce the pool boron concentration from 2000 ppm to 600 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 contrcls 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 boron DILUTloN ANALYSIS l

~ _- . . .. _

- _~ _ _. . - _ _ _ _ _ _ _ _ . _ _ . _ . . _ - . _ _ _ _ _ . - _ . . - _ _ .

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

l

3.2.3 Dilution From Domineralized Water System l

There are 3 Domineralized Water Transfer Pumps. One or two of these pumps normally run. The non-runnirg pump (s) are placed in automatic to start at a low system pressure. Each pump .l provides 275 gpm at 65 pol. l

t. l P

, Non-borated water can be provided from the domineralized water system directly to the SFP j i cooling system through a 2 inch line that is isolated by a locked closed manual vilve. If the valve  !

was be left open following a SFP makeup enokstion, it is possible that a dilutim event could take place. . Assuming a conservative makeup flowiste of 500 gpm, the dilution event would take over  !

15 hours1.736111e-4 days <br />0.00417 hours <br />2.480159e-5 weeks <br />5.7075e-6 months <br />. The domineralized water storage tank contains approximately 250,000 gallons. = In order i to achieve the dilution, the tank would have to be replenished by the water treatment facility almost l 2 times.- In addition to SFP makeup, the domineralized water makeup system provides makeup j water to each unit's Condensate Storage tank (automatically) as well as each unit's RMW storage t

tank (automatically),

)

t 3.2.4 " Dilution Resulting From SFP Heat Exchanger CCW Leak  ;

I If a leak were to occur, the low level alarm on the CCW surge tank would alert the operators to a I potential malfunction in the component cooling water system, if the level alarm failed, then the j

' level in the tank would decrease until a valve automatically opens to allow refilling the tank with  ;

Ldomineralized water. This valve could continue to cycle open, if the surge tar,k alarm in the CCW j system fails, the level alarms in the spent fuel pool (SFP) could aled be operators that the level in  :

tho' spent fuel pool is incrassing.- if the alarms failed to alert the operators to a malfunction and the j leak rate is within the makeup capabilities to the surge tank so that the suction to the CCW pumps j

). i: ~ 1 17

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c VOGTLE BORON DILUTION ANALYSIS -  ;

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

l The domineralized water storage tank contains approximateh 250,000 gallons. In order to achieve the dilution, the tank would have to be replenished by the water trertment facility alrrast 2 times. l Assuming a conservative makeup flowrate of 110 gpm, the dilution event would take over 70 hourb.

3.2.6 Dilution From Spent Fuel Pool Domineralizer When the SFP domineralizer is first placed in service after being recharged with fresh resin it can initially remove boron from the water passing (;. tough it. The demineralizer normally utilizes a mixed bed of anion an,' cation resin which would remove a small amount of boron before saturating. Because of the small amount of boron removed by the demineralizer, it is not considemd o credible dilution source for the purposes of this evaluation.

3.2.6 Dilution Resulting From Random Pipe Breaks or Seismic Eventa 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" Chilled Water or Demineralized Water), and 45 gpm (1' Utility Water) piping. These lines are seismically analyzed and supported. Howevel, the effects of a guillotine break in a 6 inch fire protection line (which envelopes a break in a 3 inch or a 1 inch line in the SFP area) is considered even though j, MEB 3-1 position allows evaluation of a crack in lieu of a break in such lines.

l l

18 VoG1LE boron DILUTION ANALYSl$

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 over 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> to dilute the pool to the 600 ppm concentrate. Each fire protection tank contains 300,000 gallons. The tanks are connected so that the total amount of water available wouk. be 600,000 gallons.

The domineralized water system consist of a 250,000 gallon tank for both units with 3 pumps each delivering a design flow of 275 gpm at t .ead 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 3 inch demineralized water pipe is 600 gpm. Assuming that the domineralized 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 tu emptying the tank and deliver approximately 1,260,000 gallons to the spent fuel pool. This amount of water is above the 465,000 gallons required to achieve a dilution to the 600 ppm concentration and is therefore a potential dilution source. A 600 gpm dilution rate would take approximately 12.9 hours1.041667e-4 days <br />0.0025 hours <br />1.488095e-5 weeks <br />3.4245e-6 months <br /> to achieve a dilution to 600 ppm.

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 300,000 gallons well water storage tank. Th;s storage tank is automatically replenished. A 45 gpm dilution rate wouH take approximately 172 hours0.00199 days <br />0.0478 hours <br />2.843915e-4 weeks <br />6.5446e-5 months <br /> to achieve a dilution to the 600 ppm concentration.

Seismic Event Piping within the immediate vicinity of the SFP is seismically analyzed and supported.

Although well beyond the requirements of MEB 3-1, for this scenario, it is conservatively assumed that seismically analyzed demineralized water, normal chilled water, and utility water 19 VOGTLE BORON DILUTION ANALYSIS

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.

The flowrate of the fire protection system is assumed to be the maximum flow through a crack in the largest single fire protection pipe p') in the SFP. This flowrate is calculated to be 168 gpm. The total flowrate of systems other than Fire Protection (Demineralized Water, Utility Water eind Normal Chilled Water is 1?45 gpm for 15 minutes, then 645 for the remainder of the event. The total time for this event would be 561 minutes or approximately 9.3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />.

If offsite power is not availabla, it would take cpproximately 23 hours2.662037e-4 days <br />0.00639 hours <br />3.80291e-5 weeks <br />8.7515e-6 months <br /> to reach the dilution endpoint.

3.3 Evaluation of Infrequent Spent Fuel Pool Configurations 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 approximately 386,000 gallons at the low level alarm. For the worst case dilution rato, if a random pipe break of a fire protection line were to occur, it would take approximately 3.1 hoves to reach the borca dilution endpoint. The amount of dilute water required for the dilution event would be 465,000 gallons.

t 20 VoGTLE BORON Dil.UTION ANALYSTS 4

1

Summary of Dilution Events

,- 3.4 .

SCENARIO FLOWRATE TIME TO DILUTION COMMENTS ~

I (GPM) (HRS) -

200 38 Requires RMW tank repler.ishment for event to occur -

Reactor Makeup Water to SFP Cooling Loop React.or Makeup Water to' 150 52 PMuires RMW tank replenishment for event to occur ,.

SFP Demineralizer 120 60 Requires RMW tank replenishment for event to occur CVCS Letdown Divert to SFPTC.

500 15.5 Requires demineralized water tank replenishmem for event to occur Demineralized Water to SFP cooling loop (normal makeup) I Component Cooling Water 110 70 Requires demineralized water tank replenishment for event to occur Interface With SFP Cooling

HX 660 N!A Maximum of 9000 gallons of water delivered due to system size l Random Normal Chilled Water pipebreak (t)

Random Utility Water 45 172 Recuires utility water tank replenishment for event to occur pipebreak (t) 2500 3.1 Requires fire protection water tanks replenishment for event to occur Random Fire Protection supply line pipebreak 600 12.9 Requires demineralized water tank replenishment for event to occur Random Demineralized Water pipebreak (t) 1413 gpm for 9.3 Assumes all nonseismic piping that is not analyzed for a seismic Seismic Event (All seismically event ruptures only in the SFP room analyzed pipes break / crack) (15 min) then 813 gpm ,

21 VoGTLE boron ottuTioN ANALYSTS 1

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

Three dilution scenariot 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 465,000 gallons of water necessary to dilute the SFP from 2000 ppm to 600 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 38 hours4.398148e-4 days <br />0.0106 hours <br />6.283069e-5 weeks <br />1.4459e-5 months <br />.

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 maximum rate of approximately 600 gpm. The demineralized water system is capable of supplying the approximately 465,000 gallons of water necessary to dilute the SFP from 2000 ppm to 600 ppm if the demineralized water tank is repeated replenished from the water treatment system. Based on the analysis in Section 3.2 the leas' mount of time for response allowed by these scenarios is 12.9 hours1.041667e-4 days <br />0.0025 hours <br />1.488095e-5 weeks <br />3.4245e-6 months <br />.

The Component Cooling Water leak and Utility Water pipebreak scenarios consider flowr% f 110 end 45 gpm. At these flowrates, it would take over 70 hours8.101852e-4 days <br />0.0194 hours <br />1.157407e-4 weeks <br />2.6635e-5 months <br /> and 172 hours0.00199 days <br />0.0478 hours <br />2.843915e-4 weeks <br />6.5446e-5 months <br />, respectively, to dilute the SFP. Personne' ounds 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 largest nonseismic piping that is not analyzed for a seismic event in the spent fuel pool area would produce an estimated flowrate of 1413 gpm for 15 minutes then 813 for the remaining time of the event. The event would take approximately 9.3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> to reach the dilution endpoint. The 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, 22 VOGTLE BORON olluTION ANALYSIS

The remaining event is the transfer of non borated water frocn the fire protection tanks to the SFP area es a result of a random pipe rupture. The maximum flowrate is estimated to be 2500 gpm resulting in a dilution from 2000 ppm to 600 ppm in approximately 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />.

For any one of these scenarios to successfully result in the dilution of the SFP from 2000 ppm to 600 ppm, the addition of 465,000 gallons of water to the SFP would have to go unnoticed. The first indication of such an event would be high level alarms in 1:1e control room from the spent fuel pool level instrumentation. If tha high level alarms fail, it is reasonable to expect that the significant increase in pool level 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 T;re pump running and fire protection tank low level would alert operators of this condition. In caess where tanks require makeup from the water treatment plant, the pertunnel 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 600 ppm from 2000 ppm is significantly longer than twelve hours in all but two cases, it can be assumed that 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 fail and the flooding isn't detected.

For any one of these dilution scenarios to successfully add 465,000 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 465,000 gallons of makeup was unusual.

23 VoGTLE boron ciLUTION ANALYSTS l

/

- - _ _ . _ _ - _ _ - - - _ _ _ - - _ _ _ _ _ - ~ - _ . - _ . _ . _a

4.0 CONCLUSION

S d 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 600 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 fo 0.95, a substantial amount of water (greater than 465,000 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 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 600 ppm. The 600 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 cak ttion has been performed on a 95/95 basis to shnw 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 wmtd be expected to remain subcritical and the health and safety of the public would be protected.

24 VOGTLE boron DttuTION ANALYSIS

._t

~

5.0 REFERENCES

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

t

2. Westinghouse Calc. Note, CAA 97-281, "Vogtle Unit'1 Boral Replacement Spent Fuel Rack Criticality Analysis with Credit For Soluble Boron."

e 25 VOGTLE BORON DILUTION ANALYSIS ~

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