ML20199B279

Forwards Corrected Addl Info Re Requested TS Changes to Allow Credit for Soluble Boron Concentration in Fuel Storage Pools.Second Page of Attachment 1,inadvertently Omitted

ML20199B279
Person / Time
Site:	Vogtle
Issue date:	01/23/1998
From:	Mccoy C SOUTHERN NUCLEAR OPERATING CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LCV-0849-M, LCV-849-M, NUDOCS 9801280220
Download: ML20199B279 (6)

Text

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C.K McCoy Southern Nuclear

'Sce Poident Operating Company. loc.

Wgtle Pneject 40 inwress Center Parkway PO Box 1795 Dirmingham. Alabama 35201 Tot 205 992 7122 Fax 705932 0403 SOUTHERN COMPANY

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January 23, 1998 LCV-0849-M Docket Nos-50-424 50-425 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555 Ladies and Gentlernen:

VOGTLE ELECTRIC GENERATING PLANT ADDITIONAL INFORMATION FUEL STORAGE POOL BORON D.1L11 HOE Southern Nuclear letter LCV-0849 K, dated January 16,1998, submitted additional information regarding requested Technical Specification changes to allow credit for the soluble boron concentration in the fuel storage pools. Letter LCV 0849 K contained two attachments. The second page of Attachment I was inadvenently omitted. The attachment has been corrected and the two attachments in LCV 0849 K are being re-sent in their entirety.

Sincerely, C. K. hicCoy l!

CKM/RJF Attachments:

1. Responses to Questions Il

2. Revised Spent Fuel Pool Boron Dilution Analysis OO!

xc: Southern NucleaI Q

Mr. J. B. Beasley, Jr.

Mr. M. Sheibani NORMS llllll1IRllulll1 Hill

- U. S. Nuclear Regulatory Comnligion Mr. L. A. Reyes, Regional Administrator Mr. D. II. Jaffe, Senior Project Manager, NRR Mr. J. Zeiler, Senior Resident Inspector, Vogtle 9901290220 990123 PDR ADOCK 05000424 P

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P RESPONSE TO NRC QUESTIONS i

pN DILUTION ANALYSIS j

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e RESPONSE TO NRC OUESTIONS ON plLUTION ANALYSIS OF THE SPENT FUFIPOOL Question 1:

"Ihe boron dilution analysis (enclosure 6) states that the two spent fuel pools (SFPs) are normally connected via the cask loading area, which provides communication between

- the two SFPs. As a result, a combined volume of 772,000 gallons of water is used in the calculation for the boron dilution times and volumes. Equation 1 in the submittal is used for this calculation, llowever, to use Equation 1, timely through mixing between the two -

pools is assumed. Provide justification how the relatively narrow channel through the cask loading area (the channel appears in drawing AX4DD304 to be approximately 1/10th the width of the pools) supports the assumption of timely, through mixing to allow use of the combined water volume. (Alternatively, the boron dilution analysis may be completed for separate SFPs).

Response

The primary source of dilution water considered in enclosure 6 was from postulated broken pipes that spray water onto the surface of the spent fuel pool. Under these conditions the water level in the two pools will rise together until exceeding the elevation of the curb around the individual pools (approximately elevation 220' 6"). At this point water will flow along the surface between the two pools (also through or over the gates between the pools) as well as over the curb from both pools onto the floor of the fuel handling building. Thereafler, the primary source of unborated water is on to the surface of a pool and the flow of water from the pools is from the surface of both pools. The flow of water from each pool will be approximately the same. Under these conditions the water flowing from the pools over the curb is expected to contain less soluble boron than the average mixture in the two pools. Therefore, the assumption of fully mixed flow from the pools is believed to be conservative.

The dilution analysis has been revised assuming that the gates between t'.9 two pools are closed, This analysis is attached.

Question 2:

Given the use of a combined volume for the boron dilution analysis, clarify the statement that the SFPs are "normally" e nnected. When are the SFPs separated ? llow long are they allowed to remain separa";d ? What controls are in place to ensure that the SFPs are/ remain connected ?

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Response

llased on discussions with reactor engineering personnel, the pools have remained connected (the gates between the two pools are open) since the filling of the Unit 2 pool.

The Unit 2 pool contains 2098 fuel storage locations and the Unit 1 pool only contains 288 storage locations. This arrangement requires the transfer of fuel between the two pools which can only occur if the gates are open.

The gates would have to be closed during activities that require draining of the cask pit or draining of one of the SFPs. There are no scheduled activities requiring the dra'ning of the cask pit. The placement of additional racks into the Unit 1 pool is expected to take place in 1998. This activity will include closing of the gates between the two pools. At some date in the future, shipment of spent fuel in spent fuel casks will occur. That activity may include periods of gate closure. There are no limits on the frequency or duration of gate closure and there are no requirements to maintain the gates open.

If a pool dilution event occurs while the gates are closed, the water level in the affected pool will rise until it over Hows the gates. At that point water will flow into the other pool until both pools reach the same level. If the addition of water continues, the level of water will eventually reach the height of the curb around the pools and over flow on to the Fuel llandling fluilding floor from both pools. Nevertheless, as discussed in the response to question I the dilution analysis has been re evaluated considering separate pools.

Question 3:

The baron dilution analysis states on Page 20 that the fire protection system (FP) flow rates range from 2100 to 4800 gpm and that the most limiting scenario includes a FP flow of 2300 gpm (seismic break of non-seismic piping). Why is 2300 gpm more limiting than 4800 ppm?

Response

The dilution of both pools as described in enclosure 6 requires over 1,070,000 gallons of water. The combined fire protection water in both tanks is only 600,000 gallons.

Therefore, extraordinary assumptions are required to produce a dilution event capable of diluting the combined pools. Make up to the fire protection tanks is available at a rate of about 650 gpm. Ily evaluating the additional amount of water needed to dilute the pool, assuming that it is supplied by the make up water pumps, and that the fire protection tanks reach emptyjust as the required amount of water is supplied to the fuel storage pool, the optimum flow rate necessary to dilute the pools in the shortest amount of time can be determined. For greater flow rates the fire protection tanks will empty and the pumps will trip prior to supplying the 1,070,000 gallons necessary to dilute the pools.

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e Lower flow rates will result in longer dilution times. This optimum flow rate was determined to be about 2300 gpm.

The fire protection system has one electric driven pump and two diesel driven pumps.

Pump flow at runout conditions is about 4800 ppm. For the analysis assuming dilu'Jon of both pools to 500 ppm, as described in enclosuie 6,2300 gpm is the optimum flow rate to minimize the time for dilution of the pools. These assumptions were used to calculate limiting dilution times, however, no mechanisms have been identified that result in flows of these magnitudes.

These assumptions do not take credit for actual location or configuration of potential failures in fire protection piping. They do not take credit for the location of fire protection piping in the vicinity of the fuel storage pools.

All of the fire protection lines in the vicinity of the SFPs are seismically analyzed and supported even though they are not designated as seismic category 1 piping. For the purposes of flooding analyses, llranch Technical Position MEll 3-1 requires the postulation of through wall cracks in moderate energy non seismic lines. There are 3 six inch fire protection lines in the vicinity of the Unit 1 pool and 3 in the vicinity of the Unit 2 pool. The postulation of a through wall crack in accordance with IITP MEB 31 would result in postulated flows well below 2300 ppm.

Question 4:

Section 3.3: Evaluation ofinfrequent SFP Configurations. The boron dilution analysis states that the most limiting configuration is when the SFPs arm marated. From a seismic event, a $!ution could occur in 1.6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />. What, if any, controls are in place to assist the operators' " heightened awareness" of a SFP dilution following a seismic event?

Such as, a procedu:e for checking the plant's physical condition or af anns (other than SFP level)?

Response

Abnonnal Operating Procedure 18036 C "Scismic Event" provides operator response following a seismic event. The procedure requires the initiation of a visual inspection of all accessible areas to deiermine damage. Following implementation of the revised Technical Specifications this procedure will be revised to include a specific reference to the possibility of dilution of the SFP due to pipe leaks.

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Question 5:

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The boron dilution analysis states on page 20 that if offsite power is not available as a result of a seismic event 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. The sources and flow rates to reach this conclusion were not provided. Please provide this information.

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Response

l With a loss of electric power, the makeup pumps to the fire protection tanks are unavailable. This significantly increases the amount of time to reach the dilution point following the emptying of the fire protection tanks.

Flow rates of systems for broken lines (without offsite power)

Fire Proiection:

4800 gpm (pump runout) 600,000 gal. limit.

Demineralized Water 120 gpm (for gravity fill) for 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> i

Normal Chilled Water:

300 gpm for 30 minutes (total water admitted is 9000 gallons)

Utility Water:

40 gpm for 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> The calculation in attachment 2 has been revised to consider a single fuel storage pool and pipe leaks in accordance with MEll 3 1.

i Question 6:

The boron dilution analysis states on page 19 that certain pipes are assumed to remain intact during/after a seismic event. Clarify that all such pipes e.re seismically qualified.

Response

- This statement referred to non seismic piping outside the SFP area that feeds piping in the SFP area, it is necessary for that piping to remain intact in order to conduct water to the SFP area. Thus the analysis inherently assumed that nonseismic piping outside the SFP area remains intact while it fails in the SFP area, j

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ATTACHMENT _2 SPENT FUEL POOL BORON DILUTION. ANALYSIS i

VOGTLE BORON DILUTION ANALYSIS

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VOGTLE SPENT FUEL POOL BORON DILUTION ANALYSIS i

i Table of Contents F

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 i

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

4.0 CONCLUSION

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5.0 REFERENCES

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VOGTLE BORON DILUTION ANALYSIS

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1.0 INTRODUCTION

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

i Dilution Sources and Flowrates Boration Sources Instrumentation 7

Administrative Procedures Piping Loss of O..' site Power impact Boron D lution 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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VoGTLE BORON DILUTION ANALYSIS

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2.0 SPENT FUEL POOL AND RELATED SYSTEM FEATURES This bion provides background information on the SFP and its relatea Jystems and features.

j 2.1 Spent Fuel Pool 4

s The design purpose of the SFP is to pro % ror safe storage of irradiated fuel assemblies. The pool is filled with borated water. The watot 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 Pit 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 pwl is approximately 386,000 gallons. The SFP lt 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 poolis 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 pocis.

3 VoGTLE boron DILUTION ANALYSIS -

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'.2 Spent Fuel Storage Racks 2

' 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 pod 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 and returns it to the pool. The supply and retum 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 crain the SFP below the water level required for radiation shielding.

2.4 Spent Fuel Pool Cleanup System t

The SFP cleanup system is designed to maintain water clarity and purity. The cleanup system is connected to the SFP cooling syttem. A portion of the SFP cooling pump (s) discharge flow, d

approximately 100 gpm, can be diverted to the cleanup loop, which includes the SFP demineralizer and filter. The filter removes particulates from the SFP water and the SFP demineralizer removes ionicimpurities.

4 VOGTLE BORON DILUTION ANALYslS i

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The refueling water cleanup loop also uses the SFP deminestlizer and filters to clean up the refueling water storaga 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 skimmers.

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

A potential dilution path exists if a valve interfacing with the spent fuel pool transfer canal (SFPTC) and the CVCS letdown syt. tem 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 procedure for transfer was complete (with error of not opening the RHT inlet and not closing two valves to the SFP inlet from the Recycb Evaporator feed demineralizers). This could result in a flowrate of up to 120 gpm to the Spent Fuel Pool Transfer Canal. The transfer cana: would fill and spill into the SFP.

1 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 Dilution ANALYSIS

The reactor makeup water (CMW)' 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 demineralizer used for flushing and sluicing. A conservative 150 gpm flowrate 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 norrnally isolated, this line will not be considered as a potential dilution flow path.

2.5.3 Domineralized Water System Them 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 demineralized water system consists of a 250,000 gallon tank for both units with 3 pumps each delivering a design flow of 275 gim 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.

2.5.4 Component Coca'ng Component cooling water is the cooling medium fo6 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 4

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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 11 operating pressures between the two systsms. Therefore, a conservative 110 gpm flowrate is estimated.

2.6.6 SFP Domineralizer Rosin Fill Connsction The SFP demineralizer 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 pe;1ormed 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 ft.el pool area has six 6 inch fim 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 would 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.

7 VoGTLE boron DILUTION ANALYSIS I

"2.5.7 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 albw for filling of th9 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 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 wate-to cause a dilution event should the pi,ne 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.

8 VOGTLE BORON DILUTION ANALfSIS

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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-borateo water to 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 Section 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 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) 3.2.6 168 gpm (MEB 3-1 crack) 3.2.6 Utility Water 45 gpm (pipe break) 3.2.6 9

VOGTLE boron DILUTION ANALYSIS

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2.6 Boration Sources 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.

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 gallonti 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 VoGTLE boron DILUTION ANALYSIS

21 ' Speat Fuel PoolInstrumentation t

' Instru' mentation is available to monitor SFP water level and temperature, and the radiation levels in the SFP enclosure. Additional instrumertation 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 iocally in the SFP area and in the control room.

A cha,1ge 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 reduction of the pool boron concentration of approximately 128 ppm.

11 VOGTLE BORON DILUTION ANALYSIS

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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 arid termination 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

' FP, They will be instructed to check the temperature and level in the pool and conditions around S

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 verifief every seven days.

Prior to implementation of the License Amendment allowing c;cdit for soluble boron in the SFP criticality analysis,= current administrative controls on the SFP boron concentration and water inventory will be evaluated cnd procodures 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 Dilution ANALYSIS

2.9 Piping

' The p'iping located inside the SFP room consists of 6 ince t inch and 2.5 inch fire protection lines, a 3 inch demineralized water line, a 3 inch normal chilled e or 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 sign'ficant flow of non-borated water to the SFP during a loss of offsite power.

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.

13 VoGTLE boron DttuTloN ANALYSTS

'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 dilution is conservatively estimated to be 386,000 gallons. This is the total volume of the SFP when 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 2), the soluble boron concentration required to maintain the spent fuel at K,n s 0.95, including uncertainties and burnup, with a 95% probability at a 95% confidence level (95/95) is 600 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 600 ppm. To dilute the pool volume of 386,000 gallons from 2000 ppm to 600 ppm would conservatively require 465,000 gallons of non-boraterlwater.

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.

10 wever, 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-Wated water. Thus, even if a pocket of non-borated water formed in the SFP, K.n would not i

be expected to equal or exceed 1.0 anywhere in the pool.

14 VOGTLE boron DiluTloN 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 Sc r/sns 3.2 and 3.3 are calcuiated based on the following equation:

t.m = In (Co / Com)V/Q (Equation 1)

Where:

tom = time to dilute Co = the boron concentration of the pool volume at the beginning of the event Com = the boron endpoint concentration 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 ar, evaluated below:

P 3.2.1 Dilution From Reactor Makeup Water Tank The following events assume that the RMW tank is automatically replenished since the normal 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 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. In order to reach the :tiution endpoint of 600 ppm, the RMW tank would have to be automatically replenished to allow for almost 3 tank volumes (465,000 gallons) of dilete reactor makeup water to enter the pool area. At an estimated flowrate 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 DoRoN Dilution ANALYSIS

(

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 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 automaticaltj replenished to allow for almost 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 endpoint.

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 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 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 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 boron DILUTION ANALYSIS

i i

8-8

'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 thu 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 15 hours1.736111e-4 days <br />0.00417 hours <br />2.480159e-5 weeks <br />5.7075e-6 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 almost 2 times, in addition to SFP makeup, the demineralized water makeup system provides makeup i

water to each unit's Condensate Storage tank (automatically) as well as each unit's RMW storage tank (automatically).

3.2.4 Dilution ResultinD 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 2

demineralized water. This valve could continue to cycle opc.n. If the surge tank alarm in the CCW system fails, tha level alarms in the spent fuel pool (SFP) could alert the operators that the level in the spent fuel pool is increasing. If the alarms failed to alert the operators to a malfunction and the leak rate is within the makeup capabilities it the surge tank so that the suction to the CCW pumps 17 VOGTLE boron DILUTION ANALYSIS

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 replenished by the water treatment facility almost 2 times.

Assuming a conservative makeup flowrate of 110 gpm, the dLution event would take over 70 hours8.101852e-4 days <br />0.0194 hours <br />1.157407e-4 weeks <br />2.6635e-5 months <br />.

3.2.5 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 ameunt of boron before saturating.

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 pom (6* Fire Protection),600 gpm (3' Chilled Water or Demineralized Water), and 45 gpm (1" Utinty Water) piping. These lines are seismically analyzed and supported. However, 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 MEB 3-1 position allows evaluation of a crack in lieu of a break in such lines.

I8 VOGTLE boron Dilution ANALYSTS l

l.

I 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 concentration. Each fire protection tank contains 300,000 gallons. The tanks are connected so that the total amount of water available would be 600,000 gallons.

The demineralized water system consists of a 250,000 gallon tank for both units with 3 pumps each delivering a design flow of 275 gom 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 3 inch demineralized water pipe is 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. 79 amount of water is above the 465,000 gallons required to achieve a dilution to the 600 p

< r < centration 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. This storage tank is automatically replenished. A 45 gpm dilution rate would 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 DlluTION ANALYSTS l

i

' 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 (6*) in the SFP. This flowrate is calculated to be 168 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. 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 available, it would take approximately 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 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 rate, if a random phe break of a fire protection line were to occur, it would take approximately 3.1 hours1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> to reach the boron dilution endpoint. The amount of dilute water required for the dilution event would be 465,000 gallons.

20 VOGTLE BORON DILUTION ANALYSIS

3.4 Summary of Dilution Events SCENARIO FLOWRATE TIME TO DILUTION COMMENTS (GPM)

(HRS)

Reactor Makeup Water to 200 38 Fsequires RMW tank replenishment for event to occur SFP Cooling toop Reactor Makeup Water to 150 52 Requires RMW tank replenishrnent for event to occur SFP Demineralizer CVCS Letdown Divert to 120 64 Requires RMW tank replenishment for event to occur SFPTC l

Demineralized Water to SFP 500' 15.5 Requires demineralized water tank repienishment for event 20 occur cooling loop (normal makeup)

Compor.ent Cooling Water

-110 70 Requires demineralized water tank replenishinent for event to occur Interface.With SFP Cooling HX Random Normal Chilled 600 N/A Maximum of 9000 gallons of water delivered due to system size Water pipebreak (t)

Random Utility Water 45 172 Requires utility water tank replenishment for event to occur pipebreak (t)

Random Fire Protection 2500 3.1 Requires fire protection water tanks replenishment for event to occur -

supply line pipebreak I

Random Demineralized 600 12.9 Requires oJmineralized water tank replenishment for event to occur Water pipebreak (t)

Seismic Event (All seismically 1413 gpm for 9.3 Assumes all nonseismic piping that is not analyzed for a seismic analyzed pipes break / crack)

. (15 min) then event ruptures only in the SFP room 813 gpm 21 VoGTLE BORON DILUTION ANALYSTS

'The evaluation of SFP dilution events in Sections 3 2 and 3 3 el:eninated from consideration all but nine of the of the dilution scenarios evaluated.

4 Three dilution scenarios involve the transfer of non-borated water from the reactor makeup water system to the SFP cooling system, cleanup svstem.s, or the transfer canal at a maximum rate of approximately 200 gpm. The reactor makeup water system is not capable of supplying the approximately 4J5,000 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 least amount 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 flowrates of 110 and 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. 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 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 DILUTION ANALYSTS

-. -. ~-

.., o 4

j The remaining event is the transfer of non-boreted 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 a

resuiting 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 the control room from the spent fuel pool level instrumentation. If the hioh level alarms fail, it is reasonable to expect that the significant increase in pool level and r..entual pool overflow that would result from a pool dilution event will be rea.1ily detected by pisnt operate in time to take mitigative actions. In the random fire protection line break case, alarms for a i 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 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 wauld 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 DILUTION ANALYSIS l

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

. 's; c. o

~

4.0 CONCLUSION

S

' A bo'ron 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 I

following:

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

465,000 gallons)is needed.

i 2 Since such a large water volume turnover is required, a SFP dilu:fon 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 i~

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

I It should be notad that this boron dilution evaluation was conducted by evaluating the time and water volumer, 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 cr!iicality 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 Ken 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.

4 d

4 d

24 VoGTLE boron DILUTION ANALYSIS

..., _ -=

5.0 REFERENCES

' '1, MAP-14720, Rev. 2 Vogtle Units 1 and 2 Spent Fuel Rack Criticality Analysis With Credit For

, Soluble Boron, Westinghouse Commercial Nuclear Fuel Division, August 1997,-

2. Westinghouse' Calc. Note, CAA 97-281, "Vogtle Unit 1 Boral Replacement Spent Fuel Rack

-Criticality Analysis v/ith Credit For Soluble Boron.'

l l

=-

25 VoGTLE BORON olLUTION AMALYSIS