ML20211N351

Proposed Tech Specs Re Limiting Conditions for Operation of Borated Water Sources,Revising Min Boron Concentration Levels.Nshc & Safety Evaluation Encl

ML20211N351
Person / Time
Site:	Summer
Issue date:	12/11/1986
From:	SOUTH CAROLINA ELECTRIC & GAS CO.
To:
Shared Package
ML20211N257	List: ML20211N254 ML20211N351
References
NUDOCS 8612180196
Download: ML20211N351 (24)

Text

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I - REACTIVITY CONTROL SYSTEMS 80 RATED WATER SOURCE - SHUTDOWN LIMITING CONDITION FOR OPERATION 3.1.2.5 As a minimum, one of the following borated water sources shall be OPERA 8LE:

a. A boric acid storage system with:

1. A minimum contained borated water volume of 2700 gallons,

2. Between 7000 and 7700 ppe of boron, and

3. A minimum solution temperature of 65'F.

b. The refueling water storage tank with:

1. A minimum contained borated water volume of 37,900 gallons,

.U00

2. A minimum boron concentration of g ppm, and ,,-

3. A minimum solution temperature of 40*F.

APPLICA8ILITY: MODES 5 and 6.

ACTION:

With no borated water source OPERA 8LE, suspend all operations involving CORE ALTERATIONS or positive reactivity changes.

SURVEILLANCE REQUIREMENTS 4.1.2.5 The above required borated water source shall be demonstrated OPERA 8LE:

a. At least once per 7 days by:

1. Verifying the boron concentration of the water,

2. Verifying the contained borated water volume, and

3. Verifying the boric acid storage tank solution temperature when it is the source of borated water.

b. At least once per 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> by verifying the RWST temperature when it is the source of borated water and the outside air temperature is less than 40*F.

SUMER - UNIT 1 3/4 1-11 ATTACHMENT I Page 1of 9 8612180196 061211 PDR ADOCK 05000395 p PDR

REACTIVITY CONTROL SYSTEMS

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B0RATEDWATERbuhCES-OPERATING LIMITING CONDITION FOR OPERATION 3.1.2.6 As a minimum, the following borated water source (s) shall be OPERABLE as required by Specification 3.1.2.2:

a. A boric acid storage system with:

1. A minimum contained borated water volume of 13,200 gallons,

2. Between 7000 and 7700 ppe of boron, and

3. A minimum solution temperature of 65'F.

b. The refueling water storage tank with:

1. A minimum contained borated water volume of 453,800 gallons, 2.

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3. A minimum solution temperature of 40*F. .

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APPLICABILITY: MODES 1, 2, 3 and 4.

ACTION:

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a. With the boric acid storage system inoperable and being used as one i of the above required borated water sources, restore the storage l system to OPERA 8LE status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> or be in at least HOT j STAN08Y within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and borated to a SHUTDOWN MARGIN equivalent to at least 2 percent delta k/k at 200*F; restore the boric acid storage system to OPERABLE status within the next 7 days or be in.

COLD SHUTDOWN within the next 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.

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b. With the refueling water storage tank inoperable, restore the tank C to OPERA 8LE status within one hour or be in at least H0T STAND 8Y .

within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.

I SUMER - UNIT 1 3/4 1-12 ATTACliMENT I Page 2 of 9

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3/4.5 EMERGENCY CORE COOLING SYSTEMS 3/4.5.1 ACCUMULATORS LIMITING CONDITION FOR OPERATION 3.5.1 Each reactor coolant system accumulator shall be OPERABLE with:

a. The isolation valve open,

b. A contained borated water vol,ume of be. tween 7368 and 7594 gallons,

,250o

c. A boron concentration of between and ?tGG.ppe, and

d. A nitrogen cover pressure of between 600 and 656 psig.

APPLICA8ILITY: MODES 1, 2 and 3.*

ACTION:

With one accumulator inoperable, except as a result of a closed a.

isolation valve, restore the inoperable accumulator to OPERABLE status within one hour or be in at least HOT STAN08Y within the next 6' hours and in HOT SHUTDOWN within the following 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />.

b. With one accumulator inoperable due to the isolation valve being closed, either immediately open the isolation valve or be in at least HOT STAND 8Y within one hour and in HOT SHUTDOWN within the following 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.

SURVEILLANCE REQUIREMENTS 4.5.1.1 Each accumulator shall be demonstrated OPERABLE:

a. At least once per 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> by:

1. Verifying the contained borated water volume and nitrogen cover pressure in the tanks, and

2. Verifying that each accumulator isolation valve is open.

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Pressurizer pressure above 1000 psig.

l SU M ER - UNIT 1 3/4 5-1 ATTACllMENT I Page 3 of 9

. EMERGENCY CORE COOLING SYSTEMS 3/4.5.4 REFUELING WATER STORAGE TANK LIMITING CONDITION FOR OPERATION 3.5.5 The refueling water storage tank (RWST) shall be OPERA 8LE with;

a. A minimum contained borated water volume of 453,800 gallons, A3co 2500

b. A boron concentration of between 294CL and 1FHb4 ppe of boron, and

c. A minimum water temperature of 40*F.

APPLICA8ILITY: MODES 1, 2, 3 and 4.

ACTION:

With the refueling water stok' age tank inoperable, restore the tank to OPERABLE status within I hour or be in at least HOT STANOBY within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in COLD SHUTOOWN within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.

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SURVEILLANCE REQUIREMENTS 4.5.5 The RWST shall be demonstrated OPERABLE:

a. At least once per 7 days by:

1. Verifying the contained borated water volume in the tank, and

2. Verifying the boron concentration of the water.

b. At least once per 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> by verifying the RWST temperature when the outside air temperature is less than 40*F.

SUMMER - UNIT 1 3/4 5-9 Amendment No. 44 ATTACHMENT I Page 4 of 9

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REACTIVITY CONTROL SYSTEMS l BASES  :

MODERATOR TEMPERATURE COEFFICIENT (Continued) involved subtracting the incremental change in the MOC associated with a core condition of all rods inserted (most positive MDC) to an all rods withdrawn condition and, a conversion for the rate of change of moderator density with temperature at RATED THERMAL POWER conditions. This value of the MDC was then transformed into the limiting MTC value -4.2 x 10 -4 delta k/k/ F. The MTC

~4 value of-3.3 x 10 delta k/k/*F represents a conservative value (with correc-tions for burnup and soluble boron) at a core condition of 300 ppm equilibrium boron concentration and is obtained by making these corrections to the limiting MTC value of -4.2 x 10'4 k/k/*F.

The surveillance requirements for measurement of the MTC at the beginning and near the end of the fuel cycle are adequate to confirm that the MTC remains within its limits since this coefficient changes slowly due principally to the reduction in RCS boron concentration associated with fuel burnup.

3/4.1.1.4 MINIMUM TEMPERATURE FOR CRITICALITY This specification ensures that the reactor will not be made critical with the Reactor Coolant System average temperature less than 551*F. This limitation is required to ensure 1) the moderator temperature coefficient is within its analyzed temperature range, 2) the protective instrumentation is within its normal operating range, 3) the pressurizer is capable of being in an OPERABLE status with a steam bubble, and 4) the reactor pressure vessel is above its minimum RT NOT temperature.

3/4.1.2 B0 RATION SYSTEMS The boron injection system ensures that negative reactivity control is

! available during each mode of facility operation. The components required to

! perform this function include 1) borated water sources, 2) charging pumps,

3) separate flow paths, 4) boric acid transfer pumps, and 5) an emergency power supply from UPERABLE diesel generators.

With the RCS average temperature above 200*F, a minimum of two boron injection flow paths are required to ensure single functional capability in the event an assumed failure renders one of the flow paths inoperable. The boration capability of either flow path is sufficient to provide K SHUT 00WN SU M ER - UNIT 1 8 3/4 1-2 ATTAGMNI' I Page 5 of 9 _

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REACTIVITY CONTROL SYSTEMS

/$ Sensfiso gy BASES nn-or As REaud Ep by h p 26 & P3 BORATION SYSTEMS (Continued)

MARGIN from expe' ted operating conditions of 1.77% delta k/k after xenon decay l c

and cooldown to 200*F. The maximum expected boration capability requireme 2475 occurs @ from full power equilibrium xenon conditions and --; ?=7 gallons of 7000 ppe borated water from the boric acid storage tanks or 64,040 gallons of g ppe borated water from the refueling water storage tank. l With the RCS temperature below 200*F, one injection system is acceptable without single failure consideration on the basis of the stable reactivity condition of the reactor and the additional restrictions prohibiting CORE ALTERATIONS and positive reactivity changes in the event.the single injection

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system becomes inoperable.

The limitE.iori for a maximum of one centrifugal charging pump to be OPERA 8LE and the Surveillance Requirement to verify all charging pumps except the required OPERABLE pump to be ino'perable below 275'F provides assurance that a mass addition pressure tra 1.ent can be relieved by the operation o,f a.! .

single PORV'.

oR AS REeueEo Bh{h .thek4GarcE0 Theborondcaabilityrequiredbelow200*Fissufficientto'providekM SHUTDOWN MARGIN To g percent delta k/k after xenon' decay and cooldown from 200'F to 140*F. This condition =-i= E : either 2000' gallons of 7000 ppa borated water l from the boric acid storagefanks or 9690 gallons of M ppe borated water 4 30o

. _ _fromAherefuelingwaterstoragetank.

Ib S A T'is nto BW _

i ~The contained water volume limits include allowance for water not available l because of discharge line location and other physical characteristics.

l Th imits oVcontairled water lume anpboron co ntration [the Tl also e contal )ent afre a p Vvalue .5 and T.0 for t solutio ecircul ed withj r a LOCA r between This p band min izes th volutto of on on topine and nimizes he effe of chl ide and ustic st ss corr t

mdchanica systems nd co=pe.ents.

The OPERABILITY of one boron injection system during REFUELING ensures that this system is available ,for reactivity control while in MODE 6. .

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3/4.1.3 MOVABLE CONTROL ASSEMBLIES The specifications of this section ensure that (1) acceptable power distribution limits are maintained, (2) the minimum SHUTOOWN MARGIN is main-tained, and (3) limit the potential effects of rod misalignment on associated accident analyses. OPERABILITY of the control rod position indicators is required to determine control rod positions and thereby ensure compliance with the control rod alignment and insertion limits.

SUMMER - UNIT 1 8 3/4 1-3 ArrAcemr I Page 6 of 9 I

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4 EMERGENCY CORE COOLING SYSTEMS l

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ECCS SUBSYSTEMS (Continued)

The limitation for a maximum of one centrifugal charging pump to be OPERA 8LE and the Surveillance Requirement to verify all charging pumps except

! the required OPERA 8LE charging pump to be inoperable below 300*F provides assurance that a mass addition pressure transient can be relieved by the i operation of a single PORV. )

The Surveillance Requirements provided to ensure OPERASILITY of each  !

component ensures that at a minimum, the assumptlons usey in the safety analyses 4 are met and that subsystem OPERA 8ILITY is maintained. Surveillance requirements

! for throttle valve position stops and flow balance testing provide assurance j that proper ECCS flows will be maintained in the event of a LOCA. Maintenance

! of proper flow resistance and pressure drop in the piping system to each injection point is necessary to: (1) prevent total pump flow from exceeding ,

runout conditions when the system is in its minimum resistance configuration, ,

(2) provide the proper flow split between injection points in accordance with the assumptions used in the ECCS-LOCA analyses, and (3) provide an acceptab.}e level of total ECCS flow to all injection points equal to or above that ass'dmed l

in the ECCS-LOCA analyses.

3/4.5.4 REFUELING WATER STORAGE TANK l

The OPERA 8ILITY of the Refueling Water Storage Tank (RWST) as part of the ECCS ensures that a sufficient supply of borated, water is available for , injection +

hv tra ECCS in the event of a LOCA. IIhe mits n NW min um v use nc bor ic ce rat on e 'sure hat ) s ffi ont ter ava able ith cor in-l me t pe it ecir 01at nc lin f1 to e co , an 2) t re tor: 11 r ai su rit cal n the col con iti i

'h A 5 ate vol s on rol ass IV. Then as foli ing ixin of t Ithp1c tro ro ins ted cept of t,e me rea ive t ns re e sist t wi RW thd.0CA nalv es.

and he l Addit onal y, t OP A81 TY the Refu ing ater tora a Tar as par of t e EC S en res hat uff cient nega ve r acti ty 1 inj ted

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in o the core to e nte et a y p sitiv inc ase n re tivi ca sed by R sys e old . S co Ido can be c sed' in vert nt pressuriza-on, los -of- ola acc' den , or ste lin rup ure. '

l The contained water volume limit includes an allowance for water not usable because of tank discharge line location or other physical characteristics.

, 1.9 l The limits en contained water volume and baron concentration of the RWST l also ensure a pH value of between . and 11.0 for the solution recirculated within containtcent after a LOCA. This pH band minimires the evolution of iodine and minimizes the effect of chloride and caustic stress corrosion on i i mechanical systems and components.

SUMER - UNIT 1 8 3/4 5-2 Amendment No. 44 ATTACILMENT I Page 7of 9

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,TheOPERABI[ITYoftheRWSTaspartoftheECCSensuresthatasufficient supply of borated water is available for injection by the ECCS in the event of e,ither a LOCA, a steamline break or inadvertent RCS depressurization. The limits ort RWST minimum volume and boron concentration ensure 1) that l sufficient water is available within containment to permit recirculation coolirsfbIto.thdcore,2)thatthereactorwillremainsubcriticalinthe cold condit%n (68,to 212 degrees-F) following a small break LOCA assuming complete mixing of, the RWST, RCS, Spray Additive Tank (SAT), containment spray' system piping and ECCS water volumes with all control rods inserted i ,,-except,t(tt w st reactive control rod assembly (ARI-1), 3) t5at the reactor will remain subcritical ir,the cold condition following a large break LOCA (break flow area > 3 9 sq. ft.) assuming complete mixing of the RWST, RCS, ECCS water and other sources of water that may eventually reside in the sump post-LOCA with all control rods assumed to be out (AR0), 4) long term subcriticality fo))oetrg a steamline break assuming ARI-1 and preclude fuel failure. \

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The eximum allowable'value for the RWST boron concentration forms the basis 2

'( 'C, I for determining the time (Post-LOCA) at which operator action is required to switch over the ECCS to hot leg recirculation in order to avoid precipitation of the solub'le boron.

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, CONTAll#4ENT SYSTEMS BASES 3/4.6.2.2 SPRAY ADDITIVE SYSTEM The OPERA 8ILITY of the spray additive system ensures that sufficient NaOH r is added to the reactor building spray in the event of a LOCA. The limits on NaOH volume and concentration ensure a pH value of between g and 11.0 for

, the solution recirculated within containment after a LOCA. This pH band

. minimizes the evolution of iodine and minimizes the effect of chloride and I caustic stress corrosion on mechanical systems and components. The contained solution volume limit includes an allowance for solution not usable because of tank discharge line location or other physical characteristics. These assump-tions are consistent with the iodine removal efficiency assumed in the accident analyses.

3/4.6.2.3 REACTOR BUILDING COOLING SYSTEM The OPERABILITY of the reactor building cooling system ensures that

1) the reactor building air temperature will be maintained within limits .

during nomal operation, and 2) adequate heat removal capacity is available

when operated in conjunction with the reactor building spray systems during post-LOCA conditions.

The reactor building cooling system and the reactor building spray system are redundant to each other in providing post accident cooling of the reactor building atmosphere. As a result of this redundancy in cooling capability, the allowable out of service time requirements for the reactor building cooling system have been appropriately adjusted. However, the allowable out of service time requirements for the reactor building spray system have been maintained consistent with that assigned other inoperable ESF equipment since the reactor building spray system also provides a mechanism for removing iodine from the reactor building atmosphere.

3/4.6.3 PARTICULATE I00INE CLEANUP SYSTEM The OPERABILITY of the containment filter trains ensures that sufficient iodine removal capability will be available in the event of a LOCA. The reduction in containment iodine inventory reduces the resulting site boundary radiation doses associated with containment leakage. The operation of this system and resultant iodine removal capacity are consistent with the assumptions used in the LOCA analyses.

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SupetER - UNIT 1 B 3/4 6-4 ATTACHMENT I l

Page 9 of 9

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• l ATTACHMENT II i NO SIGNIFICANT HAZARDS DETERMINATION Sections 3.1.2.5, 3.1.2.6, 3.5.1, and 3.5.5 identify allowable boron concentrate limits for the ECCS accumulators and RWST. The proposed changes increase the allowable boron concentrations to the following:

! MIN MAX ECCS ACCUMULATORS 2200 - 2500 ppm RWST 2300 - 2500 ppm The purpose of these changes is to increase current margin to a post-LOCA shutdown requirement (i.e., the reactor will remain subcritical in the cold condition following a large break LOCA assuming complete mixing of the RWST, RCS and ECCS water and other sources of water that may eventually reside in the sump post-LOCA with all control rods assumed to be out) in order to have i increased assurance of conformance for Cycle 4 and future cycles at Virgil C. i Suinner Nuclear Station.

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1. Will operation of the facility in accordance with this proposed change involve a significant increase in the probability or consequences of an 4 accident previously evaluated? N_0 The proposed increases in allowable boron concentrations do not significantly increase the probability or consequences of previously evaluated accidents. A review of the current safety analysis indicate:

a. The only non-LOCA safety analyses affected are those in which the i Safety Injection System (SIS) is actuated. For these accidents no 4

adverse impact will occur, and the conclusions as stated in the FSAR will remain valid. For most accidents, the higher boron concentrations are beneficial since a more rapid negative reactivity insertion will occur.

b. In the small break LOCA analysis, there is no assumption regarding the concentration of boron in the ECCS water and no credit is taken for the negative reactivity produced by soluble boron. Thus, the FSAR conclusions remain valid with the higher allowable boron i concentrations. I

c. Like small breaks, the large break analysis takes no credit for boron in the ECCS water up to the time of peak clad temperature. 1 The FSAR conclusions remain valid.

d. For maintenance of post-LOCA long term cooling, the higher boron concentrations decrease the maximum allowable time for operator action (i.e., from 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> to 11 hours1.273148e-4 days <br />0.00306 hours <br />1.818783e-5 weeks <br />4.1855e-6 months <br /> to start hot recirculation and from 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> to 18 hours2.083333e-4 days <br />0.005 hours <br />2.97619e-5 weeks <br />6.849e-6 months <br /> to subsequently alternate hot leg and  :

cold leg recirculation) to prevent boron precipitation. The t resulting operator action times, although less, are judged to still Page 1 of 2

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be adequate to assure the required actions can be accomplished to maintain post-LOCA long term cooling.

e. The increased boron concentrations and resulting lower post-LOCA containment spray and recirculating core cooling solution pH are acceptable. The design basis for pH sensitive issues (i.e., LOCA radiological consequences, hydrogen generation, and environmental conditions for equipment qualification) are maintained.

Given the above and the fact that conformance to post-LOCA shutdown requirements will be ensured through the normal Reload Safety Analysis Checklist (RSAC) evaluation process, it is concluded that the Technical Specification n:odifications do not involve a significant increase in the probability or consequence of a previously evaluated accident.  %

2. Will operation of the facility in accordance with this proposed change create the possibility of a new or different kind of accident from any accident previously evaluated? NQ The creation of a new or different kind of accident from any previous.y evaluated accident is not considered a possibility. The proposed changes increase existing boron concentration limits within current operational restraints and without compromising the performance or qualification of safety related equipment. Thus, these changes are considered to be adjustments within the Virgil C. Summer design bases .

and thus do not create the possibility of a new or different kind of accident.

3. Will operation of the facility in accordance with the proposed change involve a significant reduction in a margin of safety? NO The proposed Technical Specification changes maintain the Final Safety Analysis Report design bases and adequate margins of safety. The higher boron concentrations increase the negative reactivity insertion capability of the ECCS providing an increase in the plants margin of safety. As discussed in item 1.d above, the higher boron concentrations '

do impact safety by decreasing the allowable operator action times to prevent boron precipitation in the long term following a LOCA. However, the required operator actions can still be easily accomplished within the minimum acceptable time restraints to prevent boron precipitation.

Therefore, the proposed increases in the Technical Specification boron concentrations do not result in a significant reduction in margins of safety.

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VIRGIL C. SUMMER NUCLEAR STATION SAFETY EVALUATION FOR RWST/ ACCUMULATOR BORON CONCENTRATION INCREASE

1.0 INTRODUCTION

l The large break Loss-of-Coolant Accident (LOCA) Analysis for the Virgil C. Summer Nuclear Station (VCSNS) takes no credit for control rod insertion. Consequently, to maintain the validity of the analysis,it must be demonstrated (each cycle) that the core can be maintained subcritical via boron addition from the ECCS in the unlikely event of a LOCA h 3.0 ft.2. This post-LOCA shutdown requirement has been met for cycles 1-3 at VCSNS.

However, evaluations of potential future fuel cycle designs show that conformance is not assured with the present plant design. In order to achieve adequate design flexibility for future cycles, an increase in the accumulator and RWST boron concentration range to 2300 to 2500 ppm for the RWST and 2200 to 2500 ppm for the accumulators is pro posed. These changes to the VCSNS Technical Specifications will increase the current margin to the post-LOCA shutdown requirement without compromising safety.

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2.0 SCOPE OF EVALUATION In conjunction with the Westinghouse Electric Corporation, SCE&G has assessed the impact of increasing the RWST and accumulator boron concentration to 2300 to 2500 ppm for the RWST and 2200 to 2500 ppm for the accumulators. This assessment identified the following areas in which the boron concentration increase must be shown to have a favorable or non-detrimental impact on the VCSNS design basis:

1. Non-LOCA Safety Analysis

2. LOCA Analysis (10CFR50.46)

Small Breaks Large Breaks Long-Term Core Cooling

- Baron Precipitation

3. LOCA Related Design Consideration Radiological Consequences Hydrogen Production Equipment Qualifications Evaluation summaries for each of the above areas are provided in the following sectic,n.

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ATTACHMENT lli Page 2 of 13

3.0 SAFETY EVALUATION 3.1 FSAR Non-LOCA Safety Analysis The RWST, accumulators and the Safety injection System (SIS) are subsystems of the Emergency Core Cooling System. Upon actuation of the SIS borated water from the RWST is delivered to the reactor coolant system in order to provide adequate core cooling as well as provide sufficient negative reactivity following steamline break transients to prevent excessive fuel failures. The accumulators are a passive system and provide borated water to the RCS when the system pressure drops below approximately 600 psig.

The only non-LOCA safety analyses in which boron from either the RWST or accumulators is taken credit for, or assumed to be present, are those in which the SIS is actuated. These analyses are:

Accident Depressurization of the Main Steam System (FSAR Section 15.2.13)

Inadvertent Operation of the Emergency Core Cooling System During Power Operation (FSAR Section 15.2.14)

Minor Secondary System Pipe Breaks (FSAR Section 15.3.2)

Major Rupture of a Main Steam Line (FSAR Section 15.4.2.1)

Major Rupture of a Main Feedwater Line (FSAR Section 15.4.2.2)

- Rupture of a Control Rod Drive Mechanism Housing (FSAR

! 15.4.6)

The accumulators are active only in the steamline break analyses.

The effect of the proposed increase in the minimum RWST and accumulator boron concentration on each of the above transientsis discussed below.

3.1.1 Accidental Depressurization of the Main Steam System An accidental depressurization of the main steam system results in a cooldown of the RCS which,in the presence of a negative moderator temperature coefficient, causes a positive reactivity excursion. Borated water from the RWST enters the core following actuation of the SIS on low pressurizer pressure. The negative reactivity provided by the 2000 ppm water from the RWST limits the return to power to an accepttble level so that the minimum DNBR remains above the limiting value. As the transient proceeds and more water from the RWST reaches the RCS, the boron concentration in the RCS gradually increases, ultimately caur,ing the core to become subcritical. If the RWST boron concentration were increased to 2300 ppm more negative reactivity would be available to terminate the return to power sooner and at a reduced peak sowerlevel. Thus,the maximum core heat flux reached will be reduced. Ac'ditionally, the core would become subcritical earlier in the transient. Thus, the minimum DNBR would be

ATTACHMENT lli l Page 3 of 13

higher than for the case currently analyzed with 2000 ppm in the RWST and the conclusions in the FSAR will remain valid.

3.1.2 Inadvertent Operation of the Emeraency Core Coolina System Durina Power Operation Spurious actuation of the Emergency Core Cooling System while at power would result in a negative reactivity excursion due to the injected boron from the RWST. The decreasing reactor power causes a drop in the core average temperature and coolant shrinkage. If reactor trip on SIS actuation is assumed not to occur, the reactor will ultimately trip on low pressurizer pressure. DNBR is never below the initial value. If the RWST boron concentration were increased from the current minimum value of 2000 ppm to 2300 ppm the ne,gative reactivity excursion would occur at a faster rate causmg a more rapid drop in the core average temperature and coolant shrinkage. The reactor will trip on low pressurizer pressure as before, though at an earlier time in the transient. As before the DNBR will never decrease below the initial value. Thus, the conclusions in the FSAR will remain valid.

I 3.1.3 Minor Secondary System Pipe Breaks As discussed in the FSAR this event is bounded by major secondary system pipe ruptures discussed below.

3.1.4 Maior Rupture of a Main Steam Line A major ru pture of a main steam line results in a rapid cooldown of the RCS which,in the presence of a negative moderator temperature coefficient, causes a positive reactivity excursion. Borated water from the RWST enters the core following actuation of the SIS on low steam line pressure. The negative reactivity provided by the 2000 ppm water from the RWST limits the return to power to an acceptable level so that the minimum DNBR remains above the limiting value. As the transient proceeds and more water from the RWST reaches the RCS, the boron concentration in the RCS gradually increases, ultimately causing the core to become subcritical. If the RWST boron concentration were increased to 2300 ppm more negative reactivity would be available to terminate the return to power sooner and at a reduced peak power level. Thus, the maximum core heat flux reached will be reduced. Additionally, the core would become subcritical earlier in the transient. Thus, the minimum DNBR would be higherthan for the case currently analyzed with 2000 ppm in the RWST. The accumulators provide additional borated water after the core has become subcriticai. The additional reactivity provided by the higher accumulator boron concentration would increase shutdown margins. Thus, the conclusion of the FSAR will remain valid for the proposed higher boron concentration increases in the RWST and accumulators.

3.1.5 Maior Rupture of a Main Feedwater Line Following the rupture of a main feedwater line actuation of the SIS may occur. Although boron from the RWST is not required to maintain the reactor in a subcritical condition following a feedwater line break, the cold SIS water serves to reduce the RCS temperatures and pressures. An increase ATTACHMENT lli Page 4 of 13 i

I- - _ _ - - _ _ - _ _ - - _ . - -

in the minimum RWST boron concentration from 2000 ppm to 2300 ppm will increase the negative reactivity insertion rate without affecting the reduction of the RCS temperatures and pressures. Thus, an increase in the RWST boron concentration to 2300 ppm will have no adverse impact on the feedwater line break analysis and the conclusions in the FSAR will remain valid. ,

3.1.6 Rupture of a Control Rod Drive Mechanism Housino Following the ejection of a control rod the rapid nuclear power excursion causes the RCS to experience a large pressure rise due to the energy released into the coolant. The RCS pressure then drops as fluid inventory is lost through the break (a maximum of 2 square inches)in the control rod housing. As the RCS pressure continues to drop actuation of the SIS on low pressunzer pressure will inject borated water from the RWST into the RCS. .

i An increase in the RWST boron concentration from the current minimum of  !

l 2000 ppm to 2300 ppm will result in more rapid negative reactivity insertion i to the core and no interference with the core cooling capability. Thus, the conclusions in the FSAR remain valid. l 3.1.7 Conclusion An increase in the minimum RWST and accumulator boron concentration to 2300 ppm and 2200 ppm respectively will have no adverse impact upon the non-LOCA accident analyses. The conclusions as stated in the FSAR will remain valid.

3.2 FSAR LOCA Analysis (10CFR50.46)

For the full spectrum of postulated breaks, the ECCS is designed to limi+ the consequences of an accident to within the acceptance criteria of 10CFRSO.46. The analysis takes credit for pumped safety injection from the RWST and passive injection of accumulator water to prevent or mitigate the resulting clad temperature increase. Also, both cold and hotleg recirculation of cooling water from the containment sump to maintain long-term cooling is accounted for. The effect of an increase in the RWST and accumulator boron concentrations to 2300-2500 ppm for the RWST and 2200 to 2500 for the accumulators on these aspects of the LOCA analysis is discussed below.

3.2.1 Small Break LOCA Small break LOCA analyses for VCSNS assume that the reactor core is brought to a subcritical condition by the trip reactivity of the control rods.

There is no assumption regarding the concentration of boron in the ECCS water, and no credit is taken for the negative reactivity produced by soluble boron. Thus, the changes to the RWST and Accumulator Tech-Specs covering boron concentrations do not alter the conclusions of the FSAR small break LOCA analysis.

3.2.2 Large Break LOCA Large break LOCA analyses for VCSNS do not take credit for the negative reactivity introduced by the soluble boron in the ECCS water in determining ATTACHMENT lil Page 5 of 13

reactor power level during the early phases of the hypothetical large break LOCA. The traditionallarge break LOCA analyses performed by Westinghouse analyze the LOCA transient to a time just beyond the time at which Peak Cladding Temperature is calculated to occur. During this time period the reactor is kept subcritical by the voids present in the core. Thus the changes to the RWST and Accumulator Tech-Specs covering boron concentrations do not alter the conclusions of the FSAR large break LOCA analyses.

3.2.3 Lona-Term Coolina - Post LOCA Shutdown SCE&G's licensing position for satisfying the requirements of 10CFR50.46 Paragraph (b) Item (5) "Long-term cooling" is defined in WCAP-8339 (page 4-22). The commitment is that the reactor remain shutdown by the borated ECCS water. Since credit for the control rods is not taken for large break LOCA, the borated ECCS water provided by the RWST and Accumulators must have a concentration that,when mixed with other sources of water, will result in the reactor core remaining subcritical assuming all control rods out (ARO). Figure 1 shows the effect on the post-LOCA RCS/ Sump boron concentration as a result of changing the minimum Tech-Spec boron concentration from 2000 to 2300 for the RWST and from 1900 to 2200 for the Accumulators. The result is an increase of about 247 ppm in the RCS/ Sump boron concentration. Confirmation that this proposed mcrease will provide enough margin to keep the core subcritical for long term cooling requirements will be concluded through the normal RSAC evaluation process.

3.2.4 Lona-Term Coolina - Boron Precipitation An analysis has been performed for VCSNS to determine the maximum boron concentration in the reactor vessel following a hypothetical LOCA.

This analysis assumed a proposed maximum boric acid concentration of 2500 ppm in the RWST and accumulators and 2200 ppm in the RCS.

The analysis considers the increase in boric acid concentration in the reactor vessel during the long term cooling phase of a LOCA, assuming a conservatively small effective vessel volume. This volume includes only the free volumes of the reactor core and upper plenum below the bottom of the hot leg nozzles. This assumption conservatively neglects the mixing of boric acid solution with directly connected volumes, such as the reactor vessel lower plenum. The calculation of boric acid concentration in the reactor vessel considers a cold leg break of the reactor coolant system in which steam is aenerated in the core from decay heat while the boron associated with theboric acid solution is completely separated from the steam and remains in the effective vessel volume.

The results of the analysis show that the maximum allowable boric acid concentration of 23.53 weight percent which is the boric acid solubility limit less 4 weight percent, will not be exceeded in the vessel if hot leg injection is initiated 11 hours1.273148e-4 days <br />0.00306 hours <br />1.818783e-5 weeks <br />4.1855e-6 months <br /> after the LOCA inception. Thereafter the operator should alternate between hot and cold leg recirculation every 18 hours2.083333e-4 days <br />0.005 hours <br />2.97619e-5 weeks <br />6.849e-6 months <br />. The operator should reference this switchover time against the reactor trip /SI actuation signal. The typical time interval between the accident inception ATTACHMENT lli Page 6 of 13 4

m. .,.. .. .,em.. . . , . _ . . _ . - _ , _ . _ . , . . . . . _ . . ,, _ , _ _ , , . , . . . _ . _ _ . - _ , - - - _ _ _ . . . - . . . , - - _ . . . - , - . _ _ , . , , - - _ . _ _ _ . ,

and the reactor trip /SI actuation signal is negligible when compared to the switchover time.

Procedures philosophy assumes that it would be very difficult for the operator to differentiate between break sizes and locations. Therefore one hot leg switchover time is used to cover the complete break spectrum.

Conclusions 3.2.5 The increase in the RWST boron concentration from a range of 2000 to 2100 to a range of 2300 to 2500 ppm and Accumulator boron concentration from a range of 1900 to 2100 to a range of 2200 to 2500 ppm do not have a negative effect on the FSAR LOCA analysis. Current margin to the post-LOCA shutdown requirement is increased and continued conformance will be insured through th normal RSAC evaluation process. The higher concentrations do deciease the allowable time for operator action to initiate hot leg recirculation (24 hou s to 11 hours1.273148e-4 days <br />0.00306 hours <br />1.818783e-5 weeks <br />4.1855e-6 months <br />) and to subsequently alternate between hot and cold recirculation (every 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> to every 18 hours2.083333e-4 days <br />0.005 hours <br />2.97619e-5 weeks <br />6.849e-6 months <br />) to prevent requirements boron (11 and precip)itation 18 hours2.083333e-4 days <br />0.005 hours <br />2.97619e-5 weeks <br />6.849e-6 months <br /> inthan are still more the long term.

adequate to The resulting assure those time operator actions can be accom alished. Therefore, the higher boron concentrations do not have a c etrimental impact on maintenance of long-term cooling.

3.3 LOCA Related Desian Consideration increasing the boron concentration in the Refueling Water Storage Tank (RWST) and accumulators decreases the pH of the containment spray and recirculating core cooling solutions. A decrease in pH can decrease the elemental iodine spray removal coefficient and decontamination factor (DF), increase the rate of hydrogen production due to corrosion of zinc (galvanied and zinc based paint) and can increase the potential for chloride induced stress corrosion cracking of stainless steel.

. Based on the above considerations,2500 ppm has been determined to be an l acceptable maximum RWST and accumulator boron concentration. Details of the specific evaluations follow.

3.3.1 Radioloaical Consequences The minimum calculated spray and sump pH values are sufficient to support l

the elemental iodine spray removal coefficient and DF assumed in the FSAR LOCA dose analysis. Hence, the radiological consequences will not change as a result of the boron increase, and the FSAR dose analysis remains valid.

This conclusion is supported by spray and sump pH calculations.

l l

l l

l l

ATTACHMENT lli Page 7 of 13

Spray pH

'1 The minimum calculated spray pH is 9.2 based on a minimum sodium hydroxide flow of 55 gal /m,m. The minimum pH assumed to maximum elemental iodine removal by sprays is 8.5 (references 1 and 2). The calculated pH exceeds the minimum value and is considered sufficient to support the spray removal coefficient of 12.55 hr-1 assumed in the FSAR (Table 15.4-15).

Sump pH 4 The calculation of the minimum equilibrium sump solution pH considers the following delivered tank volumes and boron concentrations:

RWST - 467,000 gal,2500 ppm B Accumulators (3)- 22,782 gal,2500 ppm B RCS (hot zero power, no xenon)- 70,726 gal,2200 ppm B The resulting pH is 7.8. This value is sufficient to support a partition coefficient of approximately 3000 which supports the elementaliodine DF of 100 that is assumed in the FSAR dose analysis.

3.3.2 Hydrocen Production Hydrogen aroduced by the corrosion of aluminum and zincis a stroreg function o" solution pH. The corrosion rates incorporated in the FSAR Chapter 15 combustible gas analysis were based on a spray pH of approximately 11, which is consistent with the maximum NaOH (pH approximately 10.7) case shown in FSAR Figure 6.2-51s.

The corrosion data provided in Reference 3 were used to determine the effect on corrosion of reduced spray pH. Figure 5, from the reference, shows maximum zinc corrosion rates at pH 7 and 11 and minimum corrosion at approximately pH 9. Noting that the reduced pH values as well as the FSAR values are withm the above range, and that the new values will always be lower than the FSAR values, due to the increased bore.n concentration, the lower pH corrosion rates will be bounded by the FSAR cates.

Boron concentration effects on zinc corrosion were also investigated. Based on the method of reference 4, a 300 ppm increase in boron concentration, from 2200 to 2500 ppm, resulted in as much as a 6% decrease in certosion rate, dependent upon temperature and pH.

l The aluminum corrosion rates, provided in Figure 6 of Reference 3, decrease monotonically with decreasing pH. hence, aluminum corrosion will decrease with increasing boron concentration.

i To summarize, the rates of hydrogen generation due to corrosion of l aluminum and zinc, for the increased boron / decreased pH condition,will be l less than the rates specified in the FSAR. Hence, the FSAR analysis bounds the reduced pH condition.

l l ATTACHMENT lil Page 8 of 13 i

3.3.3 Equipment Qualification The primary concerns of equipment qualification are protection of the stainless steel components of the emergency core cooling system from chloride induced stress corrosion cracking, failures of electncal components required to operate post accident, and failures of containment coatings which could jeopardize the ECCS by flaking or peeling off, clogging the emergency sump and other flow paths, and thus restnct the flow of emergency core cooling water.

i Protection of Stainless Steel l l

To minimize the occurrence of chloride stress corrosion cracking of stainless steel, Westinghouse recommends maintaining the equilibrium sump solution pH a sove 7.5 (Reference 5). The mirumum calculated sump solution pH of 7.8 satisfies this requirement.

Electrical Components l

Electrical equipment testing is used to determine the ability of component seals to exclude the containment environment from the interior of the component. To maximize the challencie to the seal materials, high pH sprays in the range of 8 to 11 have traditiona ly been used.

For all modes of containment spray and ECCS operation, the solution pH with increased boron concentrat, ion will always be less than the corresponding pH with reduced boron. Hence, components qualified at higher pH are expected to have a longer post-accident service life in a lower pH (in the caustic range) environment.

Containment Coatinos Coatings are used in the containment to provide corrosion protection for metals and to aid in decontamination of surfaces during normal operation.

Like electrical equipment, coatings are tested with a high pH solution to maximize the potential deterioration of the coating and are expected to show better resistance to lower pH solutions.

ATTACHMENT lli Page 9 of 13

4.0

SUMMARY

AND CONCLUSIONS The proposed increase in the RWST and accumulator allowable boron concentration limits to 2300 to 2500 ppm for the RWST and 2200 to 2500 ppm for the accumulators has been assessed from a safety standpoint. Table 1 identifies the safety issues examined, the relevant (upper or lower) boron concentration limit, and conclusions from the safety evaluation. Based on thesa results,it is concluded that the proposed boron concentration increases will have no adverse impact on the non-LOCA Accident Analysis,the LOCA Analysis or LOCA Related Design Considerations and is thus acceptable for implementation at Virgil C. Summer Nuclear Station beginning with Cycle 4. l Confirmation that the boron concentration increases will provide enough margin to meet post-LOCA shutdown requirements will be insured through the normal Westinghouse RSAC evaluation process.

ATTACHMENT 111 Page 10 of 13

I l

5.0 REFERENCES

l

1. " Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants," NUREG-75/087, Section 6.5.2, November,1975.

2. " Standard Review Plan for the Review of Safety Analysis Reports for ,

Nuclear Power Plants," NUREG-0800, Section 6.5.2, July,1981. l

3. " Corrosion Study for Determining Hydrogen Generation from Aluminum ,

and Zinc During Post-Accident Conditions," WCAP-8776, April,1976.

4. "The Relative im sortance of Temperature, pH and Boric Acid Concentration of Rates of H2 Production from Galvanized Steel Corrosion," NUREG/CR-2812, November,1983.

5. " Behavior of Austinitic Stainless Steel in Post Hypothetical Loss of Coolant Environment," WCAP-7798-L, November,1971.

ATTACHMENT lli Page 11 of 13

~

TABLE 1

SUMMARY

OF SAFETY EVALUATION PROPOSED TECH SPEC ITEM VALUE SAFETY ISSUE CONCLUSION Boron Cocnentration 2500 ppm for both RWST & Post LOCA Boron Operator has adequate time

-UPPER LIMIT- Accumulator Precipitation to initiate HL recirculation (11 hours1.273148e-4 days <br />0.00306 hours <br />1.818783e-5 weeks <br />4.1855e-6 months <br />) and to subsequently alternate HL and CL recirculation

. (every 18 hours2.083333e-4 days <br />0.005 hours <br />2.97619e-5 weeks <br />6.849e-6 months <br />) to prevent boron precipitation.

Spray and sump pH changes do not LOCA Radiolog.ical invalidate FSAR assumptions for Conseqences elementaliodine spray removal coefficient and decontamination factor. Therfore, the FSAR dose analysis remains valid.

Hydrogen Production Rates of hydrogen generation due to corrosion of aluminum and zinc, for the increased boron / decreased pH conditions,will be leass than the rates soecified in the FSAR. The FSAR analyses remains bounding.

Equipment Qualification The increased boron / decreased pH conditions do not invalidate environment conditions assumed for equipment qualification.

2300 ppm for RWST & 2200 Non-LOCA Safety Analysis No adverse impact. The conclusions B:ren Concentration

-LOWER LIMIT- ppm for Accumulators as stated in the FSAR remain valid.

Small Break LOCA Analysis Analysis takes no credit for boron in l

i ECCS suater and is thus not affected.

l l

l Large Break LOCA Analysis Up to time of peak clad temperature,

analyses takes no credit for boron in l the ECCS water and are thus not l affected.

1 Post LOCA Shutdown Confirmation that core is kept l ( 2 3.0 ft.2) subcritical with all rods out will be l ensured through the RSAC l evaluation process.

1 ATTACHMENT 111 Page 12 of 13

FIGURE 1 2,500 3

$ 2,300 8

z o

@ 2,100 -

2 /

2

1. -T g M R0 POSED o

M 1,900 N

Si #

$ g M -CURRENT g

o 1,700 a:

2i S

N 2 1,500 1,300 500 700 900 1,100 1,300 1,500 PRE-TRIP RCS BORON CONCENTRATION (PPM)

V. C. SUMMER UNIT 1 CURRENT LIMITS FOR CYCLE 4 POST-LOCA SUMP /RCS AUXED MEAN BORON CONCENTRATION VS.

PRF,-TRIP RCS BORON CONCENTRATION ATIIFP-PK XE-ARO ATTACHMENT III Page 13 of 13