ML20113D807

Proposed Tech Specs Re Core Shutdown Margin

ML20113D807
Person / Time
Site:	Vermont Yankee File:NorthStar Vermont Yankee icon.png
Issue date:	06/28/1996
From:	VERMONT YANKEE NUCLEAR POWER CORP.
To:
Shared Package
ML20113D805	List: ML20113D801 ML20113D807
References
NUDOCS 9607030342
Download: ML20113D807 (21)

Text

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Marked-up Technical Specification Pages Proposed Change 187 Core Shutdown Margin l

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CPT?)T*:N 3.3 CONT?ct #CD SYSTIM 4.3 CONTPCL 900 SYSTIM Acellesbiliev: Acelienbiliev.

Applies to the operati nal Applies :: :he surveillance scacus of the centr:1 red requiremen=s of the c:ntr:1 : d system. system.

Chiective: Cbiective:

Tc assure the abili:y of the To verify :he abill:y of the cener:1 red sys:em := centrol concr:1 : d sys:em to con =r:1 reactivity. reactivi:y, Seecification: Seeci fient ien :

A. Reactivity Limitatiens A. Reactivity Limitatiens

1. Peacti'riev Martin . Cere 1. Peactiviev Varrin . C=re Leacine- Leacine The core leading shall C:n:: ^. : ds/shall 'e be limited := that which wi-Tarawn ellowi, g a l

=an be =ada suberi:ical [shd  : .uelir cc:rgy'when I in the =cs: reactive y c:re a era:1-ds were c nditica during the perfr[mec* cemens: ace operation cycle wi:h the 4.4.M a sM:d: r margin Jhdd highese worth, cperable 0 .5 pe cent pkfe: any g gggger con:::1 ::d in 1:s fully .ime in' the suceequen:

!bI* A'g withdrawn pesi:icn and s- fuelfrycle w*h the all ccher cperable ::ds "

hi-hes: wer-5 epers;.e inser:ed. c~n:::1 : fully /

1:hdrawn and a' .fc: hor cpera.de : ds .nserted/

2. Peactivity Marein - 2. Reactiri:V Marcin -

necera:Le cen:::t Reds In:: era:1e cen:rei Reds Centrol :=d driven which Each partially er fully t cannet be =cved with withdrawn operable i centr:1 red drive c:ncr:1 : d shall be pressure shall be exer:ised one necch ac censidered inoperable. least once each week.

If a partially or fully This tes: shall be withdrawn c:ntr:1 red perf :=ed at least once drive cannet be moved per 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> in the with drive er scram even; power operatica is pressure, the reac::: continuing with two er shall be brought to a mere in=perable centrol shutdown c ndition  : ds er in the event within 48 h urs unless power cperatien is investiga:icn centinuing with one demons:: aces that the fully er partially cause of the failure is withdrawn : d which n: due := a failed cannet be ==ved and for c=ntrol :=d drive which centr:1 red drive mechanism c=lle mechanism damage has no:

housing. The cener:1 been ruled out. The

=d directi:nal cener:1 surveillance need not be valves fer incperable c:=pleted within centr:1 reds shall be 24 h urs if the number

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l INSERT 3.3. A.1 INSERT 4.3.A.1 l l

To ensure this capability, the Verify that the required SDM is shutdown margin shall be provided met prior to each in-vessel fuel as follows any time there is fuel movement during the fuel loading in the core: sequence.

(a) 20.38% Ak/k with the highest Within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> after criticality l worth rod analytically determined; following fuel movement within the l reactor pressure vessel or control or rod replacement, verify the required shutdown margin will be met at  !

(b) 20.28% Ak/k with the highest I any time in the subsequent operation worth rod determined by test. cycle with the highest worth operable control rod fully withdrawn and all other operable With the required shutdown margin rods insened (except as provided not met during power operation, in Specifications 3.12.D and either restore the required shutdown 3.12.E). l margin within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, or be in hot  ;

shutdown within the next 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.

l With the required shutdown margin l

not met and the mode switch in the l

" Refuel" position, immediately j suspend Alteration of the Reactor i Core except for control rod insertion and fuel assembly removal; immediately initiate action to fully l insert all insenable control rods '

in core cells contaimng one or more fuel assemblies; within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />, initiate action to restore the integrity of the secondary containment system.

s

VYNPS

(

2 -

3.3 LD'. TING CONDITICNS FCR 4.3

. CPT?>T:CN SURVE*I. LANCE REQUIREe.ErIs E. Reactivitv Aremalies E.

a Rese-iviev Anemalies The reactivity equivalent of Curing the startup test I the difference between the program and startups 2

actual critical red following refueling outages, configuration and th1 l

! expected configuration the critical red 3 c=nfigurations will be i

during power o ration shall compared to the expected  !

not exceed it If this configurations ac selected Ek limit is exca

• a====

, the win be shut d=wn until the cause has been operating conditiens. These c==parisons will de usee as decermined and corrective base data for reactivity monitoring during subsequen:

j actions have been taken if power operation throughout such actions are the fuel cycle. At specific l appropriate.

b power operacing c=ndiciens,

, F. If Specification 3.3 ' the critical rod

• configuration will be through D above are nec mec, compared to the an orderly shutdown shall be c=nfiguration expected based initiated and the reactor upon appr=priately c=rrected 4

shall be in the cold past data. This c=mparison I

shutdown condition within will be made at leas: every l 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. l equivalent full power monch.

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88 O

,4

-T

.* VYNPS l

BASES:

l 3.3 & 4.3 CONTROL RCD SYSTEM A. Reactivitv Limitations Reactivity Marcin - Core Loadino l 1.

Thef' core reactivity limi ation is.ela estricti to be appfied i i

p dncipallyj(o the des n of new which y be loadfd in the Satisf agion of the m

core or into a partic- ar refueli g patter.

A imitaticn' can only e demonser ed at th time of lo6 ding and

/ must be s such that ' will app to the e tire subsgg'uent fuel cycle .j/ At each corer fueling can ethmade reactivigf of theby'at suWritical coseleastleading ill be limited so t INSfA1' R .fo.2st ak w- h the high se worth generol ro fully with awn is the ount by STA and allthe which other/ inserted.

evIcu12ted ca The valuVofatRany/

ereactivfy, in t time in th i

/ operating Mcle, Rmexce t be demonstrMion.

s the reactivity atfhe time o the a porftive quan . The va e of R sh*Il include he potentJ'al shutdown,Kity or margin zer le s assumin full a ent in t core /(CThesettling 0.25%inakallisinp'rted providedpoison tubesde as a ,(inite, prnstrable, sub / crit icalit' margin. / /

2. Reactivity Marcin - Inocerable Control Rods Specification 3.3.A.2 requires that a rod be taken out of service i if it cannot be moved with drive pressure. If a rod is disarmed l electrically, its position shall be consistent with the shutdown reactivity limitation stated in Specification 3.3.).1. This assures that the core can be shutdown at all times with the l remaining control rods, assuming the highest worth operable control rod does rod insert. An allowable patterr. for control rods valved out of service will be available to tne reactor operator. The number of rods permitted to be ir. operable could be many more than the six allowed by the Specification, particularly late in the operation cycle; however, the occurrence of more than six could be indicative of a generic control rod drive problem and the reactor will be shutdown. Also if damage within the control rod drive mechanism anc' in particular, cracks in drive internal housing, cannot be ruled out, then a generic problem affecting a number of drives cannot be ruled out.

Circumferential cracks resulting from stress assisted intergranular corrosion have occurred in the collet housing of drives at several BWRs. This type of cracking could occur in a nu=her of drives and if the cracks propagated until severance of the collet housing occurred, scram could be prevented in the affected rods. Limiting the period of operation with a potentially severed collet housing and requiring increased surveillance af ter detecting one stuck rod will assure that the reactor will not be operated with a large number of rods with failed collet housings.

B. Control Rods

1. Control rod dropout accidents as discussed in the FSAR can lead to significant core damage. If coupling integrity is maintained, the possibility of a rod dropout accident is eliminated. The overtravel position feature provides a positive check as only uncoupled d!:ives may reach this position. Neutron instrumentation response to rod movement provides a verification that the rod is following its drive.

Amendment No. G4, NVY 87-131 85

1

INSERT 89A The specified Shutdown Margin (SDM) limit accounts for the uncertainty in the demonstration of SDM by testing. Separate SDM limits am provided for testing whem the highest wonh control rod is determined analytically or by measumment. This is due to the educed uncenainty in the SDM test when the highest worth control rod is determined by measurement (e.g., SDM may be demonstrated by an iri-sequence contml md withdrawal, in which the highest worth control rod is analytically detcrmined, or by local criticals, where the highest wonh rod is determined by testing).

Following a refueling, a'dequate SDM must be demonstrated to ensure that the mactor can be made subcritical at any point during the cycle. Since core mactivity will vary during the cycle as a function of fuel depletion and poison burnup, the beginning of cycle (BOC) test must also account for changes in core reactivity during the cycle. Therefore, to obtain the SDM, the initial measured value must exceed LCO 3.3.A.1 by an adder, "R", which is the diffennce between the calculated value of maximum core reactivity during the operating cycle and the calculated BOC core reactivity. If the value of "R" is negative (that is, BOC is the most reactive point in the cycle), no correction to the BOC measured value is required. The value of R shall include the potential shutdown margin loss assuming full B4 C settling in all invened poison tubes present in the core. The frequency of 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> after reaching criticality is allowed to provide a reasonable amount of time to perform the required calculations and have appropriate verification.

When SDM is demonstrated by calculations not associated with a test (e.g., to confirm SDM during the fuel loading sequence), additional margin must be included to account for uncertainties in the calculation. During refueling, adequate SDM is required to ensure that the reactor does not reach criticality during control rod withdrawals. An evaluation of each in-vessel fuel movement during fuel loading (including shuffling fuel within the core) is required to ensure adequate SDM is maintained during refueling. This evaluation ensures that the intermediate loading patterns are bounded by the safety analyses for the final core loading pattern. For example, bounding analyses that demonstrate adequate SDM for the most reactive configurations during the refueling may be performed to demonstrate acceptability of the entire fuel movement sequence. These bounding analyses inc!gde additional margins to account for the associated uncertainties in the calculation.

VYNPS 1 l

I BASES: 3.3 & 4.3 (Cont'd)

7. Periodic verification that the Scram Discharge Volume (SDV) drain and vent valves are maintained in the open position provides assurance that the SDV will be available to accept the water displaced from the control rod drives in the event of a scram.

C. Scram Insertion Times The Control Rod System is designed to bring the reactor suberitical l at a rate fast enough to prevent fuel damage. The limiting power j transient is that resulting from a turbine stop valve closure with a failure of the. Turbine Bypass System. Analysis of this transient shows that the negative reactivity rates' resulting from the scram with the average response of 4.11 the drives as given in the above specification, provide the required protection, and MCPR remains greater than the fuel cladding integrity safety limit.

The scram times for all control rods shall be determined during each l operating cycle. The weekly control rod exercise test serves as a j periodic check against deterioration of the Control Rod System and i also verifies the ability of the control rod drive to scram. The  ;

frequency of exercising the control rods under the conditions of two l or more control rods valved out of service provides even further j assurance of the reliability of the remaining control rods.

D. Control Rod Accumulators i

Requiring no more than one inoperable accumulator in any nine-rod (3x3) square array is based on a series of XY PDQ-4 quarter core  ;

calculations of a cold, clean core. The worst case in a nine-rod l withdrawal sequence resulted in a K,gg 3,1.0. Other repeating rod sequences with more rods withdrawn resulted in K,ge 11 0. At reactor pressures in excess of 800 psig, even those control rods with inoperable accumulators will be able to meet required scram insertion times due to the, action of reactor pressure. In addition, they may be -ormally inserted using the Control-Rod-Drive Hydraulic System.

Procedural control will assure that control rods with inoperable accumulators will be spaced in a one-in-nine array rather than grouped together.

E. Reactivity Anomalies During each fuel cycle, excess operating reactivity varies as fuel depletes and as any burnable poison in supplementary control is burnad. The magnitude of this excess reactivity may be inferred from the critical rod configuration. As fuel burnup progresses, anomalous behavior in the excess reactivity may be detected by comparison of the critical rod pattern selected base states to the predicted rod inventory at that state. Power operation base conditions provide the most sensitive and directly interpretable data relative to core reactivity. Furthermore, using power operating base conditions permits frequent reactivity comparison 3. Requiring a reactivity comparison at the specified frequency amrures that a mparison will be made before the core reactivity ange exceeds it Deviations in core reactivity greater than it are not expect and require thorough evaluation. One percent rea tivity limit i considered safe since an insertion of the reactivity to the core o'1d not lead to transients exceeding design conditions of the Reac or System.

dk Amendment No. EG, 73 91

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. VYi2PS 3.12 LIMITING CONDITIONS FOR 4.12 SURVEILLANCE REQUIREMENTS OPERATION l D. Control Rod and Control Pod D. Control Rod and Control Rod Drive Maintenance Drive Maintenance xim m of tw One. 1. utf cient contro rods n -ad ace control rod / sha 1 be ichdra par ted y morp cn tw pr'or to erfo ng l cent ol 11s M any e is ma cenanc to dir eti I may be withdrawn mons ate wi a from the core for the rein of 0.2 eerce t, purpose of performing that the core can be control rod and/or control t

@made suberitical at any rod drive maintenance time during the provided the following maintenance with the conditions are satisfied: strongest operable control rod fully

1. The reactor mode switch withdrawn and all cther shall be locked in the operable rods fully

• Refuel

• position. e inserted.

frer eling acera x

( wh'ch pr ents re l 2. Alternately, if a t n one contr rod minimum of eight om be ng wi dra control rods y be ypas d for one surrounding @ b of th cent I rod on control rod out of whic maint nanc s service for maintenance cerf rtned All are to be fully (bei e _ d refueling inserted and have their interlocks shall be directional control operable.

valves electrically disarmed, the .Shd.-,J M

2. Specification 3.3.A.1 O ;;;:::: O margin shall be met, or the shall be met with the control rod directional strongest control rod control valves for a remaining in service minimum of eight during the maintenance control rod period fully withdrawn.

surrounding drive out of service or maintenance shall be disarmed electrically and' sufficient margin V m

e**

W*f S f**0 *$

cort. AMW

3. SRMs shall be operable main b ance.,gg gg dMWAtd

@ in core 9 W.4 Dpdm i quadrant containing /%s, M m.cco rd mC t.

control rod c.a which maintenance is being 3.M .1 % masure..***

performedg_and @ in an efec.eet quadrant.yugav m vu p' u cpe qua rantq sp , fi in i Ia muy

'Tha Requirements for an SRM to be considered operable are given in l Specification 3.12.B.

Amendment No. 18 232

VYNPS l

3.12 LIMITING CONDITIONS FOR 4.12 SURVEILLANCE REQUIREMENTS l OPERAT!CN i

l E. Extended Core Maintenance E. Extended Core Maintenance

~

l One. oc men. CL - -.~. Q control rods Prior to control rod j may De withcrawn,from the withdrawal for extended l

reactor core pre ided the core maintenance, that followingconditjensare satisfied:

control rods control cell shall be verified to

@ "" contain no fuel assemblies.

1. The reactor mode switch 1. This surveillance j shall be locked in the requirement is the same l

• Refuel

• position. The as that given in I refueling interlock Specification 4.12. A.

which prevents more than one control rod from being withdrawn may be bypassed on a withdrawn control rod after the fuel assemblies in the cell containing (controlled by) that control rod have been removed from l the reactor core. All l other refueling interlocks shall be i operable.

2. SRMs shall be operable 2. This surveillance in the core quadrant requirement is the same where fuel or control as that given in rods are being mcved, Specification 4.12.B.

i and in an adjacent quadrant. The requirements for an SRM to be considered operable are given in Specification 3.12.B.

3. If the spiral unload /;eload method of core alteration is to be used, the following conditions shall be met:

a. Prior to spiral unload and reload, l

the SFF.s shall be proven operable as stated in i specification

! 3.12.B1 and 3.12.B2. However, during spiral unloading, the count rate may drop below 3 cps.

Amendment No. M , M , 77 233 i

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'"(NP

. S BASES: 3.12 & 4.12 (Cont'd)

C. To assure that there is adequate water to shield and ecol the irradiated fuel assemblies scored in the pool, a mininum pool water level is established. This minimu= water level of 36 feet is established because it would be a significant change from the normal level, well above a level to assure adequate cooling (just above active fuel).

D. During certain periods, it is desirable to perfor n mai .tenance on a, 4Mje.,

@specification control rod provides / and/orassurance control rod drivci _: . . . _:Q.

that inadvertent crie: ca;1ty This does not occur during such maintenance.

The maintenance is perfor=ed with the mode switch in the ' Refuel' position to provide the refueling interlocks normally available during refueling operations as explained in Part A of these Bases, wa. c: cne firs rod, a 'ecaar

.a -s as . a se ona cor roA r0 a: er withc M gI 4 { e is cessa to ass er refu ing ir erlock on the UM i fir t con .ol ro which reven* :rcre han em ~*'-M rem Lbe nc wi .drsvn e *Me w. -4 o f The requirement that an adequate shutdown margin beS _.2._ . n Mith the control rods remaining in sernce ensures en'a t inacvertent criticality cannot occur during __

gg this maintenance.

aav ene e frne nucco margan as <a

s/snut own av n if th stren- =eaeo m- oyjalcemcas red sf acing em/4 4- dras o-/r4 -s

= N ' '; W-Mdr I Disarming the directional control valves does not inhibit control red scram capability.

E. The intent of this specification is to permit the unicading of a Ci;n '_:; r1x B portion of the reactor core for such purposes as inservice inspection requirements, examination of the core support plat. getc. This specification provides assurance that inadvertent cracacality does not occur during such operation.

3 g This operation is performed with the mode switch in the " Refuel" position to provide the refueling interlocks normally available re d 'e r ce * * *I during refueling as explained in the Bases for Specification 3.12. A.

red de t vs In order to withdraw more than one control rod, it is necessary to I mg,4 W ee, bypass the refueling interlock on each withdrawn control red which

. prevents more than one control red from being withdrawn at a time.

The requirement that the fuel assemblies in the cell controlled by the control rod be removed from the reactor core before the interlock can be bypassed ensures that withdrawal of another control rod does not result in inadvertent criticality. Each control red essentially provides reactivity control for the fuel assemblies in the cell associated with that control rod. Thus, removal of an entire cell (fuel assemblies plus control rod) results in a lower reactivity potential of the core.

One method available for unloading or reloading the cera is the spiral unicad/ reload. A rpiral unloading pattern is one by which the fuel in the outermost cells (four fuel bundles surrounding a control red) is removed first. Unloading continues by unloading the remaining outermost fuel by cell spiralling inward towards the center ca.'.1 which is the last cell removed. Spiral reloading is reverse of unloading, with the exception that two (2) diagonally adjacent bundles, which have previously accumulated exposure in-core, are placed next to each of the 4 SRMs before the actual spiral reloading begins. The spiral reload then begins in the center cell and spirals outward until the core is fully loaded.

I l Amendment No. 77 238

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. l INSERT 238A l

Refueling interlocks restrict the movement of control mds and the operation of the refueling equipment to reinforce operational procedures that prevent the reactor fmm becoming critical during refueling opemtions. During refueling operations, no more than one control md is permitted to be withdrawn from a core cell containing one or more fuel assemblies. The ,

refueling interlocks use the " full-in" position indicators to determine the position of all control l

rods. If the " full-in" position signal is not present for every control rod, then the "all-rods-in" permissive for the refueling equipment interlocks is not present and fuel loading and control rod withdrawalis prevented. The refuel position one-rod-out interlock will not allow the withdrawal of a second control rod.

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1 New Technical Specification Pages Proposed Change 187 l

Core Shutdown Margin l

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. VYNPS 3.3 LIMITING CONDITIONS FOR 4.3 SURVEILLANCE REQUIREMENTS OPERATION _

3.3 CONTROL ROD SYSTEM 4.3 CONTROL ROD SYSTEM Applicability: Applicability:

Applies to the operational Applies to the surveillance status of the control rod requirements of the control rod system. system.

Obiective: Obiective:

To assure the ability of the To verify the ability of the control rod system to control control rod system to control reactivity. reactivity.

Specification: Specification:

A. Peactivity Limitations A. Reactivity Limitations

1. Reactivity Margin - Core 1. Reactivity Margin - Core Loading Loading The core loading shall Verify that the required ,

be limited to that which SDM is met prior to each j can be made subcritical in-vessel fuel movement '

in the most reactive during the fuel loading condition during the sequence.

operation cycle with the highest worth, operable Within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> after control rod in its fully criticality following withdrawn position and fuel movement within the all other operable rods reactor pressure vessel inserted. or control rod replacement, verify the To ensure this capabi- required shutdown margin lity, the shutdown will be met at any time margin shall be provided in the subsequent as follows any time operation cycle with the there is fuel in the highest worth operable core: control rod fully withdrawn and all other (a) >0.38% Ak/k with operable rods inserted the highest worth (except as provided in rod analytically Specifications 3.12.D determined; and 3.12.E).

or (b) >0.28% Ak/k with the highest worth rod determined by test.

With the required shutdown margin not met during power operation, either restore the required shutdown margin within 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, or be in hot shutdown within the next 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.

Amendment No. GO, 81

VYNPS 3.3 LIMITING CONDITIONS FOR 4.3 SURVEILLANCE REQUIREMENTS OPERATION __

With the required shutdown margin not net and the mode switch in the " Refuel" positi?n, immediately suspend Alteration of the Reactor Core except for control rod insertion and fuel assembly removal; immediately initiate action to fully insert all insertable control rods in core cells containing one or more fuel assemblies; within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />, initiate action to restore the integrity of the Secondary Containment System.

2. Reactivity Marcin - 2. Reactivity Marcin -

Inoperable Control Rods Inoperable Control Rods Control rod driven which Each partially or fully cannot be moved with withdrawn operable control rod drive control rod shall be pressure shall be exercised one notch at considered inoperable, least once each week.

If a partially or fully This test shall be withdrawn control rod performed at least once drive cannot be moved per 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> in the with drive or scram event power operation is pressure, the reactor continuing with two or shall be brought to a more inoperable control shutdown condition rods or in the event within 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> unless power operation is investigation continuing with one demonstrates that the fully or partially cause of the failure is withdrawn rod which not due to a failed cannot be moved and for control rod drive which control rod drive mechanism collet mechanism damage has not housing. The control been ruled out. The rod directional control surveillance need not be valves for inoperable completed within control rods shall be 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> if the number 81a l Amendment No.

~ _ _ _ ___ _ _

1 VYNPS 3.3 LIMITING CONDITIONS FOR 4.3 SURVEILLANCE REQUIREMENTS OPERATION E. Reactivity Anomalies E. Reactivity Anomalies The reactivity equivalent of During the startup test the difference between the program and startups actual critical rod following refueling outages, configuration and the the critical rod expected configuration configurations will be during power operation shall compared to the expected l not exceed 1% Ak/k. If this configurations at selected limit is exceeded, the operating conditions. These reactor will be shut down comparisons will be used as until the cause has been base data for reactivity determined and corrective monitoring during subsequent actions have been taken if power operation throughout such actions are the fuel cycle. At specific appropriate. power operating conditions, the critical rod l F. If Specification 3.3B configuration will be through D above are not met, compared to the an orderly shutdown shall be configuration expected based initiated and the reactor upon appropriately corrected shall be in the cold past data. This comparison shutdown condition within will be made at least every 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. equivalent full power month.

l l

1 Amendment No. 49, 88

, VYNPS BASES:

3.3 & 4.3 CONTROL ROD SYSTEM A. Reactivity Limitations

1. Reactivity Margin - Core Loading The specified shutdown margin (SDM) limit accounts for the uncertainty in the demonstration of SDM by testing. Separate SDM limits are provided for testing where the highest worth control rod is determined analytically or by measurement. This is due to the reduced uncertainty in the SDM test when the highest worth control rod is determined by measurement (e.g., SDM may be demonstrated by an in-sequence control rod withdrawal, in which the highest worth control rod is analytically determined, or by local criticals, where the highest worth rod is determined by testing).

Following a refueling, adequate SDM must be demonstrated to ensure that the reactor can be made suberitical at any point during the cycle. Since core reactivity will vary during the cycle as a function of fuel depletion and poison burnup, the beginning of cycle (BOC) test must also account for changes in core reactivity during the cycle. Therefore, to obtain the SDM, the initial measured value must exceed LCO 3.3.A.1 by an adder, "R", which is the difference between the calculated value of maximum core reactivity during the operating cycle and the calculated BOC core reactivity. If the value of "R" is negative (that is, BOC is the most reactive point in the cycle), no correction to the BOC measured value is required. The value of R shall include the potential shutdown margin loss assuming full B 4 C settling in all inverted poison tubes present in the core.

The frequency of 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> after reaching criticality is allowed to provide a reasonable amount of time to perform the required calculations and have appropriate verification.

When SDM is demonstrated by calculations not associated with a test (e.g., to confirm SDM during the fuel loading sequence),

additional margin must be included to account for uncertainties in the calculation. During refueling, adequate SDM is required to ensure that the reactor does not reach criticality during control rod withdrawals. An evaluation of each in-vessel fuel movement during fuel loading (including shuffling fuel within the core) is required to ensure adequate SDM is maintained during refueling. This evaluation ensures that the intermediate loading patterns are bounded by the safety analyses for the final core loading pattern. For example, bounding analyses that demonstrate adequate SDM for the most reactive configurations during the refueling may be performed to demonstrate acceptability of the entire fuel movement sequence. These bounding analyses include additional margins to account for the associated uncertainties in the calculation.

2. Reactivity Margin - Inoperable Control Rods Specification 3.3.A.2 requires that a rod be taken out of service if it cannot be moved with drive pressure. If a rod is disarmed electrically, its position shall be consistent with the shutdown reactivity limitation stated in Specification 3.3.A.1. This assures that the core can be shutdown at all times with the remaining control rods, assuming the highest worth, operable control rod does rod insert. An allowable pattern for control rods valved out of service will be available to the reactor operator. The number of rods permitted to be inoperable could be Amendment No. 40, NVY 07 131, 89

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BASES: 3.3 & 4.3 (Cont'd) many more than the six allowed by the Specification, particularly late in the operation cycle; however, the occurrence of more than six could be indicative of a generic control rod drive problem and the reactor will be shutdown. Also if damage within the 1 l control rod drive mechanism and in particular, cracks in drive internal housing, cannot be ruled out, then a generic problem affecting a number of drives cannot be ruled out.

Circumferential cracks resulting from stress assisted l intergranular corrosion have occurred in the collet housing of l drives at several BWRs. This type of cracking could occur in a ,

number of drives and if the cracks propagated until severance of I the collet housing occurred, scram could be prevented in the affected rods. Limiting the period of operation with a potentially severed collet housing and requiring increased surveillance after detecting one stuck rod will assure that the reactor will not be operated with a large number of rods with failed collet housings.

B. Control Rods

1. Control rod dropout accidents as discussed in the FSAR can lead to significant core damage. If coupling integrity is maintained, the possibility of a rod dropout accident is eliminated. The overtravel position feature provides a positive check as only uncoupled drives may reach this position. Neutron instrumentation response to rod movement provides a verification that the rod is following its drive.

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VYNPS PASES: 3.3 & 4.3 (Cont'd)

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7. Periodic verification that the Scram Discharge Volume (SDV) drain and vent valves are maintained in the open position provides assurance that the SDV will be available to accept the water displaced from the control rod drives in the event of a scram.

C. Scram Insertion Times The Control Rod System is designed to bring the reactor subcritical at a rate fast enough to prevent fuel damage. The limiting power transient is that resulting from a turbine stop valve closure with a I failure of the Turbine Bypass System. Analysis of this transient

{ shows that the negative reactivity rates resulting from the scram with the average response of all the drives as given in the above specification, provide the required protection, and MCPR remains greater than the fuel cladding integrity safety limit.

The scram times for all control rods shall be determined during each operating cycle. The weekly control rod exercise test serves as a

-periodic check against deterioration of the Control Rod System and l also verifies the ability of the control rod drive to scram. The

' frequency of exercising the control rods under the conditions of two i or more control rods valved out of service provides even further i

assurance of the reliability of the remaining control rods.

D. Control Rod Accumulators l Requiring no more than one inoperable accumulator in any nine-rod (3x3) square array is based on a series of XY PDQ-4 quarter core calculations of a cold, clean core. The worst case in a nine-rod withdrawal sequence resulted in a K,gg 11.0. Other repeating rod

! sequences with more rods withdrawn resulted in K,gg 11 0. At reactor l pressures in excess of 800 psig, even those control rods with inoperable accumulators will be able to meet required scram insertion times due to the action of reactor pressure. In addition, they may j be normally inserted using the Control-Rod-Drive Hydraulic System.

Procedural control will assure that control rods with inoperable accumulators will be spaced in a one-in-nine array rather than grouped together.

E. Reactivity Anomalies During each fuel cycle, excess operating reactivity varies as fuel

! depletes and as any burnable poison in supplementary control is burned. The magnitude of this excess reactivity may be inferred from the critical rod configuration. As fuel burnup progresses, anomalous behavior in the excess reactivity may be detected by comparison of the critical rod pattern selected base states to the predicted rod inventory at that state. Power operation base conditions provide the most sensitive and directly interpretable data relative to core reactivity. Furthermore, using power operating base conditions permits frequent reactivity comparisons. Requiring a reactivity comparison at the specified frequency assures that a comparison will be made before the core reactivity change exceeds 1% Ak/k.

Deviations in core reactivity greater than 1% Ak/k are not expected and require thorough evaluation. One percent reactivity limit is considered safe since an insertion of the reactivity into the core would not lead to transients exceeding design conditions of the Reactor System.

Amendment No. 45, 44, 91 l

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, VYNPS 3.12 LIMITING CONDITIONS FOR 4.12 SURVEILLANCE REQUIREMENTS OPERATION D. Control Rod and Control Rod D. Control Rod and Control Rod Drive Maintenance Drive Maintenance l One control rod may be 1. Prior to performing this withdrawn from the core for maintenance, core the purpose of performing shutdown margin shall be control rod and/or control determined in accordance rod drive maintenance with Specification provided the following 3.3.A.1 to ensure that conditions are satisfied: the core can be made suberitical at any time

1. The reactor mode switch during the maintenance shall be locked in the with the strongest l " Refuel" position. All operable control rod refueling interlocks fully withdrawn and all shall be operable, other operable rods fu1]y inserted.

2. Specification 3.3.A.1 shall be met, or the 2. Alternately, if a control rod directional minimum of eight control control valves for a rods surrounding the l minimum of eight control control rod out of l rods surrounding the service for maintenance drive out of service for are to be fully inserted maintenance shall be and have their disarmed electrically directional control and sufficient margin to valves electrically criticality disarmed, the shutdown l demonstrated, margin shall be met with the strongest control

3. SRMs shall be operable rod remaining in service in the core quadrant during the maintenance containing the control per)m3 M21y withdrawn.

rod on which maintenance is being performed and in an adjacent quadrant.

The requirements for an SRM to be considered operable are given in Specification 3.12.B.

Amendment No M, 232

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l 3.12 LIMITING CONDITIONS FOR 4.12 SURVEILLANCE REQUIREMENTS OPERATION E. Extended Core Maintenance E. Extended Core Maintenance One or more control rods may Prior to control rod be withdrawn or removed from withdrawal for extended core the reactor core provided maintenance, that control the following conditions are rods control cell shall be satisfied: verified to contain no fuel assemblies.

1. The reactor mode switch 1. This surveillance shall be locked in the requirement is the same

" Refuel" position. The as that given in l refueling interlock Specification 4.12.A.

which prevents more than one control rod from 1 being withdrawn may be '

bypassed on a withdrawn control rod after the fuel assemblies in the cell containing (controlled by) that control rod have been removed from the reactor core. All other refueling interlocks shall be operable.

2. SRMs shall be operable in the core quadrant 2. This surveillance where fuel or control requirement is the same rods are being moved, as that given in and in an adjacent Specification 4.12.B.

quadrant. The requirements for an SRM to be considered operable are given in Specification 3.12.B.

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3. If the spiral ,

unload / reload method of )

core alteration is to be  !

used, the following conditions shall be met:

a. Prior to spiral unload and reload, the SRMs shall be proven operable as l stated in l Specification l 3,12.B1 and 4 3.12.B2. However, )

during spiral I unloading, the count rate may drop below 3 cps.

Amendment No. +6, 59, M , 233

, VYNPS BASES: 3.12 & 4.12 (Cont'd)

C. To assure that there is adequate water to shield and cool the irra-diated fuel assemblies stored in the pool, a minimum pool water level is established. This minimum water level of 36 feet is established because it would be a significant change from the normal level, well above a level to assure adequate cooling (just above active fuel) .

D. During certain periods, it is desirable to perform maintenance on a single control rod and/or control rod drive. This specification  !

provides assurance that inadvertent criticality does not occur during l such maintenance.

The maintenance is performed with the mode switch in the " Refuel" position to provide the refueling interlocks normally available during refueling operations as explained in Part A of these Bases.

Refueling interlocks restrict the movement of control rods and the operation of the refueling equipment to reinforce operational procedures that prevent the reactor from becoming critical during refueling operations. During refueling operations, no more than one control rod is permitted to be withdrawn from a core cell containing one or more fuel assemblies. The refueling interlocks use the

" full-in" position indicators to determine the position of all control rods. If the " full-in" position signal is not present for every control rod, then the "all-rods-in" permissive for the refueling equipment interlocks is not present and fuel loading and control rod withdrawal is prevented. The refuel position one-rod-out interlock will not allow the withdrawal of a second control rod. The requirement that an adequate shutdown margin be determined with the control rods remaining in service ensures that inadvertent critica-l lity cannot occur during this maintenance. Disarming the directional control valves does not inhibit control rod scram capability.

E. The intent of this specification is to permit the unloading of a portion of the reactor core for such purposes as inservice inspection requirements, examination of the core support plate, control rod, i control rod drive maintenance, etc. This specification provides assurance that inadvertent criticality does not occur during such .

operation. )

This operation is performed with the mode switch in the " Refuel" position to provide the refueling interlocks normally available during refueling as explained in the Bases for Specification 3.12.A.

In order to withdraw more than one control rod, it is necessary to bypass the refueling interlock on each withdrawn control rod which prevents more than one control rod from being withdrawn at a time.

The requirement that the fuel assemblies in the cell controlled by the control rod be removed from the reactor core before the interlock can be bypassed ensures that withdrawal of another control rod does not result in inadvertent criticality. Each control rod essentially provides reactivity control for the fuel assemblies in the cell associated with that control rod. Thus, removal of en entire cell (fuel assemblies plus control rod) results in a lower reactivity potential of the core.

One method available for unloading or reloading the core is the spiral unload / reload. A spiral unloading pattern is one by which the fuel in the outermost cells (four fuel bundles surrounding a control rod) is removed first. Unloading continues by unloading the remaining outermost fuel by cell spiralling inward towards the center cell which is the last cell removed. Spiral reloading is reverse of unloading, with the exception that two (2) diagonally adjacent bundles, which have previously accumulated exposure in-core, are placed next to each of the 4 SRMs before the actual spiral reloading begins. The spiral reload then begins in the center cell and spirals outward until the core is fully loaded.

Amendment No. M, 238