ML18026A307

Forwards Document Used to Establish Recommended Instrument Nominal Trip Setpoints & Tech Specs Limits Per 800821 Request

ML18026A307
Person / Time
Site:	Susquehanna
Issue date:	09/10/1980
From:	Curtis N PENNSYLVANIA POWER & LIGHT CO.
To:	Youngblood B Office of Nuclear Reactor Regulation
References
ER-100450, PLA-541, NUDOCS 8009160310
Download: ML18026A307 (20)

Text

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REGULA, Y

IVFORvIATin>> DtSTHIBUTIu.. SYSTE!

(RIOS)

ACCESSION IVBR:8009160310 OOC ~ DATE: 80/09/10 NOTARIZED:

NO DOCKET FACIL:50 387 Susauehenne Steam Electric Station<

Unit ir Pennsylva 0

0 87 50 388 Susauehanna Steam Electric StatjonR Unit 2F Pennsylva 00038 AUTH'AME AUTHOR AFFILIATION CURT IS, W.l>>.

Pennsyl vani e Po~er 8 Light Co.

REC IP ~ IVA~~E RECIPIENT AFFILIATION YOUNGBLOOD R 8 ~ J.

Licensing Branch 1

SUBJECT:

for0Earas document used to establish recommended instrument nominal trio setooints I Tech Spec limits oer 800821 reauest; DISTRISUTIO'u CODE:

SOD IS CORIES RECEIVED:LTR J E'ICL g SIZF.: jg TITLE: PSAR/FSAR AMDTS and Related Cor resoondence NOTES:Send IKE 3 cooies FSAR 8 all amends.

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TWO NORTH NINTH STREET, ALLENTOWN, PA.

18101 PHONE: (215) 821-5151 NORMANW. CURTIS Vice President Engineering 8, Construction 821.538t SFP 1 0 j960 Mr, BE J.

Youngblood Licensing Branch No.

1 Division of Licensing U.S. Nuclear Regulatory Commission Washington, DC 20555 Docket Nos 50-387 50-388 SUSQUEHANNA STEAM ELECTRIC STATION ADDITIONAL INFORMATION REQUEST ER 100450 FILE 841-3 PLA-541

Dear Mr. Youngblood:

As requested during the meeting on August 21, 1980, attached is a copy of the document used to establish the recommended instrument nominal trip setpoints and technical specification limits.

Very truly yours, N.

W. Curtis Vice President-Engineering

& Construction-Nuclear CTC:mks Attachment cc:

A. Hadden Savannah River goo/

5 (1(

PENNSYLVANIA POWER IL LIGHT COMPANY

EIS IDENT:

INST SETPNTS 5 TECH UPS GEHERALELECTRIC NUCLEAR ENERGY DIVIQOM 22A5261 CONT ON SNCCT 2

SN NO.

1 OOCOSIEn TITLE INSTRPHENT SETPOINTS ANO TECHNICAL SPECIFICATION LIMITS 05tfclflcATIoll QDRANNO QoTIIER LEGEIO OR KMII'FTIOIOF GROUFE TYFE'NFORHATION 00ClL'4ENT FQF

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This docuRE.nt has been prepared to record appropriate mthods for the esta is

..nt of recorrRended instrument nominal trip setpoints and technical specification liWts in a consistent and repeatable manner.

'1.2. Setooints Covered:

The setpoints considered are those associated w'ith the System and Rod Withdrrwal Block Instrumentation.

2.

'APPLI CABLE lfCUMEHTS

.2.1 General Electri c Comoan DocuiiE.nts a

2.1.1 suo ortin DocuiiE'nts.

None 3.

SYSTEM DESIGN REQUIREMENTS I

3.1 general

System design requlresunts ire contained ln the appropriate des<go docuauntacson.

lucy are utkltzed here, when oeces..ary; to insure that the nominal

~ip setpoiiit recoiiriE.ndatiors do not result-in violation of system design retlui rem'nts ~

3,2 Definitions:

The definition of terms used in this document are those contained ln lEEE Egtan ara 100-1972, IEEE Standard Olctianary of Electrical and Electronic

Terms, as further defined in this doctmE'.nt.

3.2.1 Anal tic Limit A.L. :

the value of the sensed pi'ocess variable established as part or e sa ety ana ysis, prior to which a desired action is to be initiated to prevent the process variable from reaching the associated design safety limit.

3.2.2 Calibration accurac the quality of freedom from error to which the trip setpoint is ca i rated with respect to the true desired setting. including both calibration instrLmE'.ntation accuracies and calibration procedure allowances.

3.2.3 Conformit inde erident:

the maximum deviation of the actual characterist~c (average o

upscale ana ownscale readings) from a specified curve, so positioned as to minimize the mEximum deviation.

3.2.4 Design safet limitr the dosigr; limit on a process variable Ra

's necessary to reasonably protect the integrity of physical barriers that guard against uncontrolled release of radioactivity.

GEIIERAL ELECTRIC NVCLEAR ENERGY DIVISION 22A5261

AEV, 0

SH. Ho.

3 3.2.5 ExtrenE, stead state o eratfn value:

the extrella value of the process variable anticipate uring norma steady state operation.

This value may bII either a

maximum or a mfrIimum value depending upon the process variable.

3.2..6 InstruITent accurac:

the qualf ty of freedom from error of the complete instrument channe from t sensor fnput through the trip un1t output including the combined conformity. hysteres1s and repeatabfl1ty errors.

3.2.7 Instrument drift:

the change fn the value of the process variable, at 6

n setpoint fs calibrated and a subsequent surveillance

test, due to all causes, as measured in term of the fnstruIIE.ntatfon indicator scale.

The value of the process varfable at which th trip action will actually occur at the tfna of calibration is taken to.be the intended nominal tr1p setpoint value, 3.2.8 Lfcensfno Event Report LER :

a report which must be filed with the United States uc ear Regulatory CoIIEnission by the power plant operator (Utility) when a

technical specification limit fs exceeded, e.g.,

when a trip setpoint value is found to have exceeded the corresponding technical specification limit.

3.2.9 Limftfn normal o eratin transient:

the most severe sensed plocess vari-

,able transient anticipated during noma l operation for which initiation of the trip action associated with the instrumentatfon monitoring the process is not anticipated.

3.2.10 Paximum desi fnstruIIE.ntatfon drift:

the maximum drift permitted by the instrumentation design and procurement specifications. for thi: comple 'e fnstrullant channel from the sensor through the trip unit, fnclusfvt -

'tne raximum drift represents two standard deviations of the probability distribution of instrument drift.

The maxfmun drift is specified for a period of tine equivalent to or greater than the surveillance test interval.

3.2.11 Operational 11mit:

the operational value establ fshed by the limitfng noTTnal operatfng transient.

3.2.12 Hominal Trf Setoofnt H.T.S.

the intended calibration point at which a trip a~c ion is set to operate, comnonIy the center of an acceptable range of trip operation.

measureln nts of the output for the same value of the input under the saIIa operating conditions, approaching from the saIIE. direction, for full range traverses.

3.2.14 Technical S ecification Limit T.S.L.

the limit prescribed as a license cond1tion on an important process var1able.

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%I GENERALO ELECTRIC NUCI.EAR ENERGY OIVISION 22A5261

Rsv, O

GH. No. 4 3.3 Limit Relationships:

The I.elationship between the nominal setpoint and the PROCESS VARIABLE

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FIGURE 3.1 SETPOINT AND LIMIT RELATIONSHIPS 4

G E H E 8'A L ea E LK C T R I 0 NUCLEAR ENERGY OIVlslON 22A5261 Aev. 0 sw. No. 5 4.

QNLITY 'ASSURANCE PROVISIONS 4.1 This document,has been reviewed in accordance with the current GE-HED engineering design review procedures.

5."

HANDLING, SHIPP IHG AHO STORAGE Hot applicable.

6.

RECOMKHOATIOHS

6.1 General

In ader to provide a consistent and repeatable method for estahlssnsnp instrocmnt nominai trip setpoint and technical specification limit value recornendations the procedures described in the appendices have been developed.

Oue to the'eneral characteristics of the instruaantation and processes involved

.it has been, necessary to provide three (3) different nathods.

These three (3) methods are based on computation, engineering

judgment, and historical data.

The methods are to be applied independently.

Howeve., portions of the computational method may be incorporated into the other two'methods.

Each of the methods is

. explained in a separate appendix.

'The methods and associated appendix are as

'ollows:

a. 'Computational -

Appendi x 10 b.

Engineering Judgment Appendix 20

'c.

Historical Data Appendix 30 6.2 Specific Setooint Recommendations:

Specific nominal trip setpoint and techn>ca specs

>cat>on

>m> t recomrendations along with the analytic limits are delineated in plant unique data sheets.

GENERAL EIECTRIC NOCI.EAR ENERG'I DIVISION 22A5261 Mv, 0

@ceo.

6 APPENDIX 10 10.

HE'SN FOR ESTABLISHING TRIP SETPOINTS AHD TECHNICAL SPECIFICATIOH LIMITS BY COMPUTATION a

10.1 General 10.1.1 Mhen sufficier:. inforration is availB'le regarding a dynamic proces's and the associated instrumenta.ion, it is possible to establish the nominal trip setpoint and technical specification limit values, utilizing the foll+ing procedure.

This procedure do s not attest to apply a rigorous statistical evaluation of the instrumentation paraIn ters.

The analytic limit is established through the use of computational models which include combined margins for related instrunentation paranaters but do not necessarily include separate rargins for each individual instrutIant characteristic.

Consequently, it is not practical to remove the instru-ment related margins from the models. used to establish the analytic limits.

In order to separately account for instrumentation accuracy and calibration accuracy it is therefore necessary to introduce redundancy iIito the technical specification limit establishments.

• 10.1.2 The differential between the nominal trip setpoint value and the technical specification limit is established as the maximum drift permitted by the associated instrumntation specification.

This differential allows for the maximum drift between calibrations without compromising the analytic limit since there will still be sufficient margin to account for instruaantation and calibration accuracies.

10.1.3 Once the nvminal trip setpoint and technical specification limit values have been established using 10.2 below, they are checked to insure they will not result in an unacceptable level of Licensing Event Reports (LER) or trips due to normal operational transients.

If the nominal trip setpoint and techni al specification limit values are not acceptable there are several alternatives avai'Iable.

One alternative is to establish these values using a more rigorous statistical evaluation and taking credit for instrumnt channel redundancies.

Another alternative is to replace the instrunantation design specification data with actua'.

operational data and establish the nominal trip setpoint and technical specification limit values based on this data.

10.1.4 It is recoIIIn.nded that the instrumentation parameters utilized in establish-ing the nominal trip setpoints and technical specification limits be monitored during operatioen.

Hhen sufficient operational data has been gathered.

the nominal trip setpoints and technical specification limits should be recomputed to improve plant operational aargins and further minimize LERs.

GE>IERAL ELECTRIC tILCLEARENERGY DIVISION 22A5261 SH.KO. 7 10,2 Procedure for Establf shin Hominal Tri Set oint and Technical Saecf IcatTon mTt 10.2.1 Data Reoufred:

The following data fs required to establish the nominal Analytic 'Lfmft (A.L.).

b.

Instrumentatfon accuracy.

c.

Calibration accuracy.

d.

Maximum design fnstrumentatfon drift.

10.2.2 Technical S

cfRcatfon Limit 10.2.2.1 The technical specification limit (T.S.L.) fs established so there fs at least a 0.9772 probability of providing the trip action before the process variable reaches the analytic limit fn the case where the maximum drift has occurred as shmn nn Figure 10.1.

,The maximum drift being the fnstruIIE.ntation design maxiIIam drift (0).

10.2.2.2 The fnstruIN.'ntatfon parameters involved fn establishing the'echnical specification limit are the instrumentation accuracy and the calibration accuracy.

Instrumentatfon accuracy fs the specified design accuracy'nd fs assumed to represent two standard deviations (2oa) of the fnstruIIE.ntatfon indfcation at the trip level, of the process variable.

10.2.2.3 It fs assuIIE.d that the plant operato~ will calibrate the fnstruIIE.ntatfon with an accuracy equivalent to the fnstruIIE.ntatfon resolution.

This assunytfon fs necessary since specific data related to the. plant operators calibration procedures, calibration equfpIIE.'nt, and calibration equfoI..nt maintenance are not available.

The fnstruIIE.'ntatfon resolution is taken to represent one standard deviatfon (oc) of the fnstrLmE ntatfon calibration at the trip level vf the process variable.

The instru-IIE.ntatfon includes the sensor, signal conditioning circuitry and trip unit.

10.2.2e4 In order to obtain the desired 0.9772 probability, for a one sided normal

'dfstrfbutfon, the technical -specification limit must be set two (2) standard devia-tions from the analytic lfmft.

In this case the standard deviation fs determined as the statistical conkfnatfon of the fnstruITE.ntatfon accuracy and tta calibration

accuracy, l.es a

tfoas e+ooccss.

T.S.L.

A.L. - 2 Ja~~ + ocs, for process variables that increase toward the A.Lt a or T.S.L, A.L. t 2 yeas

+ ocs, for process variables~that decrease toward the A.L.

10.2.2.5 When actual'.calibration 'accuracy data becoIIE.s available the technical specification limit cari be adjusted using this procedurE and the new calibration accuracy standard deviation.

GENERALO ELECTRIC NUCLEAR ENERGY DIVISION 22A5261 I

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GEIIERAL ELECTRIC NUCLEAR ENERGY DIVISION 22A5261 Rev.

0 SH. Ho.

9 19.2'.3 Nominal Trio Set oint 10.2.3.1 The nominal trip setpoint (N.T.S.) value is established by the maximum design instruIIE.ntation drift (0).

The nominal trip setpoint is offset froRI the technical specification limit by an amount equal to the IIEEximum design instrumenta-tion drift expected during the surveillance test interval.

As noted in the establishment of the technical specification limit this will provide an assurance of required trip actions in the case where the maximum drift has occurred.

H.T-S.

~ T.S.L. - 0, for process variablA'hat increase toward the A,L'., or H.T.S.

~ T.S.L. + 0, for process variables that decrease toward the A..L.

10.2.3.2 Actual observed drift will differ from plant to plant due to environmental

factors, IIEEintenance procedures and trip setpoint surveillance frequencies.

also, the actual observed drift characteristic aay include a statistically significant bias.

Consequently, as actual drift data is accumulated, including confirIIE.d, statistically signi ficant bias data, the nominal trip setpoint can be adjusted to reflect the instruIIE.'ntation performance.

10.3 0 eratiohal Transient Tri Avoidanc'e 10.3.1 In order to evaluate the impac'. of the nominal, trip setpoint value (Xs) on plant availability one'of two siIcple tests can be applied.

These tests are based on a distribution of difference calculation and are used here to evaluate the probability of a trip occurring due to the spectrum of normal operating transients or due to the 13miting nornal operating transient when no safety constraints are compromised.

The calculations establish the probability of avoiding a trip under safe conditions.

Five (5) factors, not previously used, are utilized in these tests.

They are predicted extreme steady state operating value for the variable (Xo), the limiting predicted norIIal operating transient, the standard deviation asscciated with the limiting operating transient (cm), the required trip avoidance probabili.ty during the limiting transient and the value of the standard deviation (ad) associated with the instrumentation drift.

In the absence of actual observed drift data the standard deviation (od) for drift is taken as one half of the maximum design instrumentation drift (0).

10.3.2 The test to evaluate the operational transient trip avoidance associated with the spectrum of nornal operating transients is based on the nominal trip set-point distribution and the operational process variable distribution as shown in Figure 10.2.

Operational Process Variable Distribution Technical Hominal Trip Setpoints Specification Distribution, H.T.S.

Limit, T.S.L.

X r

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Value, X

Area representing the probability of an undersirable trip.

Hominal Trip

Setpoint, X

Area representing the probability of an LER.

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GEIIEIIALOELECTRIC NUCI.EAR ENERGY PIVIOOll 22A5261 I

Rev.

sH. No. 11

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I 1C.3,2.1 The extreme steady state operating value (Xo) is utflfzed as the Irean of

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~.the operational variable dfstrfbutfon and the predicted normal process variable change of the limiting transient is taken as the standard deviation (at) of the operational process variable distribution.

Obviously, this fs an oversfaqlfffca-tfon of the.operational variable distribution.

However, if this test is successful it will.,'not be necessary to perform a more rigorous test.

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10.3.2.2-The setpoint dfstrfbutfon utilizes the nominal trip'setpoint value {Xs) as a mean.

The standard deviation {af) is coaquted as the statistical combination of the instrumentation drift standard deviation (ad), instruIn.'ntation accuracy (oa) and CalfbratiOn OCCuraCy (OC), i.e.,

u

~

y 2 +

IT 2 + g 2 a

c d

10.3.2.3 A one sided probability of trip avoidance based on a normal distribution fs obtained from a standard textbook statistical table for areas under'the standard

. normal curve, from ->>

to Z, where Z ~ Ã/IT, i.e., Probability and Statistics for Engineers, Miller and Freud, Prentice-Hall, Table III.

For the delta distribution

case, X

is the difference between the mans of.the two distributions.

The delta standard deviation (~a) fs the statfstical conhinatfon of the two distribution standard deviations, i.e.,

IT gg IT 2 + IT,2 t

i Therefore, when Xo fs gre:ter than X

, end X -X Z

y 2 +

CT t

when Xo fs less than X

The probability of trip avoidance is the normal distribution statistical ale value corresponding to Za.

10.3.3 The test to evaluate the operational transient trip avoidance assoriated with the limiting normal op.rating transient is based on the nominal trip setpoint distribution and the distrfbutfon of the limiting transient as shown fn Figure 10.3.

GENERALO ELECTRIC

, NUCLEAR CNERGY OIVlSION 22A5261 AEV, 0'x.

xo. 12 ltaIjnitude of thI! Limiting Transient Limiting Transient Distribution tIominal Trip Setpoint Distribution, N.T.S.

Technical Speci fication Limit, T.S.L.

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Extreme Steady State Operating

Value, X

Area Representing the Probability of an Undesirable Trip Nominal Trip

Setpoint, X

Area Representing the Probability of an LER FIGURE 10.3

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GENERALIELECTRIC NUCLEAR ENERGY DIVISION 22A5261 RKV.

0 sH. wo.

13

~ 2 10.3.3.1 The mean of the 1'fmiting operating transient distribution fs taker as the extreme steady state operating value (X ) plus, oI minus as aporopriate, the ragnitude of the limiting transient (T), f.e.,

XT Xo + T, where the process variable transient increases toward -the analytic limit and XT'~ Xo - T, where the process variable decrease toward the analytic limit.

The standard deviation associated with the limiting operating transient (crm) fs the value used for the standard deviation to be associated with the distribution of XT.

10.3.3.2 The setpoint distribution and standard deviation are to be established as stated fn Paragraph 10.3.2.2.

10.3.3.3 Usfng the method of Paragraph 10.3.2.3 but substituting XT for Xo and cm for at provides the probability of trip avoidance, i.e.,

~ XT-X

~m i

2+02 when Xo 'fs greater than Xs,'and X,.- X Z~

g 2 + g,2 when '

fs 1ess than Xs.

Note, the selection of which equation is appl'ed depends. on the relationship between X

and X

not on the relationship between XT and Xs.

10.3.4 In the event an unsatisfactory trip avoidance probability has been obtained a more rigorous definition uf'he operational process variable distribution must be established oI the nominal trip setpofnt value can be adjusted based on engineer-ing judgment to reduce the interval between it and the technical specification limit.

The alternative chose will depend on the value of the trip avoidance probability, the function of the trip signal, and an evaluation of the unique plant

'perating requireIIE.nts.

A rigorous d~ fin",tion of the operational process variable distribution should be based on the normal steady state operating value of the process variable as'he mean rather than the IIEEximum steady state operating value.

The standard deviation should be computed in a statistical manner using the normal operating transient frequency data rather than relying only on the limiting normal operating 'transient, and instrumentation redundancy and trip logic should be included in determining the nominal.rip setpoint statistical distribution.

When "consider~. the trip. logic the following expressions should be used to compute the probabilities of trip and trip avoidance.

10.3.4.1 Probability of trip avoidance

~

1 - probability of trip.

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GEIlERAL ELECTRlC NUCLEAR ENERGY DIVlSIDN 22A5261 Rsv, 0 SH. No.

14 10.3.4.2 Probability of trip, single channel

< P.

10.3.4.3 Probability of trip for one out of two taken twice logic ~ P~ (2 - P)~.

10.3.4.4 Probability of trip for two out of three logic ~ 3P~.

10.3.4.5 Probability of trip for two alt of four logic ~ P~

(3P~ - cIP + 6).

10.3.4.6 Probability of trip for one o@ of four logic ~

1 -

(1 - P)".

10.4 Licensin Event Report Avoidance 10.4.1 The probability of avoiding a LER due to instruln ntation drift is deter-mined by the associated standard deviation (ai) of the indication of the process variable.

An LER avoidance probability of at least 0.9000 is recomended.

This probability fs obtained using a statistical table for areas under the standard normal curve, from -

to Z, where Z ~ X/a, i.e., text referenced in Paragraph 10.3.2.3.

In this case, the value used for X is the positive difference between the nominal setpoint value and the technical specification limit, i.e., the maxinvm design instrumentation drift (D) as shown in Figure 10.2.

The standard deviation value used is the statistical coahination of the instrumentation drift standard deviation (crd), instrumentation accura'cy (aa)

., and caEibration accuracy (oc},

i.e.,

ai

~

e

+ a

> + ad>.

The probability of avoiding LER is the normal distribution statistical table value corresponding to Z.

10.4.2 Irf the event an avoidance probability of less than 0.9MO has been obtained one alternative is to increase the differential between the nominal setpoint value and the technical specification limit.

Such an adjustln'.nt must be based on engineering judgment or actual operational d~ift data.

GENERAL ELECTRiC NUCLEAR ENERGY DlViSiON 22A5261 aav. 0 aaxo.

15

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,5 APPENDIX 20 20.

METHOD FOR ESTABLISHING TRIP SETPOINTS AND'TECHNICAL'PECIFICATIONLIMITS BY ENGINEERING JUDGMENT 20.1 General 4

20.1.1 When it is nut practical to apply the technique outlined in Appendix 10 or when the available data is so conservative as to result in unacceptable operating restrictions, or when the Lead System Engineer considers it appropriate, engineering

)udgiiE.nt should be used to establish th nominal trip setpoint and technical specification limit values.

In order to establish a consistent pattern for the application of engineering judgment suggested guidelines are delineated belm.

20.1.2 The guidelines suggested are those of the zone setting concept.

A two zone concept is sugges ed here as adequate to establish the nominal trip setpoint and technical specification limit values.

The zones are a range'ithin which the

.trip value is adequate for its intended function but must be reported as having compromised the applicable.technical speci fication value.

20.1.3.

Zone conce~~~g-more than two zones have prev'.ously been associated with the establishment of instruin.ntation setpo',n+..In pa&icular, zones related to establishing when recalibration is, or is not, necessary, are coitEnon, i.e.,

leave.alone zone.

Since specification of the recalibration limit is not included this, documei.t these additional zones are not addressed.

However,

.he recalibra-tion limiter (leave alL'.ne zone) is an important operational consideration and

'should be established, within the acceptable trip value zones, based on the unique

~ plant operating requirements.

20.2 Acceptable Tri Value Zone:

The acceptable trip value zone is a portion of the instrunE.ntat~on tnp range which will have as it's midpoint the nominal trip

setpoint, and as it's extreme the technical specification limit.

Figure 20.1. is a representation of the trip value and zone relationship.

The acceptable trip value zone should be wide enough to allow for normal instrumentation drift during surveillance intervals.

20.3 Licensin Event Report

'20.3.1 The LER zone is the portion of the ti truRantation trip range beyond the technical specification limit.

An LER i;<ll be required when the trip value is found~within this zone.

20.3.2 The LER zone should be'stablished so that when the maximum expected drift has occu>red sufficient margin remains between the technical specificatior. limit and analytic limits to coo@ensate for instrumentation and calibration accuracies.

L I

OEIIEBAt.

ELECTRIC HUCI.EAR ENERGY DIVISION

" 22A5261 nav. 0 r

'Licensing Event Report (LER) zcne Technical Speci fication Limit

.Acceptable

~ Trip Value Zone NcnIinal Trip Setpoint FIGURE 20.1

GEIIERALO ELECTRIC NUCLEAR ENERGY DIVISION 22A5261 Rev, 0

$H. N0.17 20.4

~Exa.

les 20,4.1 An example of the use of engineering gudgrrent where it is not practical to apply the technique outlined in Appendix 10 is the interm diate range monitor (IRM)

Heutron Flux Scram.

The IRH Heutron Flux Scram exists to shutdown the reactor if neutron flux is increasing at a rate that cannot be followed by the operator.

There is no sophisticated basis for differentiating between the nominal trip set-point and the technical specification limit. g nominal trip setpoint value of 120 divisions is selected to utilize the maxiP~m range of the instruaant.

This selection has been an arbitrary one.

Allowances for instrument drift are made by providing a 2 division margin between the nominal trip setpoint and the technical specification limit (122 divisions).

20.4.2 Another example of the use of engineering gudgnant is in the establishment of the scram discharge volume water level scram nominal trip setpoint.

The scram

'ischarge volte water level scram exists to shutdown the reactor if there is not sufficient void voluae available in the scram discharge header to accomIodate the water which would be displaced by the control rods during a scram.

A water level actuated limit switch sen es the unavailable header voluIn and initiates the scram.

Mhen th'e header void voluIn above. the maximum limit switch position exceeds the minimum required discharge volurra the technical specification limit can be established at the maximum limit switch position.

This provides for a conservative technical specification limit.

The nominal trip setpoint can be established to allow for drift in accordance with Paragraph 10.2.3.1.

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GENERALO El.KCTRIC NUCLEAR ENERGY DIVlSIDN 22A5261 nev.

0 sw.m.l8 Final APPEHDIX 30 30.

METHOD FOR ESTABLISHIHG TRIP SETPOIHTS AHD TECHHICAL SPECIFICATION LIMITS BY HISTARICAL DATA 30.1 General.

A number of setpoints have noncritical functions, or are intended to provsvvee tCrr<p actions related to gross changes Sn the process var(ah1e T.hese setpoint values have been historically established as acceptable, both for regulatory and operational requirements.

The continued recomnendation of these historically accepted setpoint values

'.s a third method for establishing nominal trip setpoint and technical specification limit values.

This approach is only valid where the governing conditions renain essentially unaltered from those imposed previously and where the historical values have been adequate for their intended functions.

30.2 Technical Specification Limit.

One way of establishing the technical speci-e.!

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value, is to use the aathod of Paragraph 10.1.2.

In this case the nominal trip setpoint is fixed and the technical specification limit is established.

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