ML18087A578

Safety Evaluation Supporting Reactor Protection Sys & ESF Actuation Sys Setpoint Methodology

ML18087A578
Person / Time
Site:	Salem
Issue date:	10/26/1982
From:	NRC
To:
Shared Package
ML18087A577	List: ML18087A575 ML18087A578
References
NUDOCS 8211110066
Download: ML18087A578 (5)

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SAFETY EVALUATION SALEM NUCLEAR GENE_RATU\\G STATION -.UNIT 2

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E NGI ~!EE RED SAFETY FEATURES ACTUATION SYSTEM

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SET POI NT METHODOLOGY INTRODUCTION Public Service Electric and Gas (PSE&G) Company responded to an

~RC request 1or documentation of the methodology'which is the basis for establishing Technical Specifications (TS} Trip Setpoints and Allowable Values for the Reactor Protection.System *(RPS) and the Engineered Safety Feat~res Actuation System CESFAS).

This respnnse, d a t e d No v e m b e r 2 0, 1 9 81, c on t a i n e d t h e s e t p o i n t me t h o d o L o g y *. a n d instrument uncertainties related to the Salem -

Unit 2 plant along w*ith the responses to the NRC questi-0ns which were part of the license conditions related to thi_s subject.

An addi.tional request for informjtion was sent to the Licen~ee on April 16, 1982 tD which the licensee responded on July 19, 1982.

_EVALUATION The methodology by which the Licensee combines the channel uncertain-ties in a protection channel has been used and approved for other Westinghouse plants.

It is therefore an appropriate and acceptable (8211110066 821026 PDR ADOCK 05000311

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• methodology for Salem Unit 2 *.

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The information provided includes the various instrument channel allowance analysis assumptions, i.e., a breakdown of the individual values of errors and allowan~es used in establishing setpoints for the RPS and the ES FAS.

The basic underlying assumption is that several of the factors, which may cause errors,act independently.

This allows the use of a statistical summation of the various uncertainties instead of a conservative additive summation.

For those uncertainties known to be interdependent, the technique uses additive,summation.

A direct benefit qf the use of this techique.is a more realistic determination of the Trip Setpoint~

The methodology used to combine the ~ncertainties for a channel is a statistical combination of independeni groups.

Components which are not independent are added arithmetically into groups.

The in-

.dependent grcrups can then be systematically combined.

This methodology has been previously accepted as a procedure for determining the RPS and.ESFAS setpoint values for D.c. Cook Unit 2( 1),

North Anna Unit 1( 2 ) and most recently Virgil Summer Uni~,c 3>.

• In computing the channel statistical allowance (the total of the uncertainties in a particular protection cnannel) for the RPS Over-temperature D.T function, the Licensee omitted the :uncertainties associated with the chann~L that set~ a penalty for an axial power i m b a lance, i

• e., F 1 CD. I)

• Th i s u n c e rt a int y*

• i s i n di cat e d in

~~o t e 1 of Table 2.2-1 (Reactor Trip System instrumentation Trip Setpoints) of the Salem Unit 2 Technical ~pecifications. This channel takes its inpu~;from the top and bottom detectors of the power range nuclear instrumentation and introduces a penalty to th~ Overte~perature D.T Trip Setpoint for axial power imbalances beyond a set range.

The penalty and range are set by. the Technical Specifications.

The uncertainties associated with this penalty function are the process measurement accuracy and a rack calibration accuracy.

There pr~sently exists sufficient margin in the Overtemperature 6T channel to absorb these additional uncertainties so as to not require a change in the Trip Setpoint or Allowable Value and thus the Technical Specifications can remain as they are.

However, the table included in the licensee's submittal should be revised to re-flect these errors and the decreased margin which results from con-sideration of these errors.

The Licensee, by Lette~ dated October 8, L982, advised that a design change has beeri in~tiated to rectify this problem.

The Salem-z*

Technical Specifications will be revised to reflect this change.

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The Licensee submittal indicates a channel statistic~L-allowance that exceeds the Total Allowance (difference between the Safety Analysis Limit and the Trip Setpoint) for the Uhdervolta~e -

RCP protection channel.

This results.in a negative margin of 0.75%.

The Technical Specifications for the Undervoltage -

RCP Trip Set-point should be modified to eliminate this negative margin.

The Licensee *has *committed to.this modification in a July 19, 1982 Letter from E. Liden to S. Varga.

The current Salem Unit 2 Technical Specifi~ations List the Steam G~nerator Level -

Low Low Trip Setpoint as 17% of narrow range instrument span and the Allowable Value as 16%-

The Licensee's submittal of July 19, 1982 Lists these values as 18% and 17% re-spectively.

The Licensee,.in this s~bmi.ttal, has indicated a commitment to change the Technical Specifications so as to conform to the values established in the setpoint methodology.

This is

-acceptable.

It should be noted that the.Salem -

Unit 2 submittal notes that several protection channels are not used in the safety analyses, i.e., these channels serve as backups to.the primary protection channels.

For these channels, co~plete channel uncertainty break-

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downs were not sOpplied.

The bases for establis~ing the Trip Setpoints and the Allow~ble Values for thei~ channels are historical data and good engineering judgement~ As a,*result1 complete analytic reviews to determine the adequacy of these limiting safety system settings were not made.

Insofar that.these are not primary protection channels, the methodology f-0r them is acceptable.

SUMMARY

T h e p r o p o s e d S a l e m -

Un i t 2 R P S a n d E S F A S s e t p o i n t m e _!b o d o L o g y i s acceptable.

The Licensee has committed to make the required modi-fications as identified above and provide the necessary revisions to the Technical Specifications to address our concerns.

The staff will confirm the final documentation for conformance to the commitment and will not address these items in a supplement to this report unless an unanticipated problem is found.

RE FERENC ES

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P

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• C h e c k ( 1'~R C ), M e m o r *a n d u in t o *s.*A

• V a r g a * ( f'.!R C ), J u n e 1. 9, 1 9 8 0 *

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R

• S a t t e r f i e l d C NR c.), M e m o r a n d u m t o R *. C l a r k ( NR C ), J u n e 2 7, 1 9 8 0 *

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T.P

• Sp e i s ( NR C), Memorandum to.R.L

• T e des co ( NR C),

Apr iL 21, 198 2.

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