ML20128B154

Application for Amends to Licenses NPF-68 & NPF-81,revising Value of Z for SG Level Instrumentation,As Result of Improved Understanding of Level Measurement Errors Based on Recent Scientific Work by Instrument Soc of America

ML20128B154
Person / Time
Site:	Vogtle
Issue date:	01/22/1993
From:	Mccoy C GEORGIA POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20128B159	List: ML20128B154 ML20128B174
References
EVL-05073, EVL-5073, NUDOCS 9302020414
Download: ML20128B154 (8)

Text

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• Power va rwunt utow ycg e Hoyt  !!a9SO f cYn w ritCSpitm January 22, 1993 ELV-05073 002643 Docket Nos. 50-424 50-425 U. S. Nuclear Regulatory Commission ATTH: Document Control Desk Washington, D. C. 20555 Gentlemen:

V0GTLE ELECTRIC GENERATING PLANT REQUEST TO REVISE TECHNICAL SPECIFICATIONS REVISION TO Z FOR STEAM GENERATOR WATER LEVEL INSTRUMENTATION In accordance with the provisions of 10 CFR 50.90 and 10 CFR 50.59, Georgia Power Company (GPC) hereby proposes to amend the Vogtle Electric Generating Plant (VEGP) Unit I and Unit 2 Technical Specifications, Appendix A to Operating.

Licenses NPF-68 and NPF-81.

This amendment revises the value of Z for the steam generator level instrumentation. The Z value represents the statistical summation of errors l assumed for the instrument setpoints in the analyses. It is used in the Technical Specifications for determining reporting requirements. The proposed chan,,;s do not affect any of the steam generator level instrument setpoints.

The change in the value of Z is the result of an improved understanding of level measurement errors based on recent scientific work documented by the Instrument Society of America. The changes resulted from the reconsideration of the effects of reference leg temperature changes from the calibration temperature, downcomer subcooling and fluid velocity affects. Consideration of.these revised.

l uncertainties continues to demonstrate that the current steam generator level setpoints provide ample margin to protect the safety analyses limits. However, small changes are appropriate for the associated Z values.

An additional nontechnical change to the Technical Specifications is being incorporated with this proposal. This change removes unnecessary information following modifications that lowcred the instrument taps to elevation 333 inches, in accordance with license a.undments 34 and 14 that were issued by the NRC on August 30, 1990.

This change is requested by July 31, 1993.

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Georgia Powerkh U. S. Nuclear Regulatory Commission ELV-05073~

Page 2 The proposed changes and bases for the changes are described in' enclosure 1 to this letter. Enclosure 2 provides an evaluation pursuant to 10 CFR 50.92 showing that the proposed changes-do not. involve significant hazards considerations. Instructions for incorporation of the proposed changes into the Technical Specifications and a markup of the affected pages are provided in enclosure 3.

In accordance with 10 CFR 50.92, the designated-state official will be sent a copy of this letter and all enclosures.

Mr. C. K. McCoy states that he is a vice president of'Goorgia Power Company and  :

is authorized to execute this oath on behalf of Georgia Power Company and that, to the best of his-knowledge and belief,-the facts set forth in this letter and enclosures are true. +

GEORGIA POWER COMPANY By:

C. K. McCoy Sworn to and subscribed before me this 22 ay of , , funt4_ , 1993.

• f]{(Lqq $) hpd lL Notary' Public y

CKM/HWM/gmb l-

Enclosures:

.l. Basis for Proposed Change p 2. 10 CFR 50.92 Evaluation

3. Instructions for Incorporation and Revised Pages c(w): Georoia Power Company Mr. W. 8. Shipman Mr. M. Sheibani NORMS L S. Nuclear Reculatory Commission Mr. S. D. Ebneter, Regional Administrator Mr. D. S. Hood, Licensing Project Manager, NRR Mr. B. R. Bonsor, Senior Resident inspector, Vogtle State of Georoia Mr. J. D. Tanner, Commissioner, Depi. of Natural Resources 700775

- u-ENCLOSURE 1 V0GTLE ELECTRIC GENERATING PLANT REQUEST TO REVISE TECHNICAL SPECIFICATIONS REVISION TO Z FOR STEAM GENERATOR WATER LEVEL INSTRUMENTATION-  !

BASIS FOR PROPOSED CHANGE Ernposed Changg

]

The proposed change deletes tne following footnote from page 2-5 lof table 2.2-1,

"***The value stated inside the parenthesis is_for instrument that has the-lower. I tap at elevation-333"; the value stated outside.the parenthesis is for instrumentation that has the_ lower tap at elevation 438" ". The following changes are being made to item 13 of.the table:

For total allowance change 10.5 (21.8)*** to 21.8 For Z change 17.18-(18.21)*** to 17.6 For trip setpoint change 2 18.5% (37.8)*** to-2 37.8%

For allowable value change 2 17.8% (35,9)*** to 1 35.9%.

The proposed change also deletes the following footnote from page.3/4 3-31 of table 3.3-3 "* the'value stated inside the sarenthesis is for instrumentation that has the lower tap at elevation 333"; tie value stated outside the parenthesis is for instrumentation that has the lower tap at elevation 438" ".

The following chargos are.being made to. item 5.c of table 3.3-3:

Change total allowance from 5.1 (14.0)* to 14.0 Change Z from 2.18 (8.62)* to 10.47 Change trip setpoint from-1-78.0% (86.0)* to 5 00.0%

Change allowable value_ from _179.9% '(87.9)* th1 L'7.9%.

The following changes are being made to items 6.b.1 and 6.b.2 of table -3.3-3:

Change total allowance from 18.5 (21.8)* to 21.8 Change Z from 17.18 (18.21)* to 17.6 Change trip setpoint from 2 18.5% (37.8)* to 1 37.8%

Change allowable value from 2 17.8% (35.9)* to 1 35.9%

These changes revise the value of Z for the steam generator level instrumentation and remove the alternate values for level instrumentation tD,t became obsolete with the completion of the instrument tap relocation which was approved by NRC license amendments 34 and 14 on August 30, 1990. Except:for the-value of'Z,- this change to the Tee.:nical Specifications does not affect any of the current operatina requirements.

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R ENCLOSURE 1 (CONTINUED)

V0GTLE ELECTRIC GENERATING PLANT REQUEST-T0 REVISE TECHNICAL SPECIFICATIONS REVISION TO Z FOR STEAM GENERATOR l!ATER-LEVEL INSTRUMENTATION BASIS FOR PROPOSED CHANGE-Basis The process measurement accuracy term used by the standard Wntinghouse .

methodology for determining the steam generator water level uncertainty was previously a random value of i 2.0 percent span. This value was based on density variation as a functhn of power level and the assumption that calibration was performed at 50 percent power. More recently an improved understanding of AP level measurement system errors based on scientific work-documented by the Instrument Society of America ha:: led to a-recalculation of.

the uncertainties associated with the steam generator water level instrumentation for Vogtle Electric Generating Plant (VEGP) Units 1 and 2.-

These calculations resulted in a small revision to the value of Z as given in Technical Specifications tables 2.2-1 and 3.3 The value of Z is the statistical summation of errors assumed in the analysis excluding those associateu with the sensor and rack drift and the accuracy of their measurement.

The value of Z is only used by the Technical Specifications as a means of determining reporting requirements. This p oposed change to the Technical Specifications does' not alter any setpoints or allowable values.

On August 30, 1990, the NRC issued amendments 34 and 14 to the VEGP Units 1 and 2 licenses. These amendments added footnotes and additional values for steam generator level instruments. The footnotes and additional values. applied to steam generator instruments using a lower tap location. Since then, the taps for the steam generator level instruments have been relocated, in' accordance with amendments 34 and 14. Therefore, it is no longer necessary to maintain' the alternate setpoint informaticn that was only applicable- to the higher tap location instruments. Since both units have eliminated the higher taps and are' exclusively using the alternate values,- the footnotes and associated information-are only cosmetic and may be deleted with no effect on Technical Specifications requirements'.

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ENCLOSURE 2 V0GTLE ELECTRIC GENERATING PLANT-REQUEST TO REVISE TECHNICAL SPECIFICATIONS REVISION TO Z FOR STEAM GENERATOR WATER LEVEL INSTRUMENTATION.

10 CFR 50.92 EVALUATION Pursuant to 10 CFR 50.92, Georgia Power Company (GPC) has evaluated the proposed-revision to the Technical Specifications and has determined that operation of the facility in accordance with the proposed amendment would not involve any.

significant hazards considerations.

Backaround Westinghouse has identified that the process measurement accuracy term for steam generator water level instrumentation uncertainty calculations needs to be revised. This would impact the protection functions which use this parameter; i.e., steam generator water level - low-low, and high-high.

Previously a random value of 2.0 percent span was used for this term in  ;

setpoint uncertainty calculations for all models of- steam generator-design.

This value was based on the density variation ~ as a function.of power and level and the assumption that calibration used 50 percent power conditions. The uncertainty calculation -for-VEGP already included velocity offects.

More recently, an improved understanding.of AP level measurement system errors based on . scientific work Jocumented in an Instrument Society of America paper (G. E. Lang andTJ. P. Cunningham, " Delta-P Level Measurement Systems,"

. Instrumentation. Controls. and Au19mation in the Power Industry, .Vol',' 34,-

Proceedings of the~ Thirty-Fourth Power instrumentation Symposium, June-1991),

has led to a reinvestigation of the steam generator level p' ocess r measurement accuracy terms. The ' conclusions are that two other error components should be accounted for explicitly (i.e., reference leg temperature changes from calibration temperature and downcomer subcooling) and that fluid velocity.

effects 'should continue to be considered. In' addition, the assumption of calibration using :i0 percent power conditions was replaced withfanalysis based on the conditions assumed by the plant. These. error components are not considered to be random in nature, and therefore are treated as biases. '

With the inclusion of the additional process measurement accuracy. terms and their treatment as a bias, the existing-trip setpoints for steam generator. water s level - low-low, and high-high provide ample margin to protect the existing safety analysis limits. However, small changes of less than 2.0 percent span are required for the associated I values identified in the Technical Specifications.

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ENCLOSURE 2 (CONTINUED)

V0GTLE ELECTRIC GENERATING PLANT-REQUEST TO REVISE TECHNICAL SPECIFICATIONS REVISION TO Z FOR STEAM GENERATOR WATER LEVEL INSTRUMENTATION-10 C/R 50.92 EVALVATION 8HalYlii The analyses took credit for the process conditions assumed for the scaling calculations made by the plant. These conditions are a reference leg operating-temperature of about 1200F and a system pressure of about 1053 psia. The-scaling calculations already included a 16-inch bias for velocity head effects.

The downcomer subcooling effect-does not have to be included-in future scaling calculations since it is included in the uncertainty analysis.

For the steam generator water level - low-low setpoint, the-previous process measurement accuracy value of 2.0 percent span (which was included as a random '

independent term in the overall channel statistical allowance) was reduced to 0.0 percent span. Values were calculated for process pressure variations, reference leg temperature variations, and downcomer subcooling with respect to the calibration conditions used by the plant and included arithmetically as a positive bias.

For the steam generato- water level - high-high setpoint the previous process measurement accuracy value of 2.0 percent span (which was included as a random -

independent term in the overall channel statistical allowance) was reduced to 0.0 percent span. Explicit values were calculated for process pressure variations, reference leg temperature variations, fluid velocity effects, and downcomer subcooling with-respect to the calibration conditions used in the plant and included arithmetica11y as a negative bias.

The determination of acceptability of the existing trip setpoints and allowable values is defined in WCAP-11269, Rev. 1, November 1986, " Westinghouse Setpoint Methodology for Protection Systems Vogtle Station." The overall = impact of the ,

evaluation.is limited to changes in the Z values in the Technical Specifications from 18.21 to 17.6 for the steam generator water level - low-low function.and from 8.62 to 10.47 for the high-hich function.

-The change to the Z value does not affect setpoints or allowable values. The-Z value is only used for determining when excessive instrument setpoint drift requires reporting to the NRC. Therefore, the changes do not affect safety-

- analyses or plant responses to accidents or transier.'.s.

It is noted that the total allowance (TA), trip setpoint, and allowable-value parameters for the steam generator level setpoints have also been clarified n the Technical Specifications. Previously the Technical Specifications ha.d two values for each of these terms, which corresponded'to two possible -

instrument level tap elevations. Since both VEGP Units 1 and 2 have the lower -

level--instrument taps at 333 inches, the reference to values corresponding to an instrument tap at 438 inches have been removed from the Technical

-Specifications. This clarification' does not reflect a change to the value for any of these parameters; rather it removes values from.the Technical-t

= Specifications which are no longer applicable, following the implementation of amendments 134 and '14 to the VEGP licenses.

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4 ENCLOSURE 2 (CONTINUED)

V0GTLE ELECTRIC GENERATING PLANT REQUEST TO REVISE TECHNICAL SPECIFICATIONS- 4 REVISION TO Z FOR STEAM GENERATOR WATER LEVEL INSTRUMENTATION The proposed changes to the Technical Specifications discussed above do not affect the safety analysis limit values used in the Final Safety Analysis-Reporti (FSAR) accident analyses'to initiate.either reactor trip or an engineered safety ,

feature actuation system functions. Thus, the proposed changes do not affect i the results or conclusions of the accident analyses- as presented in the FSAR..

Results Based on the information presented above, the following conclusions can be reached with respect to 10 CFR 50.92 for the changes to _the Z terms for' the steam generator water level - low-low and high-high trip functions. j

1. lhe revised Technical Specifications do not involve a significant increase-in the probability or consequences of an' accident previously evaluated.

Operation with these revised values will not cause any-design-or analysis acceptance criteria to be exceeded. The structural and functional . integrity-of any plant system is unaffected. The steam generator water level ~ reactor trip system and-engine red safety feature actuation system functions'are, i part of the accident mitigation response and are not themselves initiators for any transient. Therefore, the probability of occurrence is not affected.

The changes to the Technical Specifications de not ai.ect the integrity of

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the fission product barriers utilized for mit:ystion of radiological dose consequences as a result of an accident. Since the Technical Specifications-revision does not afiect the results or conclusions of FSAR accident analyses, the offsite mass releases used as input to the dose -calculations -

are unchanged from those previously assumed. Therefore, the offsite dose 4 predictions remain within the acceptance criteria. Since it has been-determined that the FSAR accident analyses are not affected by these parameter modifications, it is concluded that the consequences of an accident previously evaluated are not increased.

2. The revised Z values do not create the possibility of a new or different kind of accident from any accident previously._ evaluated. The safety analysis limit values are not changed. Thus, the changes do not affect the assumed accident initiation sequences. No new operating configuration is being imposed by the Z value adjustments that would-create a new failure scenario. In addition, no new failure modes are being created for any plant equipment. Therefore, the types of accidents defined in_the FSAR continue to represent the credible spectrum of events which bound safe plant operation.

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l ENCLOSURE 2-(CONTINUED)

V0GTLE ELECTRIC GENERATING PLANT REQUEST TO REVISE TECHNICAL SPECIFICATIONS REVISION TO Z FOR STEAM GENERATOR WATER LEVEL INSTRUMENTATLQ8

3. The proposed changes do not involve a significant reduction in a margin of safety because there is no reduction ' the margin of safety associated with the revised Z values for the steam generator. water icvel - low-low and high-high trip functions. The results and conclusions of the accident analyses as presented in the FSAR remain applicable. Thus, all safety .

analysis acceptance criteria continue to be met. The margin of safety for each safety analysis is unchanged, and therefore the margin of safety associated with the steam generator level setpoints is unchanged.

Conclusion Based upon the preceding analysis, it has been determined that the proposed changes to the Technical Specifications to modify the steam generator water level- low-low and high-high associated Z term values do not involve a significant increase in the probability or consequences of an accident previously evaluated, create the possibility of a new or different kind of .

accident from an accident previously evaluated, or involve a significant reduction in a margin of safety. Therefore, it is concluded that the proposed changes meet the requirements of 10 CFR 50.92 (c) and do not involve a significant hazards consideration.

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