ML20078S658

Submits Addl Info Re Application for Amend to Licenses NPF-37,NPF-66,NPF-72 & NPF-77 for Reactivity Control Sys

ML20078S658
Person / Time
Site:	Byron, Braidwood
Issue date:	12/21/1994
From:	Saccomando D COMMONWEALTH EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM), Office of Nuclear Reactor Regulation
References
NUDOCS 9412290089
Download: ML20078S658 (5)

Text

I-1400 Opus PlacCcmmonwacith Edison C

. 9 Downers Grove.e Imnos 60515 Office of Nuclear Roactor Re December 21,1994 U.S. Nuclear Regulatory Com i gulation Washington, D.C. 20555 m ssion Attn:

Document Control Desk

Subject:

AdditionalInformati Operating Licenseson Regarding Application fo A Reactivity Controls Systems mendment to Fa Byron Station Units 1 and 2 r

MPF-37/66: NRC Docket Nos 50 454/

NPF-72/77:Braidwood Station Units 1 and 2 455 NRC Docket Nos.

References:

50-456/457 1)

Commonwealth Edison ComTeleconf m

Commission regarding the P er 15 1994, between pany an,d the Nuclear Regulat Coefficient ositive Moderator Temperature 2) ory Safety Evaluation pertaining tG. Dick letter to e

October 21,1994 3) supplement to propo. Russell dated July 26 J. Bauer letter to W transmitting addressing

• Positive Moderator T ow sed Byron and Braidwood licen, transmitting Reduced Thermal Design Flow" emperature C oefficient andse amendment 4)

J. Bauer letter to W. Russell d proposed Byron and Braidwood lated March 23,1994,

" Positive Mod Reference 4 transmitted CommDesign Flow' erator Temp a

ssir'g and Reduced Thermal amend the Technical Specificati onwealth Edison Company's (Cons for Br positive moderator temperature This amendment request wa the reduced thermal design flNuclear Regulatory Commis coefficient s subsequently (PMTC) and reduced thermal desiation a supplemented in Reference 3 on (NRC conference calls were held betw ow portion) issued the referenced Safety Eval gn flow.

Hortion of the amendme t een the NRC and Comed concof the amendment

. The crovide the NRC with a d n. During the reference teleco f ubmitted material or eral ocument that describes which sn erence, rning the PMTC e

ime methodology.are applicable to Comed's ections of the previouslyComEd agree This document is attached application of the Unfavorable Exp 2290o99 941221 osure ADOCK 05o00 4

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Commonwealth Edison

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Downers Grovo, litno:s 60515 December 21,1994 Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D.C. 20555 Attn: Document Control Desk

Subject:

AdditionalInformation Regarding Application for Amendment to Facility Operating Licenses-Reactivity Controls Systems Byron Station Units 1 and 2 NPF-37/66: NRC Docket Nos. 50-454/455 Braidwood Station Units 1 and 2 NPF-72/77: NRC Docket Nos. 50-456/457

References:

1)

Teleconference dated December 15,1994, between Commonwealth Edison Company and the Nuclear Regulatory Commission regarding the Positive Moderator Temperature Coefficient 2)

G. Dick letter to D. Farrar dated October 21,1994, transmitting Safety Evaluation pertaining to the Reduced Thermal Design Flow 3)

J. Bauer letter to W. Russell dated July 26,1994, transmitting supplement to proposed Byron and Braidwood license amendment addressing " Positive Moderator Temperature Coefficient and Reduced Thermal Design Flow" 4)

J. Bauer letter to W. Russell dated March 23,1994, transmitting a proposed Byron and Braidwood license amendment addressing

" Positive Moderator Temperature Coefficient and Reduced Thermal Design Flow" Reference 4 transmitted Commonwealth Edison Company's (Comed) request to amend the Technical Specifications for Braldwood and Byron Station addressing positive moderator temperature coefficient (PMTC) and reduced thermal design flow.

This amendment request was subsequently supplemented in Reference 3. The Nuclear Regulatory Commission (NRC) issued the referenced Safety Evaluation for the reduced thermal design flow portion of the amendment request. Several conference calls were held between the NRC and Comed concerning the PMTC portion of the amendment. During the reference teleconference, Comed agreed to provide the NRC with a document that describes which sections of the previously submitted material are applicable to Comed's application of the Unfavorable Exposure Time methodology. This document is attached.

9412290009 941221 PDR ADOCK O*.300 4

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i NRC Document Control Desk December 21,1994 If you have any questions regarding this correspondence please contact this office.

Sincerely,

,E

, och Denise M.

'ccomando Nuclear Licensing Administrator Attachment cc:

G. Dick, Byron Project Manager - NRR R. Assa, Braidwood Project Manager - NRR H. Peterson, Senior Resident inspector - Byron S. Dupont, Senior Resident inspector - Braidwood J. Martin, Regional Administrator - Region ill Office of Nuclear Facility Safety - IDNS It f

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a Attachment WCAP-11992/11993 UET Sections and Explanation of Comed Application of UET Methodolooy x

This document provides guidance as to which sections of WCAPs 11992 and 11993 (References 1 and 2) are applicable to the Commonwealth Edison (Comed) application of the Unfavorable Exposure Time (UET) methodology. The UET methodology is used for evaluating Anticipated Transients Without Scram (ATWS) risk on a deterministic basis. This document also provides details of how Comed will apply the methodology to cycle-specific calculations for the Byron /Braidwood stations.

It should be noted that Comed intends for this subset of the Westinghouse methodology to apply only until a review of the complete Westinghouse methodology previously submitted in Reference 3 can be performed. Comed is working with the Westinghouse Owners Group (WOG) to determine an appropriate licensing approach to resolve this issue for the long term.

WCAP-11992/11993 Applicable Sections WCAP-11992 describes the administration process developed by the WOG to determine ATWS risk throughout a plant's lifetime. WCAP-11993 provides results of the application of the process to show that Westinghouse plants were in compliance with the original ATWS rule basis at the time of the study.

Both WCAPs 11992 and 11993 discuss the historical perspective of the ATWS rule, the Probabilistic Risk Assessment (PRA) model used by the NRC in the original rulemaking, and the expanded PRA model developed by the WOG to calculate ATWS risk. These documents provide usefulinformation in understanding the ATWS risk model; however, since the PRA overall methodology is not being applied here, only the sections which specifically refer to the critical trajectory and UET methodologies are discussed below. Since the discussion of UET is almost identicalin both documents, the section numbers in the following discussion refer to WCAP-11992.

Section 4.3.8 discusses the pressure relief node of the WOG ATWS event tree, and provides a definition for UET.

Section 4.6.8 describes the assumptions and operating conditions at which the UET is evaluated. This section also discusses which sets of equipment availability are considered in the UET calculations.

The UET methodology is described in detailin Appendix B, Section B.7.1, "ATWS Critical Power Trajectory Methodology." This section establishes the reference plant analysis from the previous 1979 ATWS Submittal (Reference 4) as the basis for the sensitivity studies performed to determine the critical power trajectories.

reactivity feedback conditions req,uir dAs stated in WC 3200 psig for various RCS pressur to yield a peak RCS pressure equiy e

availabilities). The transient model anal e relief capacities (PORV and au transformed into equivalent stead e

valent to with steady state core evaluation mod l eedwater y state reactor conditions to allow for co limiting ATWS transients are cha e s. This transformation is possible since th ust be pressurization of the RCS and the c racterized by a relatively slow heatup a d mparison have been demonstrated to be qua i onditions at impor1 ant times during the tra e

n s -steady state.

pressure relief capacity conditions thWith the transient re nsient ritical trajectoriesritical trajectories, are determined f e reactor heatup shutdown characteristi of steady state reac(Figures B-1 A through B 1F i or each pressure relief capacity. These re, or cs t

onditions (power vs.or power versus inlet coolant temperat nfiguration.

inlet temperature) that result inn WCAP-11992), whic sulting 200 psig in the transient analysis of th a peak RCS pressure ofure, represent t e limiting ATWS event for the referenc 3mEdApplicatigo_q_f Westinghouse UET M e plant The WOG study defines the term UETethodology re reactivity feedback is not sufficient t g for a given plant configuration (initiati as the time during cycle life when the iliary feedwater flow, and PORV o prevent RCS pressure from exceedin tem capabilities, and whether orulations of UET for differe ng event, power level, manual rod inserti availability). The WOG methodology pro i g 3200 a ilities, Auxiliary Feedwater on, methodology, as applied by Comed will not manual control rod insertion has o(AFW v des for Reference 4

= city, and no co(100% PORV capacity, or both PORVs avai ccurred.

ntrol rod insertion). The critical traject enditions is shown in Figure B

.f conditions is based on a meeting bet s

e 100% AFW

-1 A of WCAP-11992. The use of this (baseory mber 15,1994.

quivalent to the original ATWS ruleAt this meeting NRC ween Comed and the NRC staff on staff per case) on was met for 95% of the cycle leng(base case)sonnel stated that this fity feedback, having a positiSince the Moderator Temperatu used to show the 3200 psig th.

c ve MTC has a dire (ct impact on the UEToe The reload specific analysis consid value. otal oower, all rods out, equilibriunitial conditions are assume m xenon) m nal equilibrium conditions (100%

power search is performed for criticalit mperature assuming a pressure of 3200 y conditions as a function of core inlet psig; and

3. Calculations which yields thewindow, since this is thneed only be done The most positivemost reactiveusing the low e

'ectory established fresulting calculated current cycle MTC core end of the configuration, previous ycle bur sign transient conditioconditions (in terms rom the transient acritical state powers i.e., the c condition nup seding the tressns (e.g.,of power versus inlet temnalysis. This compared are the s

criterion ofthose c

ctory.ycle specific which w compa core design 3200 psig). ould result in peakperature)rison how s

RCS pressurethat are greater th sufficien,t to preventHence the UETvalu critical trajectory is gThe UETis that tim an reater than the tran ie during the ycle s in MTC exce(or the time during cycle life e

c including any variati

-d in the, alyses eding 3200 psig) app ent critical s

an essing changes in supporting the basis f more dverse than thoswhen th ons that are that the UET for aS rule is appropriat l ropriately consider core reactivity feedb a ack in thisor the final ATWS rul ly, the ATWS overpre given cyclee y demonstrated fo s the ack effects f th.

o e original acceptancecore designr the basemanner, com. Furthermo e

ssure set of copliance case will remain below 5% nditions by with the criterion willbe festinghouse Ow

, or tration Process "ners Group /W met for 95% of the stinghouse Owners GWCAP 11992, Decembestinghouse P e with ATWS er,1988

ATWS

.,1988 Rule Basis for Westiroup/ Westinghouse P Rule to Request for Add nghouse PWRs," Assessment of rogram:

1

!t Addressing Positi ve Moderator TempeitionalInformation R WCAP-11993, sign Flow," Letter from D ist 16,1994

. M. Saccomando (Comed) entsegardin rature Coeffici 29, Letter fro icense December 30,1979 "m T. M. An to W. and Reduced derson (W T. Russell

,ATWS Submittal".estinghouse) to Dr S

. H. Hanauer gx'--

As stated in WCAP i1992, sensitivity studies were performed to determine the reactivity feedback conditions required to yield a peak RCS pressure equivalent to 3200 psig for various RCS pressure relief capacities (PORV and auxiliary feedwater availabilities). The transient model analysis used a point kinetics model which must be transformed into equivalent steady state reactor conditions to allow for comparison with steady state core evaluation models. This transformation is possible since the limiting ATWS transients are characterized by a relatively slow heatup and pressurization of the RCS and the conditions at important times during the transient have been demonstrated to be quasi-steady state.

I With the transient reactivity feedback conditions transformed for various RCS pressure relief capacity conditions, the reactor heatup shutdown characteristics, or critical trajectories, are determined for each pressure re!ief capacity. These resulting critical trajectories (Figures B 1 A through B-1F in WCAP-11992), which are in the form of steady state reactor power versus inlet coolant temperature, represent the locus of conditions (power vs. inlet temperature) that result in a peak RCS pressure of 3200 psig in the transient analysis of the limiting ATWS event for the reference plant configuration.

Comed App] cation of Westinghouse UET Methodoloay The WOG study defines the term UET as the time during cycle life when the core reactivity feedback is not sufficient to prevent RCS pressure from exceeding 3200 psig for a given plant configuration (initiating event, power level, manual rod insertion, auxiliary feedwater flow, and PORV availability). The WOG methodology provides for calculations of UET for different PORV availabilities, Auxiliary Feedwater (AFW) system capabilities, and whether or not manual control rod insertion has occurred.

j The methodology, as applied by Comed, will employ the " base case" set of conditions from Reference 4 (100% PORV capacity, or both PORVs available,100% AFW capacity, and no control rod insertion). The critical trajectory corresponding to this set of conditions is shown in Figure B-1 A of WCAP-11992 The use of this (base case) set of conditions is based on a meeting between Comed and the NRC staff on September 15,1994. At this meeting, NRC staff personnel stated that this approach was equivalent to the original ATWS rule (base case) used to show the 3200 psig criterion was met for 95% of the cycle length.

Since the Moderator Temperature Coefficient (MTC) is a component of the total reactivity feedback, having a positive MTC has a direct impact on the UET value.

The reload specific analysis considers the following:

1. Initial conditions are assumed to be nominal equilibrium conditions (100%

power, all rods out, equilibrium xenon)

2. A power search is performed for criticality conditions as a function of core inlet temperature assuming a pressure of 3200 psig; and

e

3. Calculations need only be done using the low end of the previous cycle burnup window, since this is the most reactive core configuration, i.e., the condition which yields the most positive current cycle MTC.

The resulting calculated critical state powers are compared to the critical trajectory establ;shed from the transient analysis. This comparison shows any core design conditions (in terms of power versus inlet temperature) that are greater than the transient conditions (e.g., those which would resuit in peak RCS pressure exceeding the stress criterion of 3200 psig). The UET is that time during the cycle that the cycle specific core design critical trajectory is greater than the transient critical trajectory.

Hence, the UET value (or the time during cycle life when the reactivity feedback is not sufficient to prevent exceeding 3200 psig) appropriately considers the effects of changes in MTC, including any variations that are more adverse than those originally modeled in the analyses supporting the basis for the final ATWS rule. Furthermore, by addressing changes in core reactivity feedback in this manner, compliance with the final ATWS rule is appropriately demonstrated for the base case set of conditions by showing that the UET for a given cycle core design will remain below 5%, or conversely, the ATWS overpressure acceptance criterion will be met for 95% of the cycle length.

References

1. " Joint Westinghouse Owners Group / Westinghouse Program: ATWS Rule Administration Process," WCAP-11992, December,1988.

2. " Joint Westinghouse Owners Group / Westinghouse Program: Assessment of Compliance with ATWS Rule Basis for Westinghouse PWRs," WCAP-11993, l

December,1988.

3. " Response to Request for AdditionalInformation Regarding a Proposed License l

Amendment Addressing Positive Moderator Temperature Coefficients and Reduced i

Thermal Design Flow," Letter from D. M. Saccomando (Comed) to W. T. Russell (NRC), August 16,1994.

4. NS-TMA-2182, Letter from T. M. Anderson (Westinghouse) to Dr. S. H. Hanauer (NRC) dated December 30,1979, "ATWS Submittal".

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