ML20080Q316

Suppl Application for Amends to Licenses NPF-37,NPF-66, NPF-72 & NPF-77,requesting TS to Address Moderator Temp Coefficient

ML20080Q316
Person / Time
Site:	Byron, Braidwood
Issue date:	02/28/1995
From:	Saceomando D COMMONWEALTH EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
NUDOCS 9503080318
Download: ML20080Q316 (6)

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MU.S. Nuclear Regulatory Commission . ,

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Subject:

Supplement to Application for Amendment to Facility Operating Licensesi ,

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, Byron Station Units 1 and 2 g NPF-37/66: NRC Dekat Nos;50-454/455

< l 3' . . Braidwood Station Unita 1 ~and 2 L .

x NPF-72/77: NRC Dockat Nos. 50-456/457 i e u nd

" Positive Moderator Temperature Coemeient"

Reference:

D. Saccomando letter to NRC dated February 15,1995, transmitting-Supplement to Positive Moderator Temperature Coemeient Proposed y

Technical Specification Amendment The Referenced letter transmitted Commonwealth Edison Company's'(Comed)

" Supplement to Byron and Braidwood Station's request to amend the Technical 3 Specifications which addressed the moderator temperature coemeient (M'IE). Part of that . _

. supplemental request proposed to expand the Operating Limits Report (OLR) to include v

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' cycle specific MTC value. Reference to the inclusion of the MTC value in the OLR was not-included in the Significant Hazards Considerations which was transmitted in the ..,

Referenced letter. Attached is a revised Significant Hazards Consideration which l supersedss that 'which was previously transmitted.

q If you have any questions concerning this correspondence, please contact'this omee.-

S* rely, H Denise M.

M mando ~'

. Nuclear Licensing Administrator 1 Attachment r .,

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, . 'cc: 1 R.' Assa, Braidwood Project Manager-NRR G. Dick, Byron Project Manager-NRR

. S. Dupont, Senior Resident Inspector-Braidwood

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H. Peterson, Senior Resident Inspector-Byron J. Martin, Regional Administrator-RIII Omce of Nuclear Safety-IDNS -

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. ATTACHMENT 'l d

[- ' EVALUATION OF SIGNIFICANT HAZARDS CONSIDERATIONS .

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,, . FOR PROPOSED CHANGES TO . -

--APPENDIX'A TECHNICAL SPECIFICATIONS OF ,l

' FACILITY OPERATING LICENSES  :

• - NPF-37, NPF-66l NPF-72, and NPF-771 -

r  ; Cdmmonwealth Edison (Comed) has evaluated the proposed amendment and determined 7 i that it involves no'aignificant hazards consideration.; According to.10.CFR 50.92(c), a t

j proposed amendment to an operating license involves .no significant hazards if operation of the facility in accordance with the proposed amendment would n'ot

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~ (1)- Involve a significant increase in' the probability or consequences of an accident previously evaluated; or J

. -(2) Create the possibility of a new or different kind of accident from any accident previously evaluated; or

-(3) Involve a significant reduction in a margin of safety. >

P A. INTRODUCTION In a letter dated March 23,1994 from J.A. Bauer to W.T. Russell, Co nmonwealth Edison -

Company (Comed) requested a Technical Specification Amendment allowing use of a.  :

Positive Moderator Temperature Coefficient (PMTC) and Reduced Thermal Design Flow (RTDF). This Amendment request was later supplemented in a letter dated July.26,.1994 from J.A. Bauer to W.T. Russell to provide additional cycle specific implementation' _.

footnotes for clarification. An additional letter dated August 16,1994, from D.

- Saccomando to W.T. Russell, transmitted responses to the NRC for an additional request' for information regarding the effects a positive MTC would have on the results of the J

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- Anticipated Transient Without Scram (ATWS) analysis. ' Co.nEd subsequently received i approval of the proposed Technical Specification Amdment on October 21,1994 in a - i letter from G.F. Dick to D.L. Farrar. However, the approval specifically excluded the 'l proposed PMTC Technical Specification chan~ge.

Based on subsequent meetings, discussions, and correspondence with the NRC, Comed is ,

resubmitting the Technical Specification Amendment request allowing use of a PMTC. t' i

The proposed changes are consistent with Standard Technical Specifications for . . .

. Westinghouse Plants (NUREG-1431). That is, the Amendment requeet proposes that the

MTC value be maintained within the limits specified in an operating limits cycle' specific T

j report with a maximum upper limit specified in the echnical Specifications. Therefore, j

- Comed proposes to expand the current Operating Limits Report (OLR) to include a cycle j

' specific M'IC value.

The MTC change would allow a nlightly positive MTC below 100 percent of rated full .

. power. The principal benefit of 15., change is that it would facilitate the design of future  !

reload cycles and yield significant fuel cost savings. The safety analyses for the Byron l and Braidwood Updated Final Safety Analysis Report (UFSAR) transients were k a nla\bytwd\pmtesupl\2 f w, ,, --, , -.3 +- - , . , , --%w , . m y- , e - , . - -=

previously based on a maximum MTC being less than or equal to 0 pcm/*F at all times when the reactor is critical. The proposed change to the Technical Specifications would allow a maximum upper limit of +7 pcm/*F MTC for power levels up to 70 percent with a linear ramp to O pcm/*F at 100 percent power. However, the proposed Technical Specification would require that the cycle specific MTC value be maintained within the limits specified in the Operating Limits Report (OLR). The basis for the MTC limit is to ensure that the value of the coefficient remains within the limits assumed in the UFSAR accident and transient analyses. In keeping with this basis, the necessary accident and transient analyses were performed with the new MTC values to ensure that the results remain within all design and safety criteria. The analysis provides the basis for the proposed MTC Technical Specification change. This analysis, WCAP-13964 " Byron and Braidwood Units 1 and 2 Increased SGTP/ Reduced TDF/PMTC Analysis Program Engineering / Licensing Report", was provided in Attachment 5 of the March 23,1994 submittal.

To accammodate the positive MTC changes and the potential oflengthened reload fuel cycles due to increased energy requirements, Technical Specification changes are also required to meet shutdown margin requirements (SDM). To assure suberiticality requ'.rements are met following a postulated loss-of-coolant accident (LOCA), the boron emcentration is increased in the refueling water storage tank (RWST) and the safety injection accumulators. These changes have already been approved by the NRC in response to the original submittal.

Determination of a cycle specific MTC value will include an evaluation of Anticipated Transient Without Scram (ATWS) risk on a deterministic basis, since the ATWS rule was based in part on a given MTC value. The Unfavorable Exposure Time (UET) methodology will be used for evaluating ATWS risk on a deterministic basis. A UET value will be calculated each cycle. UET is defined as the amount of time during the operating cycle for which the reactivity feedback is not suflicient to prevent Reactor Coolant System (RCS) pressure from exceeding 3200 psig for a given plant configuration. The ATWS risk is considered acceptable for a UET ofless than 5% of cycle length. This UET value will be updated for each core reload and 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. .

B. 10 CFR 50.92 ANALYSIS  ;

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1. The proposed changes do not involve a significant increase in the probability or  !

consequences of an accident previously evaluated. j i

An analysis program was pursued by Commonwealth Edison to justify a positive MTC, reduced reactor coolant system thermal design flow, and increased steam generator tube plugging levels. This analysis identified a need for corresponding increases in the boron concentration levels in the refueling water storage tank (RWST) and safety irdection accumulators to assure suberiticality requirements are i met following a postulated loss-of-coolant accident (LOCA). The increases in boron concentration are based on the maximum upper limit of the MTC. The corresponding Technical Specification changes required as a result of this analysis program were previously approved by the NRC, including the increases in boron  ;

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+ l concentration limits, with the exception af the positive MTC changes The safety- '

analyses necessary to support this program are documented in WCAP-13964.- The e c , results.were reviewed by Commonwealth Edison and found to be acceptable. ' All; .

m .  ? Departure from Nucleate Boiling Ratio (DNBR) design limits were determined; j

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d ( such that there was a 95 percent probability at a 95 percent confidence level that. s;

-  : DNB would not occur on the most limiting fuel rod for any Condition I or . . 4 1 Condition II event.- The riresent Technical Specification limit for Nuclear Enthalpy,  ;

K  ? ' Rise Hot Channel Factor, FL, ofless than 1.65 ensures that the DNB design basis -

q.f stated 'above would be met, thus fuel integrity will not be challenged. ~ i 4

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The accidents which are sensitive to MTC were analyzed as part of the overall . n y, program and the results were found to be acceptable. The safety functions ~of the.

p evaluated systems' and components remain unchangediThe analysis performed -  :

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- using the increased MTC value does not affect the integrity of the safety related ~ <

A systems and components such that their function to control radiological .

d consequences is affected and all fission barriers will remain intact. The effects on '}

offsite doses have been considered. The incorporation of a positive MTC, in -

e conjunction with the previously approved reduction in reactor coolant system. .

~s thermal design flow rate and increase in steam generator tube plugging levels, will ?

result in a small increase in offsite doses; however, the total doses remain a small -

fraction of the 10CFR100 limits. As such, the accident analysis acceptance criteria c

continue to be satisfied. j On a cycle-by-cycle basis, a deterministic evaluation of the impact on ATWS risk' -[

will be performed. ~An Unfavorable Exposure Time (UET) will be' calculated, where :  !

UET is defined as the amount of time during the operating cycle for which the! j reactivity feedback is not sufficient to prevent Reactor Coolant' System (RCS)  ;

pressure from exceeding 3200 psig for a given plant configuration. The UET j methodology is consistent with the Westinghouse Owner's Group methodology i presented in WCAP 11992, "ATWS Rule Administration Process" and WCAP j 11993, " Assessment of Compliance with ATWS Rule Basis for Westinghouse: l PWRs". Corrective actions will be taken, as necessary, to assure a UET ofless than 5% of cycle length.

a The relocation of the cycle-specific core operating limits for the MTC from the Technical Specifications has no influence or impact on the probability or j consequences of any accident previously evaluated. ' Byron and Braidwood Stations -  ;

will continue to operate within the _ cycle-specific MTC limits contained in the OLR. 4 The propose' amendment will require exactly the same action to be taken when  :

the OLR limL. are exceeded as are required by the current Technical Specification.

Any change to the siTC values in the OLR will be performed based on NRC- j t

approved methodology as delineated in Section 6.9.1.9 of the Technical Specifications. Each accident analysis addressed in the Updated Final Safety 1l Analysis Report (UFSAR) will be examined with respect to changes in cycle t dependent parameters, which are obtained from application of NRC-approved 5

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t' reload design' methodologies, to. ensure that the transient evaluation of new reloads" i 4, i am bounded by previously accepted 'analysian This examination, which will be D' 4' l performed under the requirements of 10CFR50.59, ensures that future reloads will ' '

i o~ not involve a'significant increase in the probability or consequences of an accident,

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' previously evaluated.  :

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? Therefore, implementation'of a positive MTC will not involve a significant increase- l in the probability or consequences of an~ accident previously evaluated. j J2c - The proposed changes do not create the possibility of a new or different type of '3':'

g  : accident from any accident previo'usly, evaluated.

ss 4 The methodology and manner of plant operation as a result of the proposed. .

. changes is unafrected.' Implementation of a positive MTC does not impact the safe;  :

operation of the reactor provided that the Limiting Conditions for Operation -

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. ~ (LCOs) and the associated action requirements are satisfied.' The assumptions do - <

6 not create any~new failure modes that could adversely impact safety related ' -~!

equipment. The reload safety limits and LCOs in the plant Technical:

Specifications will be evaluated and satisfied for each future reload core ' design.via i W the 10CFR50.59 processc All DNBR limits have been satisfied. Currently installed i equipment will not be operated in a manner different than previously designed.

No new credible limiting single failure has been created. No new or different ,

accidents or failure modes have been identified for any systems or components '

important to safety. .

The relocation of the cycle specific MTC values to the OLR will not create the - ,

possibility of a new or different type of accident. No safety.related equipment or safety function will be altered as a result of this proposed change. - The cycle :  !

specific values are calculated using NRC-approved methods 'and submitted to.the  ;

NRC to allow the Staff to continue w trend these limits. The Technical :i Specifications will continue to require operation within the analyzed core operating limits and appropriate actions will be taken, when, or if, the limits are exceeded.

j Therefore, there is not a potential for creating the possibility of a new' or different.  ;

type of accident from any accident previously evaluated.

3. The proposed changes do not involve a significant reduction in a margin of safety. l The performance and integrity of the evaluated safety related ' systems and components are not affected by the proposed change to the MTC. The radiological i consequences of all previously analyzed accidents remain within~ acceptable limits.

The proposed change to the MTC will have no effect on the availability, operability, .:

or performance of the evaluated safety related systems or components. The j incorporation of a positive MTC, in conjunction with the previously approved a reduction in reactor coolant system thermal design flow rate and increase in steam generator tube plugging levels, will result in a small increase in offsite doses; ,

however, the total doses remain a small fraction of the 10CFR100 limits. The j methodology, discussed in Attachment E, describes the determination and use of j I

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cc - the UET values in the calculation of the Primary Pressure Relief node for the :

1 ATWS event tree to determine an overall ATWS risk value. The methodology will ,

' be used by Comed to ensure that a core designed with a positive ~ M'It will not result in an unacceptable risk to core damage frequency due to an ATWS event. .

The margin of safety associated with the licensing basis safety analysis is not . ,

, , significantly reduced by the proposed changes. All acceptance criteria for the

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i specific UFSAR Chapter 15 safety analyses (non-LOCA and LOCA) have been : ,

-  ! satisfactorily evaluated and verified using NRC approved methodologies.'

J The margin of safety is not affected by the relocation of the cycle specific MTC , '

C limits from the Technical Specifications. The proposed' amendment continues to .  ;

; require ~ operation within the core limits as determined by the NRC-approved reload - '

design and ~ safety analysis methodologies. : Appropriate actions will be taken, when,7 or if, limits are exceeded. '

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The dev'elopment of the'MTC limits for future reloads will continue to conform to f those methods described in the NRC-approved documentation.- In addition, each

. future reload will involve a 10CFR50.59 safety review to assure that operation of-

' the unit within the cycle specific limits will not involve a reduction in the margin

' of safety as defined in the basis for any Technical Specification.

Therefore, there is no significant redu' ction in the margin of safety as defined in . i the bases of any Technical Specification.

Based on th'e above evaluation, Commonwealth Edison has concluded that implementation of a positive MTC does not involve a significant hazards consideration .

- with respect to the provisions of 10CFR50.92. ,

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