ML20237C342

Proposed Tech Spec Figure 3.2-2,modifying Operating Margin to Remove Some Conservatism When Small Break LOCA Analysis Repeated for T-hot Reduction Mod

ML20237C342
Person / Time
Site:	Byron, Braidwood, 05000000
Issue date:	12/04/1987
From:	COMMONWEALTH EDISON CO.
To:
Shared Package
ML19302D195	List: ML20237C332 ML20237C342 ML20237C361 ML20237C409
References
3781K, NUDOCS 8712210266
Download: ML20237C342 (8)

Text

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ATTACHMENT A PROPOSED CHANGE TO APPENDIX A

. TECHNICAL SPECIFICATIONS, FACILITY OPERATING LICENSES jiPF-37, NPF-66 AND NPF-72 Byron Braidwood Revised Pages: 3/4 2-5 3/4 2-5 8712210266 871204 PDR ADOCK 05000454 P PDR 3781K

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BRAIDWOOD- UNITS 1 & 2 3/4 2-5 1

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l ATTACHMENT B l BACKGROUND INFORMATION In order to reduce the potential for the initiation and propagation of primary water stress corrosion cracking (PWSCC) in the Model D steam generator tubes, Commonwealth Edison is taking action to operate ctron Units 1 and 2 and Braidwood Units 1 and 2 with a reduced primary system vessel outlet temperature (Thot) of 600*F. This constitutes a reduction of 18.4*F from the original design Thot of 618.4*F.

Detailed evaluations and analyses were performed to determine the impact of reduced primary side temperatures on the NSSS, NSSS/ BOP interfaces, turbine generator, and safety analyses. WCAP-ll386 (Proprietary) and WCAP-ll387 (Non-Proprietary) provide details of the results of these evaluations and analyses. These WCAP's are in Attachment C of this letter.

The evaluations and analyses described in Section 3.0 of the WCAP, Safety Evaluations, verify that no unreviewed safety question is involved and that no changes to the Technical Specifications are necessary to implement operation at a reduced vessel outlet temperature of 600*F. The current Technical Specification limits provide proper assurance that the plant will operate within the bounds of the existing safety analyses even when in a reduced power and temperature mode.

Since the small break loss of coolant accident analysis had to be repeated for the Thot reduction modification, Commonwealth Edison chose to include options in the revised analysis that provide additional operating margin. One of these options resulted in a revision to a figure in the Technical Specifications which depicts the normalized heat flux hot channel factor as a function of core height. This figure is known as the K(Z) curve.

Figure 3.2-2 of the Technical Specifications defines K(Z) as a function of core height. The curve has three distinct segments which define the limits for K(Z) at various core axial positions. The third segment, i that portion at the higher core locations defined by the points (10.8, 0.94) (

and (12.0, 0.65), represents the limiting K(Z) values assumed in the small ]

break loss of coolant accident (SBLOCA) analysis. This is due to the fact f that during a postulated SBLOCA, only the higher core elevations can j potentially become uncovered due to the offsetting effects of the relatively I slow blowdown and the makeup capability of the emergency core cooling system (ECCS). The appropriate value of K(Z) is used to calculate local hot rod power at a particular core elevation. This in turn determines the location of peak cladding temperature (PCT) during the postulated SBLOCA event. By performing analyses at the limiting condition to eliminate this third line segment, greater heat flux values can be obtained at higher axial positions and the limits on core design for hot channel factors can be relaxed. This amendment request proposes to eliminate the third line segment and in its i' place, extend the segment defined by the points (6.0, 1.0) and (10.8, 0.94) to the twelve foot core elevation, defining a new point (12.0, 0.925). A ,

description of the analyses supporting this amendment using the NOTRUMP l computer code is provided as revised marked-up pages of Chapter 15.6.5 of 1

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the Byron /Braidwood FSAR. These pages are included in the WCAP. An increase in the overall LOCA peaking factor (F g) from 2.32 to 2.40 was realized, however, the current Fg Technical Specification of 2.32 is to be ,

retained until all of the pertinent FSAR non-LOCA analyses have been  !

repeated at the higher value.

In summary, our review has concluded the Thot reduction program meets the standards of 10 CFR 50.59 and can be implemented without prior commission approval. The detailed report of the Thot reduction program has been included with this submittal as additional background information to support this amendment request regarding (ne K(Z) curve.

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1 ATTACHMENT D EVALUATION OF SIGNIFICANT HAZARDS CONSIDERATION I

Commonwealth Edison h&s evaluated this proposed amendment and determined that it involves no significant hazards consideration. According to 10 CFR 50.92(c), a proposed amendment to an operating license involves no significant hav.ards consideration if operation of the facility in accordance with the amendment would not:

(1) Involve a significant increase in the probability or consequences of an accident previously evaluated; or (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.

This proposed amendment involves a revision to a figure in the Technical Specifications, the K(Z) curve, which depicts the normalized heat flux hot channel factor K(Z) as a function of core height. The curve has three distinct segments which define the limits for K(Z) at various core axial positions. The third line segment, which is being modified, represents the limiting K(Z) values assumed in the small break loss of coolant accident.

Revision *bfthethirdlinesegmentoftheK(Z)curvehasnoeffect on the probability of a small break loss of coolant accident (SBLOCA). A new analysis of the SBLOCA, using enhanced analysis methodology and the limits of the revised K(Z) curve, has shown a reduction in the predicted

• peak clad temperature from 1779' F to 1630' F. As a result, the consequences of this previously evaluated accident have decreased.

This revision to the third line segment of the K(Z) curve will allow reactor operation with an increased heat flux hot channel factor at higher axial core locations. Reactor operation in this condition will not create the possibility of a new or different kind of accident because this condition (increased heat flux hot channel factor at higher axial core location) has been analyzed and the only relevant accident remains to be a SBLOCA. The revised analysis of this accident has shown acceptable results. Peak clad temperature is predicted to be lower than previously analyzed.

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. Finally, the revised third line. segment of the K(Z)' curve'does not involve a significant reduction in a margin of safety. The ultimate-acceptance criterion against which increased heat flux hot channel factors is evaluated is peak clad temperature (PCT). Reanalysis of the SBLOCA event for this condition with the.. latest methodology has predicted a PCT reduced from 1779' F to 1630' F. This indicates an actual increase in the margin to

.the 2200*F acceptance criterion as defined in 10 CFR 50.46. In addition, the margin to the local and core wide cladding oxidation limits has not been reduced.

For the reasons stated above, Commonwealth Edison believes this l proposed amendment involves no significant hazards consideration.

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ATTAC19fENT E APPLICATION FOR WITHHOLDING WESTINGHOUSE LETTER CAW 87-122 AFFIDAVIT OF ROBERT A. WIESEMANN PROPRIETARY INFORMATION NOTICE 3781K

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