ML20137S881
| ML20137S881 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 04/08/1997 |
| From: | Hebert J Maine Yankee |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| Shared Package | |
| ML20137S885 | List: |
| References | |
| JRH-97-76, MN-97-53, NUDOCS 9704150272 | |
| Download: ML20137S881 (6) | |
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MaineVankee i
RELIABLE ELECTRICITY SINCE 1972 329 BATH ROAD + BRUNSWICK, MAINE 04011 + (207) 798-4100 April 8,1997 MN 97-53 JRH-97-76 Proposed Change No.194 Supplement 1 1
UNITED STATES NUCLEAR REGULATORY COMMISSION Attention: Document Control Desk Washington, DC 20555
References:
(a)
License No. DPR-36 (Docket No. 50-309)
(b)
MYAPC Letter to USNRC dated August 15,1995 (MN-95-97)
Subject:
Proposed Technical Specification Change No.194, Supplement 1, Reactor Coolant Flow Rate Requirements j
Gentlemen:
Reference (b) submitted a proposed change to Maine Yankee Technical Specifications regarding reactor coolant flow rate requirements.
On March 20,1997, Maine Yankee met with the NRC at the One White Flint office to discuss the proposed change. During that meeting, among other things, we expanded upon the basis for our conclusion that the small break LOCA (SBLOCA) event and resulting peak clad temperature would not be adversely affected by our proposed Technical Specification change to reduce RCS -
flow. At your request, we are also submitting that information through this letter.
The participants in the meeting also asked several questions regarding the wording of the proposed Technical Specification. While the wording of Technical Specification 3.10.E.2 provided in Reference (b) has not changed, we have provided clarifying infonnation in the Bases for the proposed change, i
Attachment A provides a summary of the qualitative evaluation of the effects on SBLOCA of
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operation under the proposed Technical Specification change as presented to your staff on March
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20,1997. The evaluation concludes that the change will be bounded by the full power conditions.
The evaluation and results are based upon comparison of the dominant parameters (Core Power Level, LHGR Limits, Initial T n, and S/G Tube Plugging Levels) and is independent of the analysis method used to determine the full power analysis basis. Furthermore, the current SBLOCA analysis of record (updated CE Cycle 4 analysis) also bounds the allowable operating conditions defined by the proposed Technical Specification change.
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MaineYankee UNITED STATES NUCLEAR REGULATORY COMMISSION MN-97-53 Attention: Document Control Desk Page Two Attachment B provides additional information in the basis for Technical Specification 3.10.E.2 l
(Page 3.10-9) which clarifies the proposed change.
Please note that the wording of the Technical Specification in PC 194 remains unchanged as does l
the "no significant hazards evaluation".
Should you have any questions regarding the above, please contact me.
Very truly yours, James R. Hebert, Manager i
Licensing & Engineering Support Department J
c: Mr. H. J. Miller Mr. D. H. Dorman -
4 Mr. J. T. Yerokun Mr. Patrick J. Dostie Mr. Uldis Vanags i
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Attachment A I
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Qualitative Evaluation of Operation Under the Proposed Technical Specification Change on SBLOCA Proposed Change 194 i
Reactor Coolant Flow Rate Requirements l'i
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Attachment A MN-97-53 Page 2 of 4 1
t ATTACHMENT A Qualitative Evaluation of Operation Under the Proposed Technical Specification Change on SBLOCA INTRODUCTION On March 20,1997, Maine Yankee met with the NRC at the One White Flint office to discuss Proposed Change (PC) 194, Reference (b). During that meeting, among other things, we expanded upon the basis for our conclusion that the small break LOCA (SBLOCA) event and resulting peak clad temperature would not be adversely affected by our proposed Technical Specification change to reduce RCS flow. This attachment documents the presentation made to the NRC on March 20,1997 on the reduced RCS flow Tech Spec change.
4 DISCUSSION The proposed Tech Spec change allows for power operation with up to a 5% reduction in RCS flow.
To ofTset the potential impact of this reduction in flow, the allowable reactor power will be reduced (1.5% per 1% in flow). In addition, the PLHGR limits, Limiting Condition of Operations (LCOs),
and trip setpoints will also be reduced, as discussed in Reference (b). These measures more than offset the effect ofreduced RCS flow.
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The effects of the following key parameters on the SBLOCA response were presented to the NRC staff: 1) Power Level,2) LHGR Limits,3) Initial Tw, and 4) SG Tube Plugging Levels. The sections below summarizes the information presented to the NRC for each parameter.
Power Level The reduction in power level impacts the initial conditions assumed in the LOCA analysis. For a given RCS flow and inlet temperature (ta), a lower core power will result in a lower hot leg temperature, Tw. In addition, the initial fuel stored energy will be reduced. The direct impact of a lower core power level will be a slower core uncovery, lower steam temperature after core uncovery, and a lower RCS pressure response for a given rate of RCS mass depletion. These factors will result in a lower calculated Peak Cladding Temperature (PCT).
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Attachment A MN-97-53 Page 3 of 4 LHGR Limits The reduction in the peak LHGR has a direct impact on the LOCA analysis. The fuel rod heat up rate is directly impacted by the allowable peak power level in the fuel rod. This will result I
in a lower PCT.
Initial Tg
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The initial hot leg temperature is reduced as a result of the reduction in the allowable core power j
level. A reduction in Tao, will lower the RCS pressure at which vapor will be formed and as a i
result the pressure plateau will occur at a lower condition. A lower pressure plateau will result
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in lower break flow and higher ECCS flow. This leads to a less severe core uncovery, i.e. a higher minimum collapsed liquid level, and an earlier core recovery. The net impact is a lower j
calculated PCT.
SG Tube Plugging Levels The Tech Spec change does not directly impact the SG plugging levels. The current analysis addresses a plugging level of 1000 SG tubes per SG. A change above 1000 tubes per SG would require additional analysis.
Evaluation of Current Analysis of Recor.d Additional qualitative analysis has been performed to demonstrate that the current SBLOCA analysis of record (updated CE Cycle 4 analysis) also bounds the allowable operating conditions defmed by the proposed Technical Specification change.
The confirmatory order restricts the core power level to 90% of the rated power of 2700 MWth. The SBLOCA analysis performed for these conditions were compared to those defined by the proposed Tech Spec change. The most important parameter to consider in this evaluation is the hot leg temperature. The evaluation does not make a direct assumption regarding the maximum hot leg temperature but assumes a maximum cold leg temperature of 560 F. This analysis is based on the CE Cycle 4 system response which assumed a core power level of 2630 MWth (+2% uncertainty).
Under full flow conditions, the cold leg temperature assumption translates to a hot leg temperature of 610.4 F. Under the minimum mduced flow conditions (95% of rated flow) and a power of 2440 MWth (+2% uncertainty) this translates to a hot leg temperature of 609.3 F. It should also be noted that the current Tech Spec limit of T,oia is 551.3 F or 555.3 F with allowance for measurement uncertainty Thus the maximum allowable hot leg temperature at 2440 MWth and the minimum reduced flow is actually 604.9 F. This is well below the analysis supporting the confirmatory order.
Thus the hot leg temperature, the reduced LIIGR limits, and the assumed SG plugging levels, under the minimum reduced flow conditions (at 2440 MWth), are bounded by the current SBLOCA analysis.
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Attachment A MN-97-53 Page 4 of 4
' CONCLUSION The proposed reduced RCS flow Tech Spec change has been evaluated with respect to impact on the SBLOCA event and it has been determined that this change will be bounded by full power conditions and the current analysis ofrecord. This conclusion stems from the conservative reduction of power level (1.5% for each 1% of flow reduction). Thus, the reduced flow conditions are less limiting than the full power conditions with respect to the LOCA events. This evaluation is independent of the analysis method used to define the full power analysis basis and is based on a comparison of the dominant parameters. Furthermore, the current analysis of record also bounds the allowable operating conditions (dominant parameters) defined by the proposed Tech. Spec. change.
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