ML20072Q114
| ML20072Q114 | |
| Person / Time | |
|---|---|
| Site: | McGuire, Mcguire  |
| Issue date: | 11/20/1990 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20072Q104 | List: |
| References | |
| NUDOCS 9011300194 | |
| Download: ML20072Q114 (4) | |
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO AMENDMENT NO.116TO FACILITY OPERATING LICENSE NPF-9 AND AMENDMENT NO. 98 T0 FACILITY OPERATING LICENSE NPF-17 DUKC POWER COMPANY DOCKET NOS. 50-369 AND 50-370 MCGUIRENUCLEARSTATION.UNITSlAND2
1.0 INTRODUCTION
By letter dated September 4,1990, Duke Power company (the licensee) proposed amendments for McGuire Nuclear Station, Units 1 and 2.
The pro would reduce the required measured reactor coolant system (RCS) posed amendments flow rate by one percent from 97220 GPM/ loop to 96250 GPM/ loop. Additionally, an administrative change would reinove reference to the resistance temperature detector (P,TD) bypass manifold system. This system was removed from both McGuire units and previously approved by the NRC in License Amendment Hos. 84 (Unit 1) and 65 (Unit 2).
j 2.0 EVALUATION Due to tube degradation, some of the tubes in the McGuire Units 1 and 2 steam generators have been removed from service through plugging while others have i
l been sleeved and returned to service. Additional stee'd generator tubes were plugged during the recent refueling outage for Unit 2 such that the RCS flow may be reduced below that currently identified in the Technical Specifications (TSs). The amount of potential flow reduction is sufficient to require reevaluation of the Final Safety Analysis Report (FSAR) Chapter'15 transients and accidents to determine if the current analyses continue to be applicable. The proposed reduction in flow is from 97220 GPM per loop to 96250 GPM per loop, or one percent.
In its September 4,1990 submittal, the licensee esaluated the impact of operation at one percent reduction in minimum measured flow on thermal margin. The reduced flow rate resulted in a slight reduction in core departure from nucleate boiling (DNB) limits.
Consequently, the licensee developed revised core safety limits for average RCS temperature as a function of power for the reduced flaw rate.
These revised limits are identified in a proposed TS Table 2.1-1, " Ret ctor Core i
Safety Limit - Four Loops In Operation." The flow per loop identifiee on pro >osed Figure 2.1-1 is 96250 GPM, which is the minimum measured flow (MMF) rataerthanthethermaldesignflow(TDF).
The MMF differs from the TDF by an i
amount equal to instrument uncertainty.
For consistency, the terminology in TS Tai;1e 2.2-1 is changed from " design flow" to " minimum measured flow" when the loop flow of 96250 GPM is identified. These changes are acceptable.
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Removal of the RTO bypass manifold systees for McGuire Units 1 and 2 was approved by issuance of Amer:iment No. 84 to facility Operating License NPF-9 and Amendment No. 65 to Facility Operating License NPF-17 dated May 18, 1988.
Therefore, a proposed deletion of an obsolete reference to the WTO bypass mainfold in Table 2.2-1 is acceptable.
The licensee has determined that the current Overtemperature A-T (OTAT) and Overpower A-T (OPAT) setpoint equation constants (specified in TS Table 2.2-1) are conservative and provide the necessary core protection against departure from nucleate boiling (DNB) under the proposed reduction in flow.
The factors involved in establishing the setpoints include the reactor coolant temperature in each loop and the axial distribution of core power measured by excore neutron detectors.
Potential setpoint changes related to reactor coolant temperature were accounted for in the license amendments addressing the removal of the RTO bypass manifold systems and the current setpoints remain applicable to the revised TS Figure 2.1-1.
Increases in neutron flux differ 6nce between upper and lower ion chamber readings beyond a pre-defined deadband result in a decrease in trip setpoint-(see TS Table 2.2-1, Note 1).
The deadband range of the f(AI) function in the OT AT and OPAT setpoint equations is revised from its current range of
- 29% > q t
qb > 9% to - 29% > q q > 7% to define the seadband.
This changeisinaconservativedireckionwNichmaintainsprotectionintheevent of a power imbalance between the top and bottom of the core and is acceptable..
2.1 Effects of RCS Flow Reduction on Safety Analyses
~
Recent safety analyses for the McGuire units were performed for a loss-of-coolant accident (LOCA) in connection with the isolation or removal of the Upper Head l
Injection (VHI) system for the McGuire units (see NRC Safety Evaluation for Amendment No. 57 to Facility Operating License NPF-9 and Amendment No. 38 to Facility Operating License NPF-17, dated May 13, 1986).
The small and large j
break LOCAs are reanalyzed for the proposed flow reduction because a potential increase in the precFcted peak clad temperatures (PCTs) is possible as a result i
of a decrease in RCS flow rate.
The large break LOCA analysis was performed with a TOF of 93500 GPM per loop.
low to preclude the neeo for future reanalyses resulting from RCS flow related j
issues.
The current analysis thus remains conservative for the proposed reduction to 94500 GPM.
The small break analysis performed with an approved evaluation model showed that for a reduction in TOF from 95500 to 94500 GPM, the RCS cold' I
leg temperature was reduced by 0.3 deg F.
This small change had no significant impact on the margin to the 10 CFR 50.46 PCT limit of ??00 deg F.
Two plant transients were reanalyzed in connection with the UHI amendment request.
These wers the " Inadvertent Opening of a Steam Generator Relief or Safety Valve" and the " Steam System Piping Failure" events (FSAR Section 15.1.5).
The safety analyses were done with approved codes, and plant and core charecteristics without UHI were demonstrated to be tithin regulatory limits.
In the review of the effect of the RCS flow reduction, it was noted that the current licensing basis analysis was performed with a thermal design flow of 94250 GPM which is more conservative than the reduced TDF of 94500 GPM.
Therefore, the conclusions of the current licensing basis remain valid.
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'l Other transient analyses using a more conservative TDF than the reduced flow proposal were " Loss of Non-Emergency A-C Power to the Station Auxiliaries" (FSAR Section 15.2.6), " Loss of Normal Feedwater" (FSAR Section 15.2.7),
"Feedwater System Pipe Break" (FSAR Section 15.2.8), " Reactor Coolant Pump Shaf t Seizure" (FSAR Section 15.3.3), " Uncontrolled RCCA B3nk Withdrawal from a Subcritical or Low Power Startup Condition" (FSAR Section M.4.1), and "Spcctrum of RCCA Ejection Accidents" (FSAR Section 15.4.8). 1M conclusions of the current lictnsing basis, therefore, remain valid.
Othertransientevents,suchas"FeedwaterSystemMalfunctions"(FSAR ections 15.1.1, 15.1.2), " Loss of External Electric Load" (FSAR Section 15.2.2),
" Inadvertent Closure of MSIVs" (FSAR Section 15.2.4), " Reactor Coolant Pump Break" (FSAR Section 15.3.4), and "CVCS Malfunction that Results in a Decre" te in the Boron Concentration in the Reactor Coolant" (FSAR Section 15.4.6) are bounded by other events or are not affected since RCS flow is not explicitly modeled.
The " Steam Generator Tube Rupture Event" (FSAR Section 15.6.4) was reviewed to assess the effect of the flow reduction. A sensitivity study showed a slight i
increase in primary to secondary break flow and a slight decrease in atmospheric steam flow frcm the failed steam generator.
The FSAR conclusion that the doses are within the limits of 10 CFR 100 remain valid for a one percent reduction in RCS flow.
As a result of the thermal margin evaluation and transient and non-LOCA reanalysis, the licensee concluded that, even with an assumed one percent reduction, no safety criteria will be violated during transients and non-LOCAs, and the results diff er insignific antly from that in the current licensing basis analyses.
The licensee has determined that the reduction in RCS flow reduces the cold leg te.nperature less than one degree. As a result, reactor vessel internal blowdown forces are not significantly affected, and there is no adverse effect on the structural adequacy of vessel internals, core components, and coolant loop piping.
The licensee has determined that the reduction in RCS flow has a negligible effect on the containment analyses of FSAR Section 6.2.1.
This conclusion stems from the negligible change in the RCS initial fluid and metal stored energy.
As a result, mass and energy releases to containment remain unchanged, and the current analyses remain valid.
The NRC staff has reviewed the Duke Power Company request to reduce the required measured RCS flow rate by one percent and the associated TS changes.
Based on its review of the LOCA and transient analyses provided by the licensee, the staff has concluded that there is reasonable assurance that operation of l
the McGuire units 6t full power with a one percent flow reduction does not violate the safety limits associated with the accident analyses presented in the FSAR for the McGuire Units.
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3.0 ENVIRONMENTAL CONSIDERATION
These amendments involve changes in the requirements with respect to the installation or use of facility compenents located within the restricted area as defined in 10 CFR Part 20. The staff has determined that the amendments involve no significant increase in the amounts, and no significant change in the types, of any effluents that may be released offsite and that there is no significant increase in individual or cumulative occupational radiation exposure.
The Commission has previously issued a proposed finding that the amendments involve no significant hazards consideration, and there has been no public comment on such finding. Accordingly, the amendments meet the eli criteria for categorical exclusion set forth in 10 CFR 51.22(c)(9)gibility
. Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment need be prepared in connection with the issuance of these amendments.
4.0 CONCLUSION
The Commission's proposLd determination that the amendments involve no significant hazards consideration was published in the Federal Register (55 FR 40465) on October 3,1990.
The Commission consulted with the State of North Carolina.
No public comments were received, and the State of North Carolina did not have any comments.
We have concluded, based on the considerations discussed above, that:
(1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the aroposed manner, and (2) such activities will be conducted in compliance with tie Commission's regulations, and the issuance of these amendments will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor:
M. McCoy, DST /SRXB T. Reed, DRP-1/II/PDll.3 Dated: November 20, 1990
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