ML20080A043

Adequacy of Station Electric Distribution Sys Voltages for Nine Mile Point Nuclear Station,Unit 1, Technical Evaluation Rept

ML20080A043
Person / Time
Site:	Nine Mile Point
Issue date:	06/15/1983
From:	Selan J LAWRENCE LIVERMORE NATIONAL LABORATORY
To:	NRC
Shared Package
ML17054A344	List: ML20080A043
References
CON-FIN-A-0250, CON-FIN-A-250 UCID-19709, NUDOCS 8307190298
Download: ML20080A043 (12)

Text

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UCID.19709 TECHNICAL EVAL,UATION REPORT ON THE ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES FOR THE NINE MILE POINT NUCLEAR STATION, UNIT 1 (Docket No. 50-220)

James C. Selan e

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ABSTRACT l

This report documents the technical evaluation of the adequacy of the station electric distribution system voltages for the Nine Mile Point Nuclear Station, Unit 1. The evaluation is to determine if the onsite distri-bution system in conjunction with the offsite power sources has sufficient capacity to automatically start and operate all Class lE loads within the equipment voltage ratings under certain conditions established by the Nuclear Regulatory Commission. The analysis submitted demonstrates that the station's electric distribution system supplies adequate voltage to the Class 1E equip-ment under worst case conditions.

FOREWORD This report is supplied as part of the Selected Operating Reactor Issues Program II being conducted for the U. S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation, Division of Licensing, by Lawrence Livermore National Laboratory. ,

The U. S. Nuclear Regulatory Commission funded the work under the authorization entitled " Selected Operating Reactor Issues Program II,"

B&R 20 19 10 11 1, FIN No. A-0250.

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1 TABLE OF CONTEh"IS

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1. INTRODUCTION . . . ,. . '. . . . . . . . . . 1

2. DESIGN BASIS CRITERIA . . . . . . . . . . . . 2

3. SYSTEM DESCRIPTION . . . . . . . . . . . . . 2

4. ANALYSIS . . . . . . . . . . . . . . . 4 4.1 Analysis Conditio2s . . . . . . . . . 4 4.2 Analysis Results . . . . . . . . . . 4 4.2.1 Overvoltage . . . . . . . . . . . 6 4.2.2 Undervoltage . . . . . . . . . . . 6 4.3 Analysis Verification . . . . . . . . . 6

5. EVALUATION . . . . . . . . . . . . . . .' 6

6. CONCLUSION . . . . . . . . . . . . . . .. 8-REFERENCES . . . . . . . . . .. . . . . . . 9 ILLUSTRATIONS

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FIGURE 1 Nine Mile Point Nuclear Station, Unit 1 ,

Electrical One-Line Diagram . . . . . . . . . . - t 3 TABLE 1 Nine Mile Point Nuclear Station, Unit 1 '*

Class lE Equipment Voltages Ratings and Analyzed Worst Case Terminal Voltages. . . . . . . 5

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TECHNICAL EVALUATION REPORT ON THE ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES FOR THE NINE MILE POINT NUCLEAR STATION, UNIT 1 (Docket No. 50-220)

James C. Selan Lawrence Livermore National Laboratory, Nevada

1. INTRODUCTION The Nuclear Regulatory Commission (NRC) by a letter dated August 8, 1979 [Ref. 1] expanded its generic review of the adequacy of the station electric distribution systems for all operating nuclear power facilities. This review is to determine if the onsite distribution system in conjunction with the offsite power sources has sufficient capacity and -

capability to automatically start and operate all required safety loads within the equipment voltage ratings. In addition, the NRC requested each licensee to follow suggested guidelines and to meet certain requirements in the analysis. These requirements are detailed in Section 5 of this report. ,

By letters dated September 27, 1982 [Ref. 2] January 28, 1983

[Ref. 3], March 31, 1983 [Ref. 4], and a telephone conference on May 18, 1983 [Ref. 5], Niagara Mohawk Power Corporation, the licensee, submitted their analysis and conclusion regarding the adequacy of the electric distribution system voltages at Nine Mile Point Nuclear Station, Unit 1.

The purpose of this report is to evaluate.the licensee's submittal with respect to the NRC criteria and present the reviewer's conclusion on the adequacy of the station electric distribution systems to maintain the voltage within the design limits of the required Class lE equipment for the worst case starting and load conditions.

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2. DESIGN BASIS CRITERIA The design basis criteria that were applied in determining the adequacy of station electric distribution system voltages to start and operate all required safety loads within their required voltage ratings are as follows:

(1) General Design Criterion 17 (CDC 17), " Electric Power Systens," of Appendix A, " General Design Criteria for Nuclear Power Plants," in the Code of Federal Regulations, Title 10, Part 50 (10 CFR 50) {Ref. 6].

(2) General Design Criterion 13 (GDC 13), " Instrumentation and Control," of Appendix A, " General Design Criteria for Nuclear Power Plants," in the Code of Federal Regulations, Title 10, Part 50 (10 CFR 50) [Ref. 6].

(3) ANSI C84.1-1977, " Voltage Ratings for Electric Power Systems and Equipment" [Ref. 7].

(4) IEEE Std 308-1974, " Class lE Power Systems for Nuclear Power Generating Stations" [Ref. 8].

(5) " Guidelines for Voltage Drop Caiculations," Enclosure 2, to NRC letter dated August 8, 1979 [Ref. 1].

3. SYSTEM DESCRIFTION An electrical one-line diagram of the Class IE distribution systc for Nine Mile Point, Unit 1, is shown in Figure 1. This diagram is a simpli-fied form ot the updated one-line cobmitted in Reference 3. The electrical systen is designed such that during normal plant operation, the non-Class lE quxiliary systems are supplied by station service transformer (SST) No. 10 from the unit generator. The Class 1E auxiliary systems are supplied by reserve station transformers (RSST) 101N and 101S from the 115 kV system at all times (except when supplied by the emergency diesels). During unit startup, shutdown, refueling, or when SST No. 10 is out of service, the non-Class 1E auxiliary systems are then supplied by the RSST's. Automatic transfer of station auxiliaries from the SST to the RSST's will occur for low voltage, generator trip, or accident conditions. An interlock on the supply breakers to power board (PB) 101 prevent supplying power simultaneously to the power board from RSST 10lN and 101S. However, a bypass (operator controlled) exists which allows for the live bus transfer to either RSST 10lN or 10lS without tripping off the connected Joads (such as the condensate pump, reactor recir-culating pump, feedwater booster pump, etc.). Bypassing of the interlock coincident with a loss of either RSST will not enable the supplying of power to both PB 102 and PB 103 with the remaining RSST.

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TABLE 1 NINE MILE POINT, UNIT 1 CLASS 1E EQUIPMENT VOLTAGE RATINGS AND ANALY2ED WORST CASE TERMINAL VOLTAGES (in % of Equipment Nominal Voltage Ratlng)

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Rated Analyzed Rated Analyzed Nominal Voltage Rating Steady Steady Equipment (100%) State State Transient Motors 4000 Start (a) 82.6 Operate 110 106.9 90 91.8 550(b)

Start (a) 82.3 Operate 110 110 90 92.0 Starters 600/120 Pickup (c) 84.6 Dropout (c) 75.0 Operate 110 110 ,

85 91.4 Other(d)

Equipment (a) The capability of Class lE motors to start with bus voltage levels down to 85% of rated voltage was demonstrated during the 1981 diesel generator load sequence test [Ref. 4].

(b) Selected 575-volt Class 1E motors will be rewound or replaced to 550-volt nameplate rating where teruinal voltages were found to be unacceptable

[Ref. 3],

(c) Starter coils cupplied from 600/120 transformers (5:1 ratio). Size 1 starters have pickup voltage of 83 volts and drop out voltage of 64 volts.

Size 2 starters have pickup voltage of 91 volts and dropout voltage of 77 volts.

(d) From PB 167 through a 112.5 kVA transformer (4.6:1 ratio), the secondary voltage of 107 to 131 volts is equivalent to 495 to 605 volts (90-110% of 550 volts). From PB 102 and PB 103 through a 5 kVA transformer, the secon-dary voltage of 104 to 127 volta is equivalent to 3600 to 4400 volts (90-110% of 4000. volts). Tests indicated equipment would operate with a min-imum voltage of 90 volts.

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4.2.1 overvoltage

Offsite grid voltage of 121.41 kV (both 115 kV lines' in service), non-safety auxiliaries supplied by the SST, PB 101 supplied by RSST 10lS, all pumps off on PB 102 and minimum load on PB 16 (control rod drive pump and MG sets).

4.2.2 Undervoltage

Offsite grid voltage of 111.8 kV with a single 115 kV line in service (Lighthouse Hill), maximum load occt'rs two minutes after unit trip coincident with an accident, all Class 1E equipment has sequenced on and operating followed by the starting of the 2500 Hp reactor feedwater pump. Normal station auxiliary loads have completed transfer from SST to RSST.

The analysis results for the worst-case undervoltage condition indi-cated that several motors rated at 575 volts would have to be replaced or rewound to 550-volt rating to meet the -10% design ratings. Those motors to be replaced or rewound are the diesel 102 air compressors 1 and 2 on both redundant load grcupa, motors 1 and 2 for water chillers 11 and 12 and chilled water circulating pumps 11 and 12 [Ref. 3]. These motors are to be rewound by the end of the 1984' refueling outage. In additica to the above motor rerating/ replacement, the analyses also indicated that several cable feeders exhibited large voltage drops from PB 16B. Additional evaluations and a computer re-analysis with measured load currents showed a worst case voltage drop of only 2.0% would occur.

Since this voltage drop was considered acceptable and provided no voltage limitations on the equipment, cable upgrading was not required.

4.3 ANALYSIS VERIFICATION Niagara Mohawk Power Corporation verified their analytical results by performing several tests. Tests were performed for each RSST with at least a 50% loading and a 50% loading on 600-volt power boards 16B annd 17B. Recording meters were used to record electrical parameters prior to and during various load starting conditions. Analysis results for the same condition were compared to actual recorded parameters. The worst case percentage errors for steady state conditions were -0.48% on the 4160-volt base and 1.22% on the 600-volt base.

Under transient conditions, the worst-case percentage errors were -1.37% on the 4160-volt base and -2.07% on the 600-volt base. In all the test cases the test results sere higher (negative percentage error) than the analytical which demon-strates that the load flow models are conservative.

5. EVALUATION l

! The NRC generic letter [Ref. 1] stated several requirements that the plant must meet in the voltage analysis. These requirements and an evaluation of the licensee's submittals are as follows: ,

(1) With the minimum expected grid voltage and manimum load condi-tion, each offsite source and distribution system connection l

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e must be capable of starting and continuously operating all Class LE equipment within the equipment's voltage ratings.

The voltage analysie submitted by Niagara Mohawk Power .

Corporation has shown that each offsite cource connection to the onsite distribution system has the capacity and capability to start and continuously operate all Class lE i equipment (with selected 575-volt motors revound to 550-volt '

rating) within the equipment's voltage design ratings under

worst case cenditions.

1 (E) With the maximus expected of fsite grid voltage and minimum load condition, each offsite source and distribution system connection must be capable of continuously operating the required Class lE equipment without exceeding the equipment's voltage ratings.

The voltage analysis submitted demonstrated that the design rating of the Class 1E equipment will not be exceeded under worst case conditions of maximum grid voltage and minimum i plant load. l (3) The analysis must show that there will be no spurious sepa-ration from the offsite power source to the Class 1E buses by the valtage protection relays when the grid is within the normal expected limits and the loading conditions established by the NRC are being met.

The voltage analysis submitted demohstrated that the worst case voltage transients were not of such magnitude and duration to cause spurious separations from the of fsite sources under worst case conditions.

(4) Test results are required to verify the voltage analyses calcu-lations submitted.

Niagara Mohawk Power Corporation verified their analytica?

• results by test which demonstrated that the load flow model is conservative with an acceptable percentage error difference.

(5) Review the plant's electrical power systems to determine if any events or conditions could result in the simultaneous or conse-quential loss of both offsite circuits to the onsite distribution system (compliance with GDC 17).

The licensee has identified that a fault within the bus disconnect

, switch assembly between the two 115 kV transuission lines (see l Figure 1) could result in the loss of both offsite circuits.

Should this event occur, the onsita sources could be used until the switch can be isolated (approximately 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />) at which time at least one offsite source could be restored [Ref. 3]. However, l

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GDC 17 Criterion assumes the " loss of all onsite alternating current power supplies." The licensee submitted documenta-tion [Ref. 9], for the 10 CyR 50 Appendia."R" review which demonstrated core cooling can be provided by the isolation condenser (no electrical power available) for 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> without providing makeup water. This ensures that the reactor could be maintair.ed in a safe condition until the restoration (approxi-mately 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />) of at least one offsite source (delayed) is

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accomplished for supplying power to the Class 1E equipment.

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6. CONCLUSIONS l

Based on the information submitted by Niagara Mohawk Power Corporation for the Nine Mile Point Nuclear Station, Unit 1, it is conc,1uded that:

(1) The offsite power source in conjunction with the onsite distri-bution system has the capacity and capability to supply voltage to the Class lE equipment within the voltage design ratings under worst case condition with selected 575-volt motors replaced or rewound with a 550 vole rating.

(2) Spurious tripping from the offsite pources will not occur under the worst-case conditions analyzed.

(3) The Class lE equipment's maximum voltage design limit will not be exceeded under maximum grid voltage minimum plant load conditions.

(4) Acceptable test verifications were made to verify the analytical data submitted.

(5) Additional studies should be made by the licensee on the single event identified which could cause the loss of both offsite circuits. The licensee is required to submit any plans of action or design changes which would reduce the possibility of a switch fault from simultaneously interrupting both of fsite power sources.

Accordingly, I recommend that the NRC accept the voltage analyses submitted which demonstrates the adequacy of voltage to the Class lE equipment for starting and continuous operation under worst case conditions.

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l REFERENCES j

1. NRC letter (W. Gammill) to all power reactor licensees, dated August 8, 1979.

2. Niagara Mohawk Power Corporation letter (T. E. Lempges) to NRC (D. B. Vassallo),

dated September 27, 1982. l

3. Niagara Mohawk Power Corporation letter (C. V. Mangan) to NRC (D. B. Vassallo),

dated January 28, 1983.

4. Niagra Mohawk Power Corporation letter (C. V. Mangan) to NRC (D. B. Vassallo),

dated March 31, 1983.

5. Telecon, B. Hermin (liRC), M. Mosier and L. Blasiak (Niagra Mohawk Power Corp.)

and J. Selan (LLNL), dated May 18, 1983.

6. Code of Federal Regulations, T*.tle 10, Part 50 (10 CFR 50), General Design Criterion 13 and 17 of Appendix A for Nuclear Power Plants.

7. ANSI C84.1-1977, " Voltage Ratings for Electric Power Systems and Equipment."

8. IEEE Std. 308-1971, " Class lE Power Systems for Nuclear Power Generating Stations."

9. Nine Mile Point, Unit 1, Appendix "R" Review Safe Shutdown Analysis (Chapter V) letter to the NRC, dated October, 1982.

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