ML20049J814
| ML20049J814 | |
| Person / Time | |
|---|---|
| Site: | Kewaunee  |
| Issue date: | 02/28/1982 |
| From: | Udy A, Udy C EG&G, INC. |
| To: | Prevatte R Office of Nuclear Reactor Regulation |
| References | |
| CON-FIN-A-6429 EGG-EA-5694, NUDOCS 8203290118 | |
| Download: ML20049J814 (12) | |
Text
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. ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES, KEWAUNEE NUCLEAR POWER PLANT 4fod j;gfg
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._ th This is an Informal report Intended for use as a preliminary or working document Prepared for the U. S. Nuclear Regulatory Comission Under DOE Contract No. DE-AC07-761001570 FIN No. A6429 y E G n G ,a n.
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n E #daho. Inc FORM EGSG-398 (Rev. Il41) INTERIM REPORT Accession No. Report No. EGG-EA-5694 o Contract Program or Project
Title:
Selected Operating Reactor Issues Program (III)
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Subject of this Document: Adequacy of Station Electric Distribution System Voltages, Kewaunee Nuclear Power Plant Type of Document: Informal report Author (s): A. C. Udy Date of Document: February 1982 Responsible NRCIDOE Individual and NRCIDOE Office or Division: R. L. Prevatte, Division of Systems Integration, NRC This document was prepared primarily for preliminary orinternal use. it has not received full review and approval. Since there may be substantive changes, this document should not be considered final. EG&G Idaho, Inc. Idaho Falls, Idaho 83415 9 Prepared for the
. U.S. Nuclear Regulatory Commission Washington, D.C.
Under DOE Contract No. DE-AC07 761D01570 NRC FIN No. A6429 INTERIM REPORT l _ _ _
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] ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES KEWAUNEE NUCLEAR POWER PLANT 1 4 i
- February 1982 A. C. Udy Reliability and Statistics Branch
, Engineering Analysis Division
- EG&G Idaho, Inc.
1 i i l i i 0 i
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) TAC No. 12994 i Docket No. 50-305 i 4 I _ . . _ _ , - _ _ _ - . . _ . . . . _ _ . . _ . ~ , _ _ _ . . _ - _ . - _ . _ _ _ _ _ _ . _ _ . _ _ _ _ - . , _ _ . . . _ . . _ _ . - , , _ . . . . . _ _ _
i 4 t ABSTRACT g. The EG&G Idaho, Inc. report reviews the capacity and the capability of the onsite distribution system at the Kewaunee Nuclear Power Plant, in con-1 junction with the offsite power sources, to automatically start and con-tinuously operate all required safety loads. FOREWORD This report is supplied as part of the " Selected Operating Reactor Issues Program (III)" beir.g conducted for the U.S. Nuclear Regulatory 1 Commission, Office of Nuclear Reactor Regulation, Division of Licensing, by EG&G Idaho, Inc., Reliability and Statistics Branch. The U.S. Nuclear Regulatory Commission funded the work under B&R 20 19 01 16, FIN No. A6429. l i l l l 4 i i
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i i CONTENTS
1.0 INTRODUCTION
.................................................... 1
] 2.0 DESIGN BASIS CRITERIA ........................................... 1 3.0 SYSTEM DESCRIPTION .............................................. 2
- 4.0 ANALYSIS DESCRIPTION ............................................ 2 4.1 An alys i s Con d i t io n s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
/ 4.2 Analysis Results .......................................... 4 4.3 Analysis Verification ..................................... 5 5.0 EVALUATION ...................................................... 5
6.0 CONCLUSION
S ..................................................... 6 )
7.0 REFERENCES
...................................................... 7 FIGURE
- 1. Kewaunee unit one-line diagram................................... 3 1
4 TABLE
- 1. Class 1E equipment voltage ratings and analyzed worst case load termi nal vol tages . . . . . . . . . . . . . . . . . . . . . . 4
- 2. Comparison of analyzed voltages and undervoltage relay setpoints ................................................. 6 i
l . O 4 i 4 1 4 i iii
ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM V0LTAGES KEWAUNEE NUCLEAR POWER PLANT
1.0 INTRODUCTION
An event at the Arkansas Nuclear One station on September 16, 1978 is described in NRC IE Information Notice No. 79-04. As a result of this event, station conformance to General Design Criteria (GDC) 17 is being questioned at all nuclear power stations. The NRC, in the generic letter
, of August 8 1979, " Adequacy of Station Electric Distribution Systems i Vol tages ," required each licensee to confirm, by analysis, the adecuacy of the voltage at the Class lE loads. This letter included 13 specif'ic guidelines to be followed in determining if the load terminal voltage is adequate to start and continuously operate the Class lE loads.
Wisconsin Pu October 11,1979.glicWPSCo Service Company (WPSCo) responded with an analysis on clari lett r dated December 22,1980.{iedandenlargedtheirresponsewitha An additional submittal, dated May 1, 1981 resultedfromfurthergRCquestioning. Letters of September 19, 1979 and September 15, 1976 also contain information on equipment ratings and voltage conditions. A meeting between WPSCo and the NR 14, 1981 provided further information for this report.7. C on October WPSCo provided addi information requested at this meeting on November 30,1981,gional wM additional follow-up material submitted on Feburary 1,1982.g Based on the information supplied by WPSCo, this report addresses the capacity and capability of the onsite distribution system of the Kewaunee Nuclear Power Plant, in conjunction with the offsite power system, to main-tain the voltage for the required Class 1E equipment within acceptable limits for the worst-case starting and load conditions. I 2.0 DESIGN BASIS CRITERIA The positions applied in determining the acceptability of the offsite voltage conditions in supplying power to the Class lE equipment are derived from the following:
- 1. General Design Criterion 17 (GDC 17), " Electrical Power Systems,"
of Appendix A, " General Design Criteria for Nuclear Power Plants," of 10 CFR 50.
- 2. General Design Criterion 5 (GDC 5), " Sharing of Structures, Sys-tems, and Components," of Appendix A, " General Design Criteria for Nuclear Power Plants," of 10 CFR 50.
- 3. General Design Criterion 13 (GDC 13), " Instrumentation and l Control," of Appendix A, " General Design Criteria for Nuclear
- Power Plants," of 10 CFR 50.
- I J
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- 4. IEEE Standard 308-1974 " Class 1E Power Systems for Nuclear Power !
Generating Stations." ,
- 5. Staff positions as de datedAugust8,1979.jailedinalettersenttothelicensee,
- 6. ANSI C84.1-1977, " Voltage Ratings for Electric Power Systems and Equipment (60 Hz) t SixrgviewpositionshavebeenestablishedfromtheNRCanalysis guidelines and the above-listed documents. These positions are stated in Section 5.0.
3.0 SYSTEM DESCRIPTION Figure 1 is a simplified sketch of the unit one-line diagram taken from Figure 8.2-2 of the Kewaunee Final Safety Analysis Report (FSAR). It shows that the 4160V Class lE buses can be supplied offsite power by either the Reserve Auxillary Transformer (RAT) or the Tertiary Reserve Transformer (TAT). Additionally, there is a tie between buses 1-5 and 1-6. This bus tie is controlled by interlocks and administrative procedures, and is used only hen all power sources to a bus, including the diesel-generator, are lost Buses 1-5 and 1-6 each supply power to two 480V Class lE buses by separate transformers. Buses 1-51 and 1-61 can also be connected together, as can buses 1-52 and 1-62. However, technical specifications 3.7.a.4 and 3.7.a.5 prevent use of the 480V bus ties during operation. FSAR Figure 8.2-3 shows that the 120V instrument buses that use inverters for their normal power source can be powered, as an alternate source, from instrument transformers by Class lE buses 1-52 and 1-62. These instrument transformers normally supply one independent 120V AC instrument bus. 1.0 ANALYSIS DESCRIPTION 4.1 Analysis Conditions. WPSCo has determined by analysis that the maximun expected offsite grid voltage for the Reserve Auxiliary Transformer is 141.6kV and the minimum is 134.4kV. WPSCo has also determined that the maximum expected grid voltage for the Tertiary Reserve Transformer is 14.2kV and the minimum is 13.4kV. WPSCo has analyzed each offsite source to the onsite distribution system under extremes of load and offsite voltage conditions to determine
- the terminal voltages to the Class lE equipment. The worst case Class IE equipment terminal voltages occur under the following conditions:
a) The minimum steady state voltage occurs just after a unit trip from full power operation coincident with a safety injection, with only the 138kV grid available at a minimum expected voltage of 134.4kV. 2 l
345 KV SWITCHYARD ( D I 345/138/13.8 KV l N AUT0 TRANSFORMER 345 KV SWITCHYARD s VIA MAIN 13.8 KV TRANSFORMER ( 138 KV
/ TERTIARY RESERVE RESERVE AUXILIARY MAIN TRANSFORMER TRANSFORMER AUXILIARY WW WA' TRANSFORMER DG DG lA IB l-1 1-2 1-3 1-4 1-5 1-6 4160V 4160V 4160V 4160V 4160V 4160V C ASS CLASS lE us us us us 1-51 1-52 1-62 1-61 480V 480V 480V 480V b) E [] E b) E b] E KEWAUNEE UNIT ONE LINE DIAGRAM FIGURE 1 3
b) The maximum steady state voltage occurs with normal operating loads and both offsite power grids at their maximum expected voltages. This results in the lightest loading of the Class lE buses. c) The minimum expected transient voltage occurs with the manual start of a reactor coolant pump under the same conditions in a). WPSCo assumed that there would be no voltage drop in the equipment , feeder cables. 4.2 Analysis Results. Table 1 shows the projected worst case Class lE ~ equipment terminal voltages. TABLE 1. CLASS 1E EQUIPMENT VOLTAGE RATINGS AND ANALYZED WORST CASE TERMINAL VOLTAGES (% of nominal voltage) Maximum Minimum Analyzed Equipment Condition Rated Analyzed Rated Steady State Transient 4000V Motors Start -- -- 80 -- 93.7 Operate 110 109.5 90 98.8 -- 460V Motors Start -- -- 80 -- a Operate 110 109.8 90 90 -- 440V Motors Start -- -- 80 -- a Operate 110 110.5b 90 94.1 -- 480V Starters Pickup -- -- a -- a Dropout -- -- a -- a Operate a 105.2 a 86.2 -- Other Equipment ll5V AC Operate 110 104.4 90 90 -- instruments
- a. In lieu of analyzed voltage, WPSCO states that the transient voltage dips during analyzed conditions are less sev when sequence loading the diesel generators.gre It is shownthan that transient all voltage dips motors start, and the 480V starters do not drop out under more restrictive voltage conditions than analyzed. .
- b. This is in excess of the equipment rating, however it neglects the feeder cable voltage drop. With this voltage drop, the equipment would not be connected to a voltage in excess of its rating.
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Additionally, the 480V battery chargers are rated to 90% of 480V. The voltage they can be supplied with is 90% of 460V (86.2% of 480V), without challenging the degraded voltage relays. This could draw upon the capacity of the station batteries. The DC output of the battery chargers is diode isolatedfromtheDCbusandthelowestexpectedcgargeroutputvoltageis 1-1/2 volts less than the nominal battery voltage. As the battery dis-charges,ortheinputvoltagetothebatterychargerisjmproved,thebat- Failure of the tery charger would again pick up the load on the DC bus. battery chargers does not occur under minimum analyzed voltages. As a result of this review, WPSCo is verifying (replacing as necessary) that the safeguard motor MCC heaters will not trip their load ~ during the worst postulated voltage and time associated with the undervoltage relaying at the Kewaunee Station. 4.3 Analysis Verification. WPSCO has tested to verify the accuracy of the analysis assumptions. 480V Motor Cont ol Center (MCC) 1-52F was loaded at 160 amperes. The bus voltage at 480V bus 1-52 and the MCC was measured. The motor terminal voltage at selected energized loads was also measured. The measured voltages were then compared with calculated voltages using the same analysis methods used in the analysis. The test verifica-tion showed the analysis values to be within 0.55% of the actual voltage. 5.0 EVALUATION Six review positions have been established from the NRC analysis guide-linesI and the documents listed in Section 2.0 of this report. Each review position is stated below followed by an evaluation of the licensee submittals. Position 1--With the minimum expected offsite grid voltage and maximum load condition, each offsite source and distribution system connection combination must be capable of starting and of continuously operating all Class lE equipment within the equipment voltage ratings. WPSCo has shown, by analysis, that the Kewaunee Station has suffi-cient capability and capacity for continuously operating the Class 1: loads within the equipment voltage ratings (Table 1). Position 2--With the maximum expected offsite grid voltage and minimum load condition, each offsite source and distribution system connection combination must be capable of continuously operating the required Class lE o equipment without exceeding the equipment voltage ratings. WPSCo has shown, by analysis, that the voltage ratings of the Class lE equipment will not be exceeded. Position 3--Loss of offsite power to either of the redundant Class lE distribution systems due to operation of voltage protection relays, must not occur when the offsite power source is within expected voltage limits. 5
As shown in Table 2, undervoltage relays will not cause the loss of the Class lE distribution system when the offsite grid voltage is within the expected voltage limits. TABLE 2. COMPARIS0N OF ANALYZED VOLTAGES AND UNDERV0LTAGE RELAY SETPOINTS (% of nominal voltage) a Minimum Analyzed Relay Setpoint t location / Relays Voltage Time Voltage (Tolerance) 11me 4160V bus ~ Degraded grid 98.8 continuous 95 (+2 5m Loss of grid 93.7 20s 87.5-( ) 2-1/2 s
- a. L1censee has determined by analysis the minimum bus voltages with the offsite grid at the minimum expected voltage and the worst case plant and Class lE loads.
Position 4--The NRC letterl requires that test results verify the accuracy of the voltage analyses supplied. WPSCO has performed an acceptable test of their Class lE distribution system that verifies the accuracy of their analysis assumptions. Position 5--No event or condition should result in the simultaneous or consequential loss of both required circuits from the offsite power network to the onsite distribution system (GDC 17). WPSCo has analyzed the connections of the Kcwaunee station to the offsite power grid, and has determined that no potential exists for the simultaneous or consequential loss of both circuits from the offsite grid. Position 6--As required by GDC 5, each offsite source shared between units in a multi-uqit station must be capable of supplying adequate start-ing and operating voltage for all required Class 1E loads with an accident in one unit and an orderly shutdown and cooldown in the remaining units. This applies to multi-unit stations. It does not apply to Kewaunee, a
- single-unit station.
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6.0 CONCLUSION
S . The voltage analyses submitted by WPSCo for the Kewaunee Plant were evaluated in Section 5.0 of this report. It was found that:
- 1. Voltages within the operating limits of the Class lE equipment are supplied for all projected combinations of plant load and offsite power grid conditions, i
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- 2. The test used to verify the analysis shows the analysis to be an accurate representation of the worst case conditions analyzed.
- 3. WPSCO has determined that no potential for either a simultanous or consequential loss of both offsite power sources exists.
- 4. Loss of offsite power to Class lE buses, due to spurious opera-tion of voltage protection relays, will not occur with the off-
, site grid voltage within its expected limits.
7.0 REFERENCES
- l. NRC letter, William Gammill, to All Power Reactor Licensees (Except Humboldt Bay), " Adequacy of Station Electric Distribution Systems Voltage," August 8,1979.
- 2. WPSCo letter, E. R. Mathews to A. Schwencer, NRC, " Adequacy of Station Electric Distribution Systems Voltages," October 11, 1979. ,
- 3. WPSCo letter, E. R. Mathews to S. A. Varga, NRC, " Letter from Mr.
Varga to Mr. E. R. Mathews dated August 21, 1980," December 22, 1980.
- 4. WPSCo letter, E. R. Mathews to S. A. Varga, NRC, " Degraded Grid Volt-age Protection Technical Specifications and Responses to March 13, 1981, Letter from S. A. Varga to E. R. Mathews," May 1,1981, NRC-81-64.
- 5. WPSCo letter, E. R. Mathews to A. Schweneer, NRC, " Degraded Grid Voltage Questions," September 19, 1979.
- 6. WPSCo letter, E. W. James to Office of Nuclear Reactor Regulation, NRC, September 15, 1976.
- 7. NRC Memorandum, S. Maskell to R. Licciardo, " Conference on Degraded Grid Voltage Protection for the Kewaunee Nuclear Power Plant,"
October 22, 1981.
- 8. WPSCo letter, E. R. Mathews to S. A. Varga, NRC, " Degraded Grid Voltage," November 30, 1981, NRC-81-192.
- 9. WPSCo letter, E. R. Mathews to S. A. Varga, NRC, February 1, 1982, NRC-82-19.
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