ML20003C106

Technical Evaluation Rept,Adequacy of Station Electrical Distribution Sys Voltages,Dc Cook Nuclear Station Units 2 & 3, Preliminary Rept

ML20003C106
Person / Time
Site:	Cook
Issue date:	01/31/1981
From:	Weber D EG&G IDAHO, INC., EG&G, INC.
To:	Shemanski P Office of Nuclear Reactor Regulation
References
CON-FIN-A-6256 EGG-EA-5339, NUDOCS 8102260634
Download: ML20003C106 (14)

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.lanuary 1981 TECHNICAL EVALUATION REPORT, ADEQUACY OF STATION ELECTRICAL DISTRIBUTION SYSTEM VOLTAGES, D. C. COOK *

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1 This is an informal report intended for use as a preliminary or working document Prepared for the U.S. Nuclear Regulatory Commission Under DOE Contract No. DE-AC07-76ID01570 FIN No. A6256 gggg .

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t%e il#9 INTERIM REPORT Accession No Report No. EGG-EA-5339 Contract Program or Project

Title:

Electrical, Instrumentation and Control System Sul.; ort '

Subject of this Document:

Adequacy of S*.ation Electrical Distribution System Voltages, D. C. Cook Nuclear Station, Units 1 and 2 Type of Document:

Technical Evaluaticn Report Author (s):

D. . s.ese, NRC Researc1 anc Technical Assistance Report

. oa,e o, ooc men,.

January 1981 Responsible NRC Individual and NRC Office or Division:

Paul C. Shemenski, Division of Licensing This document was prepared pnmarily for preliminary or internal 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 63415 Prepared for the U.S. Nuclear Regulatory Commission Washington, D.C.

Under DOE Contract No. DE-AC07 76f D01570 NRC FIN No. A6256 INTERIM REPORT

2190F ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES D. C. COOK NUCLEAR PLANT UNIT NOS. 1 AND 2 Docket Nos. 50-315 and 50-316 January 1981 D. A. Weber Reliability and Statistics Branch Engineering Analysis Division EG6G Idaho, Inc.

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l Draft 1-14-81 TAC Nos. 13111 and 13112 L

ABSTRACT Ine Nuclear Regulatory Commission has required all licensees to analyze the electric power system at each nuclear station. This review is to deter-mine 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 squipment voltage ratings.

This Technical Evaluatioa Report reviews the submittals for the D. C. Cook Nuclear Power Station.

The offsite power sources, in conjunction with the onsite distribution system, have been shown to have sufficient capacity and capability to con-tinuously operate all required safety related loads, within the equipment -

rated voltage limits, in the event of either an anticipated transient or an accident condition. .

FOREWORD This report is s 7 plied as part of the selected Electrical, Instrumen-tation, and Control Systems (EICS) issues program being conducted for tne i

U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation, Division of Operating Reactors, by EG6G Idaho, Inc., Reliability and Statis-tics Branch.

The U.S. Nuclear Regulatory Commission funded the work under the auth-orization entitled " Electrical, Instrumentation, and Control System Sup-port," B&R 20 19 01 03, FIN No. A6256.

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CONfENTS

1.0 INTRODUCTION

...................................................... 1 2.0 DESIGN BASIS CRITERIA ............................................. 1 3.0 SYSTEM DESCRIPTION ................................................ 2 4.0 ANALYSIS DESCRIPTION .............................................. 4 4.1 Design /Operati.on Changes ..................................... 4 4.2 Analysis Conditions .......................................... 4 4.3 Analysis Results ............................................. 5 4.4 Analysis Verification ........................................ 5 5.0 EVALUATION ........................................................ 6

6.0 CONCLUSION

S ....................................................... 8 7.0 REF E REN C E S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 FIGURE

1. D. C. Cook Unit 1 electrical single-line diagram .................. 3 TABLES

1. Class IE Equipment Voltage Ratings and Analyzed Worst Case Load Terminal Voltages ........................ 5

2. Comparison of Analyzed Voltages and Undervoltage Relay Setpoints ...................................... 6 e

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ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES D. C. COOK NUCLEAR PORER STATION UNIT NOS. 1 AND 2

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 ali nuclear power stations. The NRC, in the generic letter of August 8, 1979, " Adequacy of Station Electric Distribution Systems Volt-ages," I required each licensee to confirm, by analysis, the adequacy of the voltage at the class lE loads. This letter included 13 specific guide-lines to be followed in determining if the load terminal voltage is adequate to start and continuously operate the class lE loads.

In response to the generic letter and questions from the staff, Indiana and Michigan Electric Company (IMECo) submitted information and analysis on December 17, 1979, and May 28, 1980.3 These submittals, the EG6C Idaho, Inc., report on tne D. C. Cook Unit I degraded grid protection, and the D. C. Cook Unit 1 Final Safety Analysis Report complete the infor-mation reviewed for this report.

Based on the information supplied by IMECo, this report addresass the capacity and capability of the onsite distribution system of the D. C. Cook Nuclear Power Station, in conjunction with the offsite power system, to maintain the voltage for the required class IE equipment within acceptable

limits for the worst-case starting and load conditions.

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Tne discussion and evaluation which follows will apply to both units.

= 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:

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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 struc- .

tures, Syarems, 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 Control," of Appendix A, " General Design Criteria for Nuclear Power Plants," of 10 CFR 50.

4. IEEE Standard 308-1974, " Class lE Power Systema for Nuclear Power Generating Stati s."

5. Staff positions as detailed in a letter sent to the licensee, dated August H, 1979.1

6. ANSI C84.1-1977, "Voir. age Ratings for Electric Power Systems and Equipment (60 Hz)."

Six review positions have been established from the NRC analysis guide-I lines and the above-listed documents. These positions are stated in ,

Section 5.0.

3.0 SYSTEM DESCRIPTION Figure 1 of this report is a simplified sketch of the D. C. Cook Unit I single-line diagram.

Bath safety trains of each unit can be supplied from three sources:

the " normal", " preferred", and " alternate" auxiliary sources.

With the unit producing power, the " normal" auxiliary power to each safety train is supplied from the unit generator via transformers 1-AB and 1-CD (2-AB and 2-CD for Unit 2). A unit trip results in automatic transfer to the " preferred" auxiliary source via TR-4 or TR-5 and TR-101-AB and TR-101-CD (IR-201-AB and TR-201-CD for Unit 2). After the unit generator dis connec t links have been removed, the safety buses can be supplied from the " normal" auxiliary power source via TR-1 (TR-2 for Unit 2). TR-12-EP is an " alternate" auxiliary power source to both units.

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Each 4160V bus supplies power to the 4kV motors, 600V load centers and motor control centers (MCCs), and the 575V motors and loads. The breaker control circuits for the 4160V switchgear and the 600V load centers are supplied by the station batteries and are indepei. dent of grid voltages. -

The MCC control circuits receive their control power from individual control power transformers.

IMECo supplied the equipment operating ranges identified in Table 1.

4.0 ANALYSIS DESCRIPTION 4.1 Design / Operation Changes. The voltages shown on Table 1 are baaed on the following licensee proposed changes:

1. Change the tap setting on TR-12-EP (alternate power source) from the 67kV tap to the 68.8kV tap.

2. Install undervoltage protection on the 4kV buses A and .

D for Unit 1 and 2 with a voltage setting of 89.9% for two minutes.4 .

3. Modify the existing undervoltage relays at the 4kV buses for a voltage setting of 79.9% for two seconds.

4.2 Analysis Conditions. IMEco has determined by load flow studies and review of historical data that the maximum expected offsite grid volt-age is 795.6kV, 370kV, and 72.45kV and the minimum is 744.35kV, 347kV, and 64.86kV on the 765kV, 370kV, and 69kV offsite sources, respectively.

EMECo has analyzed each offsite source to the onsite distribution system under extremes of load and offsite voltage conditions to determine the terminal voltages to IE equipment. The worst case class IE equipment terminal voltages occur under the following conditions:

1. The maximum voltage occurs when the 69kV " alternate" source is at its maximum expected value and surplying ~

the accident loads of one unit and the shutdown loads of the other unit'with TR-12-EP supplying one train in .

each unit.

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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 -- --

85 --

87.3 Operate 110 111 90 93.3 --

575V Motors Start -- --

85 --

78.1 t Operate 110 107 90 90.4 --

600V Starters Pickup -- --

85 --

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'(575V. base) Dropout -- --

70 --

78.1 Operate 110 107 90 90.4 --

Other Equipment e

a. 69kV " alternate" auxiliary source at 105%.

- . b. 345kV " preferred" auxiliary sources at minimum of 100.6%.

c. ~All other' safety-related electrical, instrumentation, and control equip-4 ment' required for safe shutdown will operate properly within a voltage 1

range of 90% to 110% of nominal or of the 575V base as applicable-1

2. - The minimum steady state voltage occurs when the 3451.V source-is at'its1 minimum expected value and TR-5 is supplying the accident-loads of one tmit and the shat-down loads'of the other unit.

3. The worst case transient voltages occur when the 345kV source is at,its minimum expected-value and TR-5 ia supplying the accident-loads of one unit, the shutd7wn loada of the other. unit, and the accident loads are bulk! started.

4.3 Analysis Result. Table 1 shows. the projected worst case class IE

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- equipment terminal voltages. . Table 2-shows a comparison of the analyzed

_ voltages with the1 undervoltage relay setpoints.

4 . 4' Analysis Verification. During a'startup of Unit 2, while Unit 1 Lwas at; power, measured voltage,1 current, and phase angle readings were made Y .I c

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TABLE 2 COMPARISON OF ANALYZED VOLTAGES AND UNDERVOLTAGE RELAY SE POINTS

(% of nominal voltage) -

Minimum Analyzed Relay Setpoint Location / Relays Voltage Time Voltage (Tolerance) Time 4160V bus Db (4kV base)

Degraded grid 93.3 continuous 89.9 + 5 2 min

+ 6 see Loss of grid 87.3 c 79.9 + 5 2 sec

+ 0.2 sec

a. Licensee 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,

b. Undervoltage relays are on bus A and D. The analyzed data is for bus D which represents the worst case. ,

c. Transient durations not provided, but the degraded grid undervoltage setpoint of two minutes is long enough to override any voltage dips

• caused by the starting of large motors or bulk loads, by IMECo at the " preferred" offsite power substation bus, the " alternate" offsite power sustation bus, and at the Unit 2 auxiliary buses. The measured values for current and voltages were employed as input data on the power distribution model previously used to compute the bus voltage levels at the auxiliary buses. Specifically, the 345kV (TR-5 feed) bus measured voltage and IE bus currents were used to calculate the voltages at the 34.5kV, 4kV, and 600V buses. These calculated voltages were then compared with the actual measured voltages. The results showed a maximum 2% error at the 600V level.

5.0 EVALUATION Six review positions have been established from the NRC analysis guide- ,

lines and the documents listed in Section 2.0 of this report. Each review position is stated below followed by an evaluation of the licensee 6

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i submittals. The evaluations are based on completion of changes described

- in Section 4.1.

Position 1--With the minimum expected offsite grid voltage and maximum load condition, each offsite source and distribution system connection

j. combination must be capable of starting and of continuously opetacing all class 1E equipment within the equipment voltage ratings.

i IMECo has shown, by analysis, that the offsite sources and the onsite I distribution system have sufficient capability and capacity for starting and continuously operating the class 1E loads within the equipment voltage I 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 1E equipment without exct.? ding the equipment voltage ratings, i .

IMECo has shown, by analysis, that the voltage ratings of the class 1E

- equipment-wil1~not be exceeded (Table 11.

Position 3--Loss of offsite power to either of the redundant class 1E distribution systems due'to operation of voltage protection relays, must not occur when the offsite power source is within expected voltage limits.  !

As sh'own in Table 2, voltage relays will not cause loss of class 1E "

- distribution systems; when the offsite grid voltage is within expected volt- ,

c ' age ' limits ..

t Position 4--The NRC letter requires that test results verify the accuracy of the voltage . analyses supplied.

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Review of the test. data submitted by IMEco indicates that the original

_ analysis is satisfactory. The. largest difference between the measured and calculated. voltage was 2% at two of.the-600V IE buses with.the. measured

- voltage llessEthan-the calculated voltage. The review considered plant

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loading conditions, instrumentation errors, and the 1.15 service factor for all class lE motors. The results are applicable to Unit 1 based on similar loading conditions and identical onsite distribution systems. .

Position 5--No event or condition should result in tne simultaneous or

• consequential loss of both required circuits f rom the of f site power network to tne onsite distribution system (GDC 17).

IMECo has analyzed the onsite connections to the offsite power grid, and determined that no potential exists for simultaneous or consequential loss of both circuits from the off site grid.

Position 6--As required by GDC 5, each offsite source shared between units in a multi-unit station must be capable of supplying adequate starting and operating voltage for all required class lE loads with an accident in one unit and an orderly shutdown and cooldown in the remaining units. .

The D. C. Cook Nuclear Station is the site of two nuclear units that -

can be supplied from these offsite cources where two of the sources are shared between units.

The IMECo analysis satisfies this position in that each shared effsite source was found to be capable of supplying adequate voltages to all class 'lE loads with a shutdown in one unit and an accident in the other.

6.0 CONCLUSION

S The voltage analyses submitted by IMEco for the D. C. Cook Nuclear Power Station were evaluated in Section 5.0 of this report. Upon the completion of changes described in Section 4.1, it was found tnat:

l. Voltages within the operating limits of the class lE -

equipment are supplied for all projected combinations of plant load and normal offsite power grid conditions; including an accident.in one unit and the safe shutdown ,

of the other unit.

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2. The test used to verify the analysis shows the analyses to have accurately determined the worst case conditions analyzed.

3. IMECo 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 spuri-ous operation of voltage protection relays, will not occur with the offsite grid voltage within its expected limits.

7.0 REFERENCES

1. NRC letter, William Gammill, to All Power Reactor Licensees (Except Humboldt Bay), " Adequacy of Station Electric Distribution Systems Voltage," Av3ust 8, 1979.

2. IMECo letter, J. E. Dolan, to Director of Nuclear Regulation, dated October 17, 1979.

3. IMEco letter, J. E. Dolan, to Director of Nuclear Regulation, dated May 28, 1980.

4. "EG&G Technical Evaluation Report on the Degraded Grid Protection for Class lE Power Systems for the D. C. Cook Nuclear Plant Unit 1,"

Rev. 1, dated August 1980.

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