ML20009F171

Adequacy of Station Electric Distribution Sys Voltages, Brunswick Nuclear Power Station Units 1 & 2, Technical Evaluation Rept

ML20009F171
Person / Time
Site:	Brunswick
Issue date:	06/30/1981
From:	Weber D EG&G IDAHO, INC., EG&G, INC.
To:	Schemanski P Office of Nuclear Reactor Regulation
References
CON-FIN-A-6429 EGG-EA-5389, NUDOCS 8107300047
Download: ML20009F171 (8)

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This is at 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. A6429 8107300047 810630 PleR RES Y Maho 8107300047 PDR

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INTERIM REPORT Accession No.

Report No. EGG-EA-5389 Contract Program or Project

Title:

Selected Operating Reactors Issues Program (III)

.. Subject of this Document:

Adequacy of Station Electric Distribution System Voltages, Brunswick Nuclear Power Station Units 1 and 2, Docket Nos. 50-325 and 50-32

Type of Document:

Technical Evaluation Report Author (s): ' --

• r D. A. Weber '1l C 3' 0SearC1 anC ec,nica Assistance Report Dit3 of Document:

June 1981 R:sponsible 14RC Individual and NRC Office or Division:

Paul C. Shemanski, Division of Licensing This document was prepared prima ily for prelimina y 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 83415

. Prepared for the U.S. Nuclear Regulatory Commission Washington, D.C.

Under DOE Contract No. DE AC07 76lD01570 NRC HN I4o. A6429 INTERIM REPORT

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0313J ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES BRUNSWICK NUCLEAR POWER STATION UNITS 1 AND 2 Docket Nos. 50-325 and 50-324 June 1981 D. A. Weber Reliability and Statistics Branch Engineering Analysis Division EG&G Idaho, Inc.

TAC Nos. 12829 and 12830

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ABSTRACT' The 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 equipment voltage ratings.

This Technical Evaluation Report reviews the submittals.for the Brunswick Nuclear Power. Station.

The offsite power sources, in conjunction with the onsite distribution system, have been shown to have sufficient capacity and capability to. auto- '

matically start as well as continuously 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 supplied as part of the " Selected Operating Reactor Issues Program (III)" being conducted for the U.S. Nuclear Regulatory -

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 the authorization, B&R 20 19 01 06, FIN No. A6429.

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CONTENTS

1.0 INTRODUCTION

...................................................... 1 2 . 0 0 E S I G N B AS I 'i CR I T ER I A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

, 3.0 -SYST M DESCRIPTION ................................................ 2 4.0 ANALYSIS DESCRIPTION .............................................. 2 4.1 Analysis Conditions .......................................... 2~

4.2 Analysis Results ............................................. 4 4.3 Analysis Verification .................. ..................... 4 4

5.0 EVALUATION ........................................................ 4

6.0 CONCLUSION

S ....................................................... 7

7.0 REFERENCES

........................................................ -7 FIGURE 1

1. Brunswick Nuclear Power Station electrical single-line diagram ........................................................... 3 TABLES

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

2. Comparison of Analyzed Voltages and Undervoltage Relay Setpoints ...................................... 6 7

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g ADEOUACY OF STATION ELECTRIC OISTRIBUTION SYSTEM VOLTAGES I

SRUNSWICK NUCLEAR POWER STATION UNITS NO. 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 all nuclear power stations. The NRC, in-the generic letter of Augu ages,"{t8,1979,"AdequacyofStationElectric-Distribution'SystemsVolt-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.

The Carolina P on October 8,197 .gwer ' andsubmittal, This Light Ccmpany ICP&L) responded the sucmittals of, July 24,to1980, the NRC }etter 15,1980,)' Decemoer 2, 1980,3 February 16, 19810, April 9, Octobyr 1981, the EG&G Idas:0, In degraded grid protection,g.,and report on theSafety the Final Brunswick Units Analysis -1 and Report (FSAR) 2 complete the information reviewed for this report.

Based on the information supplied by CP&L, this report acdresses the capacity and capability of the onsite distribution system of the Brunswick Nuclear Power Station, in conjunction with the offsite power system, to maintain the voltage for the requireo class lE equioment within acceptable limits for the worst-case starting and load conditions.

2.0 OESIGN BASIS CRITERIA

.The positions applied in determining the acceptability of the cffsite voltage conditions in supplying power to the class lE equipment are derived from the followirg:

1. General Design Criterion 17 (GDC 17), " Electrical Power Systems,"

of Aapendix 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 Ccmponents," of Apoendix A, " General Design Criteria

, for Nuclear Power Plants," of 10 CFR 50.

3. General Design Criterion 13 (GDC 13), " Instrumentation and Con-

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

4. IEEE Standard 308-1974, " Class IE Pcwer Systems for Nuclear Pcwer Generating Stations."

5. Staff positions as de datedAugust8,1979.{aileainalettersenttothelicensee, 1

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

jixreviewpositionshavebeenestablishedfromtheNRCanalysisguide-

-lines cod the above-listed documents. These' positions are stated in Section . 0.

3.0 SYSTEM DESCRIPTION A single-line diagram of the AC electrical distribution system at -

Brunswick Units 1 and 2 is shown in Figure 1. The breaker positions, open or closed, are shown for normal full-power plant operation. ,

The following system description pertains to Unit 2; Unit 1 is similar.

During normal full-power plant operations, the 1E and non-lE distribu-tion systems are supplied from the Unit Auxiliary Transformer 2 (UAT-2).

The Common B bus distribution system is supplied by the Startup Auxiliary Transformer 2 (SAT-2). Protection relays or a unit trip results in the automatic fast transfer of loads from the UAT to the Startup Auxiliary Transformer 2 (SAT-2). The SAT can be supplied from two independent 230kV sources (not shown).

The lE distribution system consists of two independent and redundant trains; each train capable of supplying the required emergency loads.

The lE 4160V buses supply the 4kV motors, 4160-480/277V unit substa-tions E7 and E8, and 480V motor control centers (MCCs) and their loads.

Control circuits for the 4160V circuit breakers are supplied from the 125/250V DC battery system and from individual 480/120V control power transformers for the MCC control circuits and circuit breakers.

Regarding Unit and ous tie breakers, CP&L states that (a) the tie breaker between non-lE Bus 28 and Bus IB can only be closed if one of the incoming bus breakers from the SATs in Unit 2 or Unit 1 is open and one of the disconnect links (2A91 in Unit 2 or lA91 in Unit 1) is removed, (b) the tie breaker between non-lE 4160V Common 8 of Unit 2 and Common A of Unit 1 can only be closed if the incoming bus line breaker to one of the buses is open, (c) the IE tie breakers between IE 4160V E4 or E2 and between E3 and El are normally open, and an accident signal will cause them to trip should they be closed, and (d) the disconnected and racked out.}E The 480V tietiebreakers between breakers between E4E7 E8 and and E3 have been (not shown) are normally open. ,

4.0 ANALYSIS DESCRIPTION 4.1 Analysis Conditions. CP&L has determined, by load flow studies -

and review of recordings, that the maximum expected offsite 230kV grid voltage is 234.6kV (1.02 pu) and the minimum 220.8kV (0.96 pu).

CP&L has analyzed each offsite source to the onsite distribution system under extremes of load and offsite voltage conditions to determine the 2

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terminal voltages to 1E equipment. The worst case class.lE equipment ter-

minal. voltages occur under..the following conditions

4 i- 1. The max 1 mum voltages occur when the 230kV grid isfat its maximum value, Unit 1 is shut down, and SAT-2 is supplying the minimum i plant auxiliary loads.  !

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, 2. _The minimum steady-state ' voltage 1 occur when the 230kV g"id is st j its minimum value concurrent with a LOCA in Unit:2 and t. simul-

, taneous shutdown cooling of Unit 1, and SAT-2 is supplying all -

i Unit 2 lE.and non-lE loads and the non-lE-loads from Unit 1 Com-

! mon A bus (tie breaker between Common B and Common A bus closed j and all other tie breakers open). *

3. The-minimum transient voltages occur under conditions of 2 above,

'except for the starting of all RHR and Core Spray System pumps

due to the LOCA in Unit 2 and simultaneous shutdown of Unit 1.

1 4.2 Analysis Result. Table I shows the projected worst case class lE equipment terminal voltages. Table 2 shows a cgmparison of the analyzed 2

voltages with the undervoltage relay setpoints.o The analyzed values in

.these tables are calculated from information supplied by CP&L.

4.3 Analysis Verification. The CP&L letter of October 15, 1980, 4 describes the test to be used to verify the analysis. A telecon on ,

~l December 19, 1980,9 provided additional information. Steady state volt-age measurements will be made at the lE buses and 230kV grid. Then, one of the non-lE 4kV circulating water pumps will-be started followed by the

j. start of one of the lE 460V screen wash pumps. The 230kV measured grid f voltage will be used as a basis for calculating the voltages at the lE 1

buses. The calculated voltages will then be compared with the measured

. voltages. The test was performe resultssubmittedApril9,1981.pneartheendofJanuary1981andthe

! 5.0 EVALUATION i

Six rpview positions have been established from the NRC analysis 4

guidelines' and the documents listed in Section 2.0 of this report. Each review-position is stated followed by an evaluation of the licensee i submittals.

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 operating all 1 class IE equipment within the equipment voltage ratings.

1 l CP&L has shown, by analysis, that the Brunswick Nuclear Power Station

• i has sufficient capability and capacity for starting and continuously oper-

! ating the class lE loads witi.in the equipment voltage ratings (Table 1).

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r TABLE 1 CLASS lE EQUIPMENT. VOLTAGE RATINGS AND ANALYZED WORST CASE TERMINAL VOLTAGES

(% of nominal voltage)

Maximum' Minimum a

Analyzed b c Eauipment Condition Rated Analyzed Rated Steady State Transient 4000V t'otors Start -- -- 75. -

76 Operate 110 lild 90 92.7 --

460V Motors Start -- --

85 --

72.39 Operate 110 llld 90 89.6 --

480V Starters Pickup -- --

85 --

70 Dropout -- --

70 --

70 Operate 110 107 85 86.5 --

Other Pickup -- --

-90 --

70.2 Equipmente Dropout -- --

70 --

70.2 Operate 110 ll6d 90 90 --

a. Analyzed voltages corrected for minimum grid voltage of 96%.

b. Analyzed voltages corrected for maximum grid voltage of 102%.

c. Transient due to start of 4kV motors: other IE equipment is operat-ing. 460V motor transient = 84.4%

d. When the units are tripped, the switchyard voltage is expected to' drop to 98%, which would result in voltages below the 110% maximum equipment safety.

e. All relay coils, solenoids, and instruments.6 f

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TABLE 2 COMPARIS0N OF ANALYZED V0LTAGES AND UNDERVOLTAGE RELAY SETPOINTS

(% of nominal voltage)

Minimum Analyzed a Relay Setpoint E Location / Relays Voltage Time Voltage (Tolerance) Time s 4160V busa Degraded grid 89.8 continuous 89.5 0.2 10 sec i 0.5 Loss of grid 74.87 less than 71.0 t 4.0 10 sec 10 sec9

a. Licensee has determined by analysis the minimum bus voltages with the offsite grid at the minimum expected voltage and the war st case plant and class lE loads.

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 equipment without exceeding the equipment voltage ratings.

CP&L has shown, by analysi , tnat the voltage ratings of the class IE equipment will not be exceeded.

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

As shown in Table 2, voltage relays will not cause loss of c! ass lE distribution systems when the Offsite grid voltage is within expt:cted volt-age limits. Also, see position 6.

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

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This position is satisfied as CP&L's test 7 verified the accuracy or the analysis. The equipment loading was sufficient to provide reasonable instrument readings and the maximum error between the measured and ..

calculated values was within the instrumentation error.

Position 5--No event or condition should result ir the simultaneous or consequential loss of both requirad circuits from the offsite power network to the onsite distribution system (GDC 17).

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r CP&L has analyzed the IE connections to the offsite power grid, and determined that no potential exists for simultaneous or c01 sequential loss f both circuits from the offsite grid.

Position 6--As required by G0C 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 Brunswick Nuclear Power Station is the site of two nuclear units.

CP&L has indicated tnat the tie breaker between Units 1 and 2 is open o during normal full-power operations 3 except that the tie breaker between Common A and Common B may be closedbe9 The status and use of these tie breakers is described in Section 3.0 of this report. Included in the CP&L analysis is the case where SAT-2 is supplying all Unit 2 loads with the tie breaker between Common A and Common 8 bus closed and a LOCA in Unit 2 and a f alse LOCA ignal in Unit 1.6 It should be noted that the CP&L analysis considers terminal voltages to non-lE equipment as well as lE equipment.

Although Tables 1 and 2 (based on a grid voltage of 0.96 nu) snow satis-factory voltages for the lE equipment, the CP&L report recognizes degraded conditions for non-lE equipment, which indicates that the switchyard volt-age should not be degraded below 97.2%. Therefore, CP&L has proposed modi-fications should the grid degrade to 97.2% and tne tie cr eaker between Common A bus and Common B bus is closed. These modifications would improve the minimum values noted in Tables 1 and 2.

6.0 CONCLUSION

S The voltage analyses submitted by CP&L for the Brunswick Nuclear Power Station were evaluated in Section 5.0 of this raport. It was found that:

1. Voltages within the operatir.g 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.

'. 2. CP&L's test has verified the accuracy of their analysis.

3. CP&L has determined tr.;t no potential for either a simultaneous or consequential loss of both offsite power sources exists.

, 4. Loss of offsite powe" 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

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

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2. CP&L letter, E. E. Ut ey, to Office of Nuclear Reactor Regulation, October 8, 1979.

3. CP&L letter, E. E. 'Jtley, to Office of Nuclear Reactor Regulation, July 24, 1980.

4 CP&L letter, E. E. Utley, to Office of Nuclear Reactor Regulation, October 15, 1980.

5. CP&L letter, E. E. Ut.ey, to Office of Nuclear Reactor Regulation,

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December 2, 1980.

6. CP&L letter, E. E. Utley, to Office of Nuclear Reactor Regulation,

• February 16, 1981.

7. CF6L letter, E. E. Utley, to Office of uclear Reactor Regulation, April 9, 1981.

8. EG&G, " Technical Evaluation Report of the Degraded Grid Protection for Class lE Power Systems for the Brunswick Steam Electric Plant Units No. I and 2," February 1980.

9. Telecon, O. A. Weber, EG&G Idaho, Inc., D. C. Stadler, CP&L, December 12, 1980.

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