ML19336A600

Adequacy of Station Electric Distribution Sys Voltages, Trojan Nuclear Power Station, Interim Rept

ML19336A600
Person / Time
Site:	Trojan File:Portland General Electric icon.png
Issue date:	09/30/1980
From:	Udy A EG&G IDAHO, INC., EG&G, INC.
To:	Shemanski P Office of Nuclear Reactor Regulation
References
CON-FIN-A-6256 EGG-EA-5252, TAC-12957, TAC-48370, NUDOCS 8010300225
Download: ML19336A600 (15)

Text

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A p E G e G,o.u..

Ff6M EG&G 396 (Rev 11 m INTERIM REPORT Accession No.

Report No. EGG-EA-5252 C::ntract Program or Project

Title:

Electrical, Instrumentation and tontrol System Support Subject of this Document Adequacy of Station Electric Dist ribution System Voltages, Trojan Nuclear Power Station, Docket No. 50-344, TAC 10. 12957 Type of Document:

Informal Report Author (s):

A. C. Udy

- Drta of Document:

September 1960 R::sponsible NRC Individual and NRC Office or Division:

Paul C. Shemanski, Division of Licensing This document was prepared primarily 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 83415 Prepared for the U.S. Nuclear Regulatory Commission Washington, D.C.

Under DOE Contract No. DE-AC07-761D01570 NRC FIN No. A6256 INTERIM REPORT hf O

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. TECHNICAL EVALUATION REPORT' ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES' p

TROJAN NUCLEAR POWER STATION Docket No. 50-344 i.

September 1980

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A. C. Udy Reliability and Statistics Branch Engineering Analysis Division EG&G Idaho,-Inc.

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TAC No. 12957-

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ABSTRACT i

The Nuclear Regulatory Commission has required all licensees to analyze the electric-power system at each nuclear station. This review is to deter-

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1 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 ratirgs.

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

i The offsite power sources, in conjunction with the onsite distribution system, has been shown to have sufficient capacity and capability to auto-matica11y 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.

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-FOREWORD.

This report is supplied as part of the selected Electrical, Instru-

~ mentation, and. Control Systems'(EICS) issues program being conducted for the' U.S. Nuclest Regulatory Commission, Office of Nuclear Reactor Regula-J tion,' Division of Operating Reactors, by EG&C Idaho, Inc., Reliability and Statistics Branch..

i The U.S. Nuclear Regulatory Commission funded ti - work under the auth--

k orization entitled " Electrical, Instrumentation, and Control System Sup-i.

port," B&R.20 19 01 03,- FIN No. A6256.

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CONTENTS 4

1.0 INTRODUCTION

1-2.0 DES IGN B AS I S CRITERIA -........................

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3.0 SYSTEM DESCRIPTION 2

4.0' ANALYS'IS DESCRIPTION 4

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4.1 Analysis' Conditions-4 1

i 4.2.' Analysis kesults 6

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4.3-Analysis Verification:

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]i 5.0 EVALUATION 7-6.0 ' CONCLUSIONS.

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7.0 REFERENCES

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FIGURE

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Trojan unit single-line diagram.

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TABLE i

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Trojan Nuclear' Power Station I

Class ' lE Equipment Voltage Ratings ~ and l

Worst Case Available Load Terminal Voltages 5-1 i

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I TECHNICAL EVALUATION REPORT ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM. VOLTAGES TROJAN NUCLEAR POWER STATION

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 gen'eric letter of August 8,1979, " Adequacy of Station Electric Distribution Systems Volt-ages," l required each licensee to confirmi by' analysis, the adequacy of

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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.

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Portland General Electric Company (PGE) supplied an analysis for this i

2 review in a letter 'of October 5,1979.

Information supplied'on g

3 January 11, 1980, subsequent additional analysis submitted for this 4

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' review on -February 25, 1980 and on June 30, 1980, and telephone con-6 versations in September 1980 complete the information reviewed for this report.

i Based on the information supplied by PGE, this report addresses the capacity and capability of the onsite distribution system of the Trojan Nuclear Power Station, in conjunction with the offsite power system, to maintain the voltage for the required class lE-equipment within accept-able limits for the worst-case starting and load conditions.

2.0 DESIGN BASIS CRITERIA s

The positions applied'in determining.the-acceptability.of the offsite voltage conditions in-supplying power to the. class IE equipment are derived

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/ General Design Criterion 17 (GDC 17), " Electrical Power Systems," of Appendix A, " General Design Criteria for Nuclear Power Plants," of 10 CFR 50

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General Design criterion 5 (GDC 5), " Sharing of struc-tures, Systems, and Components," of Appendix A, " General Design Criteria.-for, Nuclear Power Plants," of 10 CFR 50 i

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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 1E Power Systems for Nuclear Power Generating Stations" 5.

Staff positions as detailed in a-letter sent to the licensee, dated August 8, 1979I 6.

ANSI C84.1-1977, " Voltage Ratings for Electric Power Systems and Equipment.(69 Hz)."

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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.

3.0 SYSTEM DESCRIPTION Section 8.1.2 of the Trojan Final Safety Analysis Report (FSAR) and Part II of Reference 2 discuss the onsite distribution system. Figure 1 of this report is a simplified sketch of the unit single-line diagram taken f rom Figure 8.3-1 of the FSAR.

Normal Operation of the unit has the main generator supplying power to all plant loads (class 1E and non-class 1E) through the unit auxiliary transformer (UAT)

The plant loads remain ~ powered by the unit generator for the duration of the 30-second time delay after a reactor trip, before a unit trip occurs. Class IE loads' required by any design basis accident (DBA) would be sequenced onto the UAT during this 30-second period.

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22KV unit generator-230KV grid

~230KV grid-

-startup W

W W startup transformerm a

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. r q auxiliary mm transformer El 0

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unit substation WW W W unit substation transformer #1 transformer #2 TGG ;

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lE - 480V lE.- 480V lE - 480V 1E - 480V 3

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-TROJAN NUCLEAR STATION' One-Line Diagram-3

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Followiag a unit trip,' the plant auxiliary load has a fast transfer from the UAT to the'two startup transformers (SUT). The power to the

.DBA equipment 1is dropped,;and is again sequentially loaded. Upon failure of an SUT, use of' the unit generator disconnect link allows the main unit transformer and the UAT>to supply offsite power to the auxiliary and class 1E loads. This is not specifically prohibited by Technical Specifications.

Each SUI normally supplies, as the preferred source, power for one redundant safety train and one-half of the plant auxiliary loads. However, as can be seen in Figure 1, an intertie between 4160V busea A5 and A6 exists. However, Technical Speciricction limiting conditions of operation limit the use of this intertie. ~ Trojan periodic operating test POT-21-2 verifies that interties are not used.

PGE supplied the equipment operating ranges identified in Table 1.

4.0 ANALYSIS DESCRIPTION r

4.1 Analysis Conditions. PGE has provided analyses for various con-ditions.2,5 The analysis for each condition was for the buses aligned to the normal source of power without use of bus interties. Since the Techni-cal Specification 3.8.2.1, prohibits use of the interties between redundant buses during operation, the use of the interties between the class IE buses were not analyzed.

2 Among the conditions PGE used for their analysis are the' following:

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The startup. transformer tap will be the nominal tap for operating conditions,-the +2.5% tap for shutdown condi-tions,;however, PGE supplied analyses for the nominal tap for both the operating and the shutdown modes i-2.

The unit-. auxiliary. transformer tap will'be the nominal tap for operating conditions l

Auxiliary. loads, as' used in this report, refers to non-class 1E loads, a.

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TABLE 1 TROJAN NUCLEAR POWER STATION CLASS lE EQUIPMENT VOLTAGE RATINGS AND WORST CASE AVAILABLE LOAD TERMINAL VOLTAGES (in % of equipment nominal voltage rating)

Maximum Minimum Minimum Steady State Steady State Transient Equipment Nominal Voltage Rating Rated Analyzed" Rated Analyzed" Rated Analyzed a 4000V motor 110 109.5 90 96.2 70 85.4 460V motor 110 108.7 90 90.2 70 77.6 480V motor contactors pickupb c

87.5 89.4 87.5 74.4 b

dropout c

55 89.4 55 74.4 less than 480Vd The analyzed voltages are the extremes of the analyses provided by PGE, a.

using both the start-up and the unit auxiliary transformers as sole sources.

b.

These analyzed voltages for the motor contactors are at the 480V bus.

c.

The maximum voltage the 480V contactors can withstand was not provided by PGE.

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No analysis was provided for 120V AC instrumentation, as these are supplied power from inverters whose regulated output is independent of the other class lE AC buses.

3.

A load survey determined shutdown load requirements 4.

The reactor coolant pumps and heater drain pumps are considered as not tripped after the plant trip 5.

The normal plant auxiliary _ considers the following equipment as not operating:

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Fire pump b.

Control rod drive motors (not operating after a plant trip) c.

Containment spray pump d.

Charging pump 5

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. Safety injection pump-f.

Residual heat removal pump g.

-Room fans for the-above pumps 6.

Analyses-for both the unit auxiliary ~ transformers and the start-up= transformers were provided by PGE

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For the worst-case transient voltage degradation, PGE analyzed for the-start of a circulating water pump when all the' safety loads were operating.

4.2 Analysis Results. PGE has provided analyses as required by the NRC letter. While a grid vo:tage of 235kV was identified as the histor-ical low, 230kV was used for the analysis since the second level of under-voltage protection relays operate at this level.5 The historical high

-grid voltage, 240kV, was used for the maximum voltage analysis.

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Table 1 shows the worst case voltage leve1s identified from the PG1 analyses. The analyses show that all class 1E loads are capable of starting and continuously operating over a grid voltage range that is wider than the historical grid voltage range at the Trojan station.

A brief condition while starting a circuisting water pump.when the unit buses already fully loaded will. prevent contactor pickup for the 480V

.MCC loads until the voltage recovers. It will not cause contactor dropout or spurious shedding of any loads.

4.- 3 Analysis Verification. PGE verified the computer analysis.

This was done by measuring the unit generator voltage and by taking volt-age, current, and power factor measurements on auxiliary buses H1 and A5, class 1E buses A1, B01, and B03, class 1E MCC buses B21, B23, and B25, and on service water pumps P-148A and P-148C, while the Trojan unit was opera-ting at 100% capacity. All except one of the measured buses (B23, a 480V MCC) were loaded at greater than 29% of the maximum expected bus load.

Bus Bij was loaded at-19%.

The measured generator voltage and the measured loads were used in the analysis program to determine the bus and the equipment voltages. The 6

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measured voltages were then compared to the calculated voltages. The anal-ysis program accurately models the class IE distribution system, as the calculated and the. measured voltages were within +0.58% of each other.

'5.0 EVALUATION-Six. review positions have been established from the NRC analysis guide-I lines and the documents listed in Section 2 of this report. Each review position _is stated below followed by an evaluation of the licensee l

submittals.

i Position 1--With the minimum expected' offsite grid voltage and maximum load condition, each offsite source and distribution system connection combiniation must be capable of starting and of continuously operating all class 1E equipment within the rated equipment voltages.

PCE has shown, by analysis, that the Trojan unit has sufficient capa-bility and capacity for starting and continuously operating the safety related 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 rated equipment voltage.

PGE has shown, by analysis, that the voltage ratings.of the class lE equipment are not 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 off site' power source is within analyzed voltage limits.

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EG6G Idaho, Inc., will verify, in a separate report, that the require-ments of this position are satisfied (TAC No. 07328).

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

PGE-has supplied the required information which shows the calcula-tions to be conservative for all of the class lE buses and loads. The test was performed using the unit auxiliary transformer rather than the start-up transformer. However, the analysis cases using both transformers are in close correlation, so the test results are considered valid.

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).

PGE has analyzed the Trojan connections to the offsite power grid, and determined that no potential exists for violation of GDC 17.

PGE states:

i "As designed, the offsite power source does not violate I

(the) GDC 17 requirement to provide two physically independent circuits designed and located to assure a reliable offsite power source for the Trojan plant."

Position 6--As required by GDC 5, each offsite source" shared between units in a multi-unit station must be capable of supplying adequate star ing and operating voltage for.all required class IE loads with an accident in 4

one unit and an orderly shutdown and cooldown in the remaining units.

This applies to multi-unit plants. It does not apply to the single-unit Trojan station.

6.0 CONCLUSION

S The analyses submitted by PCE for this review were evaluated as stated in Section 5 of this report. These submittals show:

l Section 8.1.1 of IEEE Standard 308 permits the use of a single source a.

of 'offsite power to be shared between units of a multi-unit station.

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-The test used to verify the analysis shows the analyses to be an accurate representation of the worst case conditions anayzed 2.

Voltages within the operating limits of the class 1E equipment are supplied for all projected combinations of plant load and offsite power grid conditions 3.

PGE has determined that no potential for either a-simultanous or consequential loss' of both offsite power sources exists.

However, PGE has not verified that the voltage transient caused by starting large non-class lE londs will not shed the class 1E buses during a safety injection. EG&G Idaho Inc., is performing a separate review of the under-voltage relay protection at the Trojan station. This will evaluate the relay setpoints and time delays to determine that spurious tripping of the safety related loads will not occur with normal offsite source voltages.

7.0 REFERENCES

1.

NRC letter,. '?811iam Gammill, to All Power Reactor Licensees (Except Humboldt Bays, " Adequacy of Station Electric Distribution Systems Voltage," August 8, 1979.

2.

PGE letter, C. Goodwin, Jr., to Director of Nuclear Reactor Regulation, l

dated October 5, 1979.

3.

PGE letter, C. Goodwin, Jr.,'to Director of Nuclear Reactor Regulation.

i dated January 11, 1980.

4.

PGE letter, C..Goodwin, Jr., to Director of Nuclear Reactor Regulation, dated February 25, 1980.

1 5.

PGE letter, C. Goodwin, Jr., to Director of Nuclear Reactor Regulation,

. dated June 30, 1980.

6.

Telecon,-C. Trammell, U.S. NRC, A. Udy, EG&G Idaho, Inc., Ken Murakami, PGE, September 16 and 17, 1980, 1

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