ML18086A821
| ML18086A821 | |
| Person / Time | |
|---|---|
| Site: | Salem  |
| Issue date: | 06/30/1981 |
| From: | Weber D EG&G IDAHO, INC., EG&G, INC. |
| To: | Shemanski P Office of Nuclear Reactor Regulation |
| References | |
| CON-FIN-A-6429 EGG-EA-5380, NUDOCS 8107290248 | |
| Download: ML18086A821 (13) | |
Text
ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES, SALEM NUCLEAR POWER STATION UNITS l AND 2, DOCKET NOS. 50-272 AND 50-311 NRC Rese_arch and Technical Assistance Report
- D. A. Weber U.S~ Department of Energy EGG-EA-5380 June 1981 Idaho Operations Office
- Idaho National Enpine_er"ioQ Labora_tory __ -'---~ __ __ _ _
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I NOTICE -
1 This is an informal report intended for use a~ I I
Prepared for th~
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U. S. Nuclear Regulatory Commission1 Under DOE Contract No. DE-AC07-76ID\\ 1 FIN No. A6429 I
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RECORDS FACILITY BRANCH n
~~ EGl:..G Idaho
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n
FORM EG&G-398 (Rev. 11-79)
INTERIM REPORT Accession No. -------'--
Report No.
EGG-EA-5380 Contract Program or Project
Title:
Selected Operating Reactors Issues Program (III)
Subject of this Document:
Adequacy of Station Electric Distribution System Voltages, Salem Nuclear Power Station, Units 1 and 2, Docket Nos. 50-272 and 50-311 Type of Document:
Technical Evaluation Report Author(s):
D. A. Weber NRC Research and Technica\\
Assistance Report Date of Document:
June 1981
- Responsible 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, thi_s document should not be considered final.
EG&G Idaho, Inc.
Idaho Falls, Idaho 8341S Prepared for the U.S. Nuclear Regulatory Commission Washington, D.C.
Under DOE Contract No. DE-AC07-761001570 NRC FIN No. 86429 INTERIM REPORT
ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES SALEM NUCLEAR POWER STATION UNITS 1 AND 2 Docket Nos. 50-272 and 50-311
&lune. 1981 D. A. Weber Reliability and Statistics Branch Engineering Analysis Division EG&G Idaho, Inc.
0322J TAC No. 13009
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 ~nd capability to automatically start and operate all required safety loads within the equipment voltage ratings.
This Technical Evaluation Report reviews the submitt~ls for the Salem Nuc-1 ear Power Station.
The offsite power sources, in conjunction with th~ onsite distribution system, have been shown to have sufficient capacity and capability to continuously operate all required safety related loads, within the equip-ment rated voltage limits, in the event of either an anticipated transient or an accident condition. However, a sustained degraded grid may result in spurious separation of class lE buses from the offsite source when one 500/13.BkV Station Power Transformer is supplying all loads of both units.
FOREWORD This report is supplied as part of the "Selected Operating Reactor Issues Program (UI) 11 being conducted for the U.S. Regulatory Commission, Office.of Nuclear Reactor Regulation, Division of Operating Reactors, by EG&G Idaho, Inc., Reliability and Statistics Branch.
The U.S. Nuclear Regulatory Commission funded the work u*nder the authorization, B&R 20 19 01 16, FIN No. A6429.
ii
CONTENTS 1.O INTRODUCTION......................................................
2.0 DESIGN BASIS CRITERIA *.**..*.**....*****.**..*****.*.**.****.**.**
3.0 SYSTEM DESCRIPTION.*.****......*......***....*..*.**.***.*.***.***
-2 4.0 ANALYSIS DESCRIPTION.*******...*.....*.***.*..**.**..*****.***..*.
2
- 4. l Analysis Conditions................ ~.........................
2 4 * ?
An a 1 ys i s Res u 1 ts ***.************* ~ ******** *. * * * * * * * * * * * * * * * * *
- 4 4.3 Analysis Verification.***.*..*****************........*.*..**
4 5
- 0 E VAL UA TI 0 N. * * * *. * *... * * *. * * *....... * * *.... * *.. * * * * * *. *.. * * * * * * * * *..
4 6.0 cor~CLUSIONS.**.*.*.***....**....*...**.***.****.*. *.****.**.**.***.
7
- 7. 0 REFERENCES........................................................
FIGURE
- l.
Salem Nuclear Power Station Units 1 and 2 electrical single-line diagram showing circuit breaker alignment 8
for normal operations...***.****..****.******.**..*..****.**..**..*
3 TABLES Class lE Equipment Voltage Ratings and Analyzed Worst Case Load Terminal Voltages
- 2.
Comparison of Analyzed Vriltages with 5
the Undervoltage Relay Setpoints.*.**.***.*****.*.****.** ** *.***.*
6 i i i
ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES SALEM NUCLEAR POWER STATION UNITS 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.
7~-04. As a result of thi~
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, 11Adequacy of Station Electric Distribution Systems Volt-ages, 11 *1 required each licensee to confirm, by analysis, the adequacy of the voltage at the class lE loads. This letter included 13 specific guide-1 ines to be followed in determining if the load terminal voltage is adequate to start and continuously operate the class lE loads.
Public Service Electric and Gas Company (PSE&G) responded to the NRC letter on March 3, 1980.3. This submittal submittals of October 10, 1979,2 September 24, 1980,4 Jun~ 16, 1981,~ the NRC letter of January 19, 1981,6 and the Final Safety Analysis Report (FSAR) complete the information reviewed for this report.
Based on the information supplied by PSE&G, this report. addresses.the capacity and capabi.lity of the onsite distribution system -0f the Salem Nuclear Power Station, in conjunction with the offsite power system, to maintain the voltage for the required class lE equipment within acceptable limits for the worst-case starting and load conditions.
2.0 DESIGN BASIS CRITERIA The positions applied in determining the qCceptability of the offsite voltage conditions in supplying power to the class lE equipment are derived from the following:
- 2.
.3.
- 4.
- 5.
General Design Criterion 17 (GDC 17),
11Electrical Power
- Systems, 11 of Appendix A, 11General Design Criteria for Nuclear Power Plants, 11 of 10 CFR 50.
General Design Criterion 5 (GDC 5), "Sharing of Struc-tures, Systems, and Components, 11 of Appendix A, 11General Design Criteria for.Nuclear Power Plants," of 10 CFR 50.
General Design Criterion 13 (GDC 13), "Instrumentation and Control, 11 of Appendix A, 11General Design Criteria for Nuclear Power Plants, 11 of 10 CFR 50.
IEEE Standard 308-1974, "Class lE Power Systems for Nuclear Power Generating Stations.
11 Staff positions as detailed in ~ letter sent to the licensee, dated August 8, 1979. I
- 6.
ANSI C84~ 1-1977, "Voltage Ratings for Electric Power Systems and Equipment (60 Hz).
11 Six revi~w positions have been established from the NRC analysis guide-*
l inesl and the above-listed documents.
These positions are stated in Section 5.0.
3.0 SYSTEM DESCRIPTION Figure l of this report is a simplified sketch of the Units 1 and 2 single-line diagram showing the circuit breaker positions (opened or closed) for normal full-power ope'ration.
The class lE distribution system consists of three independent lE buses for each unit supplied from the 500/13kV Station Power Transformers (SPTs) l and 2 via the 13/4kV SPTs 11 and 12 for Unit l, and 21 and 22 for Unit 2.
The 13/4kV SPTs have automatic load tap changers.
During normal full-power operation, two of the three lE buses of one unit are supplied from one 500/13kV SPT and the third lE bus from the other 500/13kV SPT.
The four ~on-lE buses of each unit are supplied from their respective unit Auxiliary Power Transformers (APTs).
Should a unit trip, the non-lE buses will automatically transfer from the APT source to the.SPT source.
If one of the 500/13kV SPTs is out of service, the 13kV ring bus could be closed and the remaining SPT could supply all lE buses of both units.
. Each of the lE instrument buses are supplied through static inverters from AC/DC supplies and have an alternate emergency supply through an auto-transfer switch.
4.0 ANALYSIS DESCRIPTION
- 4. l Analysis Conditions.
PS&G has determined by load flow studies that the maximum expected offiite grid voltage is 530kV (106%) and the minimum 489kV (97.8%).
PSE&G has analyzed each offsite source to both units, including one 500/13kV SPT supplying all loads of both units, to determine the lE equip-ment terminal voltages.
The worst case class lE equipment terminal volt-ages occur under the following conditions:
l.*
- The maximum voltage occurs when the 500kV grid is at its maximum expected value with minimum station loads.
- 2.
The minimum voltage occurs when the 500kV grid is at its min1mum expected value, one 500/13kV transformer supplying both units, a simultaneous trip of Unit 1 and a LOCA in Unit 2.
3.*
The minimum transient voltage occurs with the start of a 6,000 hp reactor coolant pump (RCP) under conditions described in 2 above.
2
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Figure 1.
Salem Nuclear Power Station Units 1 and 2 electrical single-line diagram showing circuit breaker alignment for normal operations.
3
4.2 Analysis Result.
Table l shows the projected worst case class lE equipment terminal voltage~ under conditions of l, 2, and 3 above.
Table 2 shows a comparison of the analyzed*voltages with the undervoltage relay setpoint.
PSE&G letter of June 16, 19815 provided an analysis of a single transformer supplying both units under minimum offsite grid conditions of 489kV (97.8%) which results in a 4160V bus voltage of 3670V (88.24%).
However, the analysis was very conservative and does not give credit for operation of the automatic load tap changers (ALTC), which changes 5/8%
- every 30 seconds, resulting in a 3.75% improvement in voltage over a three-minute period.
The values in Table l and 2 give credit for the ALTCs since the grid is not expected to suddenly drop to the exact value of 489kV (97.8%). -If the grid should decay at a rate which exceeds the operation of the ALTCs then the second level undervoltage relays (or loss-of-voltage relays) will separate the lE loads from the offsite source.
The lE loads would then be re-energized by the onsite power systems.
4.3 Analysis Verification.
PSE&G's submittal of March 3, 1980,3 included test procedures and data to verify their analysis. Actual load data, obtained over a 24-hour period, was used as a basis to calculate a voltage profile. This profile was then compared with the actual measure-ments.
The results showed an error of 1% or less at the 4kV and 460V levels and a maximum error of 1.7% at the 230V level Transformer and bus loadings were sufficiently high to obtain reason-ably accurate data.
The results of the test verify the analysis.
5.0 EVALUATION Six review positions h~ve been established from the NRC analysis guide-1 inesl 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 and are based on PSE&G's analysis of one transformer supplying both units.
Position 1--With the minimum expected offsite grid voltage and maximum load condition, each offsite source and distribution system connection combination m~st be capable of starting and of continuously operating all class lE equipment within the equipment voltage ratings.
With the exception of the starting voltage of a 230V motor, PSE&G's analysis, as reflected in Table 1, shows that terminal voltages will n6t go below the continuous ratings of lE motors and the pickup and operating ratings of the motor starters during the worst-case steady-state minimum-voltage conditions. Table 1 shows the 230V motor terminal starting voltage to be 1.15% below the minimum start rating of the motor.
However, the low voltage condition is not expected to occur due to PSE&G's very conservative analysis. Therefore this position is satisfied.
Position 2~-With the maximum expected offsite grid voltage and minimum load condition, each offsite source and distribution _system *connection 4
TABLE 1 CLASS lE EQUIPMENT VOLTAGE RATINGS AND ANALYZED WORST CASE TERMINAL VOLTAGES
(% of nominal voltage)
Maximum Minimum Analyzed Equipment Condition Rated Analyzed Rated Steady State Transient a 4000V Motors Start 80 86.35 Operate 110 106 86.5b 91.5 460V Motors Start 80 86.85 Operate 110 106 86.5b 92 230V Motors Start 80 78.85C Operate 110 106 86.5b 90.75 480V Starters Pickup 85 88.45 Dropout 70 88.45 Operate 110 107 90 93.6 230V Starters
- Pickup 85 87.35 Dropout 70 87.35 Operate 110 107 90 95.75 Other Equipmentd
- a. Transient value due to the start of a non lE 6000 H.P. Reactor Coolant Pump, except where noted.
- b.
All lE motors have a service factor of 1. 15.7
- c. Transient due to the start of the largest 230V motor.
- d.
The*minimum and maximum values of lE equipment below 230V (battery chargers, inverters, etc.) were not specifically provided.
However, in their analysis of the onsite distribution system PSE&G state that all safety loads will oRerate within their voltage rating (letter of October ~1979 in Appen-dix I.
Giving credit for the automatic load tap changers on the 13/4kV Station Power Transformer, failure of lE equipmented below the 230V level is not expected.
5
TABLE 2 COMPARISON OF.ANALYZED VOLTAGES WITH THE UNDERVOLTAGE RELAY SETPOINTS
(% of nominal voltage)
Locat fon/Re lays 4160V Vital Buses D_egraded Grid Transfer relays Blackout relaysb Loss. of Voltage* relays Minimum Analyzed Voltage 92 92 86.9 Time cont.
cont.
25 secc
- a. Based on information in Reference 6.
a Relay Setpoints Voltage 91 91 70 Time 10.5 sec 13 sec inst.
- b.
Relays will operate when an undervoltage condition exists ori at least two of the three vital buses for 13 seconds ang will act to disconnect the offsite power source from the emergency buses.
- c. The value is due to the start of a non lE 6000 hp RCP motor.
The sec-ond level undervoltage scheme will be administratively bypassed d~ring: the start of the motor.6 Transient times for the start of other motors will be less than 10 seconds.
combination must be capable of continuously operating the required class lE equipment without exceeding the equipment voltage ratings.
PSE&G has shown, by analysis, that the voltage ratings of the class lE equipment will not be exceeded for the conditions* analyzed.
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 wh~n the offsite power source is within expected voltage limits.
NRC, 6ss has indicated, iri a separate report,6 that the requirements of this position are satisfied when both SPTs 1 and 2 are supplying both Units land 2 based on PSE&G 1s analysis of March 3, 1980.3 However,-a5 noted in Table 2, this position is not met when one SPT (1 or 2) is supply-i~g both units as the analyzed voltage (92~) is very close to the second-level undervoltage relay setpoint (91%).
The NRC DSS report.did not provide setpoint tolerances. Also, as noted in Section 4.2, spurious tripping may occur if. the off site grid degrades to its minimum analayzeq *value at a rate which exceeds the operation of the ALTC 1s.
6
Position 4--The NRC letterl requires that test results verify the accuracy of the voltage analyses supplied.
PSE&G has shown that the calculations accurately represent the lE buses and loads.
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).
PSE&G has analyzed the onsite connections to the offsite power grid, and determined that no potential exists for simultaneous or consequential loss of bot~ circuits from the offsite 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 req~ired class lE loads with an accident in one unit and an orderly shutdown and cooldown in the remaining units.
Salem Nuclear Power Station is the site of two nuclear units.
The six lE buses of both units are normally shared between two offsite 500/13.BkV station power transformers (SPTs).
The FSAR, Section 8.3. 1, indicates*
that, if one of the SPTs is out of service, the 13kV ring bus can be closed and the remaining SPT can supply both units.
PSE&G's analysis for this condition5 indicates that one SPT is capable of supplying the loads of both units giving credit for operation of the ALTC's.
Therefore, this position is satisfied (see position 1).
6;0 CONCLUSIONS The voltage analysis submitted by PSG&E for the Salem Nuclear Generat-ing Station 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 pl~nt load and normal offsite power grid conditions; including an accident in one unit and the safe shutdown of the other unit with power to both units supplied from one offsite transformer giving credit for operation of the ALTC's.
- 2.
The test used to verify the analysis shows the analysis to be an accurate representation of the worst case conditions analyzed.
- 3.
PSE&G 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 operation of voltage protection relays, will not occur with the offsite grid voltage within its expected limits 7
and both 500/13.8kV transformers supplying both Units 1 and ~However, spurious operation may occur with one 500/13.8kV transformer supplying both units under mini-mum grid conditions.
7.0 REFERENCES
- l.
NRC letter, William Gammill, to All Power Reactor Licensees (Except Humboldt Bay),
11Adequacy of Station Electric Distribution Systems
- Voltage, 11 August 8, 1979.
- 2.
PSE&G letter, F. P. Librizzi, to Director of Nuclear Regulation, October 10, 1979.
- 3.
PSE&G letter, F. P. Librizzi, to Director of Nuclear Regulation, March 3, 1980.
- 4.
PSE&G letter, F. P. Librizzi, to Director of Nuclear Regulation, September 24, 1980
- 5.
PSE&G letter, R. L. Mittl to Director of Nuclear Regulation, June 16, 1981.
- 6.
NRC letter, S. A. Varga, to PSE&G, F. W. Schneider, 11 Degraded Grid
. Voltage Protection for the Safety Related A-C Power System, 11 (Safety
-Evaluation) January 19, 1980.
7; Telco.n, D. A. Weber, EG&G Idaho, Inc., W. Ross, NRC, February 9, 1981.
8