ML20004B301
| ML20004B301 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 05/31/1981 |
| From: | Udy A ENERGY, DEPT. OF, IDAHO OPERATIONS OFFICE |
| To: | Shemanski P Office of Nuclear Reactor Regulation |
| References | |
| CON-FIN-A-6429 0380-J, 380-J, EGG-EA-5433, NUDOCS 8105270505 | |
| Download: ML20004B301 (11) | |
Text
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INTERIM REPORT Accession No.
Report No. EGG-EA-5433 Contract Program or Project
Title:
Selected Operating Reactor Issues Program (III)
Subject of this Document:
Adequacy of Station Electric Distribution System Voltages, Big Rock Point Plar,t, Docket No. 50-155, TAC No.12781 Type of Document:
Informal Report Author (s):
y C OSearC1 anC 8C101C8 n
A. C. Udy Assistance Repor:
Date of Document:
May 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, 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.
A6429 INTERIM REPORT
1 0380J 1
NRC Researc'a andt 'ec'anica t
Assistance Report ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES IG ROCA POINT PLANT Docket No. 50-155 l
May 1981 A. C. Udy Reliability and Statistics Branch Engineering Analysis Division EG&G Idaho, Inc.
Draft 4-28-81 TAC No.12781 g,
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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 Big Rock Point Plant.
The offsite power sources, in conjunction with the onsite distribution system, have not been shown to have sufficient capacity and capability to automatically 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 Progran (III)" being conducted for the U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation, Division of Licensing, by EG3G Idaho, Inc., Reliatility and Statistics Branch.
The U.S. Nuclear Regulatory Commission funded the work under the authorization, B&R 20 19 01 06, FIN No. A6429.
9 11
CONTENTS 1.0 I N TR OD UC T I O N......................................................
I 2.0 D ESIGN B ASIS CRIT ERI A.............................................
1 3.0 S YST EM D ESC R I P T I O N................................................
2 4.0 ANAL YS I S D ESCRI PT IO N..............................................
4 4.1 An al y s i s Co n d i ti o n s..........................................
4 4.2 An a l y s i s Re s u l t s.............................................
4 4.3 An al y s i s Ve ri fi ca ti o n........................................
4 5.0 EVALUATION........................................................
6 6.0 C O NC L U S I O NS.......................................................
8 7.0 RE F E RE N C ES........................................................
9 FIGURE 1.
Bi g Ro ck Poi nt el ec trical si ngl e-l ine di a gram.....................- -
3 TABLES 1.
Class 1E Equipment Voltage Ratings and An alyzed Wo rst Ca se Load Terminal Vol tages........................
5 2.
Comparison of Analyzed Voltages and Un dervol tage Rel ay Se tpoi nts......................................
7 Y1C,lesearc.i anc "ecinica' Assistance Repor iii
ADEQliACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES BIG ROCK POINT PLANT NRC Researci anc "echnica
1.0 INTRODUCTION
Assistance Report 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 confomance 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 Volt-ages," I required each licensee to confinn, by analysis, the adequacy of the voltage at the class 1E loads.
This letter included 13 specific guide-lines to be followed in detennining if the load terminal voltage is adequate to start and continuously operate the class 1E loads.
Consumers Power Company (CPCo) responded with letters dated February 19, 1980,2 and August 29, 1980.3 CPCo supplied further infonnation requested for this review on March 23, 1981.4 CPCo correspondence of June 14,1978,5 August 21, 1980,6 and December 12, 1980,7 were also reviewed for this report.
Based on the infonnation supplied by CPCo, this report addresses the capacity and capability of the onsite distribution system of the Big Rock Point Plant, in conjunction with the offsite power system, to maintain the voltage for the required class 1E equipment within acceptable limits for the worst-case Starting and load conditions.
2.0 DESIGN BASIS CRITERIA The positions applied in determining the acceptability of the offsite voltage conditions in supplying power to the class 1E equipment are derived from the following:
1
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,n(GDC 5), " Sharing of Structures, Sys-1 tems, and Components," of Append;x A " General Design Criteria for Nuclear Power Plants," of 10 CFR 50.
c 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 1E Power Systems for Nuclear Power Generating Stations."
5.
Staff positions as detailed in a letter sent to the licensee, dated August 8,1979.I i
6.
ANSI C84.1-1977, " Voltage Ratings for Electric Power Systems and EqJ1pment (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 e
Section 5.0.
4 3.0 SYSTEM DESCRIPTION Figure 1 of this report is a simplified sketch of the unit single-line diagram of the Big Rock Point power distribution system.
It is taken from and Figure 1.3 5
The Big Rock Point station has a single class 1E Motor Control Center (MCC-2B) which is normally powered by MCC-2A from Load Center 2 via
~
2400V/480V transformer No. 22. Transformer No.11, Load Center 1, and MCC-1 A can also supply MCC-28.
Both transformer No 11 and transformer No. 22 are energized by the same 2400V switchgear which is supplied by P
2
138KV MA N TRF.
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TO 46KV 4
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FIGURE 1 BIG ROCK Polh7 STATION POW.!R WD WlD N O.2 2 NO.11 SINGLE LINE DIAGRN4 gg g
{ LOADCENTER 1 480V LOAD CENTER 2 480v
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g CLASS lE 3
4 transformer No.1 (from the unit generator on the 138kV grid) or by the-46kV grid.
_120Y instrument and control _ panels are supplied from either MCC-1 A or MCC-28.
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4.0 ANALY3IS DESCRIPTION 4.1 Analysis Conditions. CPCo has determined that the minimum expec-ted offsite gr:o voltage is'95% of nominal. -CPCo has not described what they expect the maximum grid voltage' to be.
3 CPCo 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 1E 3
equipment terminal voltages occur under the following conditions:
i 1.
The minimum expected continuous load terminal voltage for a class IE load occurs when either the unit generator voltage is at its minimum with full-unit' loads or the 46kV grid is at its mini-mum with normal unit loads.
4 2.
The minimum expected transient load terminal voltage for a class lE load occurs when the 138kV grid is at its minimum, l
normal unit loads are running'and the 1500 hp reactor feed pump i s sta rted.
l 3.
The maximum expected. continuous load terminal voltage for a j
class lE load occurs when the unit generator voltage is at its maximum value and the unit loads are at a minimum.
4.2 Analysis Result.
Table 1 shows the projected worst case class IE~
equipment. terminal voltages.
l 4.3 Analysis Verification. CPCo has _ verified the accuracy of the i
analysis for the Big Rock Point Plant by comparing voltages obtained by an i-4 r--*
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TABLE 1.
CL ASS lE EQUIPMENT VOLTAGE RATINGS AND ANALYZED WORST CASE TERMINAL V0LTAGES (% of nominal voltage)
Maximum Minicum Analyzed Equipment Condition Rated Analyzeda Rated Steady State Transient 77.4b 440V Motors Start 80 Operate 110 109.7 90 90.4b 120V Instru.
Start and Operate 1:
d Control s 480V Starters Pickup 85 76.6 Dropou t 50 76.6 Operate e
100.5 e
88.0 a.
Bus voltage supplied by CPCo.
Assuming no feeder voltage drop, the load terminal voltage would be the same.
b.
CPCo supplied bus voltage minus the CPCo supplied worst feeder voltage drop (1.5% of steady state, 6.1% transient).7 c.
CPCo did not supply this value. However, noting the no-load voltage and transformer ratias, it is felt that the 120V nominal rating would be only slightly exceeded, while typical instruments are rated to 110%. When minimal loads are added, f$eder and transformer voltage drops would reduce this voltage to within 110..
d.
CPCo states that the worst case voltage to 120V instruments is 4.4%
below the guaranteed rating.
They state that these reduced voltages will not damage equipment prior to second _ level undervo}tage relay operation and the connection of the diesel generator to the bus.
Some downscale error in the instrumentation is expected during this period.
e.
CPCo has not supplied these ratings.
O 9
1 l
5
oscilligraph with analyzed voltates for the same condition (i.e., staady state and startup of the 100 hp fire pump on MCC-2B.) The test showed the analysis to be within the accuracy limits of the instrumentation used.
5.0 EVALUATION Six review positions have been established from the NRC analysis guide-l lines and the documents listed _in Section 2.0 of this report. Each review position is stat =
below followed by an evaluation of the licensee submittal s.
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 1E equipment within the equipment voltage ratings.
CPCo has not shown, by analysis, that the Big Rock Point Plant has sufficient capability and capacity for continuously operating the class 1E loads within the equipment voltage ratings (Table 1). The 120V instrumen-tation voltages are below the equipment minimum rated voltages; the CPCo analysis has not demonstrated that the distribution system has the capabil-ity to start any class 1E load when the offsite grid is at a minimum; and CPCo has not verified that the fire pump (required for short-term core 4
cooling) will not stall when the reactor feed pump is started.
Position 2--With the maximum expected offsite grid voltage anc minimum load condition, each offsite source and distribution system connection combination must be capable of continuously operating the required class 1E equipment without exceeding the equipment voltage' ratings.
CPCo has shown, by analysis, that the voltage ratings of the class 1E equipmer.t will not be exceeded.
i 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.
6 i
~
As shown in Table 2, voltage relays will not cause the loss of the class 1E distribution system when the offsite grid voltage is within expected voltage limits. Big Rock Point does not have a redundant class lE distribution system.
TABLE 2.
COWARISON OF ANALYZED YOLTAGES AND UNDERV0LTAGE RELAY SETPOINTS
(% of nominal voltage) a Minimum Analyzed Relay Setpoint Location /Rel ays Vol tage Time Voltage (Tolerance)
Time 2400V busa Degraded grid 93.2 continuous 90.0 (+1.0) 10.5 s
(+0.5 s) 480 V bus Lo ss of gri d.
76.65 5s less than or equal instantan-or less to 50 eous Licensee t. 'eteminea by analysis the minimum bus voltages with the a.
offsite grid at c.e minimum expected voltage and the worst case plant and class lE loads.
b.
For start of 1500 hp reactor feed pump, this produces the most degraded voltage for the undervoltage relays.
Position 4--The NRC letter requires that test results verify the accuracy of the voltage analyses supplied.
CPCo has verified, by test, the validity of the anaysis for the Big l
Rock Point Plant.
l 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).
l l
The Big Rock Point unit does not comply with GDC 17 since it has only one transfonner connecting the offsite grid to the class lE distribution system; it has only one circuit supplying 2400 V to the 2400/480V l
l l
7 l-
transfomers; and it has only or,e class lE bus.
This does not comply with GDC 17.
I 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 1E loads with an accident in one unit and an orderly shutdown and cooldown in the remaining units.
This applies to multi-unit plants.
It does not apply to Big Rock Point, a single-unit station.
6.0 CONCLUSION
S The voltage analyses submitted by CPCo for Big Rock Point were evalu-ated in Section 5.0 of this report.
It was found that:
1.
Voltages within the operating limits of the class lE equipment are not supplied for all projected combinations of plant load and offsite power grid conditions. CPCo has not demonstrated the capability of all class 1E equipment to continue running during the start of large non-class 1E loads without the' trip of themal overloads or the blowing of control fuses. The CPCo analysis has shown that voltages below the equipment rating can be supplied to instrumentation needed for the safe shutdown of the unit. CPCo should correct these potential equipment problems.
2.
The test used to verify the analysis shows the analyses to be an accurate representation of the worst case conditions analyzed.
3.
CPCo has detemined that no potential for either a simultanous or consequential loss of both offsite power sources exists.
- However, there are portions of the Big Rock Point distribution system where a single failure can negate both sources.
8
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.
7.0 REFERENCES
1.
NRC letter, William Gammill, to All Power Reactor Licensees (Except 4
Fbmboldt Bay), " Adequacy of Station Electric Distribution Systems Voltage," August 8,1979.
2.
CPCo letter, David P. Hoffman, to Director, Nuclear Reactor Regula-tion, NRC, " Adequacy of. Station Electric Distribution Systems Vol t-ages," February 9,1980.
3.
CPCo letter, David P. Hoffman, to Director, Nuclear Reactor Regula-tion, NRC, " Adequacy of Station Electric Distribution Systems Volt-ages," August 29, 1980.
4.
CPCo letter, David P. Hoffman, to Director, Nuclear Reactor Regula-tion, NRC, " Adequacy of Station Electric Distribution Systems Volt-J ages," March 23, 1981.
5.-
CPCo letter, William S. Skibitsky, to Director, Nuclear Reactor Regulation, NRC, "On-site Emergency Power Sources," June 14, 1978.
6.
CPCo letter, David P. Hoffman, to Director, Nuclear Reactor Regula-tion, NRC, " Degraded Grid Voltage," August 21, 1980.
7.
CPCo letter, David P. Hoffman, to Director, Nuclear Reactor Regula-tion, NRC, " Response to Request for Additional Information Related to the Generic Issue on Onsite Power Systems," December 12, 1980.
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