ML20041D646
| ML20041D646 | |
| Person / Time | |
|---|---|
| Site: | Zion File:ZionSolutions icon.png |
| Issue date: | 02/28/1982 |
| From: | Udy A EG&G, INC. |
| To: | Prevatte R Office of Nuclear Reactor Regulation |
| References | |
| CON-FIN-A-6429 EGG-EA-5766, EGG-EA-5766-DFT, NUDOCS 8203080284 | |
| Download: ML20041D646 (13) | |
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EGG-EA-5766 FEBRUARY 1982 if
[04 DEGRADED GRID PROTECTION FOR CLASS lE POWER SYSTEMS, gpgg ZION STATION, UNIT NOS.1 AND 2 A/7'IS l
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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 Comission Under DOE Contract No. DE-AC07-76ID0lS70 FIN k's.
A6429 dEGnGio.no 8203080284 820228 PDR RES 8203080284 PDR
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FORM EGtG M
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INTERIM REPORT Accession No.
Report No.
EGG-EA-5766 Contract Program or Project
Title:
Selected Operating Reactors Issues Program (III)
S Subject of this Document:
Degraded Grid Protection for Class lE Power Systems, Zion Station, Unit Nos. I and 2 Type of Document:
Informal Report Author (s):
A. C. Udy Date of Documen'-
February 1982 Responsible NRCIDOE Individual and NRCIDOE Office or Division:
R. L. Prevatte, Division of Systems Integration, NRC This documsat was prepared primarily for preliminary orinternal 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 g
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Washington, D.C Under DOE Contract No. DE-AC07-761D01570 NRC FIN No.
A6429 INTERIM REPORT I
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DEGRADED GRID PROTECTION FOR CLASS lE POWER SYSTEMS ZION STATION, UNIT NOS. 1 AND 2 Docket No. 50-295 and 50-304 February 1982 A. C. Udy Reliability and Statistics Branch Engineering Analysis Division EG&G Idaho, Inc.
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i Draft 2/5/82 TAC Nos. 10061 and 10062 2
ABSTRACT This EG&G Idaho, Inc. report reviews the susceptibility of the safety-I related electrical equipment, at the Zion Station, to a sustained degradation of the offsite power sources.
FOREWORD This report is supplied as part of the " Selected Operating Reactor Issues Program (III)" being conducted for the U.S. Nuclear Regulatory Com-mission, Office of Nuclear Reactor Regulation, Division of Licensing, by
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EG&G Idaho, Inc., Reliability and Statistics Branch.
The U.S. Nuclear Regulatory Commission funded the work under Authoriza-tion B&R 20-19-01-06.
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CONTENTS
1.0 INTRODUCTION
1 2.0 DESIGN BASE CRITERIA............................................
1 3.0 EVALUATION......................................................
2 3.1 Ex is ting Undervol tage Protection..........................
2 3.2 Mo d i f i c a t i o n s.............................................
2 3.3 Discussion................................................
3 N.
4.0 CONCLUSION
S.....................................................
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5.0 REFERENCES
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TECHNICAL EVALUATION REPORT DEGRADED GRIO PROTECTION FOR CLASS lE POWER SYSTEMS ZION STATION, UNIT NOS. 1 AND 2
1.0 INTRODUCTION
i On June 3, 1977, the NRC requested Commonwealth Edison (CE) to assess the susceptibility of the safety-related electrical equipment at the Zion Station to a sustained voltage degradation of the offsite source and inter-action of the offsite and onsite emergency power systems.
The letter contained three positions with which the current design of the plant was to be compared.
After comparing the current design to the staff positions, CE was required to either propose modifications to satisfy the positions and criteria or furnish an analysis to substantiate that the existing facility design has equivalent capabilities.
CE responded to the NRC letter on July 27, 1977.2 CE proposed design 3
modifications on June 26, 1980 and provided additional details on the modifications on October 1, 1980.4 Draft technical specifications have not been submitted.
2.0 DESIGN BASE CRITERIA The design base criteria that were applied in determining the accept-ablility of the system modifications to protect the safety-related equipment from a sustained degradation of the offsite grid voltage are:
1.
General Design Criterion 17 (GDC 17), " Electrical Power Systems,"
of Appendix A, " General Design Criteria for Nuclear Power Plants,"
of 10 CFR 50.5 2.
IEEE Standard 279-1971, " Criteria for Protection Systems for Nuclear Power Generating Stations."
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IEEE Standard 308-1974, " Class 1E Power Systems for Nuclear Power i
Generating Stations."
4.
Staff positions as detailed in a letter sent to the licensee, dated June 3,1977.
5.
ANSI Standard C84.1-1977, " Voltage Ratings for Electrical Power Systems and Equipment (60 HZ)."
3.0 EVALUATION This section provides, in Subsection 3.1, a brief description of the ex' sting undervoltage protection at the Zion Station; in Subsection 3.2, a description of the licensee's proposed scheme for the second-level under-voltage protection; and, in Subsection 3.3, a discussion of how the system meets the design base criteria.
3.1 Existing Undervoltage Protection. The present design utilizes I
,two undervoltage relays on each 4160V Class lE bus.
They are arranged in a two-out-of-two logic scheme that senses complete loss of voltage.
The
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relays and their logic circuitry start the diesel generator, initiate load-l shedding, and trip the incoming line breaker.
The existing logic circuitry of the undervoltage protection system does not disable the load-shed feature once the diesel generators are sup-
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plying power to the Class lE buses.
O 3.2 Modifications. To protect the Class 1E safety-related equipment from the effects of a degraded grid condition, the licensee has proposed j
adding another set of undervoltage relays to each of the 4160V Class lE buses.
Each set will be comprised of two solid-state undervoltage relays, each with a built in 10 second time delay and arranged in a two-out-of-two logic scheme, with associated auxiliary relays and timers added to the 4
undervol tage logic circuitry. The setpoint of the second-level protection relays has not been identified, but the time delay will be 5 minutes.
Should the two undervoltage relays remain tripped for 5 minutes, or if a 2
LOCA signal occurs during that 5 minute period, the diesel is started, and the undervoltage condition is annunciated in the control room, the incoming line breakers are tripped, load-shedding is initiated, and finally the diesel generator breaker is closed when the voltage and the frequency from the diesel generator are satisfactory.
Once the diesel generator is supplying its associated Class lE bus, load-shedding is blocked by the "b" contact of the diesel generator breaker.
T Proposed changes to the station's technical specifications, adding the surveillance requirements, allowable limits for the setpoint and time delay, and limiting conditions for operation for the second-level undervoltage monitors, have not been furnished by the licensee. A bases for limiting conditions of operation, as well as a bases for surveillance requirements pertaining to these relays, also has not been furnished.
3.3 Discussion.
The first position of the NRC staff letter required that a second level of undervoltage protection for the onsite power system be provided.
The letter stipulates other criteria that the undervoltage protection nust meet.
Each criterion is restated below followed by a dis-cussion regarding the licensee's compliance with that criterion.
1.
"The selection of voltage and time setpoints shall be determined from an analysis of the voltage requirements of the safety-related loads at all onsite system distribution levels."
The licensee has not yet proposed voltage setpoints.
2.
"The voltage protection shall include coincidence logic to pre-clude spurious trips of the offsite power sources."
The relay logic is arranged in a two-out-of-two logic scheme, thereby satisfying this criterion.
3.
"The time delay selected shall be based on the following conditions:
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a.
"The allowable time delay, including margin, shall not exceed the maximum time delay that is assumed in the FSAR accident an alys i s. "
There is no greater than a 10 second time delay for under-voltage protection should an accident signal be present.
The dieseis start on the accident sianal and transfer would L
then be possible.
This is within the time analyzed in the FSAR occident analysis.
I b.
"The time delay shall minimize the effect of short-duration disturbances from reducing the unavailability of the offsite power source (s)."
The licensee's proposed minimum time delay of 10 seconds is long enough to override any short inconsequential grid disturbances.
c.
"The allowable time duration of a degraded voltage condition at all distribution system levels shall not result in fail,
ure of safety systems or components."
A review of the licensee's voltage analysis" indicates that the time delay will not cause any failures of the safety-related equipment if the nominal voltage setpoint is within the allowable tolerance of the equipment voltage rating.
4.
"The voltage monitors shall automatically initiate the disconnec-tion of offsite power sources whenever the voltage setpoint and time-delay limits have been exceeded."
A review of the licensee's proposal substanth'es that this cri-terion is met.
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5.
"The voltage monitors shall be designed to satisfy the require-ments of IEEE Standard 279-1971."
The licensee has stated that the circuits associated with the undervoltage relays meet the intent of IEEE Standard 279-1971.
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6.
"The Technical Specifications shall include limiting conditions for operations, surveillance requirements, trip _setpoints with i
minimum and maximum limits, and allowable values for the second-level voltage protection monitors."
f The licensee has not proposed technical specification changes.
Instead, CE will request the technical specification changes af ter they have received a safety evaluation report on other CE nuclear stations, Dresden and Quad Cities.
The second NRC staff position requires that the system design auto-matically prevent load-shedding of the emergency buses once the onsite sources are supplying power to all sequenced loads. The load-shedding must also be reinstated if the'onsite breakers are tripped.
The licensee has modified the Zion Station to incorporate this feature in the circuit design.
The load-shed is blocked by an auxiliary contact of the diesel generator circuit breaker.
The third NRC staff position requires that certain test requirements be added to the technical specifications.
These tests are to demonstrate the full-functional operability and independence of the onsite power sources and are to be performed at least once per 18 months during shutdown.
The tests are to simulate loss of offsite power in conjunction with a simulated safety injection actuation signal and to simulate interruption and subse-quent reconnection of onsite power sources. These tests verify the proper operation of the load-shed system, the load-shed bypass when the emergency diesel generators are supplying power to their respective buses, and that there is no adverse interaction between the onsite and offsite power sources.
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These procedures are also yet to be addressed by CE in a request for technical specification changes.
4.0 CONCLUSION
S Based on the information provided by CE, it has been determined that, except for technical specification changes, including the voltage setpoint,
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the proposed changes do comply with NRC staff position 1.
All of the
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staff's requirements and design base criteria have been met. The time delay will protect the Class lE equipment from a sustained degraded voltage condition of the offsite power source should the CE setpoint be adequate.
The load-shed circuitry has been modified to comply with staff posi-tion 2 and it will prevent adverse interaction of the offsite and onsite emergency power systems.
CE has not proposed changes to the technical specifications to test the system modifications and therefore does not comply witn staff posi-tion 3.
The surveillance requirements, limiting conditions for operation, minimum and maximum limits for the trip point, and allowable values for staff position 1 also have not been incorporated into technical specifica-tions.
Therefore, CE's changes are acceptable. As the second-level under-voltage protection modifications are installed, it is recommended that CE propose technical specification changes to be approved as a supplement to this report and implemented at the earliest opportunity.
5.0 REFERENCES
m 1.
NRC letter to R. L. Bolger, CE, June 3, 1977.
2.
CE letter, R. L. Bolger to K. R. Goller, NRC, "Onsite Emergency Power Systems," July 22, 1977.
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3.
CE letter, R. F. Janecek to D. G. Eisenhut, NRC, "Second Level of Undervoltage Protection for 4KV Onsite Emergency Power Systems,"
June 26, 1980.
4.
CE letter, R. F. Janecek to T. M. Novak, NRC, " Response to Request for Information Concerning Undervoltage Protection," October 1, 1980.
5.
General Design Criterion 17, " Electric Power Systems," of Appendix A,
" General Design Criteria for Nuclear Power Plants," to 10 CFR Part 50,
" Domestic Licensing of Production and Utilization Facilities."
6.
IEEE StandP ' 279-1971, " Criteria for Protection Systems for Nuclear Power Geo,
.ing Stations."
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IEEE Standard 308-1974, " Standard Criteria for Class 1E Power Systems for Nuclear Power Generating Stations."
8.
ANSI C84.1-1977, " Voltage Ratings for Electric Power Systems and Equip-ment ( 60 HZ)."
9.
" Adequacy of Station Electric Distribution System Voltages Zion Sta-tion, Unit 1 (Unit 2)," EG&G Idaho, Inc. informal report EEG-EA-5305 (5306), A. Udy, December 1980.
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