ML20040F184
| ML20040F184 | |
| Person / Time | |
|---|---|
| Site: | Kewaunee  |
| Issue date: | 12/31/1981 |
| From: | Udy A EG&G, INC. |
| To: | Prevatte R Office of Nuclear Reactor Regulation |
| References | |
| CON-FIN-A-6429 EGG-EA-5701, NUDOCS 8202080428 | |
| Download: ML20040F184 (13) | |
Text
EGG-EA-5701 l
l DECEMBER 1981 1
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DEGRADED GRID PROTECTION FOR CLASS lE POWER SYSTEMc x
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- i This is an 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 E G n 3,a n.
4 8202080428 811231 PDR RES 8202080428 PDR
n EGsG.
p FORM (G&GrM6 (Rev 11 Fin INTERIM REPORT Accession No.
Report No.
EGG-EA-5701 C,ontract Program or Project
Title:
Selected Operating Reactor Issues Program (III) i Subject of this Document:
Degraded Grid Protection for Class lE Power Systems, Kewaunee Nuclear Power Plant Type of Document:
Technical Evaluation Report Author (s):
A. C. Udy Date of Document:
December 1981 Responsible NRC Individual and NRC Office or Division:
R. L. Prevatte, Division of Systems Integration This document was prepared prirnarily for preliminary or internat 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 ai Prepared for the U.S. Nuclear Regulatory Commission Washington, D.C.
Under DOE Contract No. DE-AC07-761001570 NRC FIN No.
A6429 INTERIM REPORT
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D DEGRADED GRID PROTECTION FOR CLASS lE POWER SYSTEMS KEWAUNEE NUCLEAR POWER PLANT A. C. Udy Reliability and Statistics Branch Engineering Analysis Division EG&G Idaho, Inc.
December 1981 6
TAC No. 10030 Docket No. 50-305 Draft 12/17/81 J
O ABSTRACT This EG&G Idaho, Inc. report reviews the susceptibility of the safety-related electrical equipment, at the Kewaunee Nuclear Power Plant, to a sustained degradation of the offsite power sources.
FOREWORD lhis 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 16, FIN No. A6429.
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CONTENTS 1.0 I N TR O D U CT I O N.......................................
1 2.0 DESIGN BASE CRITERIA...............................................
2 3.0 E V A L U AT I O N.........................................................
2 3.1 Exis ting Undervol tage Protect ion..............................
2 3.2 Modifications.................................................
3 0
3.3 Discussion....................................................
3
4.0 CONCLUSION
S........................................................
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5.0 REFERENCES
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DEGRADED GRID PROTECTION FOR CLASS lE POWER SYSTEMS KEWAUNEE NUCLEAR POWER PLANT
1.0 INTRODUCTION
O On June 3, 1977, the NRC requested the Wisconsin Public Service Corporation (WPSCo) to assess the susceptibility of the safety-related electrical equipment at the Kewaunee Nuclear Power Plant to a sustained voltage degradation of the offsite source and interaction of the offsite and onsite emergency power systems.I The letter contained three posi-tions with which the current-design of the plant was to be compared. After comparing the current design to the staff positions, WPSCo was required to either propose modifications to satisfy the positions and criteria or fur-nish an analysis to substantiate that the existing facility design has equivalent capabilities.
2 WPSCo responded initially on August 4,1977 with proposed technical specification amendment No. 29. WPSCo responded to questions on their submittal on September 19, 1979,3 on October 11, 1979 and on October 14, 4
1980.5 On January 28, 1981, WPSCo submitted revised proposed technical specification amendment No. 29a.6 Telephone conversations in Feburary and March of 1981 resulted in revised proposed-technical specification amendment No. 29b, dated May 1, 1981.7 This also provided information for a related review (TAC 12994).
WPSCo met with the NRC to provide additional information.0 The meet-ing concluded that WPSCO would docket some of this information. This was i
done on November 30, 1931.9 This also modified technical specification e
table TS 4.1.1.
A telephone call on December 16, 1981 provided additional informa tion.10 i
This report reviews the above submittals, and in particular, the pro-posed technical specification amendment 29b, as modified on November 30, 1981.
I
- 2. 0 DESIGN BASE CRITERIA The design base criteria that were applied in determining the accepta-bility of the system modifications to protect the safety-related equ pment i
from a sustained degradation of the offsite grid are:
a 1.
General Design Criterion 17 (GDC 17), " Electrical Power Systems,"
of Appendix A, " General Design Criteria for Nuclear Power Plants,"
e.
of 10 CFR 50.II 2.
IEEE Standard 279-1971, " Criteria for Protection Systems for Nuclear Power Generating Stations."
3.
IEEE Standard 308-1974, " Class lE Power Systems for Nuclear Power Generating Stations."I 4.
Staff positions as detailed in a letter sent to the licensee, dated June 3,1977.I 5.
ANSI Standard C84.1-1977, " Voltage Ratings for Electrical Power Systems and Equipment (60 Hz)."
3.0 EVALUATION This sect in provides, in Subsection 3.1, a brief description of the existing undervoltage protection at Kewaunee; in Subsection 3.2, a descrip-tion of the licensee's proposed modifications for the second-level under-voltage protection: and in Subsection 3.3, a discussion of how the proposed modifications meet the design base criteria.
t 3.1 Existing Undervoltage Protection.
Each class lE bus (1-5 and 1-6) at Kewaunee has four loss of voltage relays.
Initially these were set at 68% (of 4160V), and af ter September 15, 1976 were changed to trip at 80%.
Each bus then had two channels of relays consisting of one instantaneous relay and one time delay relay in series.
Additionally, the output of the reserve auxiliary transformer, the tertiary auxiliary transformer and the 2
main auxiliary transformer were monitored by two voltage relays.
Only the bus relays, at 80%, automatically start the diesel-generators.
3.2 Modi fica tions. The modification proposed by the licensee for second-level undervoltage protection will consist of two undervoltage relays (set at 95% of 4160V,12%) either of which alarms a common annunci-ator after 610.5 seconds with the bus voltage below the setpoint.
Should both relays trip, they initiate a common timer with a time delay (before a
automatic bus stripping and diesel-generator loading) of 2712 minutes.
Should the bus voltage recover within this time delay, the system will reset itself.
Additionally, the loss of voltage relays are to be set at 87.512% (of 4160V) with less than or equal to 2-1/2 seconds time delay.
Changes to the unit technical specifications added a requirement to test and calibrate the new relays. When one of the undervoltage-six second time delay relays is out of service, it is required to be placed in the tripped condi tion.
I 3.3 Discussion.
The first position of the NRC staff letter required that a second level of undervoltage protection system for the onsite power system be provided.
The letter stipulates other criteria that the undervoltage protection system must meet.
Each criterion is restated below followed by a discussion 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 distribution system levels."
The licensee proposed setpoint of 95 +2% is in accordance with s
the analysis submitted on October 11, 1979.g All class lE motors are identified as having a service factor of 1.15.
This effectively allows them to operate at a lower terminal voltage than the rated limit.
This allows some margin between the set-point, as reflected down to low voltage (less than 600V) loads and the load required voltage.
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2.
"The voltage. protection sh'all include _ coincidence logic to pre-clude spurious trips of the offsite power sources."
The proposed modification incorporates a one-out-of-two logic to 1
alarm, a two-out-of-two logic, with a common time delay relay to actuate bus shedding and diesel generator loading.
e 3.
"The time delay selected shall be based on the following _ con-r ditions:"
a.
"The allowable time delay, including margin, shall not exceed the maximum time delay that is assumed in the FSAR accident analys is. "
The proposed maximum time delay of the second-level under-voltage relcy channels exceeds the maximum time delay that is assumed in the FSAR. WPSCo states that " continued opera-tion of these loads at a condition above the first level (87.5% +2%) will not unacceptably degrade the equipment required to mitigate a Design Basis Accident."7-This was furtner substantiated in a WPSCo meeting with the NRC.0 Some 480V MCC heaters are being replaced as a result of the investigation required by the NRC to ' verify this statement.9 A schedule for thi< replacement will be agreed to between WPSCo, the Office of Nuclear Reactor Regulation and the Office of Inspection and Enforcement.10 b.
"The time delay shall minimize the effect of short-duration j
disturbances from reducing the unavailability of the offsite power sourcels)."
i The licensee proposed minimum time delay of twenty-five minutes is sufficient to' ride through the start of a reactor coolant pump with the grid in a degraded' condition. The licensee's proposed minimum time delay is long enough to override any short, inconsequential grid disturbances or motor starting transients in the station.
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c.
"The allowable time duration of a degraded voltage condition at all distribution system voltage levels shall not result in failure'of' safety systems or components."
The licensee maintains that the systems and components will 0
not f ail in the time period needed for the automatic opera-tion of the second evel undervoltage' channels.
o 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 substantiates that this cri-terion is met.
5.
"The voltage nonitors shall be designed to satisfy the require-ments of IEEE Standard 279-1971."
The licensee has stated in his proposal that the modifications are-designed to meet 'or exceed IEEE Standard 279.3 6.
'"The technical specifications shall include limiting conditions for operation, surveillance requirements, trip setpoints with minimum and maximum limits, and allowable values for the second-level voltage protection monitors."
I Calibration is once per operating cycle as required by the NRC and in proposed technical specification section 4.6.a.5 and Table 4.1-1.
The new limiting condition for operation proposed by the licensee consists of placing the six-second time delay relay in a tripped condition if it is out of service. There is no requirement for a channel check as WPSCO indicates that this is not practical.9 A channel functional test is called for in Table TS 4.1-1 as requested by the NRC. Thus, the surveillance requirements, where allowed by system design, meet this NRC posi-tion. The allowable tolerance of the degraded voltage time delay 5
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relays, while not placed in technical specifications, are docketed, and this is acceptable to the NRC.0 The second NRC staff position requires that the system design automat-ically 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 Kewaunee station utilizes load-shedding on loss of offsite power.
Once onsite sources supply the class lE buses, load shedding will not occur, however, it is reinstated for certain (non-diesel failure) trips of the onsite breakers.2 The third NRC staff position requires that certain test requirements be added to the technical specifications. These tests were 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 shut-down. The tests are to simulate loss of offsite power in conjunction with a safety-injection actuation signal, and to simulate interruption and sub-sequent 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.
The proposed technical specifications comply with the requirement to test by simulated loss of offsite power in conjunction with a safety injec-tion signal for 5 minutes or more under load.
Interruption and subsequent reconnection of the onsite power sources is not tested because interruption would occur only on a bus fault or mechancial failure of the diesel.
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either case, the automatic reconnection of a diesel generator to the class lE distribution system would not occur.
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4.0 CONCLUSION
Based on the information provided by WPSCo, I find that the proposed modifications and technical specification revision 29b as modified on November 30, 1981, comply with the criteria of the NRC in meeting G
position 1.
4 I also find that staff position 2 is complied with and that the revised technical specifications comply with position 3.
5.0 REFERENCES
1.
NRC letter, A. Schwencer to E. W. James, WPSCo, dated June 3,1977.
2.
WPSCo letter, E. W. James to A. Schwencer, NRC, August 4,1977.
3.
WPSCo letter, E. R. Mathews to A. Schwencer, NRC, " Degraded Grid Volt-age Ques tions," September 11, 1979.
4.
WPSCo letter, E. R. Mathews to A. Schwencer, NRC, " Adequacy of Station Electric Distribution Systems Voltages," October 11, 1979.
5.
WPSCo letter, E. R. Mathews to S. A. Varga, NRC, October 14, 1980.
6.
WPSCo letter, E. R. Mathews to S. A. Varga, NRC, " Degraded Grid Volt-age Protection Technical Specifications," January 2 8, 1981, NR C 10.
7.
WPSCo letter, E. R. Mathews to S. A. Varga, NRC, " Degraded Grid Volt-age Protection Technical Specifications and Responses to March 13, 1981, letter from S. A. Varga to E. R. Mathews," May 1,1981, NR C 64.
8.
Interoffice memo, S. Maskell, NRC to R. Licciardo, NRC, " Conference on Degraded Grid Voltage Protection for the Kewaunee Nuclear Power Plant," October 22, 1981.
9.
WPSCo letter, E. R. Mathews to S. A. Varga, NRC, " Degraded Grid Voltage," November 30, 1981, NRC-81-192.
s 10.
Telecon, R. Licciardo, NRC, C. Schrock, WPSCo, A. Udy, EG&G Idaho, Inc., December 16, 1981.
- 11. General Design Criterion 17, " Electric Power Systems," of Appendix A,
- General Design Criteria for Nuclear Power Plants," to 10 CFR 50,
" Domestic Licensing of Production and Utilization Facilities."
12.
IEEE Standard 279-1971, " Criteria for Protection Systems for Nuclear Power Generating Stations."
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13.
IEEE Standard 308-1974, " Standard Criteria for Class 1E Power Systems for Nuclear Power Generating Stations."
14.
ANSI C84.1-1977, " Voltage Ratings for Electric Power Systems and Equipment (60 Hz)."
- 15. WPSCo letter, E. W. James to A. Schwencer, NRC, September 15, 1976.
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