ML20052A199
| ML20052A199 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 03/29/1982 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20052A197 | List: |
| References | |
| NUDOCS 8204270584 | |
| Download: ML20052A199 (6) | |
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- SAFETY EVALUATION,BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO. 52 TO FACILITY OPERATING LICENSE NO. DPR-68 TENNESSEE VALLEY AUTHORITY BROWNS FERRY NUCLEAR PLANT, UNIT NO. 3 DOCKET NO. 50-296 Authors: Cick Clark, Dick Prevatte, Al Udy 1.0 Introduction By letter dated December 11,1981 (TVA BVNP TS-171), the Tennessee Valley Authority (the licensee or TVA) requested changes to the Technical Specifications (Appendix A) appended to Facility Operating License No.
DPR-68 for the Browns Ferry Nuclear Plant, Ur.it 3.
The proposed amendment and revised Technical Specifications would accommodate operation of Browns Ferry Unit 3 (BF-3) with a modified electric distribution system. The electrical modifications, reanalysis of the electrical systems and changes to the Technical Specifications.also resolve the generic issues of degraded grid protection for class IE power systems and adequacy of station electric distribution system voltages for BF-3 (Mult'i-plant Actions B-48 and B-23, respectively). These issues were raised by NRC's generic letters of June 3, 1977.; August 8,1979 and December 13, 1979 and responded to by TVA in their letters of July 22,1977; May 2, May 12, and May 17, 1978; September 4,1979; March 14, May 1, and August 6,1980; April 9, and June 8,1981 as well as in the submittal of December 11, 1981 referred to initially above.
2.0 Backaround As a result of our generic l'etter of June 3,1977 and a trip of Browns Ferry Uni: 2 (BF-2) on October 17, 1977, TVA initiated a detailed evaluation of the Browns Ferry electrical distribution systems.
The studies indicated that under certain postulated accident conditions and postulated system degradation, an undervoltage condition might exist. To correct this possible condition, TVA proposed a number of short-term modifications which we approved in May and June 1978.
Engineering design was also started on longer term permanent modifications which are the subject of this safety evaluation.. The permanent modifications to Units 1 and 2, which share many electrical systems, was completed during the six-month outage of Unit 1 in the spring, summer and fall of 1981 and during the June 1981 outage of Unit-2. These modifications were approved by our letter of September 3,1981, transmitting Amendment Nos. 75 and 72 to Facility License Nos. OPR-33 and DPR-52 for Units 1 and 2.
Our safety evaluation supporting these amendments contained all pertinent background information, a description of the grid system and interconnections and extensive information en de design of the plant electrical power system.
82042705W
2 The design for the permanent modifications to BF-3 was submitted by TVA's letter of December 11, 1981. Our evaluation of these proposed modifications isLcovered in this safety evaluation. The proposed modifications were also evaluated with respect to whether the modifications adequately resolved two generic multi-plant concerns-namely, degraded grid protection for Class 1E power systems and adequacy of station electric distribution. system voltages (multi-plant actions B-23 and B-48, respectively).
A detailed review and technical evaluation of the proposed modifications and-changes to the Technical Specifications submitted by TVA's letter of December 11, 1981 was performed by EG&G, under contract to the NRC, and with general supervision by NRC staff. This work is reported by EG&G in " Degraded Grid Protection for Class lE Power Systems, Browns Ferry Nuclear Plant Unit No.
3,"
EGG-EA-5719 dated February 1982 (Enclosure 1) and in " Adequacy of. Station Electric Distribution System Voltages, Browns Ferry Nuclear Plant, Unit 3,"
EGG-EA-5720 dated February 1982 (Enclosure 2). We have reviewed these r.eports t
and on the basis of our evaluation discussed below, we concur in our contractor's conclusions that: 1) the proposed electrical design modifications and proposed changes to the. Technical Specifications are acceptable and 2) the offsite power system and the onsite distribution system are capable of providing acceptable voltages for worst-case station electric load and grid voltages.
3.0 Evaluation - Degraded Grid Voltage l
3.1 Evaluation Criteria e
t i-The criteria used by EG&G in its technical evaluation of the proposed changes
. include General Design Criterion (GDC)-17 (" Electric Power Systems") of Appendix A to 10 CFR 50; IEEE Standard 279-1971 (" Criteria for Protection Systems-for Nuclear' Power Generating Stations"); IEEE Standard 308-1977 (" Voltage Ratings for Electrical Power Systems and Equipment - 60 Hz"); and staff positions defined in our letter to TVA dated June 3,1977.
3.2 Description of Modifications ine following electricd1 systems design modifications were performed at BF-3 during the current' outage.
i I
a)
Installation of a second level of undervoltage relays on each 4160 volt shutdown board for Unit 3.
The second level degraded grid voltage relaying will consist of a two-out-of-three logic for 1
each shutdown board. When the 4160 volt shutdown board voltage is i
below 3920 (+20) volts for 4.3 (+5%) seconds the relays will start
-the diesel generator for the affected board. After an additional 2.9 (+5%) seconds, the offsite source breaker is tripped allowing the diesel generator to supply the affected shutdown board.
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3 b)
Installation of overvoltage alarms annunciated in the control room for the 4160 volt shutdown boards, c) Annunciation in the control room if the 161 Kv grid deteriorates below 166 Kv. This power source is normally^ operated between 160 and 170 Kv.
The minimum voltage of 166 Ky is required by this source to supply accident loads on one unit and safe shutdown loads on all other units.
This alarm will allow TVA to take action and maintain the voltage above 166 Kv.
Since the above modifications have been implemented, the start bus d) loss-of-voltage ~ relaying is no longer required, and hence these relays have been removed.
3.3 Findings
We have reviewed the EG&G Technical ~ Evaluation Report and concur in its findings that:
(1) The proposed degraded grid modifications will protect the Class 1E equipment and system from sustained degraded voltage of the offsite power system over the full range of system voltage fluctuations analyzed.
(2) The existing load shedding circuit is blocked while the diesel generator is supf ying the safety loads and is reinstated when the diesel generator breaker is tripped. This will automatically prevent load shedding when the diesel generators are supplying safety loads.
This meets the staff position and is acceptable.
(3) Additions and changes to the plant Technical Specifications including the surveillance requirements, allowable limits for setpoint and time delay, and limiting conditions for operation (LCOs) have been provided by the licensee. An analysis to substantiate the limiting conditions for operation and minimum and maximum setpoint limits were -included as part of the modification proposal. We have reviewed the changes and additions to Technical Specifications and find the LCOs and surveillance requirements acceptable.
We therefore find the Browns Ferry Unit 3 proposed design modifications and Technical Specifications for degraded grid protection for Class.lE power systems acceptable.
4.0 Evaluation - Adequacy of Distribution System Voltages 4.1 Basis for Review TVA was requested by NRC letter dated August 8,1979 to review the electric-
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power system at Browns Ferry Nuclear plant. The review was to consist of:
- )
Determining analytically the capacity and capability of the offsite power system and onsite distribution system to automatically start as
4 well as operate all required loads within their required ' voltage ratings in the event of 1) an anticipated" transient, or 2) an accident (such as LOCA) without manual shedding of any electric loads.
b) Determining if there are any events or conditions which could result in the simultaneous, or consequential loss of both required circuits from the offsite network to the onsite electric distribution system leading to violation of the requirements of GDC 17.
The August 8,1979 letter included staff guidelines for performing the required voltage analysis and the licensee was further required to perform a test in order to verify the validity of the analytical results. TVA responded by letters dated September 4,1979 and December 11, 1981.
4.2 Evaluation Criteria The criteria used by EG&E in this technical evaluation of the analysis includes GDC 5 (" Sharing of Structures, Systems, and Components"), GDC 13
(" Instrumentation and Control"), GDC 17 (" Electric Power Systems") of Appendix A to 10 CFR 50; IEEE Standard 308-1974 (" Class IE Power Systems for Nuclear Power Generating Stations"), ANSI C84.1-1977 (" Voltage Ratings for Electric Power Systems and Equipment - 60 Hz"), and the staff positions and guidelines provided in the NRC letter to TVA dated August 8,1979.
l 4.3 Results of System 4 1ysis TVA analyzed each offsite power source to the onsite distribution system under maximum and minimum load conditions. The analyses were performed with the
'offsite power sources at maximum and minimum anticipated voltages of 550 Kv and 465 Kv, respectively, on the 500 Ky system and with 170 Ky and 162 Kv, respectively, on the 161 Ky system. TVA has determined that the required minimum voltage on the 161 Kv system is 162 KV when the shutdown boards are powered from the common station service transformers and 164 Ky when powered from the cooling tower transformers. The switchyard voltage will be maintained within the limits of 162 Kv and 170 Ky by automatic capacitor switching and manual operatcr action. Annunciators are provided to assist the operator in ensuring that this voltage is maintained. The analysis included the effects on the Clast. lE equipment with all LOCA loads on one unit, shutdown loads on the other units and simultaneous start of a residual heat removal pump and core spray pump. These conditions produced the worst-case loading on the shutdown boards under minimum grid conditions.
It has been established that the 4160 volt and 480 volt emergency loads will operate satisfactorily within the voltage limits when supplied from the 500 Kv grid. When the 161 KV grid is supplying the offsite power source, this voltage must be maintained above 164 Ky if the cooling tower transformers are used and above 162 Kv if the common station service transformers are used. The design modificat' ions adding the. automatic capacitor banks and annunciators should allow this voltage to be maintained within proper limits.
If these capacitor banks or operator actions allows the voltage to fall below the nuired level, the degraded grid undervoltage relays will provide the
?rotection necessary to ensure that safety equipment is not exposed to degraded
e 5
Th' use of the capacitor banks could cause an over.31tage condition voltages.
e under the minimum loading condition. TVA has provided an overvoltage alarm that annunciates in the control room if the voltage on the 4160 volt shutdown board exceeds 110%. This overvoltage' condition is not considered significant since the alarm will allow operator action.to reduce this overvoltage and any significant loading of equipment on the buses could additionally reduce the voltage to within safe operating limits. TVA has committed to verify by tests the results of this analysis.
These tests are to be completed by March 1983. TVA has not outlined the scope of these tests. As a minimum we require that the criteria outlined in Section 4.4 of the enclosed TER be incorporated into the TVA's verification test program.
4.4 Design Cnanges As a result of the initial voltage analysis TVA has proposed the following design changes:
1.
On-load tap changer for unit station service transformer 38, 2.
Installation of a generator breaker.
3.
Removal of the automatic alternate feed for' the Class lE 120 volt instrument and control buses. A manual alternate feed is still avail able.
4.
Replacement of the existing 480/208/120 volt instrument and control transformers with self regulating and larger capacity transformers.
The installation of the generator circuit breaker changes the normal and alternate supply to the Class 1E distribution system.
Operation of the generator circuit breaker will allow backfeeding from the 500 Ky switchyard as the immediate access source of offsite power to the onsite distribution system.
The breaker is designed to open automatically on a unit trip or maximum fault current.
The use of the generator breaker has been previously evaluated by us and approved for use in Browns Ferry Units 1 and 2 by Amendment Mos. 75 and 72 to Facility Licenses Mcs. DPR-33 and DPR-52, issued on September 3,1981.
In the event that the generator breaker should fail to operate, additional sources of offsite power are available from the 161 Kv grid through the common station service or cooling tower transformers.
4.5 Findinos We have reviewed the EG&G Technical Evaluation Report and concur in the findings that:
(1) TVA has provided a voltage analysis to demonstrate that after the proposed modifications are accomplished, the Class 1E equipment voltages will remain within acceptable operating limits for the postulated worst-case conditions.
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-6 (2) The tests proposed by TVA with the incorporation' of the methods out-lined in Section 4.4 of the TER will adequately verify the voltage-analysis accuracy.
(3) TVA's reaffirmation of compliance with GDC 17 requirements is acceptable.
(4) Loss of offsite power to the Class lE buses, due to spurious operation of the voltage protection relays, will not occur with the offsite grid voltage within its expected limits.
(5) The design modifications to the BF-3 electrical systems are acceptable.
5.0 Environmental Considerations We have determined that this amendment does not authorize a change in effluent types or total amounts nor an increase in power level and will not result,in any significant environmental impact.
Having made this determination, we have furthe,- concluded that this omendment involves an action which is insignificant from the standpoint of environmental impact and pursuant to 10 CFR 51.5(d)(4) that an environmental impact statement, or negative declaration and environmental impact appraisal need not be prepared in connection with the issuance of this amendment.
6.0 Conclusion We have conclude 4 based on the considerations discussed above: that (1) because the amendment does not involve a significant increase in the probability or
. consequence of accidents previously considered and does not involve a significant decrease in a safety margin, the amendment does not involve a significant hazards consideration, (2) there is reasonable assurance that the health and safety of the public will' not be endangered by operation in the proposed manner, and (3) such activities will be conducted in compliance with the Commission's regulations and the issuance of this amendment will not be inimical to the common defense and security or to the health and safety of the public.
Cated: March 29, 1982
Enclosures:
1.
EGG-EA-5719 2.
EGG-EA-5720 O
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EGG-EA-5719 TECHNTCAL EVALUATION REPORT FEBRUARY 1982 1
DEGRADED GRID PROTECTION FOR CLASS lE POWER SYSTEMS, BROWNS FERRY NUCLEAR PLANT, UNIT NO. 3 l
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This is an informal report intended for use as a preliminary or working document gh g'D Prepared for the U. S. Nuclear Regulatory Comission l'b
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INTERIM REPORT Accession No.
EGG-EA-5719 Report No.
Contract Program or Project
Title:
Selected Operating Reactors Issues Program (III)
Subject of this Document:
Degraced Grid Protection for Class lE Power Systems, Brc'. ens Ferry "uclear Plant, Unit No. 3 Type of Document:
Infernal Report Author (s):
A. C. Udy Date of Document:
February 1982 Responsible NRCIDOE Individual and NRC/ DOE Office or Division:
R. L. Prevatte, Division of Systems Integration, NRC This document was prepared primarily 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.
Icano Falls. Idaho 83415 Prepared for the U.S. Nuclear Regulatory Commission Washington, D.C.
Under DOE Contract No. DE AC07 76tD01570 NRC FIN No.
A6429 INTERIM REPORT t
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DEGRADED GRID PROTECTION FOR CLASS 1E POWER SYSTEMS i
BROWNS FERRY NUCLEAR PLANT, UNIT NO. 3 February 1982 l
A. C. Udy -
Reliability and Statistics Branch Engineering Analysis Division i
EG&G ~ Idaho, Inc.
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CONTENTS
1.0 INTRODUCTION
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1 2.0 D ES I GN B ASE CR I TER I A............................................
1 3.0 EVALUATION......................................................
2 3.1 Exis ting Undervol tage Pro tection..........................
2 3.~2 Modifications.............................................
2 3.3 Discussion................................................
2
4.0 CONCLUSION
S.....................................................
5
5.0 REFERENCES
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DEGRADED GRID PROTECTION FOR CLASS lE POWER SYSTEMS BROWNS FERRY NUCLEAR PLANT, UNIT NO. 3
1.0 INTRODUCTION
On June 3,1977, the NRC requested the Tennessee Valley Authority (TVA) to assess the susceptibility of the safety-related electrical equipment at the Browns Ferry Nuclear Plant to a sustained voltage degradation of the offsite jource and interaction 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, the TVA 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.
TVA responded inita}1y on July 22, 1977.2 Additional information was rovided on May 2
- 1978, and reference 2 was amended on May 12, 1978.4 I
roposed technicai specifications to correspond with references 3 and 4 were submitted on May 17, 1978.b Revised proposed technical specificc-tions were provided in response to NRC questioning on August 6, 1980.0 April 9,1981.g on this submittal resulted in a replacement submittal of NRC questionin This last submittal is the most current proposed design for Units 1 and 2 of the Browns Ferry Nuclear Plant. A submittal contain-ing proposed modifications to the Unit 3 technical s11,1981.gecifications, descrip-A letter of tion and analyses gas provided on December 1976 describes the unuetvoltage protection prior to the September lj, Time sequencing of the degraded voltaggmonitoring system, "RC letter.
and other information, was provided on June 8,1981 2.0 DESIGN BASE CRITERIA The design base criteria that were applied in determinin'g the accep-tablility of the system modifications to protect the safety-related equip-ment from a sustained degradation of the offsite grid voltage are:
1.
General Design Criterion 17 (GDC 17), " Electrical Power Systems,"
of Appendix
" General Design Criteria for Nuclear Power Plants,"
of 10 CFR 50 Nuclear Power Generating Stations."g Protection Systems for )
IEEE Standard 279-1971, " Criteria f 2.
1 Generating Stations."g " Class 1E Power Systems for Nuclear Pow IEEE Standard 308-197 3.
datedJune3,1977.getailedinalettersenttothelicensee, Staff positions as 4.
Systems and Equipment (60 HZ)."ge Ratings for Electrical Power ANSI Star.dard C84.1-1977, " Volt 5.
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"The selection of voltage and time setpoints shall be determined 1.
from an analysis of the voltage requirements of the safety-related loads at all onsite s stem distribution levels."
The TVA has provided voltage and time setpoints per this NRC The degraded voltage relays trip on undervoltage requirement.
The diesel generator will start after a time delay (3920V+1/2%).
and after an additional time delay, the normal offsite power will These setpoints and time delays were chosen to pro-be tripped.
vide adequate voltage to the most limiting 480V equipment.
2.
"The voltage protection shall include coincidence logic to pre-clude spurious trips of the offsite power sources.
The relay logic for each shutdown board is arranged in a two-out-of-three logic scheme, thereby satisfying this criterion.
3.
"The time delay selected shall be based on the following conditions:
"The allowable time delay, including margin, shall not a.
exceed the maximum time delay that is assumed in the FSAR accident analysis."
The TVA has identified the maximum length of the time delay between the degraded voltage condition and ghe diesel gener-ator accepting this load, as 9.35 seconds.
Separate action as a result of an accident signal will also start the diesel The diesel generators will be started and ready generators.
to accept load within the time analyzed in the Final Safety Analysis Report with an accident and a sustained 4160V shut-down board undervoltage or loss of voltage.
"The time delay shall minimize the effect of short-duration b.
disturbances from reducing the unavailability of the offsite power source (s).
The licensee's proposed minimum time delay of 6.48 seconds to the t' rip of offsite power is long enough to override any short inconsequential grid distrubances. Further, review of the licensee's analysis shows that any voltage dips, caused by the start of large motors, will not trip the offsite source.
"The allowable time duration of a degraded voltage condition c.
at all' distribution system levels shall not result in fail-ure of safety systems or components."
The licensee's analysis shows that the time delay will not cause failures of safety-related equipment, because the voltage setpoint is within the allowable tolerance of the rated voltage of the equipment.
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4.0 CONCLUSION
S Based on the information provided by TVA, it has been determined that the proposed modifications comply with NRC staff position 1.
The existing load-shed circuitry fully complies with staff position 2.
TVA has proposed changes to the Technical Specifications to comply with the staff position 3.
It is therefore concluded that the TVA proposed modifications and the technical specification changes for this topic are acceptable for Unit No. 3.
of the Browns Ferry Nuclear Plant.
5.0 REFERENCES
1.
NRC letter to TVA, G. Williams, Jr., dated June 3, 1977.
2.
TVA letter, J. E. Gilleland to Director of Nuclear Reactor Regulation,
^
NRC, July 22, 1977.
3.
TVA letter, J. E. Gilleland to E. D. Case, NRC, May 2,1978.
4.
TVA letter, J. E. Gilleland to Director of Nuclear Reactor Regulation, NRC, May 12, 1978.
5.
TVA letter, R. H. Davidson to E. D. Case, NRC, May 17, 1978.
6.
TVA letter, L. M. Mills to H. R. Denton, NRC, August 6, 1980, TVA BFNP TS 143.
7.
TVA letter, L. M. Mills to H. R. Denton, NRC,' April 9, 1981, TVA BFNP TS 156.
8.
TVA letter, L. M. Mills to H. R. Denton, NRC, December 11, 1981, TVA BFNP TS 171.
9.
TVA letter, J. E..Gilleland to Director of Nuclear Reactor Regulation, NRC, September 15, 1976.
10.
TVA lettdr, L. M. Mills to H. R. Denton, NRC, June 8, 1981.
- 11. 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."
12.
IEEE Standard 279-1971, " Criteria for Protection Systems for Nuclear Power Generating Stations."
/
13.
IEEE Standard 308-1974, " Standard Criteria for Class lE Power Systems for Nuclear Power Generating Stations."
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- A-0 TECHNICAL EVALUATION REPORT
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FEBRUARY 1982 ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES, BROWNS FERRY NUCLEAR PLANT, UNIT NO. 3
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Report No.
EGG-EA-5720 Contract Program or Project
Title:
Selected Operating Reactors Issues' Program (III)
Subject of this Document:
Adecuacy of Station Electric Distribution System Voltages, Browns Jerry Nuclear Plant, Unit No. 3 Type of Document:
Informal Report Author (s):
A. C. Udy Date of Document:
February 1982 Responsible NRC/ DOE Individual and NRCIDOE Office or Division:
R. L. Prevatte, Division of Systems Integration, NRC This cocument was prepared primarily for preliminary or internat use. it has not received f ull review and approval. Since there may be substantive changes, this document should not be considered final.
EG&G Idaho. Inc.
Idaho Falls. Idaho 33415 Prepared for the U.S. Nuclear Regulatory Commission.
Washington, D.C.
Under DOE Contract No. DE AC07 761001570 NRC FIN No.
A6420 INTERIM REPORT
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0010j ADEQUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES BROWNS FERRY NUCLEAR PLANT, UNIT NO. 3 February 1982 A. C. U' y d
Reliability and Statistics Branch Engineering Analysis Division EG&G Idaho, Inc.
Docket No. 50-296 TAC No. 13106 O
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CONTENTS
1.0 INTRODUCTION
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2.0 DESIGN BASIS CRITERIA...........................................
1 3.0 SYSTEM DESCRIPTION..............................................
2 4.0 ANALYSIS DESCRIPTION............................................
2 4.1 De s i gn /Operatio n Ch ang es..................................
2 4.2 Analysis Conditions.......................................
5 4.3 Analysis Results..........................................
5 4.4 Analysis Verification.....................................
5 5.0 EVALUATION......................................................
6
6.0 CONCLUSION
S.....................................................
8
7.0 REFERENCES
8 FIGURE 1.
Key Diagram of Normal and Standby Auxiliary Power System........
3 TABLES 1.
Class lE Equipment Voltage Ratings and e
Analyzed Worst Case Load Terminal Voltages......................
4 2.
Con.?arison of Analyzed Voltages and Uncervoltage Relay Setpoints....................................
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ADEOUACY OF STATION ELECTRIC DISTRIBUTION SYSTEM VOLTAGES BROWNS FERRY NUCLEAR PLANT, UNIT N0. 3
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 generic letter ofAugujt8,1979,"AdequacyofStationElectricDistributionSystemsVolt-ages,'
required each licensee to confirm, by analysis, the adequacy of 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.
Septemoer 4,1979.}ey Authority (TVA) responded initially with a letter of Tennessee Val
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"9 December 11, 1981.3 Based on the information supplied by the TVA, this report addresses the capacity and capability of the onsite distribution system of Unit No. 3 of the Browns Ferry Nuclear Plant, 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 acceptability of the offsite voltage conditions in supplying power to the Class 1E equipment are derived from the following:
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 (GDC 5), " Sharing of Structures, Sys-tems, and Components," of Appendix A, " General Design Criteria for Nuclear Power Plants," of 10 CFR 50.
3.
General Design Criterion 13 (GDC 13), " Instrumentation and Con-trol," of Appendix A, " General Design Criteria for Nuclear Power
?lants," of 10 CFR 50.
4 IEEE Standard 308-1974, " Class lE Power Systems'for Nuclear Power Generating Scations."
5.
Staff positions as dejailed in a letter sent to the licensee, dated August 8, 1979.
6.
ANSI CS4.1-1977, " Voltage Ratings for Electric Power Systems and Equipment (60 Hz) 1
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Except for item 4, the above modifications are scheduled to be completed during the fall 1981 outage.
em 4 is presently scheduled for completion during the spring 1985 outage 4.2 Analysis Conditions. The TVA has determined by contingency plan-ning that the maximum expected 500 kV offsite grid voltage is 550 kV and that the minimum is 465 kV.
By grid stability analysis and contingency planning, TVA has determined that the maximum expected 161 KV offsite grid voltage is 170 kV and that the minimum is 162 kV. The 161 kV switchyard voltage will be maintained within these limits by both automatic capacitor switching and by manual action.
The TVA 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 equipment terminal voltages occur when connected to the 161 kV grid under the following conditions:
1.
The minimum expected continuous Class lE load terminal vo'tages occur when the 161 kV grid is at 162 kV, and shutdown boards 3EA, 3EB, 3EC and 3ED are powered by the common station service trans-formers. However, when a cooling tower transformer is providing power for the shutdown boards, the grid voltage must be maintained above 164kV for the load terminal voltages to be equivalent.
2.
The minimum expected transient Class 1E load terminal voltages occur under the conditions above, with the simultaneous start of a residual heat removal pump.and a core spray pump..
3.
The maximum expected continuous load terminal voltages occur when the grid is at 170 kV and no station loads are assumed.
~
4.3 Analysis Result. Table I shows the projected worst case Class 1E equipment terminal voltages.
4.4 Analysis Verification TVA has proposed to test the analysis for the Browns Ferry Nuclear Plant.I The test will cover the use of unit station service transformers, common station service transformers and cool-ing tower trans, formers.
Voltages, current and power will be measured at the grid, 4kV bus and 480V shutdown boards.
These measurements will be used to verify the analysis cajculations. This verification is scheduled to be completed by March 1983.
TVA has not outlined the scope of the test.
As a minimum, the test should:
a.
record the grid, load and intermediate bus voltages down to the 480V level,
~
b.
include steady state measurements and transient measurements of the start of both a large Class lE load and' a large non-Class lE load (not simultaneously),
9 5
3
.m TABLE 2.
COMPARIS0N OF ANALYZED VOLTAGES AND UNDERVOLTAGE RELAY SETPOINTS a
Minimum Analyzed Relay Setpoint Voltage Location / Relays Voltage Time (Tolerance)
Time 4.16kV shutdown boarda D
Degraded grid 3923 V
. continuous 3920 + 20 V 4.3 + 0.43 sec 7.2 7 0.72 secc 3597 V less than
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4 sec.
Loss of grid 3923 V continuous 0V 1.5 + 0.1 sec 3597 V less than 4 sec.
a.
Licensee has determined by anclysis the minimum bus voltages with the offsite grid at the minimum expected voltage and the worst case plant and Class lE loads.
b.
Diesel-generator start, c.
Trip of offsite power sources.
starts. Furthermore, spurious trips of this offsite source are possible.
The Browns Ferry design includes an ala'rm when the grid voltage drops below 166kV, which is above the grid voltage that is shown necessary by the analysis. This would alert the operators to follow plant procedures to increase the grid voltage. Verification test results (see Section 4.4) that show the analysis as conservative would eliminate this concern for the second source of offsite power.
Pos ition 4--The NRC letterI requires that test results verify the accuracy of tne voltage, analyses supplied.
Tne TVA has committee to test to verify the accuracy of the supplied voltage analysis.
Position 5--No event or condition should result in the simultaneous or consequential Toss of both required circuits from the offsite power network to the onsite distribution system (GDC 17).
-The TVA has analyzed the Unit No. 3 connections of the Browns Ferry Nuclear Plant to the offsite power grid, and has determined that no potential exists for the simultaneous or the conseque'ntial loss of both 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 start-ing and operating voltage for all, required Class lE loads with an accident in one unit and an orderly shutdown and cooldown in the remaining units.
7