ML20041D235
| ML20041D235 | |
| Person / Time | |
|---|---|
| Site: | La Crosse File:Dairyland Power Cooperative icon.png |
| Issue date: | 01/31/1982 |
| From: | Udy A EG&G, INC. |
| To: | Prevatte R Office of Nuclear Reactor Regulation |
| References | |
| CON-FIN-A-6429 EGG-EA-5674, NUDOCS 8203040605 | |
| Download: ML20041D235 (9) | |
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l EGG-EA-5674 JANUARY 1982 DEC."ADED GRID PROTECTION FOR CLASS lE POWER SYSTEMS,
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.y 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
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INTERIM REPORT Accession No.
Report No.
EGG-EA-5674 Contract Program or Project
Title:
Selected Operating Reactors Issues Program (111)
Subject of this Document:
Degraded Grid Protection for Class lE Power Systems, La Crosse Boiling Water Reactor Type of Document:
Informal Report Author (s):
A. C. Udy Date of Document:
January 1982 Responsible PMCIDOE Individual and NRC/ DOE Office or Division:
R. L. Prevatte, Division of Systems Integration, NRC 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 l
NRC FIN No.
A6429 l
l INTERIM REPORT l
0374J DEGRADED GRID PROTECTION FOR CLASS lE POWER SYSTEMS LA CROSSE BOILING WATER REACTOR Docket No. 50-409 A. C. Udy Reliability and Statistics Branch Engineering Analysis Division EG&G Idaho, Inc.
January 1982 1-25-82 TAC No. 10031 i
E_.
ABSTRACT This EG&G Idaho, Inc. report reviews the susceptibility of the safety-related electrical equipment, at the La Crosse Boiling Water Reactor, 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 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 06, FIN No. A6429.
e 11
CONTENTS I
1.0 INTRODUCTION
2.0 D E S I G N B AS E CR I T E R I A...............................................
1 1
3.0 E V AL U AT I O N.........................................................
3.1 Existi ng Undervol tage Protection..............................
2
~
3.2 Mo d i f i c a t i o n s.................................................
2 3.3 Discussion....................................................
2 4
4.0 CONCLUSION
S........................................................
5.0 REFERENCES
5 iii
DEGRADED GRID PROTECTION FOR CLASS 1E POWER SYSTEMS LA CROSSE BOILING WATER REACTOR
1.0 INTRODUCTION
On June 3, 1977, the NRC requested the Dairyland Power Cooperative (DPCo) to assess the susceptibility of the safety-related electrical equip-ment at the La Crosse Boiling Water Reactor (LACBWR) to a sustained voltage onsite emergency power systems.ge and the interaction of the offsite and degradation of the offsite sour The letter contained three positions with which the current design of the plant was to be compared. After com-paring the current design to the staff positions, DPCo 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.
By letter dated July 22, 1977,2 DPCo responded to the NRC letter, deferring the submittal of a Sep rt n the subject DPCo sent information to thp NRC on March 17, 1980, and March 28, 1980.4 On September 9, 1980, DPCo submitted proposed technical specifications for this review.
Additional-information agd voltage analys9s were obtained in March 13, 1980 and May 12, 1980.8 A formal request for chang 19, 1976,ing the technical specifications was made on dated November December 8. 1981.9 This request contained changes besi&ts those related to this review.
2.0 DESIGN BASE CRITERIA The design base criteria that were applied in determining the accept-ability of the system modifications to protect the safety-related equipment from a sustained degradation of the offsite grid are:
1.
General Design Criterion 17 (GDC 17), " Electrical Power Systems,"
ofAppendixA,"Generaj0" 9"
Plants," of 10 CFR 50 Nuclear Power Generating. Stations."g Protection Systems for IEEE Standard 279-1971, " Criteria f 2.
GeneratingStations."g" Class 1EPowerSystemsforNuclearPower IEEE Standard 308-197 3.
o dated June 3,1977.getailed in a letter sent to.the licensee, Staff positions as 4.
5.
ANSI Standard C84.1-1977, "Voltge Ratings for Electrical Power Systems and Equipment (60 Hz)."
3.0 EVALUATION This section provides,'in Subsection 3.1, a brief description of the existing undervoltage protection at La Crosse; in Subsection 3.2, a 1
description of the licensee's propoted modifications for the second-level undervoltage protection; and in Subsection 3.3, a discussion of how the proposed modifications meet the design base criteria.
3.1 Existing Undervoltage Protection.
480V essential buses lA and IB each have undervoltage relays that start the corresponding diesel generator and transfer the bus from the offsite power source to the diesel generator.
The trip setpoint is equal to 328V with a time delay of less than 2.5 s on loss of power.
One-out-of-two relay logic is used.
Any loads required to mitigate the consequences of an accident are not shed from the bus and restart when the diesel-generator output is switched onto the bus.
480V essential buses l A and IB receive power from 480V buses l A and IB, respectively.
Each of these buses also has undervoltage relays that are normally set at 220V, These relays isolate 480V buses l A and 1B from 2400V buses l A and 18, respectively. This action is independent from the isolation of 480V essential buses l A and 1B from 480V buses l A and 1B.
These relays only affect the essential buses indirectly and do not have any control over the starting and loading of the diesel generators.
3.2 Modifications.
The setpoints of the existing undervoltage relays on the 480V essential buses will be raised to be equivalent to a nominal bus voltage of 372V (353V lower limit, 390V upper limit) with a time delay between 1.9 and 2.1 s on complete loss of power.
A second set of undervoltage relays would be installed on each 480V essential bus that has a setpoint equivalent to a nominal bus voltage of 400V (380V lower limit, 420V upper limit) with a time delay of 9 + 0.9 s.
These relays will use a two-out-of-three coincidence logic to staTt the diesel generator within the time delay assumed in the FSAR accident analy-sis.
These voltage monitors are to be designed to meet the applicable requirements of IEEE Standard 279.
Both the loss-of-power and the second-level undervoltage relays will, on a trip, separate its bus from offsite power, start the diesel generator (D-G) and transfer the bus to the D-G when the D-G output is sufficient.
Proposed changes to the unit technical specifications (adding the surveillance requirements, allowable limits for the setpoints and time delays, and limiting conditions of operation for the second-level under-voltage relays) were also furnished by DPCo.
l
- 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 mus t meet. Each criterion is restated below followed by a dis-cussion regarding the licensee's compliance with that criterion.
l.
"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."
2
ment. gas provided voltage and time setpoints per the NRC require-DPCo The degraded voltage relays trip on undervoltage (400+20V). The diesel generator will start af ter a time delay.
Transfer from the degraded offsite grid to diesel generator power 4
will occur af ter the diesel generator voltage and frequency are adequate. The voltage setpoint was chosen utilizing a separate voltage analysis that determined the voltage requirements of the g
safety related loads 2.
"The voltage protection shall include coincidence logic to preclude spurious trips of the offsite power sources."
The proposed modification inco porates two-out-of-three logic that satisfies this guideline.
i 3.
"The time delay selected shall be based on the following conditions:
t i
a.
"The allowable time delay, including margin, si.all not exceed the maximum time delay that is assumed in the FSAR accident analysis."
OPCo has proposed a time delay of 9 + 0.9 s.3 This is within the 20-s time delay assumed iii the FSAR accident analysis, including 10 s for the diesel generators to be started and available, b.
"The time delay shall minimize the effect of short-duration disturbances from reducing the unavailability of the offsite power source (s)."
l This time delay is sufficiently long that the effect of cart-duration disturbances will not reduce the availability of the offsite power sources.
)
c.
"The allowable time duration of a degraded voltage condit' ion at all distribution system levels shall not result in fail-ure of safety systems or components."
1 DPCo has shown that equipment operation at reduced voltage levels for this time period will not result in the-f ailure of safety systems or their components.
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."
i The DPCo design meets this requirement, d
5.
The voltage monitors shall be designed to satisfy the require-4 t
ments of IEEE Standard 279-1971."
4 3
The licensee has stated in his proposal that the modifications
- will be designed to meet the applicable IEEE Standard 279 requirements.
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."
The licensee has proposed technical specifications for the second-level voltage protection monitors that meet these requirements.
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 La Crosse Class 1E buses do not shed any essential loads. This satisfies this NRC position.
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 technical specifications as modified by Reference 9 comply with the requirement to test by simulated loss of offsite power in conjunction with a safety-injection signal, and to test the simulated interruption and subsequent reconnection of the onsite power sources.
4.0 CONCLUSION
S Based on the information provided by DPCo, it has been determined that the proposed modifications comply with NRC Positicn 1.
NRC Position 2 is complied with.
DPCo has proposed changes to the technical specifications to ade-quately test the system modifications. The proposed technical specifi-cations comply with NRC Position 3.
The DPCo proposed modifications and technical specification changes for the degraded grid protection for Class lE power systems are acceptable.
4
I 5.0 REFER ENCES 1.
NRC letter to DPCo, dated June 3,1977.
2.
DPCo letter, J. P. Madgett, to Director of Nuclear Reactor Regulation, NRC, " Emergency Power Systens for Operating Reactors," July 22, 1977, LAC-4793.
3.
DPCo letter, F. Linder, to Director of Nuclear Reactor Regulation, NRC, "0ns ite Emergency Power System," March 17,1980, LAC-6824.
4.
DPCo letter, F. Linder, to Director of Nuclear Reactor Regulation, NRC, "Onsite Emergency Power System," March 28,1980, LAC-6841.
5.
DPCo letter, R. M. Brimer, to C. Cleveland, EG&G Idaho, September 9, 1980, LAC-7130.
6.
DPCo letter, J. P. Madgett, to Director of Nuclear Reactor Regulation, NRC, " Evaluation of Degraded Grid Voltage Con.dition," November 19, 1976, LAC-4350.
i 7.
DPCo letter, F. Linder, to Division of Operating Reactors, NRC, "Ade-i quacy of Station Electric Distribution System Voltage for La Crosse Boiling Water Reactor," March 13, 1980, LAC-6822.
8.
DPCo letter, F. Linder, to Division of Operating Reactors, NRC "Ade-quacy of Station Electric Distribution System Voltage for the _a Crosse Boiling Water Reactor," May 12,1980, LAC-6912.
9.
DPCo letter, F. Linder to Director of Nuclear Reactor Regulation, NRC,
" Application for Amendment to License," December 8,1981, LAC-7970.
i 10.
General Design Criterion 17, " Electric Power Systems," of Appendix A,
" General Design Criteria for Nuclear Power Plants," to 10 CFR Part 60,
" Domestic Licensing of Production and Utilization Facilities."
11.
IEEE Standard 279-1971, " Criteria for Protection Systens for Nuclear Power Generating Stations."
12.
IEEE Standard 308-1974, " Standard Criteria for Class lE Power Systens for Nuclear Power Generating Stations."
' 13.
ANSI C84.1-1977, " Voltage Ratings for Electric Power Systens and Equip-ment ( 60 Hz)."
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