ML20039G371
| ML20039G371 | |
| Person / Time | |
|---|---|
| Site: | La Crosse File:Dairyland Power Cooperative icon.png |
| Issue date: | 11/30/1981 |
| From: | Udy A EG&G, INC. |
| To: | Donohew T Office of Nuclear Reactor Regulation |
| References | |
| CON-FIN-A-6429 EGG-EA-5674, NUDOCS 8201180114 | |
| Download: ML20039G371 (7) | |
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EGG-EA-5674 NOVEMBER 1981 dd DEGRADED GRID PROTECTION FOR CLASS lE POWER SYSTEMS,
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.rge;%g 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-AC07-761001570
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INTERIM REPGRT
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l Acct.ssion No EGG-EA-5674 Report No i
s Contract Program or Project
Title:
i Selected Operating Reactors Issues Program (III)
Subject of this Document:
Degraded Grid Protection for Class lE Power Systems, La Crosse Boiling Water Reactor, Docket No. 50-409, TAC No. 10031 Type of Document:
f Informal Report I
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j Author (s):
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A. C. Udy i
Date of Document.
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November 1981 l
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Responsible NRC Individual and NRC Office or Division:
J. N. Donohew, Division of Licensing i
j This document was prepared primarily for preliminary or internal use. It has not received full raview and approval. Since there may be substantive changes, this document should not be considered fenal 4
l EG&G Idaho. Inc j
I' Prepared for the I
i U.S. Nuclear Regulatory Commission Washington, D.C.
Under DOE Contract No. UE-AC07-761001570 NRC FIN No.
A6429
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INTERIM REPORT L
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DEGRADED GRID PROTECTION FOR CLASS lE POWER SYSTEMS i
LA CROSSE BOLLING WATER REACTOR Docket No. 50-409 A. C. Udy Reliability and Statistics Branch Engineering Analysis Division EG&G Idaho, Inc.
November 198!
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i 11-18-81 TAC No. 10031 u
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 so rces.
FOREWORD This report is supplied as part of the " Selected Operating Reactor Issues Program (III)" being conducted for the U.S. Nuclear Regulatory Conmission, Of fice 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.
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CONTENTS
1.0 INTRODUCTION
1 2.0 DESIGN BASE CRITERIA...............................................
1 3.0 EVALUATION......................................................... 2 3.1 Existing Undervoltage Protection.............................. 2 3.2 Modifications................................................ 3 3.3 Discussion....................................................
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4.0 CONCLUSION
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5.0 REFERENCES
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r DEGRADED GRIO PROTECTION FOR CLASS lE POWER SYSTEMS LA CROSSE BOILING WATER REACTOR t.0
?N fR000CTION On June 3, 1977, the NRC requested the Dairyland Power Corporative (DPCo) to assess the susceptibility of the safety-related electrical equip-ment at the La Crosse Boiling Water Reactor (LACBWR) to a sustained voltage degradation of the of fsite source and the interaction of the offsite and onsite emergency power systems.I Tne letter contained three positions with which the currcqt design of the plant was to be compared. After com-paring % e current design to the staff positions, OPCo 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 subnittal of a reoort on the subject.
OPC0 sent information to the N'tC on Marcn 17, 1980,3 and March 28, 1980.4 On September 9, 1980,5 OPCo submitted pro:0 sed technical specifications for this review.
A formal request for changing the technical specifications has not been made.
Additional information and voltage analyses were obtained in the letters dated November 19, 1976,6 March 13, 1980,7 and May 12, 1930.8 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 aegradation of the offsite grid are:
1.
General Design Criterion 17 (GOC 17), " Electrical Power Systems,"
of Apoendix A, " General Design Criteria fnr Nuclear Power Plants," of 10 CFR 50.9 1
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2.
IEEE Standard 279-1971, " Criteria for Protection Systems for Nuclear Power Generating Stations."10 3.
IEEE Standard 308-1974, " Class 1E Power Systems for Nuclear Power Generating Stations."II 4
Staf f positions as detailed in a lettet sent to the licensee, dated June 3, 1977.l 5.
AUSI Standaro CS4.1-1977, " Voltage Ratings for Electrical Power Systems and Eauipment (60 Hz)."12 3.0 E/flUATION This section provides, in Subsection 3.1, a brief description of tna existing undervoltage protection at La Crosse; in Subsection 3.2, a description of the licensee's prooosed 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 18 each have undervoltace 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 tiitigate 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 lA and IB receive power from 480V buses lA and IB, respectively.
Each of these buses also has undervoltage relays that are normally set at 220V. These relays isolate 480V buses lA and 18 from 2400V buses IA and 1B, respectively.
This action is independent from the isolation of 480V essential buses lA and 1B fcam 480V buses lA and IB.
These relays only affect the essential buses indirectly and do not have any control over the starting and loading of the diesel generators.
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3.2 Modifications.
The setpoints of the existing undervoltage relays on the 480V essential buses will be raised to be ec'aivalent to a nomMal bus voltage of 372V (353V lower lim:t, 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 start ti.e 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.
j Both the loss-of-power and the second-level undervoltace relays will, f
on e 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.
L Proposed changes to the unit technical specifications (adding the l
Surveillance requirements, allowable limits for the setpoints and time delays, and limitina conditions of operation for the second-level under-voltage relays) were also furnished by DPCo.
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i 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 must meet. Each criterion is restated below followed by a dis-cussion regarding the licensee's compliance with that criterion.
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1.
"The selection of voltage and time setpoints shall be determined from an analysis of the voltage requirements of the safety-rel ted loads at all onsite distribution system levels."
i DPCo has provided voltage and time setpoints per the NRC require-0 i
ment.I DPCo has provided appropriate analysis separately i
that inoicates that the setpoint tolerance on the second-level undervoltage relays is wide enough that it overlaps both above 3
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the minimum expected voltage (from the offsite source) and below the voltage needed to maintain the load terminal voltage within equipment ratings.
2.
"The voltage orotection shall include coincidence logic to preclude spurious trips of the offsite power sources."
The pr oposed modification incorporates two-out-of-three logic that satisfies this guideline.
3.
"The time delay selected shall be based on the following conditions:
a.
"The allowable time delay, including margin, shall not exceed the maximum time delay that is assumed in the FSAR accident analysis."
DPCo has proposed a time delay of 9 + 0.9 s.3 This is within the 20-s time delay assumed in the FSAR accident analysis, including 10 5 for the diesel generators to be started and availaole.
b.
"The time delay snall minimize the effect of sncrt-duration disturbances from reducing the unavailability of the offsite power source (s)."
This time delay is sufficiently long that the effect of short-duration disturbances will not reduce the availability of the offsite power sources.
c.
"The allowable time duration of a degraded voltage condition at all distribution systen levels shall not result in fail-ure of safety systems or components."
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DPCo has shown that equipment operation at reduced voltage levels for this time period will not result in the failure 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."
The DPCo design meets this requirement.
S.
The voltage monitors chall be designed to satisfy the require-ments of IEEE Standard 279-1971."
The licensee has stated in his proposal that the modifications will be designed to meet the applicable IEEE Standard 279 reauirements.
6.
"The technical specifications shall include limiting conditions for operation, surveillance requirements, trip setpoints with minimum and naximur: limits, and allowable values for the second-level voltage protection monitors."
Tne lictrsee has proposed technical specifications for the second-level voltage protection monitors that meet these requirements.
The second NRC staff position requires th,i 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.
a The La Crosse class lE buses do not shed any essential loads.
This meets the intent of this NRC position.
The third NRC staf f 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 l
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3 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 conjenction 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 cenerators are supplying power to their respective buses, and that there is no adver:.e interaction between the onsite and offsite power sources.
9 The current technical specifications comply with the requirement to test by simulated loss of offsite power in conjunction with a safety-injection signal, and to test to simulate interruptior: and suosequent 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 position 1.
However, I recom-mend that DPCo place a tighter tolerance on the second-level undervoltage relay setpoint to keep the setpoint below the expected bus voltage (when supplier from offsite power) yet above the voltage required to maintain the equip.m t terminal voltages above the minimum equipment rating.
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-
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cations comply with NRC position 3.
However, the proposed changes to the technical specifications nave not been formally submitted.
The DPCo proposed modifications and technical specification changes are acceptable. There is no reason to delay the formal submittal of the technical specification changes.
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S.0 REFERE NCE S 1.
NRC letter to DPCo, dated June 3,1977.
I 2.
DPCo letter, J. P. Madgett, to Director of Nuclear Reactor Regulation, NRC, " Emergency Power Systems for Operating Reactors," suly 22, 1977, l
LAC-4793.
t 3.
nPCo letter, F. Linder, to Director of Nuclear Reactor Regulation, NRC, "Onsite 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.
S.
DPlo letter, R. M. drimer, to C. Cleveland, EGlG Idaho, Septeirter '),
1980, LAC-7130.
6.
DPCo letter, J. P. Madgett, to Director of Nuclear Reactor Regulation, NRC, " Evaluation of Degraded Grid Voltage Condition," November 19, 1976, LAC 4350.
7.
DPCo letter, F. Linder, to Division of Operating Reactors, NRC, "Ade-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 La Crosse Boiling Water Reactor," May 12, 1980, LAC-6912.
9.
General Design Criterion 17, "Electsic Power Systems," of Appendix A,
" General Design Criteria for Nuclear Power Plants," to 10 CFR Part 50,
" Domestic Licensino of Production ano Utilization Facilities."
10.
IEEE Standard 279-1971, " Criteria for Protection Systems for Nuclear power Generating Stations."
11.
IEEE Standard 308-1974, " Standard Criteria for Class lE Power Systems for Nuclear Power Generating Stations."
12.
ANSI Cd4.1-1977, " Voltage Ratings for Electric Power Systems and Equip-ment (60 Hz)."
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