ML20023A868
| ML20023A868 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 08/31/1982 |
| From: | Udy A EG&G, INC. |
| To: | Prevatte R Office of Nuclear Reactor Regulation |
| References | |
| CON-FIN-A-6429 EGG-EA-5377, TAC-10032, NUDOCS 8210280394 | |
| Download: ML20023A868 (13) | |
Text
I EGG-EA-5377 AUGUST 1982 Q AC d6tarch.andlpr &,,,y / kc0gh n,g h g ex DEGRADED GRIO PROTECTION FOR CLASS lE POWER SYSTEMS gg
[fh MAINE YANKEE ATOMIC POWER STATION er A. C. Udy I
I Idaho National Engineering Laboratory Operated by the U.S. Department of Energy 1
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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 U
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FCRW EG4G 396 ta oua Accession No.
EGG-EA-5377 Report No.
Contract Program or Project
Title:
Selected Operating Reactors Issues Cubject of this Document.
Degraded Grid Protection for Class lE Power Systems, Maine Yankee Atomic Power Station Type of Document:
Letter Report Author (s):
A. C. Udy Date of Document:
August 1982 i
Responsible NRC Individual and NRC Office or Division:
R. L. Prevatte, Division of Systems Integration EG&G Idaho, Inc.
~
Prepared for the U.S. Nuclear Regulatory Commission Washington, D.C.
Under DOE Contract No. DE-AC07-781D01570 NRC FIN No. A6429
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j DEGRADED GRID PROTECTION FOR CLASS lE POWER' SYSTEMS l
MAINE YANKEE ATOMIC POWER STATION I
August 1982 i
A. C. Udy Reliability and Statistics Branch
.'~
Engineering Analysis' Division EG&G Idaho, Inc.
1 1-1 i
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i TAC No. 10032 Docket No. 50-309 l-
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ABSTRACT This EG&G Idaho, Inc. report reviews the susceptibility of the.
safety-related electrical equipment, at the Maine Yankee Atomic Power Station, to a sustained-degradation of the offsite power sources.
FOREWORD This report is supplied as part of " Selected Operating Reactor Issues" being conducted for the U.S. Nuclear Regulatory Comission, 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 authorization B&R 20 19 10 11, FIN No. A6429.
Selected Operating Reactors Issues FIN No. A6429 11 i
t CONTENTS ABSTRACT..............................................................
ii FOREWORD..............................................................
i i
1.0 INTRODUCTION
1 2.0 DESIGN BASE CRITERIA.............................................
I o
3.0 E V AL UAT I O N.......................................................
2 3.1 Exi sti ng Undervolt age P rotection...........................
2 3.2 Mod i f i c at i o n s..............................................
3 3.3 D i sc u s s io n.................................................
3
4.0 CONCLUSION
S......................................................
6
5.0 REFERENCES
7 e e e 111
DEGRADED GRID PROTECTION FOR CLASS 1E POWER SYSTEMS MAINE YANKEE ATOMIC POWER STATION
1.0 INTRODUCTION
On June 3,1977, the NRC requested the Maine Yankee Atomic Power Com-pany (MYAPCo) to assess the susceptibility of the safety-related electrical equipment at the Maine Yankee Atomic Power Station to a sustained voltage
. degradation of the offsite source and the interaction of the offsite and
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onsite emergency power systems.1 The letter contained three positions 1
with which the current design of the plant was to be compared. After com-paring the current design to the staff positions, MYAPCo 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 dateo July la, 1977,2 MYAPCo responded to the NRC letter.
-0n May 5, 1980, a meeting was held between the NRC and MYAPCo.3 The NRC positions were fully explained in this meeting. As a result, MYAPCo sent some information to the NRC on July 24, 1980.4 On October 2, 1980, a formal request for information that was still unavailable was sent to MYAPCo by the NRC.5 On January 20, 1981, MYAPCo submitted design modifications and answers to the request for additional information.0 Additional information was submitted on March 5, 1981 and August 11, 1982.8 The 7
modifications consist of the installation of a coincident second-level 1
undervoltage (UV) protection system for the Class lE equipment. To date, MYAPCo has not supplied or committed to supply the required technical specifications.
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 i
1.
General Design Criterion 17 (GDC 17), " Electric Power Systens,"
of Appendix A, " General Design Criteria for Nuclear Power Plants," of 10 CFR 50.9 2.
IEEE. Stand ard 279-1971, " Criteria for Protection Systems for Nuclear Power Generating Stations."10 3.
IEEE Standard 308-1974, " Criteria for Class lE Power Systems for Nuclear Power Generating Stations.""
4.
Staff positions as detailed in a letter sent to the licensee, dated June 3,1977.I ANSI Standard C84.1-1977, "Voltge Ratings for Electrical Power 5.
Systems and Equipment (60 Hz)."
3.0 EVALUATION This section provides, in Subsection 3.1, a brief description of the existing undervoltage protection at the Maine Yankee Atomic Power Station; in Subsection 3.2, a descrip' tion of the licensee's proposed 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 On each of the two 4160V Class lE buses, there are two electromagnetic inverse time undervoltage relays to detect loss of power. They are arranged in a two-out-of-two logic schene with a setpoint of 3255V.13 Should this relay logic detect a loss of voltage, the offsite power feed breakers to that bus will be tripped, the diesel generator associated with that bus will be started, and selected 4160V loads will be dropped.
The diesel-generator breaker automatically closes as the generator voltage and frequency become acceptable, a
2
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3.2' Modifications The licensee has proposed to change the Maine Yankee undervoltage protection scheme. In addition to the existing loss-of-voltage relay protection, each bus will be protected against sustained degraded voltage.
Two undervoltage relays per bus will detect any voltage below 3720 1 40V on each of the 4160V Class lE buses. An instantaneous alarm occurs if any relay is tripped. A two-out-of-two logic per bus in coincidence with an accident signal would, after a ten second time delay, automatically open the bus offsite source breaker. This is turn actuates the loss-of-voltage relays. With no coincident accident signal, manual operator intervention is required to restore the voltage, as no automatic action would occur.
MYAPCo has not supplied technical specifications regarding the set-points, the allowable upper and lower limits of the setpoint tolerance, the time delays, the allowable limits of the time delay, limiting conditions of operation, surveillance, or testing requirements.
3.3 Discussion I
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 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."
MYAPCo has provided voltage and time setpoints per this NRC requirement. The degraded voltage relays trip should the voltage be lower than 3720 1 40V. After ten seconds below this setpoint concurrent with an accident signal, the offsite source circuit breaker is tripped and the loss of voltage relays initiate diesel 3
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. generator start, load shedding and load sequencing. This
.setpoint and time delay were chosen to provide acequate voltage to the most limiting 480V equipment.
L2.
"The voltage protection shall include coincidence logic to' pre-clude spurious trips of the offsite power sources."
The proposed modification incorporates two-out-of-two logic that-satisfies this criterion.
3.
"The time delay selected shall be based on the following conditions:
a.
"The allowable time delay, incluaing margin, shall not exceed the maximum time delay that is assumeo in the FSAR accident analysis."
The time delay will be approximately ten seconds. Tne time delay will be finalized in the technical specification submittal, and must assure that emergency core coolant is delivered within the time delay assumed in the FSAR.
b.
"The time delay shall' minimize the effect of short-duration disturbances from reaucing the unavailability of the offsite powersource(s)."
The licensee's proposed time delay is long enough to override any short term grid disturbances or voltage perturbations caused by the starting of large motors.
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."
4 l
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r The licensee has shown that the time delay will not cause the failure of safety-related equipment, because the setpoint was chosen to provide adequate voltage to the most limiting (480V) equipment.
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 logic proposed by MYAPCo meets this NRC criterion.
5.
"The voltage monitors 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 satisfy the requirements of IEEE Standard 279.
6.
"The technical specifications shall include limiting conditions for operation, surveillance requirements, trip setpoints with minimum ana maximum limits, and allowable values for the second-level voltage protection monitors."
The licensee has not proposed any technical specifications for tne second-level voltage protection monitors.
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.
Bypass of the load shedding feature is automatic when the diesel generator circuit breaker is closed.0 MYAPCo is modifying the emergency buses at the Maine Yankee Atomic Power Station to reinstate automatic load shedding should the diesel generator circuit breaker be opened subsequent to the diesel generator being connected to the, bus.7 l
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The third NRC staff position requires that certain test requirements I
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 I
there is no adverse interaction between the onsite and offsite power sources.
The current technical specifications comply with the requirement to test by simulated loss of offsite power in conjunction with a safety-injection signal. However, MYAPCo has not included testing in the technical specifications to simulate interruption and subsequent reconnec-tion of the onsite power sources.
4.0 CONCLUSION
S i
Based on the information provided by MYAPCo, it has been determined i-that protection of the Class lE equipment from sustained degraded grid r-voltages concurrent with an accident condition meet Criterion 1 of th'e l'
I June 3,.1977 letter. For non-accident conditions, the automatiic discon-nection requirement is not met.
Instead of providing this automatic dis-connection feature, the licensee has provided a list of available redundant
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systems 7 (that are not exposed. to the same degraded voltage) that, if required, are capable of obtaining and maintaining the unit in a safe i
shutdown condition. This equipment listing will be reviewed and evaluated by the Reactor Systems Branch and the Auxiliary Systems Branch of the NRC to determine acceptability.
m e
The load shed circuitry will be modified to fully comply with NRC l
Criterion 2, and this will prevent adverse interaction of the offsite and onsite emergency power systems.
6 a_
To" complete this topic, MYAPCo should provide:
1.
Technical specifications to cover the setpoint, time delays and their tolerances, the limiting conditions of operation, surveil-lance thsting for the undervoltage protection relaying system and
-a test that' simulates a loss of offsite power coincident with an accident signal, verifying the start of the diesel generator, and load shedding and load sequencing. Additionally, this test should verify that the load shedding and the load sequencing are reinstatid ifIthe diesel generator breaker is tripped.
2.
Plant operating procedures that specify operator actions for a degraded grid under non-accident conditions.
5.0 REFERENCES
1.
NRC letter to MYAP~o, dat'd June 3, 1977.
e 2.
MYAPCo letter, E. W. Jackson, to Office of Nucleac Reactor Regulation, 1
NRC, July 18, 1977, WMY-77-72.
3.
Meeting May 5, 1980, MYAPCo and NRC, Bethesda, MD.
-4.
MYAPCo letter, D. E. Vandenbur gh, -to Office of Nuclear Reactor Regula-tion, NRC, " Mitigating i..he Effects of Grid Degradation on Safety Rela-s ted Electrical Equipment," July 24, 1980, WYR-80-83.
- 5.
NRC letter, R. A. Clark, to MYAPCo, R. H. Groce, October 2,1980.
6.
MYAPCo letter, R. H. Grcce, to Office of Nuclear Reactor Regulation, NRC, "Mitiga*.ing the Effects of Grid Degradation on Safety-Related Electrical Equipment," January 20, 1981, FMY 81-5.
7.
MYAPCo letter, J. H. Garrity to NRC, attention Division of Licensing, "Mitisating the Effects of Grid Degradation on Safety-Related Electrical Equipment," March 5,1981, FMY 81-32.
8.
MYAPCo letter, J. H. Garrity to NRC, attention R. A. Clark, " Degraded Grid' Voltage," August 11, 1982, MN-82-153.
9.
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."
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- 10. IEEE Standard 279-1971. " Criteria for Protection _ Systems for Nuclear Power Generating Stations."
- 11. IEEE Standard 308-1974, " Criteria for Class lE Power Systems for Nuclear Power Generating Stations."
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- 12. ANSI C84il-1977, " Voltage Ratings for Electric Power Systems and Equip-ment (60 Hz)."
- 13. MYAPCo letter, E. W. Jackson, to Office of Nuclear Reactor R$gulation, NRC, July 18, 1977, WMY-77-72.
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