ML20002C619
| ML20002C619 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 12/31/1980 |
| From: | Cleveland C IDAHO NATIONAL ENGINEERING & ENVIRONMENTAL LABORATORY |
| To: | Shemanski P Office of Nuclear Reactor Regulation |
| References | |
| CON-FIN-A-6256 EGG-EA-5310, NUDOCS 8101100590 | |
| Download: ML20002C619 (13) | |
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- daho lac f CM4M EG&G Fa6 thew I t F91 INTERIM REPORT Accession No.
Report No.
ECC-EA-5310 Contract Program or Project
Title:
Electrical, Instrumentation and Control System Support Subject of this Documents Technical Evaluation Report on the Degraded Grid Protection for Class lE Power Systems for the Trojan Nuclear Plant - Docket No. 50-344 Type of Document:
1 Technical Evaluation Report Author (s):
C. J. Cleveland Date of Document:
December 1980 Responsible NRC Individual and NRC Office or Division:
Paul C. Shemanski, NRC-NRR This document was prepared primarily for preliminary or internal use. lt has not received full review and approval. Since there may be substantive changes, this document should not be considered final.
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EG&G Idaho, Inc.
Prepared for the l
U.S. Nuclear Regulatory Commission l
Washington, D.C.
Under DOE Contract No. DE-AC07 761D01570
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1684F TECHNICAL EVALUATION REPORT DEGRADED GRID PROTECTION FOR CLASS lE PO'4ER SYSTEMS TROJAN NUCLEAR PLANT Docket No. 50-344 December 1980 C. J. Cleveland Reliability and Statistics Branch Cngineering Analysis Division l
EG&G Idaho, Inc.
Draft 12-11-90 TAC No.07328 I
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ABSIRACT In Jane 1977, the NRC sent all licensees a letter outlining three posititions the staff had taken in regards to the onsite emergency power system. Portland General Electric Company (PGE) was to assess the suscept-icility of the safety-related electrical equipment at the Trojan Nuclear Plant (TNP) to a sustained voltage degradation of the offsite source and interaction of the orfsite and onsite emergency power systems. This report coatains an evaluation of PGE's analyses, modifications, and Technical Specification changes to comply with these NRC positions.
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l CONTENTS r
1.0 INTRODUCTION
I 2.0 DESIGN BASE CRITEEIA.
1 3.0 EVALUATION.
2 3.1 Existing Undervoltage Protection 2
3.2 Modification 2
3.3 Discussion 3
4.0 CONCLUSION
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5.0 REFERENCES
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TECHNICAL EVALUATION REPORT DEGRADED GRID PROTECTION FOR CLASS lE POWER SYSTEMS TROJAN NUCLEAR PLANT
1.0 INTRODUCTION
on June 3, 1977, the NRC requested the Portland General Electric Company (PGE) to assess the susceptibility of the safety-related electrical equipment at tne Trojan Nuclear Plant (TNP) to a sustained voltage degrada-tion of the offsite source and interaction of the offsite and onsite emer-gency power systems.I 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, PGE 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.
By letter, dated July 19, 1977, PGE proposed certain design modifica-tions to satisfy tne criteria and staff positions. A request for additional information, to clarify some points in PGE's proposal, was sent to PGE by tne NRC on October 1, 1979.3 PGE responded by letters dated December 11, 5
1979 and January 11, 1980. The modifications consist of the instal-lation of a second-level undervoltage protection system for the class lE equipment. The NRC required that the setpoint, surveillance requirements, test requirements, and allowable limits were to be included by PGE in the plant Technical Specifications.
1 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 equipment from a sustained degradation of offsite grid are:
1.
General Design Criterion 17 (GDC 17), " Electrical Power Systems," of Appendix A, " General Design Criteria for Nuclear Power Plants," of 10 CFR 506 1
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IEEE Standerd 279-1971, " Class IE Power Systems for Nuclear Power Generating Stations"7 3.
IEEE Standard 308-1974, " Class lE Power Systems for Nuclear Power Generating Stations"8 4.
Staff positions as detailed in a letter sent to the licensee, dated June 3, 19771 5.
ANSI Standard C84.1-1977, " Voltage Ratings for Electri-cal Power Systems and Equipment ( 60 11Z )."9 3.0 EVALUATION This section provides, in Subsection 3.1, a brief description of the existing undervoltage protection available to the TNP; in Subsection 3.2, a description 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. The present design uses two undervoltage relays on each of the two station 4160V class IE safety buses to detect a loss of of fsite power. These relays have a setpoint of 2560V (61.5%). When offsite voltage drops to this value and persists for at least one second, the offsite source breakers are tripped, load shedding is initiated, and the emergency diesel generators a're started. The diesel generator breakers are closed automatically as soon as the unit reaches rated voltage and speed.10 c-Load shedding, once the diesel generators are supplying the class IE buses, is not bypassed. The licensee's bases for retention of the load-shed feature is that it provides for automatic resequencing of the loads fol-lowing any temporary loss of bus voltage.
3.2 Modification. The licensee has proposed, firstly, to add two
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more undervoltage relays to the existing two that sense loss of offsite power. These will be arranged in a two-out-of-four coincidence logic.
They will maintain the same setpoint and time delay as was previously indi-cated, and the logic circuitry will perform the same sequence as stated above.
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Secondly, to protect the class IE buses from a sustained degraded voltage, each of the two 4160V class IE buses will be provided with a set of four definite time (4 see time delay) undervoltage relays. These relays will be arranged in a two-out-of-four coincidence logic to energize two timers, eitner of which will initiate tripping of the bus supply breaker.
The relays will have a nominal setpoint of 3850 + 80V (94% of bus voltage) with a relay / timer combined time delay of 55 + 5 sec.
These relays will initate tripping of their respective bus supply breakers, and tnereby causing the existing undervoltage relays (loss-of-voltage) to initiate the sequence of events as in Subsection 3.2 for the following two conditions:
1.
An SI signal is present and undervoltage below the set-point persists for four sec.
2.
No SI signal and undervoltage below the setpoint per-sists for a maximum of 60 sec.
Load shedding is being maintained once the diesel generators are sup-plying their respective buses. The licensee's bascs for this will be dis-cussed below.
Proposed changes to the plant's Technical Specifications, adding the surveillance requirements, allowable limits for the setpoint and time delay, and limiting conditions for operation for the second level undervoltage monitors were also furnished by the licensee. An analysis to substantiate the limiting conditions and minumum and maximum setpoint limits was also part of the proposal.
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I 3.3 Discussion. The first position of the NRC staff letter required that a second Icvel 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 fol-lowed by a discussion 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-related loads at all onsite system dis-tribution levels."
The licensee's proposed setpoint of 3850V at the 4160V bus is 96% of the motor-related voltage of 4000V. This setpoint reflected down to the 480V buses will be greater than 90% of the motor-rated voltage. As the motors are the most limiting equipment in the system, l
this setpoint is acceptable. The licensee's analysis considered these factors.
2.
"The voltage protection shall include coincidence logic to preclude spurious trips of the offsite power sources."
The proposed modification incorporates a tt-out-of-four logic scheme, thereby satisfying this criterion.
3.
"The time delay selected shall be based on the fol-lowing conditions:
The allowable time delay, including margin, shall a.
not exceed the maximum time delay that is assumed in the FSAR accident analysis."
The proposed time delay of four seconds, with a S1 signal present, does not exceed this maximum time delay. This is substantiated by the licensee in his proposal.
Without the presence of a SI signal, the time j
delay of 60 seconds will not be the cause of any l
thermal damage to the safety-related equipment.
The setpoint is within voltage ranges recommended I
by ANSI C84.1-1977.
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"The time delay shall minimize the effect of short-l duration disturbances from reducing the unavail-ability of the offsite power source (s )."
The 60-seconds time delay would allow the starting of the 12.47 kV reactor coolant pumps (6000 hp) without tripping the offsite source.
"The allowable time duration of a degraded voltage c.
condition at all distribution system levels shall not result in failure of safety systems or com ponen t s. "
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A review of the licensee's voltage analysisll indicates that the time delay will not cause any failures of the safety-related equipment since the voltage setpoint is within the allowable tolerance of the equipment-rated voltage.
4.
"Tne voltage monitors shall automatically initiate the disconnection of of fsite power sources whenever the voltage setpoint and time-delay limits have been exceeded."
A review of the licensee's proposal substantiates that this criterion is met.
5.
"The voltage monitors shall be designed to satisfy the requirements of IEEE Standard 279-1971."
The licensee has star?d in his proposal that the modi-fications are designed to meet or exceed IEEE Stan-dard 279.
6.
"The Technical Specifications shall include limiting conditions for operations, surveillance requirements, trip setpoints with minimum and maximum limits, and allowable values for the second level voltage protec-tion monitors."
The licensee's proposal for rechnical Specification changes does include all the required items.12,14 l
The setpoint of 3850 + 80V does not infringe into the I
expected operating envelope and will not compromise the life of the motors. Spurious trips are thereby not i
foreseen. The limiting conditions for operation, cali-bration checks, and surveillance requirements meet the criteria of the staff's positions.
The second NRC staff position requires that the system design auto-matica11y prevent load shedding of the emergency buses once the onsite sources are supplying powar co all sequenced loads. The load shedding must also be reinstated if the onsite breakers are tripped.
In the event an adequate basis can be provided for retaining the load-shed feature when loads are energized by the onsite power system, the licensee's bases for the set,oint and limits must be documented, i
The licensee has elected to retain the load-shed feature once the l
diesel generators are supplying their respective buses. As stated above, the second level undervoltage relays trip the offsite breakers at the set-point of 3850 + 80V. This action activates the loss-of-voltage relays set 5
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These relays iaitiate load saedding. Siace the offsite source oreaxers are already tripped when the diesel generators are supplying tae class lE buses, a voltage below 2560V would be needed to load shed tne cases.
It is tne licensee's contention that only mechanical or electrical componeat failures of the diesel generator could cause tne voltage to reach this level and that tne second redundant safety train would safely shut down tae plant.
Inis bases for retaining the load-shed feature and the oases for the setpoint and limits are documented in his proposal.
rae tnird NRC staff position requires that certain test requirements oe added to the Techaical Specifications. These tests were to demonstrate the full-functional operability and independence of the onsite power sources and are to oe performed at least once per 18 months during shutdown. The tests are to simulate loss of offsite power in conjunction with a safety injection actuation signal and to simulate interruption and subsequent reconnection of onsite power sources. These tests verify the proper oper-ation of tue load-shed system, the load-shed bypass when the emergency diesel generators are supplying power to their respective buses, and that taere is no adverse interaction between the onsite and offsite power sources.
The testing procedures proposed by the licensee do comply with the tull intent of this position.13 Load shedding on offsite power trip is I
tested.
Load sequencing, once the diesel generator is supplying the safety buses, is tested. Tne time durations of the tests will verify that the time delay is sufficient to avoid spurious trips and tnat the load-shed I
oypass circuit is functioning properly.
4.0 CONCLUSION
S Based on the information provided by PGE, it has been determined that tne proposed modifications comply with NRC staff position 1.
All of the staff's requirements and design basc criteria have toes met.
The modifica-tioas will protect the class lE equipment from a sutt4ined degraded voltage l
l coadition of the offsite power source.
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The existing load,hed circuitry, although it is not bypassed once the diesel generators are supplying the class IE buses, will not cause inter-action of the onsite and offsite sources.
The proposed changes to the Technical Specification do adequately test the system modifications and do comply with staff position 3.
The surveil-lance requirements, limiting conditions for operation, minimum and maximum limits for the trip point, and allowable values meet the intent of staff position 1.
It is therefore concluded that PGE's proposed modifications and rech-nical Specification changes are acceptable. It is also recommended that these modifications be incorporated in the plant design before Cycle 4 and that tne Technical Specification changes be implemented at that time.
5.0 REFERENCES
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1.
NRC letter (A. Schwencer) to PGE (C. Goodwin, Jr.), dated June 3, 1977.
2.
PGE letter (C. Goodwin, Jr.) to NRC (A. Schwencer), dated July 19, i
1977.
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3.
NRC letter (A. Schwencer) to PGE (C. Goodwin, Jr.), dated October 1, l
1979.
l 4.
PGE letter (C. Goodwin, Jr.) to NRC (A. Schwencer) dated December 11, 1979.
5.
PGE letter (C. Goodwin, Jr.) to NRC (A Schwencer), dated January 11, 1980.
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6.
General Design Criterion 17, " Electric Power Systems," of Appendix A,
" General Design Criteria of Nnclear Power Plants," to 10 CFR Part 50,
" Domestic Licensing of Production and Utilization Facilities."
l 7.
IEEE Standard 279-1971, ' Criteria for Protection Systems for Nuclear l
Power Generating Stations."
t 8.
IEEE Standard 308-1974, " Standard Criteria for Class IE Power Systems for Nuclear Power Generating Stations."
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9.
ANSI C84.1-1977, " Voltage Ratings for Electric Power Systems and l
Equipment," (60 HZ).
1 10.
Fina? cafety Analysis Report (FSAR) for the Trojan Nuclear Plsat (TNP).
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11.
PGE letter (C. Goodwin, Jr.) to NRC (A. Schwencer), dated February 25, 1980.
12.
PGE letter (C. Goodwin, Jr.) to NRC (A. Schwencer), dated April 3, 1980.
13.
PCE letter (C. Goodwin, Jr.) to NRC (A. Schwencer), dated November 30, 1977.
14.
PGE letter (B. D. Withers) to NRC (R. A. Clark), dated November 12, 1980.
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