ML19341B904
| ML19341B904 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 10/31/1980 |
| From: | White R LAWRENCE LIVERMORE NATIONAL LABORATORY |
| To: | |
| Shared Package | |
| ML19341B901 | List: |
| References | |
| CON-FIN-A-0231, CON-FIN-A-231 TAC-12746, UCID-18690, NUDOCS 8102280100 | |
| Download: ML19341B904 (13) | |
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ATTACHMENT UCID.18690 l
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TECHNICAL EVALUATION OF THE PROPOSED DESIGN MODIFICATIONS AND TECHNICAL SPECIFICATION CHANGES ON GRID VOLTAGE DEGRADATION (PART A)
FOR THE RANCHO SECO NUCLEAR GENERATING PLANT l
l Robert L White i
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October 1980 w
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_2 n. a m m w -, m m for w o u-a w =t.riw dh The opumans and h maand aso those of the author sad may or may not be those of the t =M.
N Dis work was suppared by the Cassed Semens !$sdaur RW e-under et U% wah the UniendSensesDeparumsee of Emmy.
81022801CC
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ABSTRACT This report docutents the technical evaluation of the proposed design modifications and Technical Specification changes for protection of Class 1E equipment f rom grid vc1tage degradation for the Rancho Seco Nuclear Generating Plant. The review criteria are based on several IEEE standards and the Code of Federal Regulations. The evaluation compares the submittals made by the licensee with the tTRC staff positions i
and the review criteria and presents the reviewer's conclusion on the acceptability of the proposed system.
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FORE'JORD This report is supplied as part of the Selected Electrical, Instrumentation, and Control Systems Issues (SEICSI) Program being conducted for the U. S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation, Division of Operating Reactors, by Lawrence Liversore National Laboratory, Engineering Research Division of the Electronics Engineering Department.
The U. S. Nuclear Regulatory Commission funded the work under the authorization entitled " Electrical, Instrumentation and Control System Support,"
S&R 2019 04 031, FIN A-0231.
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TABLE OF CONTENTS Pa ge 1.
INTRODUCTION.
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DESIGN BASIS CRITERIA 3
3.
EVALUATION 5
3.1 Existing Undervoltage Protection 5
3.2 Modifications.
5 3.3 Discussion.
6 3.3.1 NRC Staff Position 1: Second Level of Under-voltage or Overvoltage Protection with a Time Delay 6
3.3.2 NRC Staff Position 2:
Interaction of Onsite Power Sources with Load Shed Feature.
8 3.3.3 NRC Staff Position 3: Onsite Power Source Testing 9
3.4 Technical Specifications 9
4 CONCLUSION 11 REFERENCES 13 i
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m TECHNICAL EVALUATION REPORT PROPOSED DESIGN MODIFICATIONS AND TECHNICAL SPECIFICATION dHANGES ON CRID VOLTAGE DECRADATION FOR THE RANCHO SECO NUCLEAR GENERATING PLANT (Docket No. 50-312)
Robert L. White Lawrence Livermore National Laboratory, Nevada 1.
INTRODUCTION Sy letter dated June 3,1977 [Ref.1], the U. S. Nuclear Regulatory Commission (NRC) requested the Sacramento Municipal Utility District to assess the susceptibility of the Rancho Seco Nuclear Generating Plant Class lE electrical equipment to sustained degraded voltage conditions at offsite power sources and to the interaction between the offsite and onsite emergency power systems.
In addition, the NRC requested that the licensee conpare the current design of the emergency power systems at the plant facilities with the NRC staff positions as stated in the June 3,1977 letter [Ref.1], and that the licensee propose plant modifications, as necessary, to meet the NRC staff positions, or provide a detailed analysis which shows that the facility design has equivalent capabilities and protective features.
- Further, the NRC required certain Technical Specifications be incorporated into all facilities' operating licenses.
By letters dated August 1, 1980 [Ref. 2], June 20, 1978 (Ref. 3],
July 19,1977 (Ref. 4], and September 22, 1980 (Ref. 5], Sacramento Municipal Utility District proposed certain design modifications and p*ovided draft Technical Specifications.
The design modifications include the installation of a degraded voltage protection system for the Class lE E
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equipment. The proposed draf ts of the Technical Specifications are in regard to the relay setpoints, calibrations, system tests, and surveil-lance requirements associated with the proposed voltage protection systen.
The purpose of this report is to evaluate the licensee's proposed desir.n modifications and Technical Specification changes and to determine that they stet the criteria established by the NRC for the protection of Class 1E equipment from a grid voltage degradation.
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DESIGN BASIS CRITFRIA The design basis criteria that were applied in determining the acceptability of the system modification to protect the Class 1E equipment from degradation of grid voltages are as follows:
(1) General Design Criterton 17 (GDC 17), " Electric Power Systems," of Appendix A, " General Design Criteria for Nuclear Power Plants," in the _ Code of Federal Regulations,
Title 10, Part 50 (10 CFR 50) [Ref. 6].
(2)
IEEE Standard 279-1971, " Criteria for Protection Systems for Nuclear Power Generating Stations" [Ref. 7].
(3) IEEE Standard 308-1974, " Class 1E Power Systems for Nuclear Power Generating Stations" [Ref. 8].
(4) NRC Staff positions as stated in a letter dated June 3, 1977
[Ref. 1]. -
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3.
EVALUATION l
3.1 EXISTING UNDERVOLTAGE PROTECTION I
The Rancho Seco Nuclear Generating Plant has two 4160-volt and two 480-volt Class 1E buses.
The existing undervoltage protection design uses a single undervoltage relay on each 4160-volt Class 1E bus.
If the voltage drops below 3534 volts (85% of 4160 volts), the undervoltage relay will energize a set of load-shedding relays.
The load-shedding relays initiate the disconnection of the emergency 4160-volt buses from the off-site source, load shed the emergency 4160-volt buses, start the emergency diesel generators, and provide an enabling signal for the load-sequencing timing circuit. When the emergency diesel generator reaches the required voltage it is connected to the emergency buses and load-sequencing will be-gin automatically, if a safety injection (SI) signal exists.
The existing Rancho Seco design complies with NRC Staff Position 2 requiring the system to automatically prevent load shedding of the energency buses once the onsite souces are supplying power to all sequenced loads on the emergency buses.
The preserc design will also reinstate the load-shedding feature if the emergency diesal generator breakers are tripped.
3.2 MODIFICAIIONS The licensee has proposed a design change to establish an automatic degraded voltage protection circuitry.
The modification consists of incorpo-rating the existing undervoltage protection scheme with a degraded voltage protection scheme.
The proposed scheme will consist of 3 undervoltage relays monitoring each 4160-volt emergency bus.
The 3 undervoltage relays will be arranged in a 2-out-of-3 coincident logic with a setpoint of 3771 volts + 38 volts (90.6% of 4160 volts) with a time delay of 12 seconds
+ 1.2 seconds.
There will be only one loss of voltage-degraded voltage pro-tection system.
The relays are of the inverse time-voltage type.
Upon complete loss of voltage the under/oltage relays will trip in less than one second.
i The licensee has provided draft Technical Specification changes t
to document relay setpoints, surveillance requirements, limiting conditions for operation, and diesel generator test procedures for the proposed changes as presented in this evaluation.
3.3 DISCUSSION This section presents a statement on the NRC staf f position f rom their June 3,1977 letter (Ref.1] followed by an evaluation of the licensee's design.
i 3.3.1 NRC Staff Position 1: Second Level of Undervoltage
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or Overvoltage Protection with a Time Delay This position is to be met by the licensee meeting certain criteria.
Each criterion has been evaluated against the licensee's proposal and is addressed below.
(1)
"The selection of voltage and tice setpoints shall be determined from an analysis of the voltage requirements of the safety-related loads at all onsite system distri-bution levels."
The licensee's proposed degraded voltage setpoint is 3771 volts + 38 volts (90.6% of 4160 volts).
The proposed time-delay setpoint is 12 seconds + 1.2 seconds.
The licensee's analysis shows that this setpoint and tine delay are satisfactory for both 4000-volt and 460-volt Class IE loads atd for relays, contactors, and other components whose functional performance would be inadequate because of unc3rvoltage.
(2)
"The voltage protection shall include coincidence logic to preclude spurious trips of the offsfee power sources."
The proposed modification for degraded voltage protection incorporates a 2-out-of-3 coincidence logic.
Each 4160-volt Class lE bus will have 3 phas--to-phase undervoltage relays.
The logic will initiate a signal to trip the circuit breakers from the offsite source when 2 of the 3 independent input channels are actuated.
(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."
The proposed time delay of 12 seconds j; 1.2 seconds does not exceed the maximum time delay that is assumed in the FSAR accident report.
(b)
"The time delay shall minimize the effect of short-duration disturbances from reducing the availability of the of fsite power sources."
The licenste's proposed time delay of 12 seconds j; 1.2 seconds is long enough to override any grid disturbances of short duration.
This has been con-firmed by testing.
(c)
"The allowable time duration of a degraded voltage condition at all distribution system levels shall not resub in failure of safety systems or components."
A review of the licensee's voltage analysis indicates that the time delay will not cause any failure of any equipment connected to and associated with the Class lE emergency power system.
(4)
"The undervoltage monitors shall automatically initiate the disconnection of offsite power sources whenever the voltage setpoint and time delay limits have been exceeded." _
The 2-out-of-3 coincident logic circuitry will automatically initiate the disconnection of offsite power sources when-ever the voltage degrades below the voltage setpoint for a period of time exceeding the proposed time delay.
(5)
"The voltage monitors shall be designed to satisfy the requirements of IEEE Standard 279-1971."
The licensee states that the degraded voltage monitors were designed to satisfy the requirements of IEEE Standard 279 and IEEE Standard 603.
(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 v31tage protec-tion monitors."
The licensee has provided draf t Technical Specifica-tion changes to document voltage setpoints, surveillance requirements, limiting conditions for operation, and diesel generator test procedures for the degraded voltage protection system.
3.3.2 NRC Staff Position 2:
Interaction of Onsite Power Sources with Load-Shed Feature The second position requires the system to be designed to prevent automatic load shedding of the emergency buses once the onsite sources are supplying power to all sequenced loads.
If an adequate basis can be pro-vided for retaining the load-shed feature, the licensee must assign maxi-mum and minimum values to the setpoint of the load-shed feature.
These setpoints must be documented in the Technical Specifications.
The load-shedding feature must also be reinstated if the onsite source supply breakers are tripped.
The present design for Rancho Seco meets NRC Staf f Position 2.
An auxiliary "b" contact from the diesel generator circuit breaker is used to prevent load-sheuding when the emergency diesel generator is energizing -
the Class 1E buses.
If the diesel generator circuit breaker is tripped, the load-shedding logic circuitry will be automatically reinstated.
3.3.3 NRC Staff Position 3:
Onsice Pover Source Testing The third position requires that certain test requirements be included in the Technical Specifications.
These tests are to "... demonstrate the full functional operability and independence of the onsite power sources at least once per 18 months during shutdown." The tests are to simulate loss of offsite power in conjunction with a safety-injection actuation sig-nal and to simulate interruption and subsequent reconnection of onsite power sources.
These tests will verify the proper operation of the load-shed system, the load-shed bypass circuitry, and that there is no adverse interaction between the onsite and offsite power sources.
The licensee states that Rancho Seco will meet Position 3 with a test of the system by simulating a loss of offsite power in conjunction with i
a SI signal.
The test sequence will be bus de-energization, load shedding, voltage restoration, and load sequencing.
The operating time on emergency onsite power will be at least 5 minutes.
The licensee will also interrupt the emergency diesel generators while they are supplying the Class 1E buses to test the reinstatement of the load-shedding circuitry, the load-shedding l
operation and then upon re-energization of the emergency buses by the onsite power source, test the load-sequencing circuitry.
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3.4 TECHNICAL SPECIFICATIONS i
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Sacramento !funicipal Utility District's proposed draf t of i
the Rancho Seco Nuclear Generating Plant's Technical Specifications reflect i
the proposed design modifications.
Specifically, the proposed changes:
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w (1) Include the trip setpoints for the degraded voltage protection sensors and the associated time delays with tolerances (3771 volts j; 38 volts (90.6* of 4160 volts] and 12 seconds j; 1.2 seconds).
(2) Provide the required coincidence logic (2-out-of-3).
(3) Incorporate action statements regarding liniting condi-tions for operations when the number of operable channels for degraded voltage protection is reduced.
j (4) Provide the instrument surveillance requirements for channel check, channel calibration, and channel func-tional test.
(5) Provide the surveillance requirements to demonstrate at least once per 18 months that the loss of offsite power in conjunction with a safety actuation signal will pro-vide the seqt nce of Class 1E bus de-energi:ation, load shedding, voltage restoration, and load sequencing.
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4 CONCLUSION Based on the information provided by Sacramento Municipal Utility District, it has been determined that the proposed modifications to Rancho Seco Nuclear Cenerating Plant comply with NRC Staff Position 1.
All of the staff's requirements and design basis criteria have been met.
The modifica-tions will protect the Class 1E equipment from a sustained degraded voltage condition of the offsite power source.
The present design complies with Position 2 and will prevent load-shedding when the Class lE buses sr2 being energized by the onsite emergency source.
The design also prevents adverse interaction of the offsite and onsite emergency power systems.
The proposed draft of the Technical Specifications and the method of testing the logic circuitry have been reviewed and found to comply with Position 3.
Accordingly, we recommend that the NRC approve the proposed design modifications, and find the draft Technical Specifications acceptable.
t REFERENCES 1.
NRC letter (R. W. Reid) to Sacramento Municipal Utility District (J. J. Mattimoe), dated June 3, 1977.
2.
Sacramento Municipal Utility District letter (J. J. Mattimoe) to NRC (R. W. Reid), dated August 1, 1980.
3.
Sacramento Municipal Utility District letter (J. J. Mattimoe) to NRC (K. R. Go11er), dated June 20, 1978.
4.
Sacramento Municipal Utility District letter (J. J. Matticoe) to NRC (R. W. Reid), dated July 19, 1977.
5.
Sacramento Municipal Utility District letter (W. C. Walbridge) to NRC (R. W. Reid), dated September 22, 1980.
6.
Code of Federal Regulations, Title 10 Part 50 (10 CFR 50), General Design Criterion 17 (GDC 17), " Electric Power Systems" of Appendix A
" General Design Criteria for Nuclear Power Plants."
7.
LEEE Standard 279-1971, " Criteria for Protection Systems for Nuclear Power Generating Stations."
8.
LEEE Standard 308-1974, " Criteria for Class 1E Power Systems for Nuclear Power Generating Stations."