ML17341B471

Proposed Design Mod & Tech Spec Changes on Grid Voltage Degradation for Turkey Point Nuclear Generating Plant, Units 3 & 4, Technical Evaluation Rept

ML17341B471
Person / Time
Site:	Turkey Point
Issue date:	10/28/1982
From:	Selan J LAWRENCE LIVERMORE NATIONAL LABORATORY
To:	NRC
Shared Package
ML17341B469	List: ML17341B468 ML17341B470 ML17341B471
References
CON-FIN-A-0250, CON-FIN-A-250 NUDOCS 8211110549
Download: ML17341B471 (14)

Text

ENCLOSURE 2

TER ABSTRACT This report documents the technical evaluation of the proposed design modification and Technical Specification changes for protection of Class 1E equipment from grid voltage degradation for the Turkey Point Nuclear Generating Plant,, Units 3 and 4.

The review criteria are based on several IEEK standards and the Code of Federal Regulations.

The evaluation finds that the licensee has not provided sufficient information on the undervoltage protection system to allow a complete evaluation into the adequacy of protecting Class lE equipment from sustained voltage degradation.

FOREWORD This report is supplied as part of the Selected Electrical, Instrumentation, and Control Systems Issues Program bei.ng conducted for the U. S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation, Division of Licensing, by Lawrence Livermore National L'aboratory.

The U. S. Nuclear Regulatory Commission funded the work under the authorization entitled "Electrical, Instrumentation and Control System Support,"

B&R 20 19 04 031, FIN A-0250.

8211110549 82i028 PDR,'DR ADQCK 05000250

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TABLE OF CONTENTS.

Page INTRODUCTION~

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DESIGN BASIS CRITERIA 2

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EVAL'UATION

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3.1 Existing Undervoltage Protection 3-2 Modificat'ions 3 '

Discussions

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-3.3.1 NRC Staff Position 1:

Second Level of Under-Voltage or Overvoltage Protection with a Time Delay 3.3.2 NRC Staff Position 2:

Interaction of Onsite

.Power Sources with Load Shed Feature.

3.3.3 NRC Staff Position 3:

Onsite Power Source Testing 3.4 Technical SPecifications

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CONCLUSION

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6 REFERENCES

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8 ILLUSTRATION' Figure 1

'Turkey Point Nuclear Generating

Plant, Units 3 and 4

Electrical One-Line Diagram 3

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TECHNICAL EVALUATION REPORT ON THE PROPOSED DESIGN MODIFICATIONS AND TECHNICAL SPECIFICATION CHANGES ON GRID VOLTAGE DEGRADATION FOR THE TURKEY POINT NUCLEAR GENERATING PLANT, UNITS 3 AND 4 (Docket Nos. 50-250, 50-251)

James C. Selan Lawrence Livermore National Laboratory l.

INTRODUCTION By letter dated June 3,

1977 [Ref. 1], the U.

S. Nuclear Regulatory Commission (NRC) requested Florida Power and Light Company (FPL), the licensee, to assess the susceptibility of the Class 1E electrical equipment to sustained degraded voltage conditions at the offsite power sources and to the interaction between the offsite and onsite emergency power systems at the Turkey Point Nuc3.ear Generating Plant, Units 3 and 4.

In addition, the NRC requested that the licensee compare 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 protect'ive features.

Further, the NRC.required certain Technical Specifications be incorporated into the facility's operating license.

By letters dated July 21, 1977 [Ref. 2], November 9,

1979 [Ref. 3],

January 1'4, 1981 [Ref. 4], and May 10, 1982 [Ref. 5], the licensee proposed certain design modifications to the undervoltage protection system.

The design modifications include the installation of a degraded voltage protection system for the Class 1E equipment.

The purpose of this report is to evaluate the licensee's,proposed design modifications, Technical Specifi'cation changes, and~ proposed LCO's to'etermine that they meet the criteria established by the NRC for the. protection of Class 1E equipment from grid voltage degradation.

2.

DESIGN BASIS CRITERIA, The design basis cri.teriai that were applied in determining the

'cceptability of the system modific:ation to protect t:he Class lE equipmen't from degradation of grid voltages aire as folllow4:

(1)

General Design Criterion 17 (GDC 17'), "Electric Power Systems," of Appendix A, "General Design Criteria for Nuclear Power Plants,"

Code of Federal Regulations Title 10, Part 50.(10 CFR 50) [Ref. 6].

(2)

IEEE Standard 279-19'71, "Criteria for Protection Systems" for Nuclear

.Power Generating Stat.ions'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 l.et.,ter dated, June,'3, 1977

[Ref, 1].

3.

EVALUATION 3.1 EXISTING iJhDERVOLTAGE 1.'ROTECTION The present undervoltage protection desij~n utilizes two undervolta'ge

'elays on each of thie 4160-volt Class 1E buses (Buses A and

'B of Figure 1).

The relays are instantaneous type HGA whic:h respond at 40% - 50% of 4160 volt.

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These relays are used as loss-of-voltage protkctio6.

The relay logic (2-out-of-2) is such that actuation of one relay (Al or A2) on "A" bus in conjunct:ion with the'ac'tuation of its interconnecited relay (Bl or B2) on "B" bus will initiate the offsite source disconnection, load shedding, diesel generator starting and subsequent load sequencing on both buses.

For exampl.e, the starting of diesel'enerator 3 and the dis-connection of startup transformer 3 is initiated')'r the actuation of relay Al on bus 3A and rel'ay B2 on bus 3B or thie actuat ioin of 'relay Al and the starting sequencing of diesel generat:or 4.

This logic scheme resu11s in two separate and 'redundant circuits, The load sheclding feature is bypassed when the Class 1E buses ar' being supplied by the cli.esel. generators.

240KV SYSTFH HAIN TRANS.

Ii DISC. I.INKS UNIT AUX.

TRANS.

4 STARTUP TRANS.

4 HAIN TRANS.

3 TRANS.

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TRANS, 3

DISC.

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)480'V 3D FIGURE I TURKEY POINT UNITS 3 AND 4 ELECTRICAL ONE-.LINE DIAGRAM i

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MODIFICATIONS The licensee, is proposing design changes to the existing underv'oltage protection system and are as follows:

(1)

The logic of the existing relays will be reconnected such that the offsite source disconnectiong load shedding, diesel generator starting, and, load sequencing vill occur only for that

'bus on which the, loss of voltage occurs.

'The logic will remain 2-out-of-2 but the scheme on bus A

will now be independent of 'that on bus B.

.*(2)

The installation of two additi'onal im'rerse time relays (type IAV) on.each 4160-volt Class 1E bus

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The function of these relays will be to protect 'the Class 1E equip-ment from sustained degraded voltagesd These relays function similar to and utilize the same logic as the loss-of-voltage relays except

'viW the~"b" contact of the diesel generator breaker.

Thus, when the breaker

closes, the relays will be bypasd'ed'd disable the load shedding feature (3)

The:installation of two additi'on@1 'in0tantaneous relays (type ITE27H) on each 480-volt Class 1E load centers These relays in a 2-out-of-2 logic will 'be interlocked with a safety injection (SI) signal Wlhen, actuated after' time delay due to a degraded'olt'age condition concurren't with a SIP existing timers will then initiate the source disconnection, load shedding,

'difisel generator starting, and subsequent load sequencing~.

3.3 DISCUSSION This section presents a statement on the NB'C staff position from their June 3,

1977 letter [ref. I] followed by an evaluation of the licendee" s'esign.

3.3.1 NRC Staff posltlon 3,:

Second Level of Undervtltage ot Overvoltage Protect:Lon wttt a Tfne Delay This position is to be met by the liceInsbe meeting certain criter'a.

'ach criterion has been evaluated against the licensee's proposal and is addressed below.

( l)

"The 8< lect inn oF volt~gc and time sctpoints shall be determined from an analysis of the voltage requirements of the safety-related loads at all onsite system distribution levels."

The licensee has not submitted the voltage setpoints and

'ssociated time delays for the proposed additional relays.

However, the licensee states.[Reft

4) that the voltage set-points for the additional relays on the 4160-volt buses will be chosen to actuate when the voltage degrades below that required to safely operate the running Class LE equipment.

The voltage setpoint for the 480-volt load center relays will be selected to actuate when.the voltage degrades below that required to safely start all Class LE loads.

The time delay will be based on load acceleration times.

The licensee is required to verify that the voltage and time setpoints seLected were based on an analysis of the. voltage requirements of the Class LE equipment at all Class LE voltage distribution levels.

r-(2)

"The voltage protection shall include coincidence logic to preclude spurious trips of the offsite power sourc'es."

The proposed coincident logic of 2-out-of-2 will preclude spurious trips from the offsite sources.

(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 licensee has not submitted the time delays with tolerances associated with the proposed design changes nor has provided the.time del'ay assumed in the FSAR accident analysis.

The licensee is required to verify that the time delay with tolerances does not exceed the maximum time delay assumed'n the FSAR acci-dent analysis.

(b)

"The time delay shall minimize the effect of short-duration disturbances from reducing the availability

.of the offsite power sources."

The licensee has not finalized the selection of the setpoints (voltage and time)

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Therefore, a determina-tion cannot be made on the adequacy of the time delay for minimizing the effects of short duration transients.

The licensee is required to verify that the time delay selected will be such that the effects of short duration transients will not cause the availability of the off-site sources to be reduced.

(c)

"The allowable time duration of a degraded voltage condition at all distribution system levels shall not re'suit in 'fa:Ll'ure of safety systems or components."~

Since the t:Lme delay has not been finalized, a verifica'-

t:ion that a.Ll Class 1E equipment at all voltage distxi-butfon leve.'Ls wil'1 be.adequately protected hps not b6en'rovided by the licen.ee-The licensee does state

[]Ref. 4] that the setpoints selected will ensure adequa't'e'rotection to the running and starting Class lE equipment>>

The licensee f.s required to verify that the t,ime delay

'elected is protecting all the Class 1E equipment at all Class IE voltage distribution levels

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(4)

"The, undervoltage monitors shall, automaticall.y inf.tiate the disconnection of offsite power soux'ce's whenever the voltage setpoint and tfme delay limits hav~ been exceeded."

The operation of the:TAV relays 'on'h'e 4160-volt Class lE buse.s in a 2-out-of-2 coincident logic.will automatically initiate the disconnection from the off.ite source whenever the vo.'Ltage and time delay setpoints are exceeded.

Should a degraded voltage occur concurx'ent with a safety injection

signal, the relays (ITE-27H) located.on the 480-volt Class lE load center buses in a 2-out-of-2 logic will initiate the'uto-d:Lsconnection from the dr gr'aded 'offsite source.

(5)

"The. voltage monitors shall, be designed to satisfy the requirements of IEEE Standard 279-1971."

The licensee states

[Ref. 4] that the design modification.

comply with the ingle. failure requirement of IEEE 279-1971.

However, the licensee has not've'rifie'd that the proposed design modifications meet all.'he req'uirements of IEFE, 279-1971.

The licensee is required to verify that the proposed de. ign changes to thh Clads lE power system meet all the requirements of IEEE 279'-1971'such as qualification, fndependence, te. tibility, et'.)'.

(6)

"The Technical Specifications shal>l. f.nclude l,imiting condi-tXons for operation, surveillhnc'e req'uirements, trip setpoints with minimum and maximum limits, and allowable'value.

for the second-level voltage protecti*n hokitbrs."

The licensee has not submitted appropriate Technical Specifi-cation changes to reflect the~de'sign iinodfiications to the under-voltage protection system.

The ~lieenhee is requfred to submit

" Technical Specifications changes~

t6 document the setpoints

with,

,tolerances, surveillance require'mer'its',

and limiting conditions for operation.

3'.2 NRC Staff Position 2:

Interaction of Onsite Power Sources with Load Shed Feature The second position requires the system 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 provided for retaining the load-shed

feature, the licensee must assign m'axinum and min-imum values to the setpoint of the load-shed. feature.

These setpoints must be be documented in the Technical Specifications.

The load-shedding feature must also be reinstated if the onsite source supply breakers are tripped.

The licensee is bypassing the load-shed feature once the onsite sources are supplying the Class 1E buses.

This bypassing is accomplished by the interlocking of the load-shed relays on the 4160-volt Class 1E buses with the "b" contact of the diesel generator breaker.

Tripping of the breaker will automatically reinstate the load-shed feature.

The licensee is required to provide details on the bypassing/reinstatement of.the relays on the 480-volt Class 1E load center buses.

3.3.3

%tC Staff Position 3:

Onsite Power Source Testing The third position requires that certai'n.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 inconjunction with a safety-injection actuation signal 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'nter-action between the onsite and offsite power sources.

The licensee has not submitted appropriate Technical Specifications to document that the testing requirements of this position are met.

The licensee is required to submit tests in the Technical Specifications which will demonstrate the operability and independence of the onsite sources, loss of off-site power in conjunction with an SI, and the interruption and subsequent recon-nection of the onsite sources.

3;4 TECHNICAL SPECIFICATION The licensee has not provided appropriate Technical Specification changes on the design modifications to the undervoltage protection system.

The Technical Specification changes required by the 'licensee are to incude:

(1)

Voltage and time delay trip setpoints with tolerances of the undervoltage relaying system.

(2)

The required coincident logic'minimum 2-out-of-2).

(3)

Surveillance requirement.

for a channel check at least once per 12 hour1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.;,

a channel functional test at.least once per 31 days and a channel calibration at least, once per 18 months (refueling)

(4)

Limiting conditions for operation including action statements when the number of required channels is less than the minimum number required.

(5)

Test requirements to demonstrate the operability and independence of the onsite sources and the undervoltage relaying circui,ts'odifications.

CONCLUSIONS Based on the information submitted by Florida Power and Light Company, it has been determined, that insufficient information has been submitted on the design modifications to deterxgine that all the requirements of NRC Staff Position 1 are met.

The information still. required from the licensee for'i'val-'ation is as follows:

(1)

Verification analysis which demonstrates that the selected'oltage/time setpoints with tolerances of the undervoltage'.rkla'ys're protecting all Class lE equipment at all voltage distriibution levels and will'inimize the effect's of short duration transients.

(2)

Voltage and time delay setpoi6ts'i'th'tolerances of the proposed design modifications.

(3)

Technical Specifications changes for the design modifications including the setpoints (volta'ge'an'd t!ime).with tolerances, surveillance requirements, and limiting conditions for opekatio'n (including action statements).'4)

Verification that the time delay selected does not exceed the.

maximum time delay assumed in 'th6 FSAR accident analysis.

(5)

Verifcation that the, design mo'dific'ations to the Class 1E power system will comply with all the requirements of IEEE 279-1971.

The licensee is bypassing the load-'shhd feature once the onsite'ources're supplying the Class IE equipment and is a'uto-reinstating the feature folio~~in'g breaker tripping.

Therefore, NRC Staff Position 2 is met.

Details of thjs ',cir-cuitry modification was provided for the load-shed relays on the 4169-'olt busks but not for the relays on t'e 480-volt load c'ent!er,'buses.

The licensee is required to submit details of the bypassing/reinstatement at the 480-volt level.

The lf.censee has not provided appropriate Technical Speci.fications

, whi'ch demonstrate that the'esting requirements of NRC Staff Position 3 are met.

Therefore, the licensee is required to submit Technical Specifications to include test requirements Qhich will demonstrate the full functional oper-ability and independence of the onsite sources.

The tests are to simulate loss of offsite power in conjunction with an SI and. the interruption of the onsite sources with subsequent reconnection.

These requirements will verify that there is no adverse interaction between onsite and offsite sources and the load-shed feature and the load-shed 'bypassing circuitry.

J REFERENCES 1;

NRC letter to Florida Power and Light Company (FPL), dated June 2,. 1977.

2.

FPL letter (R. E. Uhrig) to NRC (George Lear), dated July 21, 1977.

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"FPL letter (R. E. Uhrig) to NRC (W. G. Gammill), dated'. November 9, 1979.

4.

FPL letter (R. >. Uhrig) to NRC'(T. M. Hovak), dated January 14, 1981.

5.

FPL letter (R. E. Uhrig) to NRC (T. H. Novak), dated May 10, 1982.

6.

Code of Federal Regulations, Title 10, Part 50 (10 CFR'0),

General Design Criterion 17 (GDC, 17), "Electric Power Systems" of Appendix A "General Design Criteria for Nuclear Power Plants."

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IEEE Standard 279-1971, "Criteria for Protection Systems for Nuclear Power Generating Stations."

8.

IEEE Standard 308-1974, "Criteria for Class lE Power Systems for Nuclear Power Generating'Stations."

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