ML20212M339

Forwards Draft Safety Evaluation Supporting Computer Program for Predicting Transient & steady-state Responses of Auxiliary Power Sys.Draft Will Be Incorporated Into SER on Vol 2 of Nuclear Performance Plan

ML20212M339
Person / Time
Site:	Sequoyah
Issue date:	01/13/1987
From:	Youngblood B Office of Nuclear Reactor Regulation
To:	White S TENNESSEE VALLEY AUTHORITY
References
NUDOCS 8701300087
Download: ML20212M339 (11)

Text

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Docketflos.: 50-327 ,..

and 50-328 3 3 JAN iS87 ifr. S. A. White fianager of Nuclear Power Tennessee Valley Authority 6N 38A Lookout Place 1101 Market Street Chattanooga, Tennessee 37402-2801

Subject:

Transmittal of Draft Safety Evaluation on Brarch Technical Position PSB-1 The staff has prepared the enclosed draft safety evaluation on the Tennessee Valley Authority (TVA) Branch Technical Position (BTP) PSB-1.

The staf f intends to incorporate this evaluation into the Safety Evaluation Report (SER) on Volume 2 of the Nuclear Performance Plan which addresses Sequoyah.

Based on its review, the staff has found the TVA response to BTP PSB-1 acceptable. You shculd assure that any safety-related employee concerns pertaining to this issue ere appropriately addressed prior to the start-up of the Sequcyah units.

If you have any questions, please contact the Sequoyah Project f'anager, Mr. Joseph Holonich at (301) 492-7270.

Sincerely,d\

B. J. Youngbicod, Director

• PWR Project Directorate #4 Division of PWR Licensing-A

Enclosure:

As stated

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Mr. S. A. White Tennessee Valley Authority Sequoyah Nuclear Plant cc:

Tennessee Department of Public Regional Administrator, Peofon Ti Health ATTN: Director, Rureau of U.S. Nuclear Regulatory Commission, 101 Ma rietta Street, N.W., Suite 2900 Environmental Health Services Atlanta, Georgia 30323 Cordell Hull Building Nashville, Tennessee 37?l9 J.A. Kirkebo ATTN: D.L. Williams Mr. Michael H. Mobley, Director Tennessee Valley Authority Division of Radiological Health 400 West Summit Hill Drive, W12 Al? T.E.R.R.A. Buildiro Knoxville, Tennessee 37902 150 4th Avenue North Nashville, Tennessee 37203 Mr. Bob Faas Westinghouse Electric Corp. County Judge -

P.O. Box 355 Hamilton County tourtheuse Pittsburgh, Pennsylvania 15230 Chattanooga, Tennassee 37402 R. L. Gridley Tennessee Valley Autnority SN 1578 Lookout Place Chattanooga, Tennessee 3740?-7801 M. R. Harding Tennessee Valley Authority Seouoyah Nuclear Plant P.O. Box 2000 Soddy Daisy, Tennessee 37379 Resident Inspector /Sequoyah NPS c/o U.S. Nuclear Regulatory Commission 2600 Igou Ferry Road Soddy Daisy, Tennessee 37379 H.L. Abercrombie Tennessee Valley Authority Seouoyah Nuclear Plant P.O. Box 2000 Soddy Daisy, Tennessee 37379

, 4.1 Pranch Technical Position PSR-1 4.1.1 Summary of issue in order to verify the validity of voltage drop calculations for the Sequovah Nuclear Plant Auxiliary Power System (APS), the staff recommended by letter dated March 26, 1986 that TVA perform a new verification test es prescribed in Branch Technical Position PSB-1 (part B.4) since the staff could not conclude that TVA had adequately demonstrated that a new verification test was not I

necessary. This recommendation was largely based on the staff's review of TVA's October 2,1980 test report and finding of inconsistency in load valves used in the analysis with what was secured during the test. Also, there have been chances in the APS configuration and the computer procrams used for the above voltage drop calculations. A meeting was held on April 16, 1986, during which TVA presented additional infomation and clarification to their October i

2, 1980 test report in support of its position that performina additional verification testing of the APS at Sequoyah was not necessary. Subsecuently, TVA agreed to provide additional information for further staff review as follows:

1) Confirmatory analysis to demonstrate that the new computer procram is com-parable to the old computer procram which was used in the original test report by inputting the same load values into the new computer program and comparing the calculated voltages.

2) Analyses to demonstrate that there is no significant configuration change between the 1980 and 1986 systems by inputting the data from the July 12 and 16, 1980 tests into the 1980 A 1996 system models and comparino the calculated voltages.

3) More detail on how the two tests (.luly 19 and 16,1980) were conducted and description of how the circuit breakers were aligned for each configuration.

On June ?,1986, TVA provided a response along with a report titled "NRC Branch Technical Position PSR-1 Reanalysis."

The staff has reviewed the additional information and has re-evaluated the previous position on the need for the verification test.

However, the staff still could not conclude that sufficient basis was provided to demonstrate that no new verification test was necessary since the computer program could not predict the transient response of the system. The staff transmitted its evaluation expressing this conclusion to TVA by letter dated August 1,1086 and also transmitted additional questions requiring further clarification on the transient analysis on August 7,1986. Ry letter dated September 11, 1986, TVA provided their response to these ouestions, and aua-mented this response by letter dated December 3, 1086. The staff has reviewed the information provided by TVA on the need for verification testing. Its evaluation is presented below.

4.1.? Evaluation 4.1.2.1 Computer Hardware and Program Changes Since the mainframe computer (MC) and its program "VNEW" which were used for the previous verification test have been replaced by the personal computer (PC) with a new program called " RADIAL", the staff was concerned whether the proaram l

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W RADIAL /PC is equivalent to the old program VNEW/MC regarding analytical tech-niques and assumptions. At the April 16, 1986 meeting, the staff requested a confirmatory analysis using the July 12, 1980 test configuration to demonstrate that there is no appreciable difference in the calculated voltages of the two (i.e., RADIAL /PC vs. VNEW/MC). TVA also included a Stone & Webster computer program. All three computer programs were run by using an identical set of loads for each board. The results were as follows BOARD VNEW RADIAL STONE & WEBSTER 6.9 kV Start BUS A 7152 7151 7148 6.9 kV Start BUS B 7011 7008 7005 6.9 kV Unit Bd IB 7011 7008 7005 6.9 kV Shutdown Bd 1A-A 7004 7002 6998 480 V Shutdown Bd 1Al-A 495 495 495 480 V RX Vent Bd 1A-A 483 483 Not Conducted The staff review of the results of these analyses finds that the voltage . values obtained from the three computer programs show no appreciable voltage dif-ferences. Consequently, this indicates that both computer programs' analytical techniques and assumptions are equivalent for the steady state. However, this comparison requires verification of the steady state and transient response characteristics of the two computer programs. This test result failed to demonstrate the transient response and the steady state at 120/208 volt level.

Therefore, the replacement of the old computer program with the new computer program appears to be verified for the steady state case only down to the 480 volt level.

In the evaluation transmitted to TVA by its August 1,1986 letter, the staff requested additional justification for not performing the PSB-1 test down to the 120/208 V level. TVA responsed to this issue by describing their two 120 V ac control power systems as follows: one is the 120V ac Vital Instrumentation and Control Power System (VCPS) fed from the vital inverters and the other con-sists of Class 1E 120 V ac Motor Control Centers (MCCs) supplied from the 480/120 V control power transformers. For the 120 V ac VCPS, the vital inverters are designed to maintain the output voltage regulation within 2% of 120 V ac with an input voltage of 480 V ac 7.5%. In addition, upon loss for unacceptable degradation) of the 480 V ac input, the battery will supply the loads with no interruption of regulated power. For the Class IE 120 V ac PCCs, TVA referred to their recent transient voltage calculations which were performed under worst-case conditions (i.e., the worst expected transient voltage at each MCC) to demonstrate that adequate voltage exists to pick up the control devices (i.e., motor starter, solenoids, relays, etc.) for expected transient conditions.

The staff review has found that TVA's new computer program can adequately predict the response of the Sequoyah power system down to the 480 V level, the VCPS through its inverter and battery backup design eliminates the effects from 480 V ac degraded voltage input or transients, and the worst case transient calcula-tions indicate that the 480/120 V ac MCC control power transformers can ade-quately perform their safety functions.

The staff concurs with the TVA assessment that the 120 V ac VCPS design features and the voltage calculations performed for the worst case 120 V ac MCC voltages assure that adequate voltage will be available to components supplied by the 120 V ac control power system. Thus, no additional PSB-1 related tests to demonstrate system response at the 120/208 V level are necessary.

1.1.2.2 Change Out of 100 Valve Motors Another concern identified by the staff was that the replacement of 100 valve notors with the motors of different electrical characteristics rey affect the plant steady state load making it necessary for the new system loadings to be re-analyzed. However, TVA indicated that this charge out will only affect the transient loading and voltage whereas the steady state load remains the same.

Therefore, the staff finds that the change out of 100 valve n.cters represents no overall load increase for the steady state ccr.dition.

4.1.2.3 Addition of Two Start Buses and One Comn,on Station Service Transformer In response to a staff concern that TVA had added two nce stert buses which could result in new loads or impedance, TVA explained that the two additional start buses were not actually added, but instead, the original two start buses were split into four buses, thus no new loads or impedances woulo be added.

Although the third common' station service transformer has been added, the cir-cuit breakers are normally open making the transformer available as a backup for either of the other stetion service transformers. TVA den.onstrated that ,

this change has little effect on the overall Sequoyah APS cor. figuration by performing a comparison of the voltage analyses between the 1980 (two start FLses) and 1986 (four start buses) configurations. The compariser was perforried Usino the July 12 and 16, 1980 test data and the new computer progran. TFr results are summarized as follows:

TEST I TEST II (July 12, 1980) (July 16, 1980) t CONFIGURATION CONFIGURATION BOARD 1980 1986 1980 1986 F.TTV Start EUS A 7T5T 7135 70T5 7DTI 6.9 kV Start BUS B 7051 7045 7067 7062 6.9 kV Unit Bd IB 7051 7045 7067 7062 6.9 kV Shutdown Bd 1A-A 7044 7038 7060 7055 4F0 V Shutdown Bd 1Al-A 501 500 501 501 4E0 V RX Vent Bd 1A-A 493 500 494 501 Start of EPCW pp (Tern. V) Not Conducteo C705 6695 Start of Aux. BLG E)H f/fl 1A Not Conducted 495 458 As can be seen for the above results the analyses show oc appreciable voltage difference (max.1.5%) betweer the 1900 and 1986 configurations. Therefcre, this incicates that the new configuration has not changed the old electrical syster configuration significantly.

4.1.2.4 Reanalysis of the 1900 Verification Test Results With respect to the verification tests performed at Sequoyah in 19P0, TV/., in its June 2, 1986 response, explained how the circuit breakers were aligred fer each test configuration.

The staf f review of the test procedure found that a comparison was madt Letween the calculated board voltages, based on load values derived (not neasured) f ron

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breaker alignment and the supply voltages, and the board voltages cbtained from the tests. The staff found that this procedure deviated from our Branch Technical Position PSB-1 (Part B.4) which requires measurements of bcth leads and voltages for a given test configuration and then, using the, raeasurer' icad values on each board as input to the computer model to calculate the voltages.

Subsequently, the analytically derived voltage values and the test results are compa red. To be consistent with our present PSB-1 procedure, during the meeting on April 16, 1986, the staff requested new analyses be performed by using the load values obtaired during the tests as input to the new computer pregr6m. The results are as follows:

TEST I TEST II (July 12, 1980) (July 16, 1980)

BOARD PEASURED ANALYSIS % MEASURED ANALYSIS 7 T.T IV Start BUS A 7200 7154 D.6 7000 7045 V.6 6.9 kV Start BUS B 7000 7051 0.7 7000 7067 1.0 6.9 kV Unit Bd IB 7100 7051 0.7 7090 7067 0.3 6.9 kV Shutdown Bd 1A-A 7000 7044 0.6 7100 7060 0.6 4P0 V Shetdchn Bd IAl-A 495 501 1.2 500 501 0.2 480 V RX Vent Bd 1A-A 404 493 1.9 489 494 1.0 Start of ERCW pp Not Ccrducted 6787 6705 1.2 (Tem V)

Start of AUX. BLG Not Conducted 466 450 1.F EXP FAN 1A TVA used board meters, test meters and brush recorders for taking test measure-rents. However, due to calibrction prublems the brush recorcer failed to yield consistent results. As a result, TVA's Jure ?, 1986 response did not include the measured values obtained from the brush recorder. It is also indicated that current transfonner and pcwcr transformer inaccuracies were present.

Because the allched accuracy limit was not specified by the staff in Position 4 of FSAR Question 0.33, TVA stated that all measurements were taken by the board neters whose accuracy was limited to 5%. Therefore, a 5% tclerance was estab-lished cs the raximum acceotable difference between the measured voltages ari calculated voltages.

4.1.2.5 Branch Technical Position PSB-1 (PART E.a)

TVA perferred the 1980 verification tests at Sequoyah in response to a staff ouestion which was askcd during the licensing review (FSAR Ouestien 8.33).

i This questier was a precursor to Branch Technical Position PSB-1 (Part B.4) which was issued as part of the Standard Review Plan ir Jnly 1981. Part B.4 of PSB-1 provides detailed guidance for perfonnance of their verificction tests.

Although Question 8.33 does not explicitly foclude all of the guidance of Part B.4 of PSB-1, it does so by clear implication. Therefore, the staff evaluation of the 1980 tests was based cr. establishing a correlation between these tests and the testing and expected test rcsults specified in Part B.4 of PSB-1. In the April 16, 1900 meeting, TVA concurred that the intent of posi-tion 4 of (uestion E.33 requirement is the sare as Part E.4 of PSC-1 require-ments, even though the PSB-1 requirements are Fore specific.

I Part B.4 of PSB-1 states the following:

a) leadfep the station distribution buses, including all Class IE buses dct.n to the 120/208 Y level, to at least 307; _.

b) recording to the existing grid crd Class IE bus voltages and bus loeding ocwn the 120/208 volt level at steady conditiers and during the starting of both a large Class IE and ncn-Class IE motor (not concurrently);

hote:

to rainilaize the number of instrumented locations, (recorders) during the motor starting transiert tests, the bus voltages and Iceding need only be recorded on thet string of buses which previously showed the lowest analyzed voltages.

c) usir.g the analytical techniques and assumptions of the previous vcltage erelyses and the measured existing grid voltage and bus loading conditicrs recorded during conduct of the test, calculate new set of voltages for all the Class IE buses down tc the 120/E08 volt level; d) compare the analytically derived voltage values agairst tFe test results.

L'ith sced ccrrelation (within 37) between the analytical results and the test results, is tre validity of the mathervatical model used in the voltage arelysis established. However, the above procedure involves testing c' teth the steady state erd trcnsient response characteristics. In order to perfom the transient motor testing, the starting of both a large class 1E erd ncn-class IE is required.

The intent of such a transient test reccirerrent is to detect potential spuricus loaa sheocing motor is started.or separation of class IE system fren offsite power when a large The ability of the computer rodel to predict the effects of the motor transient in the systen is verified by cortparirr tFe data raeasured duririg the trenstent test with the computer predicted transient values. Upon ccrplction of both the steady state and transient analyses, the validity cf the tretherratical model is verified.

Lased on its review of the June 2, IcF6 submittal, the staff has concluded that there is reasoneble assurance that TVA's new ccrputer program can adequately predict Sequoyah /.PS steady-state response characteristics. However, the staff made the following firidir.gs en the transient aspect of the PFP 1 test.

1.

The test report indicated instrurrent recording problems such that starting retor dip values were not reliably estchlished (i.e., no transiert dett for the motor and the class IE busts).

1.

The selected r.otor sizes (700 hp are 1EO hp) were not large enough to shu.

cr,y significant transient effect (the dip was only for one cycle). The Erarich Technical position PSE-1 (pert B.4) requires starting of both 4.

large class 1E and a large non-class if irotor (not concurrently).

2.

L'o transient voltage analysis wet perforried by comparing resuits ei cM-culations performed by the new corputer program with the data obtained during the starting of large trators.

Subsequent to the staff's August 1,1986 evaluation, the staff transnitted a request for additional information covering the transient aspects of the PSC-1 test. Cr September 11, 1986, TVA provided its response to the questions and further augmented this response by letter dated Decernber 3,1986.

In the absence of an explanation regarding the transient measurements taken curing the starting of large n:cters and how these values were used to assure the computer model's ability to accurately predict trensient effects, TVA pro-vided the brush recorder traces (voltage and currer.t) taken at the motor tenainals for the 460 Y Auxiliary Building General Supply UFCS) fan and the largest f.f kV Essential Raw Cooling Water (EfCk) pump on the 6.9 kV shutdown beard. The measured voltage values for the equipment have been cerrpered with theold(VNEW)andnew(RADIAL /1900and1966 configuration)voltagevalves calculated fron the computer programs.

MEASURED CALCULATED VOLTAGES H.P. VOLTAGE VNEW RADIAL (80) RADIAL (86) DIFF (%)

ERCW Pump 7F 6787 M7 6703 6695 1.4 ABGS Fan 150 466 449 459 45E 3.8 TVA found the maximum deviation to be 3.8r between the measured voltage ar.d the voltege calculated using the old program (VNEl.') with loading derived fror the closed circuit breaker configuration and individual load ratings. The deviation in this case is more than the 3% guideline described in PSE-1. However, the measured voltages when compared with the new corcuter program voltages derived using r.easured bus load values were within 2%. Therefore, the staff concluces that TVA's new con.puter model can accurately predict the transient respor.se cf the system.

With respect to the request to " provide the brush recorder traces of load currents obtained during the ncter starting transient tests whicF were used in the transient calculatinns perforr.ed of ter the test to predict systen tus volteges," TVA provided the measureo startirs and running currents for pbese A and C of the 6.6 kV ERCW punp and 460 V ABGS fan. Although the brush reccrder traces incleted both the voltage and current neasurercents, the main focus of PSB-1 deals only with the voltages available in the C1tss IF buses. Therefore ,

the measured current values were not used to calculate bus voltages, but pro-vided to show the actual length of the notor startine transient as oppcsed to the voltage traces which changed very little due to the stiffness of the ptwer source. However, the measured nFese A starting currents were used to calculate the first-cycle voltage dips which were compared with the measured voltage values. The two results were found to be the sane.

Curing its review of these recordings, the staff found a difference in the phase A ana phase C running current values which could be indicative of a phase unbalance condition or a rneter abnormality. In addition, these un-balancec current values, if used, pctertially could affect the system bus voltage calculations.

By letter dated December 3, 1986, TVA explained that the differences in the Otasc A and C current readings are nut indicative of a phase current unbeler.cc, but are due to instrument calibration problems. The fact that no real crbelance

between phase A and C existed was substantiated by a corrperison of the board instrumentation reters reasbring the same currents. I.e., the board meter readings indicated no substantial difference in chase A and C currents.

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The staff has reviewed the reccrdings of the voltage traces and finds then con-sistent with the licensee's discussion of the trotor transients. Thereforc, the staf f concurs with TVA that no actual unbalance of rctor phase currents existeo and that the voltage traces are adecuate for the PSB-1 analysis.

To accress the one cycle voltage dip experierccd during the motor starting transient test, TVA provided the brush recorder traces of the terrrinal voltage and current for the 6.6 kV ERCW pump and 460 V ABGS fan which they obtained during the tactor transient tests. The current traces clearly indicated that the acceleration times were about one second for the ERCW pump ard about seven socords for the ABGS fan. TVA determined from the voltage traces that the 6.6 kV ERCW purap motor start dio depress the teminal voltage for approyirately the acceleration tirae (i.e. , 60 cycles). However, the measured voltage die for the 460 V APGS fan was for only approximately 6 cycles. For both cases, the worst part of the voltage dip occurred during the first cycle. TVA, further, concluded that this ccrresponds to the instant that the rnotor rotor is locked and the reter just starts to accelerate. TVA further stated that there was no reasurable voltage sag at either the 6.9 kV or the 480 V switchgear buses during rcctor start.

Based on its review of TVA's brush recorder traces, the staff finds the TVA assessrcent of the Dotor starting voltage transients acceDtable.

In regard to an additional staff concern of whether conservatism was used in calculating the ettects of starting large motors, TVA stated "Our analyses are not a true transient calculation which would show the exponential voltage rccovery due to the change in n.otcr incdance while accelerating. Der clicula-tiers essume that the voltage dip is at its lowest Doint for the entire accel-eration tire of the motor." Further, TVA stated " cur transient analyses model the 6.9 kV shutdown beard voltage depressed at the I cycle voltace for the entire acceleration time of the 6.6 kV required starting loads."

The staff finds that the TVA transient analysis model represents a rore con-servative condition with respect to the motor starting vcitage and its duration for the voltage recovery time. Therefore, it concludes that the TVA method for c61culating the effects of startirg large rcotors results in a more conservative transient voltage calculation ther the exponential voltage recovery which actually occurs during rnotor acceleration.

In response to e staff request for the worst case voltage calculation on Class 1E boards duriro the starting of a reactor coolant purcp follcwing an acci-

, dent, TVA deterrnineo the worst case for the 6.9 kV Class IE shutdown boards te be. approximately two minutes after e safety injection and phase B contair,rtrt isolation with the 161-kV grid at a rinimum of 159 kV. Although the voltage at the 6.9 kV Class IE boards dipped to 6761 V upon starting the 6000 hp reactor coolant pump, TVA stated that the board recovered to 690? Y ef ter 6pptoximately 14 seconds. Further, IVA stated that this voltage transient dces r.ot drop out the 6.9 kV Clast IE shutdown boards degraded voltus e relays and adequate vcitage wct1d be available for Class IE leads.

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1 The staff has reviewed this assessment and concludes that the Sequoyah APS is capable of successfully starting a reactor coolant pump following an accident under minimum grid voltane without adversely affecting Class JE loads.

4.1.3 Findings For the steady state aspect of the test, the staff finds that:

1.

The new configuration has not affected the overall voltage profile of the 6.9 kV boards.

2.

The change out of 100 valve motors represent no overall load increase.

3.

The replacement appears of the old computer program with the new computer program to be acceptable.

4 '

Despite the fact that our Position 4 of Question 8.33 contained no specific the consistency 5',

Seouoyah metering was of the results between the anal-accuracy req yses and test values (within ?%) show that the model consistently predicts steady state system performance.

5.,

Although no test and analyses were perfomed down to 170/70R volt level where ability of the class 1E control circuit to pick up the control devices such as starter, relay, and solenoid is determined, TVA has demonstrated that adequate control voltage is available to components supplied by the 120 V ac processing.

Therefore, no additional test are necessary.

As for the transient aspect of the test, the staff finds that:

1.

based on its evaluation of the TVA ,fustification regarding 170 V ac control power system design features and calculations, no additional PSB-1 related transient tests for the 120/708 y level are necessary; 2.

based on its review of the brush recorder voltage and current measurements taken at the terminals of the ERCW and ARGS motors and the supporting information provided by TVA, (1) the differences between the calculated transient voltages from the new computer pro voltages are within the PSR-1 guideline, (2) gram the and onethe measured cycle voltaae transient dip is an accurate measure of the actual minimum transient volta difference in recorded currents (between phases A and C) ge, andto(31 is due a the recorder calibration problem and is not indicative of a current unbalance problem; 3.

in comparison with the exponential voltace recovery model nomally used in calculating the effects of starting large motors, TVA's transient analysis model, which assumes the voltace dip at its lowest point for the entire accelerating time of the motor, is conservative; and 4.

TVA has provided the worst case calculation for voltages on Class IE buses and found pump that an following theaccident.

APS is capable of successfully starting a reactor coolant

, 9 4.1.4 Conclusion Based on its review of the steady-state and the transient calculations provided by TVA, the st4t f ccccludes that there is sufficiert tasis for..TVA's new computer progran to predict the transient and the sitccy-state responses of the

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Sec;uoyah APS. Thus, a new verit1cetion test for the APS voltace study ur. der PSB-1 is not required.

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