ML19210A364
| ML19210A364 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 09/16/1976 |
| From: | Arnold R METROPOLITAN EDISON CO. |
| To: | Reid R Office of Nuclear Reactor Regulation |
| References | |
| GQL-1313, NUDOCS 7910290594 | |
| Download: ML19210A364 (7) | |
Text
NRC roRu 195 u.s. NUCLE AR RE GULATORY C' 4ISS 4
DOCKET NUMOE R 50-289 (2 76)
NRC DISTRIBUTION FOR PAR'. 50 DOCKET MATERIAL TO:
R.W. REID FROM: METR DATE OF DOCUME NT METROPOLITAN EDISON CO.
9-16-76 READING, EA.
DATE RECEIVED R.C. APNOLD 9-22-76 SLETTER ONOTORIZED PRCP INPUT FORM NUMCE R OF COPIES RECElvF D Z ORIGIN AL
@ V NC LASSIFIE D OccPy 240 CESCH'pTION ENCLOSU RE LTR. RE OUR Sal 2-76 LTR.....TRANS TFE FOLLOWING, RESPONSE TO OUESTIONS CONCERNING ThE PLAhi OPERATIOJ AND EQUIPMENT FAILURES DURING A DEGRADED GRID VOLTAGE........
( 1 CARBON SIGNED CY. RECEIVED)
( 7 PAGES)
DO NOT REMOVE ACKN0rLEDGED PLANT NAME:
THREE MILE ISLAND #1 1491 020 SAFETY FOR ACTION /INFORMATION ENVIRO SAB 9-22-76 I
I I ASSTCNED AD1_ _
3 AOSIGNED AD;
-BRANCH CHIEF:
REID BRANCH cMTrF-
-7ROJECT MANAGER:
ZWETZIG PROJECT FSNAGER!
fIC, ASST.:
INGRAM LIC. ASST >t M "ERDERY 1
INTERN.{L DISTRIBUTION
- ~; FTT3 SYSTEMS SAFETY PTP:T 9YSTrvs SITE SAFETY &
C-ftRC PDR HEIhEMAN TFnr9Cn ENVIRO ANALYSIS I
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SCHROEDER BENAROYA DENTON & FTTT FR i
OfLD LAINAS TOSSICK & STAFF ENGINEERING
/ IPPOLITO ENVIRO TECTI _
MIPC MACCARRY KIRKWOOD FRNST CASE KNIGHT I
BALLARD HANAUER SIHWEIL OPERATING REACTORS SPANCT TR HARLESS PAWLICKI STELLO 9TTF TFFH PROJECT MANAGEMENT REACTOR SAFETY OPERATING TECli.
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METROPOLITAN EDIS COMPA o BSICIARY OF GENERAL PUBLIC UTILITIES CORPORATION t..~
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TELEPHONE 215 - 929 3601 p.!
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September 16, 1976 1
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D kg Director of Nuclear Reactor Regulation C
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R. W..Reid, Chief
'D Operating Reactors Branch A e,
%,. J' -.g U. S. Nuclear Regulatory Commission i,,,
Washington, D. C.
20555
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Lear Sir:
Three Mile Island Nuclear Station Unit 1 (TMI-1)
Docket Number 50-289 Operating License DPR-50 Enclosed please find responses to questions 1 tvarded by your letter of August 12, 1976, concerning pisnt operatico, and equipment' failures
.during a degraded grid voltage.
Sincerely, Signed: R. C. ARNOLD
~
21. C. Arnold Vice President RCA:JJM:eg 1491 021
la.
Describe the plant conditions under which the plant auxiliary systems (safety related and nonsafety related) vill be supplied by offsite power. Include an estimate of the fraction of normal plant operating time in which this is the case.
The plant auxiliary systems are fed by two full size auxiliary trans-forcers which are connected to different 230 kv busses and provide a source of power for startup, shutdown, and after shutdown requirements.
Each of the auxiliary transfor=ers has two isloated secondary windings, one at 6900 volts and one at h160 volts.
The 230 kv substation incorporates a breaker-and-a-half scheme for high reliability and is connected to the existing Metropolitan Edison Company 230 kv transmission network by three circuits, two full capacity circuits going north to Middletown junction on separate double circuit towers and one-half capacity circuit going south to Jackson single circuit towers. TMI Unit 1 generates electric power at 19 kv vhich is fed through an isolated phase bus to the unit main transformer bank where it is then stepped up to 230 kv transmission voltage and delivered to the substation.
In view of the above, the plant auxiliary system (safety-related and non-safety related) are nor= ally supplied by offsite power 100% of the time.
Ib.
The voltage used to describe the grid distribution system is usually a " nominal" value. Define the normal operating range of your grid system voltage and the correspow'. dug voltage values at the safety related busses.
The nominal value of the grid voltage is 230 kv.
The nomal operating range of the grid voltage is 232 to 236 kv.
The corresponding voltage values at the safety related busses on full load are the following:
Grid voltage 232 kv 236 ky 4160 v Bus (lD or 1E) 3999 7 y 4071 9 y k80 v Bus IP 445 7 h53 9 v k80 v Bus 1R hkS.6 456.9 y h80 v Bus is kh6.9 k55 2 v h80 v Bus IT 450 7 h59 0 v 1c.
The transformers utilized in power systems for providing the required voltage at the various system distribution levels are normally provided with taps to allov voltage adjustment. Provide the results of an analysis of your design to determine if the voltage profiles at the safety related busses are satisfactory for the full load and nc load conditions on the system and the range of grid voltage.
There are five fixed 230 kv voltage taps at the auxiliary transformers.
The are 218.5 kr, 22h.24 kv, 230 kv, 235 75 kv, and 241.5 kv.
The present 1491 022
2 tap setting is at 230 kv and voltage profiles for this tap setting at the safety related busses for the full auxiliary load and no-load conditions on the system and the range or grid voltage indicated in 1b above are as follows:
Bus Full Load No Ioad 230 y 232 kv 236 hv 232 kv 236 kv 4160 v 3999 7 y 4071.9 y 4196.2 y h268.5 480 v (1P) kk5.7 v 453.9 y h84.2 v 492.5 k80 v (1R) hh8.6 v 456.9 y h84.2 v 492.5 480 y (1s) kh6.9 v h55.2 y h84.2 v 492 5 480 v (IT) h50.7 y h59.0 v 484.2 v 492.5 The voltage profiles at the safety related busses for the other tap settings have also been calculated and are found to be satisfactory for the full load and no load conditions on the system and the range of grid voltage.
14.
Assumin's the facility auxiliary loads are being carried by the station generator, provide the voltage profiles at the safety busses for grid voltage at the normal maximum value, the nor=al minimum value, and at the degraded conditions (high or lov voltage, current, etc.) which wou'.4 require generator trip?
Based on Penn-Jersey Matrix (PJM) criteria, the maximum limit of 230 kv grid voltage is 2hl.5 and the minimum limit is 218.5 kv.
The degraded voltage condition which requires a generator trip is an overvoltage condition which is 118" of 230 kv or 271.8 kv.
Assuming the station auxiliary loads are being carried by the station generator only, the voltage profiles at the safety busses for grid voltage at the normal
==v4mm value, the normal minimum value and at the degraded conditions which would require generator trip are the following:
Bus Normal Minimum Nor=al Maximum Degraded Maximum 230 kv 218.5 241.5 271.8 kv 4160 v 3756.25 h171.07 4717 9 kh80 v (1P) 417.87 465.28 527 9 480 v (1R) h20.68 h68.25 531.1 480 v (IS) h19.05 h66.51 529 2 480 v (IT) 422.79 470.39 533.2 le.
Identify the sensor location and provide the trip setpoint for your facility's loss of offsite Power (undervoltage trip) instrumentation.
Include the basis for your trip setpoint selection.
Undervoltage tripping relays are included in each of the kl60 volt E.S. busses 1D and lE and the h80 volt busses 1P, 1R, 1S, and 1T.
Undervoltage trip setpoints are as follows:
1491 023
3 Bus Setpoints k kv 3588 volts h80 v kl0 volts The undervoltage relays on the E.S. switchgear have been set to operate at a point sue.h that there vill be no detrimental conditions on the system. The contacts on the h kv system are set to close at a slover rate than the 480 volta system due to a problem that arose during preoperational testing. During the " loss of offsite power" test, the h80 volt undervoltage relays did not trip before the h kv relays, thus exceeding diesel generator block-1 loading conditions.
In order to rectify the problem, the 4 kv relays were set to operate at a slower rate than the k80 volt system, but still within a tolerance acceptable to operate a motor under slight undervoltage conditions.
The original and present basis for the undervoltage trip setpoints is to maintain the bus voltage above motor starting voltage.
if.
Assuming operation on offsite power and degradation of the grid system voltage, provide the voltage values at the safety related buses corresponding to the ma*um value of grid voltage and the degraded grid voltage corresp.nding to the undervoltage trip setpoint.
The voltage values at tle safety related busses corresponding to the maximum value of grid voltage (2hl.5kv), and the degraded grid voltage corresponding to the undervoltage trip setpoint (209 kv corresponding to k kv undervoltage trip setting of 3588 volts) are as follows:
Bus Voltage 230 kv 209 kv 2hl.5 kv 4160 v 3588 h171 480 v (1P) 399 h65 h80 v (1R) 401 h68 480 v (1s) too h66 480 v (IT) hok 470 i
Ig.
Utilizing the safety related bus voltage values identified in (f),
evaluate the capability of all safety related loads, including related control circuitry and instrumentation, to perform their safety functions Include a definition of the voltage range over which the safety related components, and nonsafety components, can operate l
continuously in the performance of their design function.
1 l
At the safety-related bus voltage values identifiec in (f) above, corresponding to the maximum grid voltage (241 5 kv), there is no problem as far as operation of safety-related equip =ent is concerned.
i 1491 024 i
I
4 However, at the safety-related bus voltage values corresponding to the degraded grid voltage viz., 209.19 Kv, one could hypothesize a situation wherein the 480 V bus undervoltage trip devices trip all 480 V E-S/Non E-S loads off the 480 volt busses, but because of the inherent time lag built into the 4 kv undervoltage tiip relays described in " Basis for Unk teltage Trip Settings" in le above, the 4 kv bus might not clear and a further hypothesis of an E-S signal appearing during such conditions might result with the h80 volt E-S motors not being available until the h kv bus clears.
However, the above is a highly improbable situation since with only one of 3-230 kv lines available for plant operation and UMI Unit i not on line, the grid voltage is expected to be about 95.6% of nominal, viz., 219.88 kv and it has to be pointed out that the reactor may not be made critical with less than two 230 kv lines in service nor may operations be continued with only one 230 kv line in service unless Unit 1 generator is estrying its own auxiliaries ('DfI-1 Techni::al Specifications, para. 3.7.2).
Therefore, the degradation of grid voltage to that corresponding to the undervoltage trip setpoint is an extre=ely unlikely aituation in view of the facts mentioned in the previous paragraph and this would probably be a gradual change which can be respoaded to by proper g
operator action. The safety-related bus voltages corresponding to a degraded Crid voltage of 219 88 kv (approximately 220 kv) are the following:
Buss Voltage 230 Kv S20 Ky h160 v 3783.29 y h80 v (IP) 420.96 y h80 v (1R) h23.78 h80 v (IS) h22.14 h80 v (IT) h25.89 All safety-related equipment including control circuitry and instrumen-i l
tation have been designed to operate satisfactorily at the above reduced i
bus voltages.
I Testa made at TMI-1 on starters /contactors supplying power to three phase h80 volt ES equipment have shown that they operate satisfactorily to a voltage of 384 volts and minimum pickup values have ranged from 241 volts to 336 volts and dropout values have ranged from 140 to 261 volts.
Ih.
Describe the bus voltage =cnitoring and abnor=al voltage alarms available in the Centrol Room.
There are voltmeters on each of the 4160 and h80 volt busses.
- Also, potential transformer alar =s (indicating one out of three undervoltage i
1491 025
5 relays has operated) and undervoltage a'. arms on the h160 and 480 volt busses are available in the Control Room.
2.
The functional safety requirement of the undervoltage trip is to detect the loss of offsite (preferred) power system voltage and initiate the necessary actions required to transfer safety related busses to the onsite power system. Describe the load shedding feature of your desi n (required prior to tressferring to the onsite (diesel generator)
E systems) and the capability of the onsite systems to perform their function if the load shedding feature is maintained after the diesel generators are connected to their respective safety busses. Describe the bases (if any) for retention or reinstatement of the load shedding function after the diesel generators are connected to their respective busses.
The loss of AC power from the auxiliary transformers vill result in undervoltage relay action on the h kv engineered safeguards bussea 1D and 1E.
The operation of the h kv bus undervoltage relays vill result in tripping of all motors connected to the busses except for the engineered safeguards block-1 loads. The h kv feeders to the 480 volt unit substations are not tripped by b kv bus undervoltage, however, the 480 volt unit substation busses have their own undervoltage relays which will trip all 480 velt motors connected to their respMtive busses.
The load shedding feature in not maintained after the diese.f. generators are connected to their respective safety bueses and therefore this part of the question is not applicable to TMI-1.
3.
Define the facility operating limits (real and reactive power, voltage, frequency and other) established by the grid stability analyses cited in the FSAR. Describe the operating procedures or other provisions
. presently in effect for assuring that your fac'11ty is being operated within these limits.
The facility operating limits established by the grid stability analyses are not cited in the FSAR. However, there is a generatoi-trip on over-voltage at 118% of 230 kv neminal voltage at 60 Hz.
Also there is an underfrequency trip which trips the Jenerator at 57.5 Hz.
h.
Provide a description of any proposed actions or modifications to your facility based on the results of the analyses performed in response to items 1-3 above.
As a result of the above analyses, it is concluded that no modifications to the Class 1E distribution system at TMI-1 is required.
1491 026