ML20037B650
| ML20037B650 | |
| Person / Time | |
|---|---|
| Site: | Dresden, Quad Cities, Zion, LaSalle  |
| Issue date: | 08/13/1976 |
| From: | Ziemann D Office of Nuclear Reactor Regulation |
| To: | Bolger R COMMONWEALTH EDISON CO. |
| Shared Package | |
| ML20037B651 | List: |
| References | |
| TASK-08-01.A, TASK-8-1.A, TASK-RR NUDOCS 8010270599 | |
| Download: ML20037B650 (5) | |
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Docket Pos.' 50-10 7/249 5 - 34/265 s=
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=u: h4 Comonwealth Edison Company dM I.I....I ATTH: ~ Hr. R. L. Bol ger -
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Assistant Vice President
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c.E: DRESDEN NUCLEAR POWEP. STATION UNIT N05.1, 2 AND 3
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QUAD CITIES NUCLEAR POWER STATIC" UNIT NOS. 1 AND 2 E=
Provided herein as Enclosure 1 is a description of events which
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occurred at Hillstone 'Jnit No. 2 during July 1976 relating to y WE::
plant operation and equipment failures during a degraded grid
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F On July 27, 1976, all utilities with operating reactor facilities s
received telephone notification from the NRC of the events at the Millstone Unit No. 2 facility. At that time members of your staff were asked to investigate the vulnerability of your facility to similar degraded voltage conditions and to provide a response by telephone vitnin 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.
As a result cf our initial investigation and evaluation of the
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potential generic implications of the events at Millstone and our preliminary discussions with several licensees, we consider'it 1
necessary to reouf re all operating reactor licensees to conduct a thorough evaluation of the problem and to submit fonnal reports.
Therefore, we request that you conduct an investigation of the
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=E issue as it affects your facility using the Reouest for Infer ation detailei in Erclosure 2 as a guide, and orovide the ar.alyses and results "ithin P dcys of your recciet of this letter.
Se signc't orirical and 39 ccaies of voor rerponse vill he necess, ry.
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a Comolwealth Edison Company AUG 13 y This recuest for oeneric information was approved by GAO under a blanket clearance number B-130225 (R0072); this clearance expires July 31,1977.
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Sincerely,
. Original Signed by.
DennkYU." lit 4sttr;.th[ef Operating Reactors Branch p2 Division of Operating Reactors Enc 10: ares:
DISTRIBUTION 1.
Description of Events Docket (5) hillstone Unit No. 2 NRC PDR (5) 2.
Request for Information Local PDR (2)
ORB #2 Reading cc w/ enclosures:
KRGoller tir. Charles Whit:3 ore TJCarter President and Chairnan OELD - Swanson/Treby/Karman i:
Iowa-Illinois Gas and 01&E(3)
Electric Company DLZiemann 206 East Secord Avenue WEConverse Davenport, Iowa 52801 PWO'Connor RDSilver itr. John W. Rowe MGrotenhuis Icha, Lincoln & Beale RMDiggs (2)
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Counselors at Law DEisenhut One First National Plaza, 42nd Floor TBAbernathy Chicago, Illinois 60603 JRBuchanan ACRS ( 16)
Anthony Z. Roisman, Esquire VSTello Roisman, Kessler and Cashdan Dross 1712 N Street, N. W.
EVerdery i.ta s hi n':to n, D. C.
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ENCLOSURE NO. 1 5..-
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' DESCRIPTION OF' EVE'NTS 3=b h@ii=
'MILi. STONE' UNIT NO. 2
=w On July 20, 1976, Northeast Nuclear Energy Company (NNECO) reported
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that, following a trip of Millstone Unit No. 2 on July 5,1976, several
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motors powered from 480 volt (Y) motor control centers failed to start
- 1. 9 as required. The failure of the 480 y motors to start was traced to JE blown control power fuses on the individual motor controllers.
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controllers receive control power through 480 v/120 y transformers within m':
the controller.
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NNECO's investigation disclosed that, as a result of the plant trip, the grid voltage dropped from352 kv to 333 kv. This voltage drop,
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transformers involved, reduced the control power and voltage within B;gg individual 480 y controllers to a voltage which was insufficient to actuate the main line controller contactors.
As a result, when the
,1 motors were signalled to start, the control power fuses were blown, i ;= =s Subsequent testing by NNEC0 showed that the contactors required at b-'
least 410 y to function properly.
NNECO concluded that under similar low voltage conditions, the opera-.
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bility of 480 v Engineered Safety Feature equipment could not be assured.
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NNECO's immediate' corrective action was to~ raise the setpoint of the Engineered Safeguards Actuation System (ESAS) " loss of power" under-
=5 voltage relays to assure that the plant would be separated from the T.
grid and emergency power system (dual) operation would be initiated before
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the control voltage fell-below that required for contactor operation.
sis A trip'of the undervoltage relays causes the emergency' buses to be.
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de-energized and a load shed signal 'to strip the emergency buses, the diesel generators to start and power the emergency buses, and required safety related loads to sequence start on the buses.
On July 21, 1976, NNECO reported that the earlier corrective action taken was no longer considered appropriate because durirs starting of a circulating water pump, the voltage dropped below the new ESAS under-voltage relay setting. This de-energized the eme'rgency buses, caussd load shedding to occur, started the' diesel generators and began sequencing
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loads onto the emergency buses in accordance with the design.
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during sequencing of the loads onto the buses, the voltage again dropped 2.1 : 1.~
below the undervoltage relay setting which caused the load shed signal
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to strip the buses.
The rest:lt was energized emergency buses with ne load _ quorlied.
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ENCLOSURE NO. 2 h
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.q REQUEST FOR INFORMATION
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Evaluate the design of your facility's Class IE electrical distribution
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system to detemine if the operability of safety related equipment, including associated control circuitry or instrumentation, can be adversely affected by short tem or 1ong term degradation in the grid e:
system voltage within the range where the off site power is counted on s=+
to supply important equipment. Your response should address all but not-
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be limited to the following:
9 57 a.
Describe the plant conditions under which the plant auxiliary systems
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(safety related and non-safety related) will be supplied by offsite g;., -
power.
Include an estimate of the fraction of normal plarit operating time in which this is the case.
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The voltage used to describe the grid distribution system is usually a " nominal" value.
Define the nomal operating range of your grid system voltage and the corresponding voltage values at the safety
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related buses.
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The transfomers utilized in power systems for providing the 71 required voltage at the various system distribution levels are j.i nomally provided with taps to allow voltage adjustment.
Provide the results of an analysis of your design to determine if the voltage profiles at the safety related buses are satisfactory for the full load and no load conditions on the system and the range of grid voltage.
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As:;uming the facility auxiliary loads are being carried by the stat; ion generator, provide the voltage profiles at the safety buses for grid voltage at the nomal maximum value, the nomal minimum value, and at the degraded conditions (high or low voltage, current, etc.) which would
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require generator trip.
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Identify the sensor location and provide the trip setpoint for your facility's Loss of Offsite. Power (undervoltage trip) instrumentation.
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Include the basis for your trip setpoint selection.
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Assuming operation on offsite power and degradation of the grid system voltage, provide the voltage values at the safety related buses
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corresponding to the maximum value of grid voltage and the degraded grid voltage correspondir,J to the undervoltage trip setpoint.
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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 perfom their safety functions.
Include a definition of the voltage range over which the safety related components, and non-safety components, can operate continuously in the perfomance of their design function.
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Describe the bus voltage monitoring and abnonnal voltage alarms available in the control room.
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The func'tional 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 buses to the onsite power systen. Describe the load shedding feature of your design (required prior to transfering to the onsite [ diesel generator]
systems) and the capability of the onsite systems to perfom their function if the load shedding feature is maintained after the diesel
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generators are connected to their respective safety buses.
Describe the bases (if any) for retention or reinstatement of the load shedding function after the diesel generators are connected to their respective buses.
n 3.
Define the facility operating limits (real and reactive power, voltage, frequency and other) established by the grid stability analyses cited in
=E the FSAR.. Describe the operating procedures or other provisions presently
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in effect for assuring that your facility is being operated within these limits.
4.
Provide a description of any proposed actions or modifications to your facility based on the results of the analyses perfomed in response to items 1-3 above.
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