ML19259C520
| ML19259C520 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 10/15/1976 |
| From: | Stolz J Office of Nuclear Reactor Regulation |
| To: | Roe L TOLEDO EDISON CO. |
| Shared Package | |
| ML19259C517 | List: |
| References | |
| NUDOCS 7906230125 | |
| Download: ML19259C520 (5) | |
Text
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R. C. DeYoung F. J. Williams ACRS (16)
J. Miller J. Stolz
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E. Hylton Docket 40. 50-346 L. Engle R. Heinenan D. Ross Toledo Edison Company J. Knight, SS ATTN: Mr. Lcwell E. Roe R. Tedesco Vice President, Facilities V. A. !1oore Developcent H. Denton Edison Plaza bcc-J. R. Buchanan, tiSIC 300 !!adison Avenu
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T. B. Abernathy, TIC Toledo, Ohio 43652 Gentlemen:
EQUIPLIEriT FAILURES CURING A DEGRADED GRID VOLTAGE CO:DITIM AT FilLLSTONE, U!!IT 2 Provided herein as Enclosure 1 is a description of events which occurred at.'!illssone Unt: Ho. 2 during July 1976 relating to plant operation and equipment failures during a degraded grid voltage condi tion.
27, 1976, all utilities with operating reactor facilities On July received telephone notification from the ilRC of the events at the tiillstone 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 resconse by telephone within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.
As a result of our initial investigation and evaluation of the potential generic imolications of the events at itillstone and our preliminary discussior.s with several licensees, we consider it necessary to require all plants presently in review for an operating license to conduct a thorough evaluation of the problen and to sui: nit fonnal reports. Therefora, we request that you conduct an investi-gation of the issue as it affects your facility using tr.e Request for Infurmation detailed in Enclosure 2 as a guide, and provide tP.e analyses and results within 30 days of receipt of this letter or explain why you cannot meet this schedule and provide the schefule you will meet.
EXHIEIT 6 p ge 1 f5 The signed original and 39 copies of your resconse will be necessary.
cci13 a 2283 327 7 D0623 01
Toledo Edison Cenpany c't l
This request for generic information was approved by GAO under a blanket clearance number B-130225 (R0072); this clearance expires July 31, 1977.
Sincerely.
OnsnM suped by
_ John F. Stolz 2 John F. Stolz, Chief Light Water Reactors Branch ?!o.1 Division of Project ibnager.ent
Enclosures:
1.
Description of Events Hillstone Unit tio. 2 2.
Request for Information cc:
Mr. Con 31d ;i. Hauser, Esq.
The Cleveland Electric Illuminating Company P, O. Box 5000 Cleveland, Ohio 44101 Gerald Charnoff Esq.
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Shaw, Pittman, Potts and Trowbridge
"'" 17th Street, fl. W. -
nasnington. D. C.
20036 Leslie Henry, Esq.
Fuller, Seney, Henry and Hodge 300 ftdison Avenue Toledo, Ohio 43604 EXHIBIT 6 page 2 of 5
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DESCRIPTION OF EVENTS
'HILLSTONE UNIT NO. 2 On July 2b,1976, Northeast Nuclear Energy Compa'ny (NNECO) reported that, following a trip of Millstone Unit No. 2 on July 5,1976, several motors powered from 480 volt (v) motor control centers failed to start The failure of the 480 y motors to start was traced to as required.
These blown control power fuses on the individual motor controllers.
controllers receive control power through 480 v/120 y transformers within the controller.
NNECO's investigation disclosed that, as a result of the plant trip, kv to 333 kv. This voltage drop, the grid voltage dropped from352 in conjunction with additional voltage drops associated with the transformers involved, reduced the control power and voltage within individual 480 y controllers to a voltage which was insufficient to As a result, when the actuate the main line controller contactors.
motors were signalled to start, the control power fuses were blown.
Subsequent testing by NNECO showed t!It the contactors required at least 410 y to function properly.
NNECO concluded that under similar low voltage conditions, the opera-bility of 480 v Engineered Safety Feature equipment could'not be assured.
NNECO's immediate corrective action was to raise the setpoint of the Engineered Safeguards Actuation System (ESAS) " loss of power" under-voltage relays to assure that the plant would be separated from the grid and emergency power system (dual) operation would be initiated before the control voltage fell below that required for contactor operation.
A trip of the undervoltage relays causes the emergency buses to be de-energized -a..d 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 during starting of a circulatir.g water pump, the voltage dropped below the new ESAS under-This de-energized the emergency buses, caused voltage relay setting.
load shedding to occur, started the diesel generators and began sequencing
- However, loads ontn the emergency buses in accordance with the design.
during sequencing of the loads onto the buses, the voltage again dropped below the undervoltage relay setting which caused the load shed signal to strip the buses.
The result was energi ed emergency buses with no' loads supplied.
2283 429 EXHIBIT 6 page 3 of 5
AfQUC51 FCW < ! es p Des me.A t f e se 1.
Evaluate the design of your facility's Class IE electrical distribution system to detemine if the operability of safety related equipnent, including associated control circuitry or instrumentation, can be adversely affected by short tem or long tem degradation in the grid system voltage within the range where the of fsite power is counted on to supply important equipment.
Your response should address all but not be limited to the following:
a.
Describe the plant conditions under which the plant auxiliary systems (safety related and non-safety related) will be supplied by of fsite power.
Include an estinate of the fraction of nomal plant operating time in which this is the case.
b.
The voltage used to describe the grid distribution system is usually a " nominal" val ue.
Define the nomal operating range of your grid system voltage and the corresponding voltage values at the safety related buses.
c.
The transfomers utilized in power systems for providing the required voltage at the various system distribution levels are 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.
i
.i d.
Assuming the facility auxiliary loads are being carried by the station 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 require generator trip. _
e.
Identify the sensor location and provide the trip setpoint for your facility's Loss of Offsite Power (undervoltage trip) ine'rumentation.
Include the basis for your trip setpoint selection.
f.
Assuming operation on offsite power and degradation of the grid system voltage, provide the voltage values at the safety related buses corresponding to the maximum value of grid voltage and the degraded grid voltage corresponding to the undervoltage trip setpoint.
g.
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 f unc tio ni.
Include a definition of the voltage range over which the safety related ccmponents, and non-safety ccmponents, can operate continuously in the perfomance of their design function.
2283 330 PM $ bub-
%Tj s
..r.
h.
Describe the bus vol tage monitoring and abnonnal voltage alarms 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 buses to the onsite power system.
Describe the load shedding feature of your design (required prior to transfering to the onsite [ diesel generator]
systens) and the capability of the onsite systems to perform their function if the load shedding feature is maintained af ter the diesel 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.
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 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 performed in response to items 1-3 above.
2283 531 EXHIBIT 6 page 5 of 5