ML20148K971
| ML20148K971 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 03/23/1988 |
| From: | Silady J COMMONWEALTH EDISON CO. |
| To: | Murley T Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML20148K979 | List: |
| References | |
| NUDOCS 8804010087 | |
| Download: ML20148K971 (4) | |
Text
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. ev2vsa 14:24 CECO-NUCLEM LICEN51NG 294 3974 NO.684 POO2eOOS l
i CommonweaNh Edison G
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33drese Reply to. Poet gf(;e gox 737 CNeago,inros 60690 0767 March 23, 1968 Mr. Thomas R. Murley, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Coestission Washington, DC 20555
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Subject:
Dresden Station Units 2 and 3 Under-voltage Settings for 4KV Relays Request for Waiver of Compliance MRS Docket Wes 50-237 and_50-249
Dear Mr. Murley:
cn March 21, 1988, Dresden Station identified an apparent discrepancy between the Technical Specification value for the 4KV emergency bus under-voltage trip (3092V) and the current trip value (2930V).
It has been determined that the value in Table 3.2.2 of both the Dresden Units 2 and 3 Technical Specifications is not consistent with the engineering and design basis upon which the actual trip value is based.
]
As indicated in Table 3.2.2, the value of 3092V ' corresponds to 3255V-54. While 3255V is equivalent to the proper tap setting for the relay 1
(93V sensed voltage), the manner in which this type of relay functions results in an actual trip value which is 90% of the tap setting. This corresponds to a primary voltage of 2930V.
If the Table 3.2.2 column labeled "Trip Level setting" is intended to represent the actual trip voltage (rather than the reley's tap setting), a Technical Specification change is needed to be consistent *:sith the proper basis for the under-voltage trip. The actual relay tap setting and tirse dial setting are in accordance with the engineering and design basis. This basis is discussed further in the Attachment.
In addition, the Attachment addresses the reset lunction described in Item 2 of taa "Remarks" column of Table 3.2.2.
In order to avoid an unnecessary impact on plant opgrations, a Temporary Walver of Corapliance is requested until an appropriate license amendment can be prepared and processed.
Since the proper settings are being used, there is no effect on the safety of plant operations and no significant hazards consideration exists.
i 8804010087 880325 PDR ADOCK 05000237 P
i
, March 23, 1988 T.B. Murley Your concurrence is therefore requested with continued operation of Dresden Units 2 and 3 under a Temporary waiver of compliance as a result of this inappropriate Technical specification value. An appropriate amendment will receive expeditious On-Site and off-site Review and will be submitted for NRC Staff review and approval as soon as possible. We believe a reasonable schedule for this effort can support a submittal by March 28, 1988.
If for any reason this does not appear to be achievable, the Dresden Project Manager and the Region will be notified immediately.
please contact this office should further information be requirsd concerning this request.
Very truly yours, ga J. A. Silady Nuclear Licensing Administrator la Attachment cci A.S. Davis - RIII Admin.
M.A. Ring - RIII M. Grotenhuis - NRA M.C. Parker - ILWS NRC Resident Inspector - Dresden
- SUBSCRIBRD AND '
to befor me Lhis day of 'h 4A f
._, 1988 (Y
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V ' Notary Pub 1'ic 4391X
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I ATTAcHMENY Dresden Station Design B: sis for 6
"First tavel" 4XV Under-Voltace_ Relay Settings An aggarant inconsistency between the Technical Specifications and the l
as-set condition of 4XV emergency bue under-voltage relays has raised questions about safe opeestion. Our evaluation has determined that the actual relay settings meet the design basis.
Since the relay operates on an inverse time curve, a range of 4KV voltage bus values are acceptable based on the time to perform the design basis safety function trip.
The FSAR des'gn basis of this "first level" under-voltage relay is to sense a loss of offsite power.
Upon sensing a loss of pcwer to the 4KV bus, the diesel-generator is started, nonessential loads are tripped, ant essential loads are not restered until bus voltage is reestablished.
In addition, this relay is set to accommodate bus voltage drops due to motor starting.
"Second level" under-voltage relays are provided for degraded voltage protection.
These relays are set at approximately 3700V.
The IAV relay used for this first level under-voltage function is a time delay relay designed to be used for protection against abnor.aal voltage conditions.
The settings are accomplished by selecting the proper voltage tap and time dial settings.
This particular relay is set by selecting one of seven discreet voltage taps ranging between 55V and 140v.
Nomin-si voltage on the 4KV bus is 4160V.
This is reduced by a potential device with a 35:1 ratio, making the sensed voltage 118.85.
Based upon the relay's available tap settings, the 93V tap was selected. This 93V setting equates to 3255V on the primary bus.
This setting provides a trip at 83.7V i 5%, which is 2930V or aporoximately 70% of rated voltage, thus providing a voltage cushion for motor starts.
The adjacent discreet tap settings are 105V and 82V, which equate to 3675V and 2870V, respectively. For this type relay, with the design specified time dial setting, the trip would be expected at 90%
of these values. The 93V is the a.ost appropriate for meeting the design rcquirements. This tap setting ensures prompt sensing of a loss of off-site power and provides assurance that the bus will remain available during anticipated loading sequences.
Approximately 70% of neeninal voltage has been considered ar. industry standard for detection of '.oss of off-site power.
This rule of thumb has existed in the power industry for years and has recently been referenced in NURDG-0800 Branch Technical positio.1 pSB-1 adequacy of shutdown electric distribution system voltages (Rev. 2 - July, 1981).
The reset functi6n of both the first and the second level under-s'altage schemes are one in the saa:s since they are tied in series. Upon the diesel-generator closing into the bus at 4160V, both unior-voltage relay resets will be satisfied. The second level under-voltage will reset at 3800V or greater instantaneously.
The first level under-voltage will start reset at 3255V and will follow the reset curve associated with tap and time dial settings.
One point on the curve is defined at 4160V and a time delay of 2.5 seconds.
Upon reset, a permissive contact will allow ECCS pumps to start.
pump starting is controlled by the LOCA initiation and load sequencing logic control circuits.
3800V, or 91% of nominal, is the lowest voltage that reset begins and is within all motor specifications.
i i
The under-voltage relay reset function is periodically tested using surveillance procedures (DOS 6600-3-4-5-6-9).
During this surveillance, off-site power to the 4KV bus is removed and a simulated accident signal is initiated.
Diesel-generator loading sequences are observed. Reset functions and timing are verified to be within design requirements.
The adequacy of the 93V setting and the design specified time dial setting for the relays has been demonstrated by plant operation and surveillance testing. Diesel-generator loading sequences are periodically tested, and this relay setting has not resulted in tripping of loada during these surveillances.
Given the design basis and the actual performance of the present under-voltage relay setting, the setting will provide the intended safscy functions for control of the 4KV emergency buses.
The relay setting and reset are within the design basis.
As described in this lett6r, the actual 4KV bus trip voltage is expected to be 2930V i 5%.
4 March 25, 1988 DISTRIBUTION:
Docket Nos. 50-237/249 Docket File PDIII-2 Plant File NRC & Local PDRs ACRS (10)
PDIII-2 r/f JPartlow Mr. D. L. Butterfield, Jr.
LLuther EJordan Nuclear Licensing Manager MGrotenhuis OGC-Rockville Comonwealth Edison Company E, s m._
P.O. Box 767 t,,r %
Chicago, Illinois 60690 p.g
Dear Mr. Butterfield:
SUBJECT:
TEMPORARY WAIVER OF COMPLIANCE FOR TECHNICAL SPECIFICATION TABLE 3.2.2 RE: UNDERVOLTAGE SETTING FOR 4 KV RELAYS Re:
Dresden Nuclear Power Station, Unit Nos. 2 and 3 By letter dated March 23, 1988, you requested a temporary waiver of ccepliance from Technical Specification Table 3.2.2 for Units 2 and 3 which requires an undervoltage trip of 3092 volts instead of 2930 volts.
Your letter prcvided a discussion and a basis for the waiver.
It is our understanding that your letter will be followed by an amendment request early next week.
We have reviewed your request and find that your current practice with respect to the undervoltage trip adequately meets the safety intent of the Technical Specifications and is therefore acceptable on an interim basis. This letter confirms our oral approval for the temporary waiver of compliance to extend for 2 months from the date of this letter.
By that time, an arrendment to the Technical Specification is expected to be issued.
Sincerely,
's Gary Holahan, Assistant Director for Regions III & V Reactors Division of Reactor Projects - III, IV, V and Special Projects cc:
A. B. Davis C. Norelius M. Ring W. Forney T. Ross See Attached List f
- PREVIOUSLY CONCURRED LOLSHAN FOR PDIII-2*
PDIII-2*
PDIII-2*
REG.IIIviatele.;
MGrotenhuis/ww Lluther DMuller EGREENMAN/VIRGILIO GHOL HAN 3/24 /88 3/
/88 3/24 /88 3/22/88 3[y788 wr-
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!l Mr. L. D. Butterfield, Jr.
Dresden Nuclear Power Station Comonwealth Edison Company Units 2 and 3 cc:
Michael Miller Esq.
Sidley and Austin One First National Plaza Chicago, Illinois 60603 Mr. J. Eeniganburg Plant Superintendent Dresden Nuclear Power Station Rural Route il Morris, Illinois 60450 U.S. Nuclear Regulatory Comission Resident Inspection Office Dresden Station Rural Route #1 Morris, Illinois 60450 Chainnan Board of Supervisors of Grundy County Grundy County Courthouse Morris, Illinois 60450 Regional Administrator Nuclear Regulatory Comission, Region III 799 Roosevelt Road Glen Ellyn, Illinois 60137 Mr. Michael C. Parker, Chief Division of Engineering Illinois Department of Nuclear Safety 1035 Outer Park Drive 5th Floor Sprindield, Illinois 62704 l
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CM Fir 1 National P'aze. CNeago, mirne 4
C Apose ReMy to. Poet M sox 757 CNcago,lihros 60690 0767 g g4 g March 23, 1988 Mr. Thomas R. Murley, Director Office of Nuclear Reacto-Regulation U.S. Nuclear Regulatory cossaission Washington, DC 20555 subject: Dresden Station Units 2 and 3 Under-voltage 3ettings for 4KV Relays aequest for Waiver of compliance etc Docket Wes. 50-237 and 50-249 Dear Mr. Murleys on March 21, 1988, Dresden Station identified an apparent discrepancy between the Technical Specification value for the 4KV emergency bus under-voltage trip (3092V) and the current trip value (2930V).
It has been determined that the value in Table 3.2.2 of both the Dresden Units 2 and 3 Technical Specifications is not consistent with the engineering and design basis upon which the actual trip value is based.
As indicated in Table 3.2.2, the value of 3092V corresponds to 4255V-5%.
While 325',V is equivalent to the proper tap setting for the relay (93V sensed voltage), the manner in which this type of relay functions results in an actual trip value which in 90% of the tap setting. This corresoonds to a primary voltage of 2930V.
If the Table 3.2.2 column labeled "Trip 1,evel Setting" is intended to represent the actual trip voltage (rather than the relay's tap setting), a Technical specification change is needed to be consistent with the proper basis for the under-voltage trip.
The actual relay tap setting and tirne dial setting are in aenordance with the engineering and l
design basis.
i This basis is discussed further in the Attachment.
In addition, l
the Attachment addresses the reset function described in Item 2 of the "komarks" column of Table 3.2.2.
In order to avoid an unnecessary impact on plant operations, a Temporary Waiver of compliance is requested until an appropriate license amendment can be prepared and processed.
Since the proper settings are being used, there is no effect on the safety of plant operations and no significent hazards consideration exists.
ymtJOl &f ffD
i t
T.B. Murley March 23, 1988 Your concurrence is therefore requested with continued operation of Dresden Units 2 and 3 under a temporary Waiver of Compliance as a result of this inappropriate Technical Specification value. An appropriate amendment will receive expeditious On-Site and Off-Site Review and will be riubmitted for WRC Staff review and approval as soon as possible. We believe a reasonable schedule for this effort can support a submittal by March 28, 1988.
If for any reason this does not appear to be achievable, the Dresden Project Manager l
and the Region will be notified innediately.
Please contact this office should further information be required j
concerning this request.
Very truly yours, lb J. A. Silady Nuclear Licensing Administrator j
i la Attachment r
cet A.B. Davis RIII Admin.
M.A. Ring - RIII M. Grotenhuis - WRR M.C. Parker - IDW8 NRC Resident Inspector - Dresden SUBSCRIBED AND-to befor se Lhis day of 'h AAA i
_, 1988 e aA 74
) lbno k Notary PubI1c 4391K i
I ATTAcHMENY Dresden Station Design Basis for 6
"First IAvel" 4XV Under-Voltaqt_ Relay Settings An apparent inconsistency between the Technical Specifications and the as-set conditien of 4XV emergency bus under-voltage relays has raised questions about safe operation. Our evaluation has determined that the actual relay settings meet the design basis.
Since the relay operates on an inverse tims curve, a range of 4XV voltage bud values are acceptable based on the time to perform the design basis safety function trip.
l The FSAR design basis of this "first level" under-voltage relay is to l
sense a loss of offsite power. Upon sensing a loss of power to_the 4KV bus, the l
diesel-generator is started, r.onessential loads are tripped, and essential loads are not restored until bua voltage is reestablished.
In addition, this relay is set to acconmodate bus voltage drops due to motor starting.
"Seccnd level" under-voltage relays are provided for degraded voltage protection. These relays are set at :pproximately 3700V.
The IAV relay used for this first level under-voltage function is a time delay relay designed to be used for protaction against abnormal voltage conditions. The settings are accomplished by selecting the proper voltage tap and time dial settings. This particular relay is set by selecting one of seven discreet voltage taps ranging between 55V and 140V.
Nominsi voltage on the 4XV bus is 4160V. This is reduced by a potential device with a 35:1 ratio, making the sensed voltage 118.85.
Based upon the relay's available tap settings, the 93V tap was selected. This 93V setting equates to 3255V on the primary bus.
This setting provides a trip at 83.7V + 5%, which is 2930V or approximately 70% of rated voltage, thus providing a voltage cushion for motor starts.
The adjacent discreet tap settings are 105V and 82V. which equate to 3675V and 2870V, respectively.
For this type relay, with the design specified tires dial setting, the trip would t,e expected at 90%
of these values. The 93V is the most appropriate for meeting the design requirements.
This tap setting ensures prompt sensing of a loss of off-site power and provides assurance that the bus will remain available during anticipated loading sequences.
Approximately 70% of nominal voltage has been considered an industry standard for detsetion of loss of off-site power.
This aule of thumb has existed in the power industry for years and has recently been referenced in NUREG-0800 3 ranch Technical position pSB-1 adequacy of shutdown electric distribution system voltages (Rev. 2 - July, 198U.
The reset function of both the first and the second level under-voltage schemes are one in the same since they are tied in series. Upon the diesel-generator closing into the bus at 4160V, both under-voltage relay resets will be satisfied. The second level under-voltage will reset at 3800V or greater instantaneously.
The first level under-voltage will start reset at 3255V and will follow the reset curve associated with tap and time dial settings. One point on the curve is defined at 4160V and a time delay of 2.5 seconds. Upon reset, a permissive contact will allow ECCS pumps to start.
pump starting is controlled by the LOCA inPiation and load sequencing logic control circuits.
3800V, or 91% of nominal, is the lowest voltage that reset begins and is within all motor specifications.
.-..~ - ss -. -. ~.. ~
e-
&+-
c-i 2-The under-voltage relay reset function is periodically tested using surveillance procedures (DOS 6600-3-4-5-6-9).
During this surveillance, off-site power to the 4KV bus is removed and a simulated accident signal is initiated.
Diesel-generator loading sequences are observed. Roset functions and timing are verified to be within design requirements.
The adequacy of the 93V setting and the design specified time dial setting for the relays nas been demonstrated by plant operation and surveillance testing. Diesel-generator loading sequences are periodically tested, and this relay setting has not resulted in tripping of loads during these surveillances.
Given the design basis and the actual performance of the present under-voltage relay setting, the setting will provide the intended safety functions for control of the 4KV emergency buses.
The relay setting and reset are within the design basis. As described in this letter, the actual 4KV bus trip voltage is expected to be 2930V 2 5%.
a