ML17199W146
| ML17199W146 | |
| Person / Time | |
|---|---|
| Site: | Dresden  |
| Issue date: | 03/28/1988 |
| From: | Silady J COMMONWEALTH EDISON CO. |
| To: | Murley T Office of Nuclear Reactor Regulation |
| References | |
| 4418K, NUDOCS 8804110084 | |
| Download: ML17199W146 (6) | |
Text
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., _,....,.r*- __.. \\ 851 Commonll!Alth Edison One First Nati-Plaza, Chicago, Illinois Address Reply to: Post Office Box 767
~hicago, Illinois 60690 - 0767
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Kr. Thomas E. Murley, Director Off ice of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, DC 20555 Karch 28, 1988
Subject:
Dresden Station Units 2 and 3 Proposed License Amendment for 4KV Undervoltage Setting NRC Docket Nos. 50-237 and 50-249 References (a):
Letter from J.A. Silady to T.E. Murley dated Karch 23, 1988 (b):
Conference Call between CECo (J.S. Abel,
Dear Kr. Murley:
E.D; Eenigenburg, et.al.) and NRC (G.K. Holahan, W.G. Guldemond, et.al) on Karch 22, 1988.
The referenced letter requested a Temporary Waiver of Compliance concerning the subject trip level settings in Table 3.2.2 of the Dresden Station Units 2 and 3 Technical Specifications.
Verbal approval was received per Reference (b), provided that Commonwealth Edison submit an appropriate amendment on a reasonably expeditious schedule.
Pursuant to 10 CFR 50. 90 and. 10 CFR 50. 59, Commonweal th Edison Company (CECo) proposes to amend Provisional Operating License DPR-19 and Facility Operating License DPR-25 to correct the discrepancy between. the Table 3.2.2
- value for the 4K emergency bus undervoltage trip (3092V) and the current trip value (2930V).
It has been determined that the value in Table 3.2.2 is not consistent with the engineering and design basis upon which the actual trip value is based. discusses the functional operation and design basis of these "first level" relays which are designed to detect a complete loss of bus voltage, as well as the "second level'" relays which protect safety-related equipment from the effects of a degraded voltage condition.. summarizes each of the specific changes to Table 3.2.2, its footnotes, and the related bases section. provides the affected Technical Specification pages with the proposed changes incorporated and identified by change bars. provides the CECo evaluation of potential significant hazards considerations as a result of the proposed amendment and concludes that
.norie exist.
- 8804110084 880328 I !----"\\
PDR ADOCK 05000237 I
- P DCD LJ
T.E: Hurley 2 -
March 28, 1988 The proposed amendment has received On-Site and Off-Site Review approval.
CECo has notified the State of Illinois of our request by providing a copy of this letter and the Attachments to the designated State Official.
In accordance with 10 CFR' 170, a fee remittance in the amount of
$150.00 is 'enclosed.
If you have any further questions concerning this submittal, please contact this office.
Very truly yours, 9a~
J. A. Silady Nuclear Licensing Administrator lm
Enclosure:
Fee Remittance Attachments (4) cc:
A.B. Davis - Region III Administrator M.A. Ring - Region III 4418K H. Grotenhuis -
NRR NRC Resident Inspector - Dresden H.C. Parker - IDNS r -.
ATTACHMENT 1 DISCUSSION OF PROPOSED AMENDMENT A.
BACKGROUND During a procedure revision review of Dresden Operating Surveillance (DOS) 6600-9, Testing of ECCS Undervoltage and Degraded Voltage Relays, it was determined that the 1st level undervoltage relay settings for the 4KV Emergency Buses were not in agreement with the Technical Specifications Table 3.2.2 (Instrumentation that Initiates or Controls the Core and Containment Cooling System).
The undervoltage relays (type IAV69A) monitor the 4KV Emergency Buses and consist of two contacts which close upon undervoltage (right hand contact) and overvoltage (left hand contact).
During the performance of DOS 6600-9 the undervoltage contact is verified to close at 83.7 :t 5\\ volts which corresponds to bus voltages of 2930 :t 5\\ volts.
However the Technical Specification Table 3.2.2 states that the Trip Level Setting shall be "greater than or equal to 3092 volts" (equals 3255 less 5.\\ tolerance).
B.
FUNCTIONAL OPERATION OF THE.EMERGENCY BUS*.* RELAYS Nominal voltage on each emergency 41<'.( bus is 4'i60 volts.
This voltage is monitored thru 35:1 ra~io potential devices by four undervoltage relays.
Two of these relays, the degraded voltage.relays (2nd level undervoltage) protect the c.la~s. lE, s~fety-related equipment from the effects of a degraded voltage condition.
This pai-r oe solid state undervoltage relays with an inherent seven second time delay are arranged in a two-out-of-two logic scheme that initiates a load shed of nonessential loads from the emergency.bus,* tripsem~rgency bus. normal feed breakers, and auto starts the emergency diesel if bus voltage remains less than 3784 volts for greater than 5 minutes.
If an Emergency core Cooling System (ECCS) initiation signal is present at any time during this degraded voltage condition the load shed/diesel start will occur immediately.
once the diesel generator has restored bus voltage, these relays (upon resetting and in conjunction with the 1st level undervoltage relays) provide a permissive for restarting the ECCS pumps or other loads previously shed and inhibit any subsequent load sheds from degraded (2nd level) undervoltage as long as the diesel generator is supplying the emergency bus.
The remaining two relays (1st level) are type IAV69A time delay undervoltage. and overvoltage relays which provide a two-out-of-two logic scheme that sense a complete loss of bus voltage. If bus voltage drops below the undervoltage contact closure voltage the contact will close with a time delay whose length is dependent upon the magnitude of the voltage drop.
Assuming an instantaneous drop to zero voltage there will be a time
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delay of approximately 2.1 *seconds-.
A smaller voltage drop would require a longer delay.
This time delay would accommodate bus voltage drops due to motor starting.
Closure of the undervoltage contact on both relays initiates load shed of non-essential load~ ftom the emergency bus, trip of emergency bus normal feed breakers, and auto starts t.he emergency diesel.
once the diesel generator has restored bus voltage, __ these relays provide a permissive for restarting the ECCS pumps* or other loads previously shed.
This occurs upon closure. of the overvoltage contact, which is also time delay to close (approximately*2.5 seconds)*and works in conjunction with the 2nd level undervoltage relays.*.-
The reset function of both the first and the second undervoltage schemes are one in the same since they are tied in series.
Upon the diesel generator closing into the bus at 4160V, both undervoltage relay resets will be satisifed.
The second level undervoltage will reset at approximately 3800V or greater instantaneously.
The first level undervoltage relay 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.
In the event of a design basis loss of coolant accident with loss of offsite power the ECCS pumps would sequentially start.
The FSAR design basis requires in this case that the load shed occurs, diesel generator starts and closes onto the emergency bus, and that the Low Pressure Coolant Injection (LPCI) and Core Spray pumps load sequentially within 30 seconds of the initiating event (Section 8.i.3.1).
This design feature is demonstrated each refueling outage during the ECCS undervoltage test.
C.
DESIGN BASIS FOR TRIP SETTINGS It has been determined that the value in Technical Specification Table 3.2.2 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 Trip Level Setting for the undervoltage on 4KV emergency buses is 3092 volts which corresponds to 3255 less 5% volts.
This value (3255 volts) corresponds to the proper tap setting for the relay (IAV69A) of 93 volts (sensed voltage).
The tap setting, however, provides the value at which the overvoltage contact of the relay closes which represents the reset condition.
The actual undervoltage contact closure is a function of the relay design and is 90% of the tap setting based on a time dial setting of 1.0 which corresponds to 83.7 volts (sensed voltage).
This represents a*
bus voltage of 2930 volts or approximately 70% of nominal voltage.
Based on the available tap settings, 93 volts is the most appropriate for meeting
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the design requirements and provides an undervoltage trip of approximately 70% of nominal voltage, which has been considered an industry standard for detection of loss of off-site power.
The 70% level is also referenced in the Standard Review Plan (NUREG-0800) as part of Branch Technical Position PSB-1 on adequacy of shutdown electric distribution system voltages (Revision 2 - July, 1981).
D.
CONCLUSION Based on this discussion, Technical' Specification changes are proposed to specify the actual undervoltage trip voltage *tn order to make the Technical Specifications consistent with the design basis and existing relays for 1st level undervoltage protection.
The current wording in the "Remarks" column of Table 3.2.2 includes reference to the reset function (Remark #2).
This is potentially a sourc~ of confusion since the voltage at which reset may occur is not the same as the trip value, although they are interrelated as 4iscussed in sections Band c.above.
The reference to the reset function has therefore been removed from Table 3.2.2 and instead is addressed in the Bases section.
This is acceptable since use of the proper tap setting and time dial setting establishes both the proper trip and the reset value due to the design of this type of relay.
provides a swmnary of the proposed changes arid Attachment 3 includes the specific pages with the changes incorporated.
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ATTACHMENT 2
SUMMARY
OF CHANGES Technical Specification Table 3.2.2 ("Instrumentation That Initiates or Controls the Core and Containment Cooling Systems"):
a)
For the Trip Function "Undervoltage on 4KV Emergency Buses", change the following items:
i)
"2/Bus" to "2/Bus (6)"
Adds note 6, as described below.
ii)
"Undervoltage on 4KV Emergency Buses" to "4KV Emergency Buses Loss of Voltage" Clarifies that the trip function is for instrumentation that monitors for bus loss of voltage which is the design basis of these relays.
iii)
"Greater than or equal to 3092 volts (Equals 3255 less 5\\
tolerance)" to "Trip on 2930 volts+/-. 5\\ decreasing voltage."
Specifies proposed undervoltage trip setpoint.
iv)
Remarks column was changed to identify that the undervoltage trip setpoint is associated with the diesel generator auto start, trip of the emergency bus normal feed breakers, and load shed of non-essential loads.
The reset function is now discussed in the Bases section.
b)
For the Trip Function "Degraded Voltage on 4KV Emergency Buses" change the following items:
i)
"2/Bus" to "2/Bus (6)"
Adds note 6.
ii)
"3748" to "3784".
corrects a typographical error.
c)
Table 3.2.2 (Notes).
Add note 6:
This note provides clarification of the actual relay logic in that there are two 1st level or two 2nd level undervoltage relays in series (one trip system) per bus. It specifies that both relays must be operable and provides appropriate actions in the event that either of these relays becomes inoperable.
Technical Specification Bases Section 3.2 (page B3/4.2-33):
Added bases discussion for 1st and 2nd level undervoltage relays including clarification of the reset function.
4418K