ML20237L708
| ML20237L708 | |
| Person / Time | |
|---|---|
| Site: | McGuire, Mcguire  |
| Issue date: | 08/17/1987 |
| From: | Tucker H DUKE POWER CO. |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| RTR-REGGD-01.097, RTR-REGGD-1.097 NUDOCS 8708200306 | |
| Download: ML20237L708 (6) | |
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DETHE POWER GOMPANY P.O. BOX 03180 oHARLOTTE, N.o. 28242 a-2 IIALB.TUCKEk '
(704) 073-4531 Tzt.zPHONE vice reassomwr NUCLEAE P AK) DUCTION August 17, 1987
> U.S.. Nuclear Regulatory Commission l
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! Document Coat oltDesk.
. WAihiddon,"D.C.'"20$55 S bject:- 'McGuire Nuclear Station Docket Nos. 50-369,-50-370 Gentlemen:-
.By letter dated March 23, 1987, NRC provided the Staff's Safety Evaluation Report and contractor's Technical Evaluation Report documenting the results of Staff
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review of McGuire submittals regarding conformance to Regulatory Guide (RG) 1.97, Revision 2.
. Staff review of instrumentation for accumulator: tank level and pressure, and for containment sump water temperature Nd not been completed.
Duka has determined that existing instrumentation is ad uate.
NRC has determined that steam generator level is needed over the range from tube sheet to separators to indicate integrity of the secondary system and the capa-
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,bility. of decay heat removal, as noted. in RG 1.97.
The Staff has requested a schedule ' for compliance with the requirement to install and make operational environmentally. qualified and seismic Category I, wide range instrumentation.
Duke and HRC Staff met on July 29, 1987 to discuss this matter further and to seek resolution. of the open item.
The attachment to this letter provides additional technical information that was provided at the meeting and describes a modifica-y tion to.the plant to provide qualified wide range steam generator level instru-mentation. NRC acceptance of this modification design is required.
Duke -intends to install and make operational this instrumentation during the end of cycle 5 refueling outages of.esch McGuire unit.
Currently, these are projected i
to begin in the 3r_d quarter of 1988 for Unit 1 an.d the 3g quarter of 1989. for d
Unit 2.
Approximate 1y'four months prior to each outage, Duke finalizes an outage plan.. Duke will, at that time, finalize modifications to be installed as well as
.other work ' activities to ' be accomplished during the respective outage.
NRC will I
be advised of any changes to this intended installation schedule.
Duke ~ considers this installation. schedule acceptable because of the substantial
- effort.necessary to design modifications and to properly implement them.
Duke has had discussion with both NRC Region II and ONRR relative improvements to the j
1 8708200306 870817 03 PDR ADOCK 05000369
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LDocument Control Desk August 17, 1987 Page 2 modification control program and does not desire to - compromise the process in l
place.
A normal modification implementation schedule will assure adequate con-trols are maintained and ' will assure installation of a quality system.
Imple-i mentation on a schedule sooner than the one proposed would possibly compromise quality.-
Very truly yours, Gy Hal B. Tucker RLG/248/jgc xc:
Dr. J. Nelson Grace, Regional Administrator U.S. Nuclear Regulatory Commission - Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 W.T. Orders NRC Resident Inspector McGuire Nuclear Station Darl Hood, Project Manager Division of Licensing Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D.C.
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~ Document Control Desk
- 1 August 17, 1987 Page 3 bxc: S.O. Addison g
M.L. Clayton
, i T.L. McConnell.
E.O.!McCraw R.G. Morgan.
D.W. Murdock
,F.C. Poley
-A.L.
Snow G.B. Swindleturst-J.E. Thomas i
N.A. Rutherford
- I R.O.~ Sharpe-
.MC-801.01 (14) 1 i
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DUKE POWER C0MPANY McGUIRE NUCLEAR STATION STEAM GENERATOR (SG) LEVEL INSTRUMENTATION Use of SG Level Instrumentation for RG 1.97 Post Accident Monitoring The regulatory position on the use of steam generator level instrumentation for Regulatory Guide 1.97 is vaguely stated in the document as "to monitor operation". The purpose is clarified on page 12 of "Conformance to Regulatory Guide 1.97, Mc.Guire Nuclear Station, Unit Nos. 1 and 2",
EGG-NTA-7087, July 1986.
This document states "The purpose of this variable is for the identi-fication and mitigation of an accident and for determining the availability of the steam generators as heat sinks". The purpose is thus threefold:
- 1) acci-
. dent identification, 2). accident mitigation, and 3) determination of steam generator heat sink availability.
Accident identification is best accomplished using the narrow range level
- instrumen t. - There are several reasons for this, including:
1)
Since the narrow range lower level tap is only a few inches above the top of the U-tube bundle, going offscale low on this instrument is a direct indication of imminent tube uncovery.
2)
Accidents initiated at full system pressure and temperature are likely to be more severe than those initiated from lower conditions.
The narrow range instrument is calibrated at hot conditions and is therefore appro-priate for use in identifying these accidents.
3)
Use of the narrow range instrucent for accident identification simplifies the operator's task since this instrument is already being used by him to verify automatic safety system functions such as reactor trip or auxil-iary feedwater actuation.
4)
Use of the narrow range instrument for accident identification further simplifies the operator's task by requiring him to look only at one steam generator level instrument for accident identification (the current emergency procedures already use narrow range level for accident iden-tification).
Accident mitigation is accomplished via the McGuire emergency procedures. The procedures make extensive use of steam generator level, referring almost exclusively to the narrow range instrument.
The lone exception, for proce-4 dures mitigating design basis events which cause a harsh environment inside containment, is EP/13.5, RESPONSE TO SG LOW LEVEL.
This procedure does use l
the wide range level instrument but treats a failed instrument conserystively.
Wide range level is used here to determine the rate at which to refill a hot, dry steam generator for the case in which a secondary heat sink is available.
Refill guidance for no secondary heat sink (beyond design basis event) is provided in a separate procedure. In EP/13.5, the wide range is used to determine whether the steam generator is drained to the lower level tap (offscale low on the wide range instrument).
If so, it is assumed to be dry.
The wide range setpoint used for this is corrected for normal and post-acci-dent instrument errors, reference leg heatup error, and for the lack of temperature compensation.
Since the wide range instrument is not qualified, J
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the _ operator is directed in the procedure to assume the steam generator is dry if this instrument is unavailable or is suspected of failure.
Making the assumption is conserva tive since it results in a slower refill rate.
Note that, contrary to page 12 of EGG-NTA-7087, this procedure cannot "cause a
' harsh environment in containment and a need for wide range steam generator
[ level) indication".
The determination of steam generator heat sink availability is made in EP/10, CRITICAL SAFETY FUNCTION STATUS TREES, or by the related Safety Parameter Display System if it is available. Heat sink availability is judged by narrow range steam generator level and by feedwater flow, as described in the Westing-house Owners Group Emergency Response Guidelines (ERGS).
This approach was approved by the NRC in a June 1, 1983 SER on the ERGS.
'Although the McGuire narrow range steam generator level instrument does not have the range suggested in RG 1.97, from tubesheet to separators, its narrow range is longer, on both an absolute and relative basis, than the narrow ranges on most domestic Westinghouse steam generators.
The following are the results from an informal survey to determine the relevant data:
Steam Percent of Domestic Narrow Distance from Lower Generator Westinghouse Steam Range Narrow Range Tap to Medel Generators Span (in)
Top of U-tubes (in) 27 4
85 6
44 14 153 27 51 41 144 26 D2 2
233 5
D3 9
233 5
D4 7
233 1
D5 7
128 101 E
4 179
-9*
F 11 128 97
- The tops of the U-tubes are above the lower narrow range level tap on Model E steam generators Most domestic Westinghouse steam generators have a shorter narrow range than the McGuire units (McGuire Unit I has D2 generators while McGuire Unit 2 has D3 generators).
Because of the relative position of the lower narrow range level tap and the top of the U-tubes most domestic units with Westinghouse steam generators go offscale low on the narrow range level, ins t rument on a normal reactor trip.
This could cause entry into their equivalent of EP/13.5 l
for this situation (ERGS specify that this is a yellow priority challenge to the Heat Sink Critical Safety Function and is therefore at the operators discretion). Because of the longer narrow range on the D2 and D3 models, the McGuire units do not go offscale low on the narrow range level instrument for a normal reactor trip.
" Normal" here means a trip not associated with a loss or reduction of main feedwater prior to trip.
Such initiating events may still lead to loss of narrow range indication.
They would, however, then truly be indicative of a low steam generator level condition which may require operator attention.
The above arguments demonstrate that the McGuire narrow range steam generator level instrument is fully acceptable for operator use in accident identifica-tion, accident mitigation, and in determination of steam generator heat sink availability.
The McGuire units have narrow range instruments which are longer, both on an absolute and relative basis, than the corresponding in-struments at units with most other Westinghouse steam generator models.
This extra length allows for more complete monitoring of steam generator level transients following reactor trips.
DESCRIPTION OF EXISTING NARROW RANGE STEAM GENERATOR LEVEL INSTRUMENTATION' McGuire has four redundant, safety-related channels of instrumentation per steam generator.
The instrumentation is powered by Class 1E buses.
Trans-mitters and the electronics are environmentally and seismically qualified.
Outputs from the electronics, including control and indication are electric-ally isolated.
Control room indicators are provided for each channel and are the same device as used in safety-related circuits.
Each steam generator has one channel recorded.
Three channels per steam generator are also available on the plant con:puter.
UPGRADE OF WIDE RANGE STEAM GENERATOR LEVEL TRANSMITTERS Duke will replace the existing in-containment transmitters with seismically and environmentally qualified transmitters and to relocate them to the Annu-lus.
This modification will make use of existing impulse lines that are located in the Annulus.
These impulse lines are off the same steam generator taps to which the existing transmitters are connected.
The channel electron-ics will be identical to that used for safety-related applications.
Power will be supplied by a highly reliable battery backed supply configured in an auctioneering mode with a highly reliable regulated power supply.
Control room display will be via seismically mounted indicating recorders.
The recorders are by the same manufacturer and of similar design to those used in safety-related applications.
Indication will also be available through the plant computer.
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