ML20155B615
| ML20155B615 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 09/23/1988 |
| From: | Gridley R TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| Shared Package | |
| ML20155B618 | List: |
| References | |
| TAC-62260-F, NUDOCS 8810060372 | |
| Download: ML20155B615 (14) | |
Text
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TENNESSEE VALLEY AUTHORITY CHATTANOOGA. TENNESSEE 37401 SN 1578 Lookout Place SEP 231988 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Hashington, D.C.
20555 Gentlemen:
In the Matter of
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Docket Nos. 50-259 lennessee Valley Authority
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50-260 50-296 BROHNS FERRY NUCLEAR PLANT (BFN) - RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION - OVERLOAD PROTECTION OF THE HOTOR CONTROL CENTER CIRCUITS (TAC 62260-F)
This letter provides TVA's response to the August 10, 1988 NRC request for additional information on the above subject.
The following documents are enclosed for your review.
QIR EEB 87031 - Motor Overload Heater Section SCR BFN 8536 R2 Thermal Overload Heater Calculations:
ED-Q2268-87322 480V Reactor MOV Board 2A (w/ data sheet attachments 1-6, 11, 13, 14)
ED-Q2268-87324 480V Reactor MOV Board 2C (w/all attachments)
Drawings:
480V Reactor MOV Board 2A DCA-H1239-003, -004, -005, -006 480 V Reactor MOV Board 2C DCA. H1239-011. -012, -013 480V Shutdown Aux Power 45N 779-2, -3.-6.-7.-14.-15.-16,-17 The quality information report (QIR EEB 87031) contains the criteria used for selection of the thermal overload (TOL) heaters.
TVA was requested to provide the condition adverse to quality reports (CAQRs) written to document the inadequate TOL heaters identified during plant walkdowns.
Significant condition report (SCR) BFN 8536 R2 was written to document that the TOL heaters ratings and settings were not documented in design drawings.
To resolve this condition, BFN is generating calculations using updated design standards to specify the appropriate TOL heaters for each application.
The proper TOL heater and settings are documented on design drawings (enclosed Design Change Authorizations (DCAs)) for implementation in the field.
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Please refer any questions concerning this submittal to Patrick Carter at
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(205) 729-2689.
Very truly yours, TENN S E VAL Y AUTHORITY gI R. Gridley, M ager Nuclear Ltcer.stng and Regulatory Affairs Enclosures l
cc (Enclosures):
l Ms. S. C. Black. Assistant Director l
for Projects TVA Projects Division I
U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852 I
l Mr. F. R. McCoy, Assistant Director for Inspection Programs TVA Projects Division U.S. Nuclear Regulatory Commission Region II i
101 Marietta Street, NH, Suite 2900 l
Atlanta, Georgia 30323
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Browns Ferry Resident Inspector Browns Ferry Nuclear Plant l
Route 12, Box 637 l
Athens, Alabama 35611 j
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I U.S. Nuclear Regulatory Commission ggpggggg Please refer any questions concerning this submittal to Patrick Carter at (205) 729-2689.
Very truly yours.
TENN S E VAL Y AUTHORITY R. Gridley, M ager Nuclear Licensing and Regulatory Affairs Enclosures cc (Enclosures):
Ms. S. C. Black, Assistant Director forProjects TVA Projects Olvision U.S. Nuc? ear Regulatory Commission One White Flint, North 11555 Rockville Pike Rockville, Maryland 20852 Mr. F. R. McCoy, Assistant 01 rector for Inspection Programs TVA Projects Division U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, NH, Suite 2900 Atlanta, Georgia 30323 Browns Ferry Resident Inspector Browns Ferry Nuclear Plant Route 12, Box 637 Athens, Alabama 35611
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QUALITY INTORMATION RELEAJE EEB 87031 1
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Page 2 of 6 QIt EEB 87031 ATTACHMENT 1 W
MOT 0E OVERLOAD HEATER SELECT 10W j
The purpose of this QIt is to establish criterla, effective lamediately, for the selection of thermal overload (TOL) heaters to protect continuous-duty ac and de motors and motor operated valves for Browns F,erry, Sequoyah, Watts Bar, and Bellefonte Nuclear Plants.
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Apolleability 5
These erlteria shall be applied as follows:
Esistlnt Deslan Each project Lead Electrical Engineer' shall review the installed thermal overload heaters obtained by the Design Baseline and/or verification program for his plant to determine if sized properly, and if not replace the ICL prior j
to restart and/or fuel 1,oad of each unit except for the following caset i
h I-for safety-related and selected non-safety-related loads le.g., emergency bearing oil pump) performance of funetton takes precedence ower load protection; therefore, it is acceptable not to adequately protect the load as long as the following can be shown c
1.
If adequate testing of the motor or motor-operated val;e under its design flow or load and with the currently installed TOL can be documented to show that !nadvertent telpping would not occur, or 2.
If the currently installed TOL can be analytically shown to provide protection at least as conservative as the selection guidelines given in g
this criterla.
If this cannot be shown, then testing under its design flow or load must be g,
performed (only for non-ambient-compensated circults) or the TOL aust be replaced in accordance with this criteria.
Esisting installed TOL relays shall be documented on "b" size drawings for each applicable load center that includes:
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Compartment number 2.
Motor starter alze, if applicable 3.
TOL ranufacturer and model number T.
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'ite m **mt MOTOR OVERLOAD HEATER SELECTION (continued)
,N-Wew Desit_n All requirements must be met for any new design initiated af ter the issue date
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of this QIR. All thersel overload relays added must be documented on "b" size drawings that include the same information that is noted above for the existlns design.
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L":!!UCTIONS I
Motor overload protection ph!!osophies and their references should be as follows y
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Continuous Duty Motors
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7 Reference! National Electric Code - Articles 430-32 and 430-34 5
f Continuous duty motors (ac and de) shall be protected against overload by separate overload heaters selected to trip at the followlbs percent of motor nameplate full-load current e
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i-Motors with a marked service 125 percent i
factor not less than 1.15
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Motors with a marked temperature 125 percent
's, rise not over 40*C I
All other motors 115 percent
.i Where the selected overload heater is not sufflelent to start the motor or to P'
carry the load current, the next higher-size overload heater shall be permitted provided the trip current of the device does not exceed approstaately the following percentage of motor full-load current rating:
Motors with a marked service 140 percent i
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factor not less than 1.15 E
Motors with a marked temperature 140 percent rise not over 40*C e
All other motors 130 percent Motor-Operated Valves (MOV)
Referencet IEEE Transactions - Vol. PAS-100. No. 1. January 1981, page 43, Motor Overload Protection for Motors on Motor-Operated Valves.
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QIt EEB 87031 MOTOR OVERLOAD HEATER SELECTION (continued)
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i Motor-operatai "l e a at tars shall be protected against (1) stator winding
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o v e rh e a t t r' t e c ;,, c s ; ilds overloads and (2) stator winding and rotor t
overheating during locked rotor.
Selection of the thermal overload heaters shall be selected to trip as follows:
motor naaeplate full-load current times service factor Not less than the g
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motor duty rating (15 minute typ! cal) except
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as noted below.
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I 2001. of motor nameplate full-load current: 1 2 minutes and i
F 1 8 minutes j
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P motor nameplate locked rotor current: 1 10 seconds g
i 15 seconds with 15 seconds being preferable.
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$5' If the above selection criterla cannot be satistled for a unique application,
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then priority should be given to the criterla given for locked rotor and f
full-load current. *the rated full load current time can be reduced to not a
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less than 200 percent of the valve maalaws stroke time. For small k
horsepower MOVs where the smallest TOL available exceeds the time liraits P
listed above, selection if the TOL !s acceptable.
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If the TOLs for M07s are not bypassed for accident conditions, the selection f
criterla listed above and the additional selection criteria listed below i
meets the requirements of Regulatory Guide 1.106 position C2.
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To address TOL drif t, inaccurseles, etc., the minlaua operating band for maslaus anblent temperature given by the manufacturer of the TOL should be
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used to determine operating time for the TOL.
Additionally. TOLs for F.07s 4
y should not be compensated for temperature differences between the controller and the M07.
l 70Ls for valves that may be automatically repositioned by an accident signal h
innedtately after testing during operation shall allow this duty cycle without i
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- tripping, j
r Justification 3
If thermal overload protection devices are not bypassed under accident j
conditions NRC Regulatory Culde 1.106 position C.2 states the following 1.
The trip setroint of the thermal overleed protective devices should be established with all uncertainties resolved in favor of completing the i
safety.related action.
j 2.
With respect to those uncertaintles, consideration should be given to (a) variations la the ambient temperature at the installed location of the overload protection devices and the valve motors (b) Inaccuracles in motor heating data and the overload protective device trip characteristics j -
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and the matching of these two items, and (c) setpoint drift.
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The selection criteria estabilshed for MOYs in this QIt w!!1 meet the requirements of Regulatory Culde 1.106 stated above for the following reasoas:
The selection criteria selects a Tot that will actuage in a maalaum of 15 t
seconds for locked-rotor current to protect the motor operator from damage. Abnormal conditions such as a frozen bearing, tight packing, mid-travel obstruction, and torque or limit switch failures can cause a MOT to draw locked-rotor current.
If a safety-related valve has a frozen bearing, the motor will not move and failure of the motor is imminent.
If the valve esperiences partial binding, due to tight packing, that permits restricted movement of the valve, then the motor may draw a current anywhere from full load current to locked rotor catrent dependirs on the degree of binding. If the binding is severe enough to cause locked-rotor current, then failure of the motor is imminent.
For other degrees of binding, the selection criteria allows sufficient margin in the setting to l
accommodate increased stoke time. If a safety-related valve encounters an obstruction during travel and the torque produced,ascoeds the setting of its torque switch, the switch will actuate instantaneously to doenerg! e the elrcuit.
If, however, the torque switch has failed to operate or is bypassed, the MOV vould have drawn locked-rotor current with motor fa!!ure being imminent.
Likewise, if a M0Y reaches the end of its stroke and Its llait switch falls to operate, then the MOV would draw locked-rotor current with motor failure being immistat.
From the discussion above, it is reasonable to trip the M07 for conditions where severe motor damage or
,1 failure is imminent.
L4eving the MOY connected under these conditions i.
could adversely degrade, possibly to failure, the other connected loads to
~h the board, although this would be within the single failure criteria.
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With respect to other uncertaintles Ilsted above (i.e. Variations in 1
temperature, inaccurseles in motor heating data and overload deflees, and h!
setpoint drif t) selection criteria for the 70L5s for MOVs do not t
compensate for differences in ambient temperature of the controller /MOV
~q and requires that the alnimum operating band of the manuf acturer's TOL k
curve be utilized. This approach is conservative and wl)1 minialte the
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effects of any insecuracles in device operatlen.
Constraints in Applying the Above CritetLa
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Automatic protection is not provided for successive starts where the motor is not given sufficient time to cool before starts.
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QIt EES 87031 MOTOR OVERLOAD HEJ.fEt SELfCTION (continued)
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For protecting continuous duts motors, overload relays are designed with a current versus ambient temperature characteristic that closely follows the corresponding characteristic of a typteal motor with class 8 Insulation.
As long as both are in sintlar non-accident ambient temperatures (typically,10-18'C of each other, manuf acturer's,tecommendations should hr.
be followed), the selection of the overload beater follows routine f
lastructions included la its manufacturer application data. Vben the difference in non-accident ambient temperatures is more than recommended j'i-by the manuf acturer's application cata, the motor full-load current must p.
F be multiplied by a correction factor before a heater can be selected.
That correction factor is the ratto of the motor amblent temperature correction factor and the overload heater amblent temperature correctler f actor, both of which are given in manuf acturers' application data.
The current correction factor is larger than unity when the temperature at the y,
starter is higher than at the motor, and less than unity for th9 opposite temperature relationship.
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Browns Ferry design drawings do not reflect over load (01.) element ratings.
Since the ratings of these devices are not reflected on OE drawings, there is no d
indication that their ratings have been selected or reve!wed by the appropriate OE
,5 designers.
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lf ves, mitate Attachment 5 of NEP 9.1 ano i
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stench chier/Proiett Engineer /ONO A Owahty Site Managee IOistesge se reovered.4e* block Joj it no. oewrioe.n dioen ts O No B22 '870120011
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The overload elements were originally documented on 'E drawings but these drawings G
j were not maintained.
g overload elements only,This appears to be a documentation discrepancy applicable to i
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DNE Project Engineer ANI(For ASME Code items Only) 1 NU CON Project Manager DNOA Site Quality Manager jj
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f' SCRBFNEEB8536R1 ATTACHMENT 1
.,qg Corrective Action:
The current lack of documentation concerning Browns Ferry overload element ratings will be resolved as follows:
- 1. The 4807AC and 2507DC motor control centers will be walked down and the installed overloads tabulated.
- 2. A sizing criteria or guideline will be established.
- 3. The overloads identified in the field walkdown (item 1) will be evaluated for conformance with the sizing criteria (item 2).
- 4. Any improperly applied overload elements will require that the overload element and its associated components be evaluated for possible damage and replacement.
- 5. All properly sized overloads and/or replacement overloads will be reflected on a "B" size drwaing which will be produced to document overload ratings.
- 6. Documentaticn of OL elements will ensure future changes will include proper OL elvment consideration.
The schedule for completing this effort is determined by the Unit 2 resta;t and is therefore required by D::c,;.bv. 1, 1^ A 67-Mdace 2/, j 907, gg,j,gg, 2'468 A O
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