ML19343B935
| ML19343B935 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 02/10/1981 |
| From: | Mills L TENNESSEE VALLEY AUTHORITY |
| To: | Ippolito T Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8102180313 | |
| Download: ML19343B935 (8) | |
Text
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TENNESSEE VALLEY AUTHORITY 86^WeMRufIt'r"eUS%he'r'W February 10, 1981 Director of Licensing Attention:
Mr. Thcrass A. Ippolito, Chief Operating Reactors Branch No. 2 U.S. Nuclear Regula tory Commission Washington, DC 2G55
Dear Mr. Ippolito:
In the Matter of the
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Docket No. 50-259 Tennessee Valley Authority
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50-260 50-296 Enclosed is our response to T. M. Novak's letter to H. G. Parris dated August 4, 1980, which requested information regarding the Browns Ferry resotoe building crane. Please call us if you have any questions regarding this matter.
TENNESSEE VALLEY AUTHORITY g
y-['}y {
e is.' M. Mills, Manager Nuclear Regulation and Safety Subscribed and gworn to bef e
me this /8 b day of 1981.
a O (l u }h $ h Y h Y k Notary Public My Com:sission Expires Enclosure e
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An Equal Opportunity Employer
ENCLOSURE BROWNS FERRY REACTOR BUILDING CRANE 1.
A direct comparison of the allowable stresses provided in Tables 12.2-14 and 12.2-15 of the Browns Ferry FSAR with those given in CMAA 70-1975 cannot be made since they are inter'*related through actual design factors such as the ratio of the trolley weight to hook load.
In order to assess the degree to which actual design stresses comply with the allowable stresses given in CMAA 70-1975, the crane was reanalyzed using the load combination given in CMAA 70-1975. The results of this analysis as shown below indi-cate that the CMAA 70-1975 allowable stresses are not exceeded for the structures in question.
Maximum Actual CMAA Allowbie Stress (ksi)
Stress (ksi)
Box girder:
12.2 17.6 tension compression 11.6 17.6 shear 2.6 13 2 End trucks:
tension 7.8 14.4 compression 7.8 14.4 shear 32 10.8 Trolley frame:
tension 13 5 14.4 compression 13 5 14.4 shear 19 10.8 4
2.
The electrical features designed into the General Electric stepless
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I de adjustable voltage drive systems for the main hoist, auxiliary hoist, bridge, and trolley effectively ensure smooth acceleration and deceleration regardless of the operator's movement of the con-trols. The major features involved in this acceleration control process are:
(a) Timed acceleration - The rate of change of the speed reference volt.ge is limited through a resistor-capacitor network. This softens any abrupt control movement by the operator.
(b) Armature voltage' sensing - When a stop is made by returning the control to the "off" position, an armature voltage relay will prevent the brake from setting until the motor back emf and hence speed drops to a-preset level.
Initial slowing is provided by the much smoother regenerative braking feature whereby the kinetic energy of the moving parts is converted to electrical energy and pumped back into the electrical system.
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' (c) Current limit - The static SCR voltage regulators incorporate current limiting circuits set at the following percentages of rated armature currents; main and auxiliary hoists 200 percent, bridge and trolley 150 percent. This limits the torque available for acceleration and thereby smooths speed changes.
(d) Static reversing - Reversing of all drives is accomplished through static SCR voltage regulators which effect a smooth voltage reversal instead of the abrupt reversal found in magnetic contactor controls.
'.-is eliminates the possibility of plugging and jogging in the usual sense of applying full power (forward or reverse) to promote limited movement.
(e) Load float - Each hoist is provided with a load float feature actuated from a thumb switch on the master switch control.
Operation of this switch holds the brake off independant of the hoist or lower switch and litits the speed reference voltage to 25 percent of its full value. This allows a load to be accurately positioned (up and/or down) without the shock producing effect of the brakes setting and releasing as the load is maneuvered.
( f) Drif t point - The br.idge and trolley drives are provided with a drif t point feature which operates essentially the same as described under 2(e) above for " Load float."
(g) Slow-down limit switches - The bridge and trolley are provided with a set of limit switches which are actuated before reaching the maximum travel limit switches. Actuation of these switches automatically limits the speed reference voltage to 25 percent of its full value. Tr's provides an automatic slowdown feature which limits deceleration produced by actuation of maximum travel limit switches or contact of bumpers with their stops.
The hoist brakes are electrically connected so as to release only when the motor is energized. From a stopped condition, the hoist brakes are i
actually prevented from releasing until the motor is producing torque.
This is accomplished through a torque proving relay which senses armature
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loop current and delays release of the brakes until a preset level of current is reached. This prevents shock producing load sag on initiation of the hoisting motion.
The bridge and trolley brakes are electrically connected so as to release only when the motor is energized for normal operation. It is possible to i
release these brakes by actuating the " drift point" switch with the motor deenergized. This is not regarded as a safety hazard since no movement of the load is involved in the brake release.
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3 The maximum critical load (MCL) which will be imposed on the crane is the reactor vessel head which with its lifting device will weigh 105 tons.
The design rated load (DFL) to which the crane will be maintained and tested is 125 tons. The MCL, which is actually the maximum working load (MWL), is 84 percent of the DRL.
This margin of capacity provides for any degradation of components which might not be detected through our preventive maintenance program.
Devices which limit the hoist motor torque output and thus the load on mechanical components are:
a.
Inverse time delay overload relay on MG set ac motor - This relay is set at 150 percent of full lead current and limits sustained overloads.
b.
Hoist motor current limit circuit - This electronic torque limit is set at 200 percent of full load current and represents the upper limit of torque production of the motor.
Instantaneous overcurrent relay - This relay is set to trip at c.
250 percent of full load current for the hoirt motor and serves as a back up to the current limit circuit described in (b).
A 2 ore direct and flexible system for limiting the load on the crane is in the process of design at this time. This consists of a load cell load detector with digital readouts and variable trip points.
With this system a trip point may be selected slightly above the load to be lifted which if exceeded would stop the motor and set the brakes. This system will effectively limit the stress experienced by the hoisting system components and protect the load from load hang-up conditions.
4.
At the time of design and fabrication of the reactor building crane lamellar tearing was not considered.
A review of actr.a1 fabrication drawings indicates that structural and welding details were used which would neither be expected to cause nor be vulnerable to lamellar tearing. The design is such that tee and uorner welded connections in the main structural members are loaded primarily in shear or compression and are made with fille *, welds of 5/16-inch or smaller.
There is no evidence or suggestion in available technical literature to indicate that welds of this size would induce sufficient shrinkage stress to create lamellar tearing.
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5.
The critical load besring rotating parts listed below were analyzed for cumulative damage from fatigue. The endurance limit was t4 ken as a conservative 40 percent of tensile strength, Since the ma c'. mum stress for each part is less than one-half the endurance limit, no fatigue damage is indicated.
1 Maximum Endurance Part Material Stress (KSI)
Limit (KSI)
Drum A36 10.9 23.2 Drum Shaft 4140 22.0 44.0 Ring Gear 4140 20.0 44.0 Pinion 4340 29.5 72.0 Pinion Dear r -
Shaft C1140 21.0 44.8 6.
The auxiliary hoist is used in handling some critical loads. The maximum critical load (MCL) handled by the auxiliary hoist is limited by administrative control to one ton. The maximum critical load (MCL) handled by the auxiliary hoist is limited by the Browns Ferry Technical Specifiction to 1,000 pounds over spent fuel assemblies in the spent fuel storage pool. The design rated load (DRL) and maximum working load (MWL) is five tons.
The auxiliary hoist is designed as a single-failure-proof lifting system except for attachment points. The following features are included:
a.
There are two independent hoisting ropes each terminating at a crosshead at the hook (one-part double reeving).
b.
The drum is provided with structural devices to limit the drop and prevent disengagement from the braking system should the drum, shaft, or bearings fail.
c.
The hoist is equipped with two spring set electrically released brakes connected to the drum through mechanically l
separate gear trains. Each brake is sitad for 125 percent of the full load motor torque at the point of application.
l d.
Two independent overhoist-lir.it switches of different design are provided to prevent two blocking.
7.
For a MCL of 105 tons for the main hoir.t the maximum dynamic rope stress is 15.14 percent of the breaking strength. This is with 15 percent impact. The 15.6 percent given in response to APCSB 9-1 did not include impact.
-For a MCL of one ton for the auxiliary hoist the maximum dynamic rope stress is 4.16 percent of the breaking strength.
8.
The spent fuel cask is the only load for which dual attaching points from the lower block are provided. The load-block assembly illustrated in figure 12.2-22d is schematic to the extent that the safety cables are actually safety links that were made from alloy steel bars (ASTM A322). These links can support three times the weight of the critical load they handle. These links were designed with a safety factor of 5.1 based on the critical load they handle.
The links are not loadea during norma; cask handling but are pinned to the redundant lifting beam. With th' pin connection the impact would be negligible in case of a hook failure.
The redundant links were tested to 127 percent of their design rated load.
Dual attaching points from the lower block ~are not provided for any other critical loads and the safety factor for the attaching slings j
vary from 4.86 to 7.13 There are critical loads that are handled that are above 10 percent of the load-carrying capability of the hook.
9 a.
All special lifting devices used with this crane were purchased on the NSSS contract; therefore, they will have to be analyzed by the General Electric Company to determine conformance with ANSI N14.6-1978.
b.
All slings, purchased by TVA are in accordance with ANSI B30 9-1971 except two identical slings that have a safety factor of 4.86 instead of five. All slings are marked or tagged to identify the use for which they were purchased.
10.
The Division of Nuclear Power (NUC PR) will perform a field test of the overspeed control device as delineated in Item 6.2 of Jhe scoping document for Preoperational Test No. TVA-2 as recommended by EN DES.
11.
The travel limit switches are inspected and tested in accordance with ANSI B30.2.0-1976.
Frequent and periodic inspection require-ments have been imposed through NUC PR Division Procedures Manual N74M15.
Concemling the testing of the current-limiting device on the hoist motor, the current limit should be set at 200 percent current l
rating; this value should be verified on the hoist regulator. The instantaneous overcurrent relays and the overload relays should also be' tested.
NUC PR will revise the associated electrical maintenance instructions to include these tests.
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. 12.
The actual temperature on the refuel floon. periodically drops to 40-45 F when the auxiliary boilers are not available for building heat during extremely cold weather. Therefore, administrative control may be necessary to prevent use of the reactor building crane belov 65 F.
The cold-proof test of the crane and nondestructive examination of critical welds will be' performed by NUC PR under the direction of EN DES.
However, these r/civities must be scheduled at the con-venience of other crittaal reruel flaor activities.
13.
As stated in our response to APCSB 9-1 the bridge and trolley 3
brakes are not rated for maximum motoc torque and the bridge has only one brake for each driving motor.
To meet the intent of the request the trolley braking system will be upgraded by increasing the torque rating of each brake to'the maximum torque rating of the motor, and the bridge braking system be upgraded by relocating each bridge drive motor and adding an additional brake between the drive motor and its reducer. Each of two drive brakes for each drive motor on the bridge or trolley should be rated for 100 percent of maximum driving torque of its respective motor. _
14.
The seismic analysis of the reactor ouilding crane was performed by idealizing the crane as a lumped-mass mathematical model. The stiffness of the model is the stiffness of the crane girders. The trolley was assumed to be rigid End was idealized in the mathe-matical model as rigid links connecting the crane girders. The trolley was assumed to be pinned to the crane girders in order to maximize the inertial effects of the trolley. The maximum load on the crane during a seismic event was assumed to be 150 kips, which is 60 percent of the design rated load.
A modal analysis was performed for motion transverse to the_ crane girders. The analysis considered two cases of trolley position; one case for the trolley at the centerline of the girders and one for the trolley at the end. Seismic responses were calculated for each case by use of the response spectrum method of analysis.
Acceleration response spectra at the 'levation of the crane runway were taken from the seismic analysis of the reactor building and used as input to the mathematical model. A damping value of one percent of critical damping was used in the response analysis for both the operating base ea. 2. quake and design base earthquake events.
In both the longitudinal and vertical directions, the crane was designed for pseudostatic seismic loads caused by the zero period
. acceleration (ZPA) of the acceleration response spectrum at the evaluation of the crane runway.
The seismic loads were combined on an absolute basis with other loads in the appropriate loading combinations. Seismic loads from only one horizontal direction at a time were considered to occur
. simultaneously with'the vertical direction.
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15 The welds whose failure could result in the drop of a critical load were post weld heat treated. The only examination made for these welds was visual. The 125 percent overload test.and conservative stress levels were used to ensure adequate design.
16.
a.
Cast iron was not used for load-bearing ccmponents as required l
by NUREG-0554 b.
The ratio of the main hoist drum diameter to the rope diameter is 49.6: 1.
There are no sheaves on the auxiliary hoist.
The ratio of the auxiliary hoist drum diameter to the rope diameter is 38.4:1.
These exceed the Fequirements of the CMAA70.
c.
The load blocks were not nondestructively examined by surface and volumetric techniques.
d.
The auxiliary handling system has part direct lift or whip style reeving that requires no lower or upper block. This system is provided with two up-travel limit switches to stop j
the hoist, set the brakes, and prevent hook over travel.
e.
Both main and auxiliary hoist drums are provided with guards i
to prevent the hoisting ropes from leaving the grooves on the drum.
f.
The control system design complies fully with item 6.2 of NUREG-0554.
The reactor building crane is not used to handle individual spent fuel elements, therefore, interlocks as recommended in Regulatory Guide 1.13 are not included in the design.
g.
Interlocks were provided that permit only one control station l
to be operable at any one time, h.
Only one contractor nameplate was provided. This stated the design rated load for the main and auxiliary hoist. This is a 12-inch by 18-inch sign located near the center of the bridge.
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l 1.
Ederer Incorporated provided TVA with electrical equipment and mechanical maintenance manuals specifying lubrication, inspection, and preventive maintenance requirements; however, an operating manual as described in Item.9.0 of NUREG-0554 was i
not supplied.
J.
.The-re$2 tor building crane is listed as a CSSC item in Appendix A of the Browns Ferry Nuclear Plant Operational Quality Assurance Manual. Therefore, all inspection, testing, and l
' operational requirements, as listed in the Division Procedures i
Manuals N78S2 and N74M15, are auditable by NUC PR Quality Assurance Staff.
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