ML19318A597
| ML19318A597 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 06/19/1980 |
| From: | Durall J TENNESSEE VALLEY AUTHORITY |
| To: | Ippolito T Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8006230438 | |
| Download: ML19318A597 (10) | |
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- -. - TE, NNESSEE VACLEY. AUTHORITY y.
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JUN I 91980-3 e
r Director of Nuclead Reactor Regulation-
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i Attentions Mr.: Thomas'A. Ippolito, Chief
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Branch No.-3 t
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Division of Operating Reactors l'
, U.S. Nuclear Regulatory Connission f'
Washington, DC 20555:
Dear Mr..Ippolito:
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-Docket Nos.- 50-259.,
In the Matter of the
. Tennessee Valley' Authority
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50-260 n-50-296 ~
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In' response;.to'your May 16, 1980, letter to H. G. Parris requesting i
' information regarding turbine' discs at'our Browns Ferry Nuclear Plant,
.we,are providing as an enclosure a response to each of.-the~ site
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specific. general questions and a response to each of'the generic questions..
Based on,the enclosed responses'to your questions,. continued' operation of l
the Browns'Forry Nuclear Plant is justified and the operating licenses
- for Browns. Ferry units 1, 2,'and 3 should not be modified, suspended,
~ - or revoked.-
Very truly yours, f-
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' TENNESSEE VALLEY AUTHORITY L
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5 James R. Durall
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An Equal Opportunity Employer
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a ENCLOSURE REQ',iEST FOR INFORMATION RELATED TO TURBINE DISCS BROWNS FERRY NUCLEAR PLANT 50-259, 50-260, 50-296 SITE SPECIFIC CENERAL QUESTIONS Question I Provide the following information Ior each LP turbine:
A.
Turbine type B.
Number of hours of operation for each LP turbine at time of last turbine inspection or if not inspected, postulated to turbine inspection C.
Number of turbine trips and overspeeds D.
For each disc:
1.
type of material including material specifications 2.
tensile properties data 3.
toughness properties data including Fracture Appearance Transition Temperature and Charpy upper steel energy and temperature 4.
keyway temperatures 5.
critical crack size and basis for the calculation 6.
calculated bore and keyway stress at operating design overspeed 7.
calculated K data 1c 8.
minimum yield str tth specified for each dise Response.
A.
N-1, 1800 RPM, tandem compound, 6-flow, condensing B.
Refer to Table 1 for tha number of hours of operation since last inspection and postult.ced to next inspection.
Response (Continued)
C.
The number of turbine trips and overspeed tests for each unit through May 1980 is shown below:
Unit Turbine Trips Overspeed Tests Total 1
113 7
120 2
91 4
95 3
70 J
74 274 15 289 D.
Answers to these questions involve data which are proprietary to the General Electric Company (GE).
Information was provided directly to the NRC during a meeting between GE and NRC representatives on April 21, 1980. The NRC has informed us that this information is an' acceptable reply to this question.
Question II Provide details of the results of any completed inservice inspection of LP turbine rotors, including areas examined, since issuance of an operating license. For each indication detected, provide details of the location of.the indication, its orientation, size, and postulated cause.
Response
In January-1980 an inservice wheel bore ultrasonic inspection was completed on the LPC rotor of Browns Ferry unit 1.
The results of the test are given below:
Test Results An ultrasonic inspection was recently performed on all the shrunk-on wheels assembled on the LP-C shaft of the subject unit. The wheel bore region was inspected using the special ultrasonic test procedures developed by GE for inspecting assembled wheels. This test searches for radial-axial cracks in the vicinity of the wheel bore and keyway surfaces.
In addition, an ultrasonic. inspection was performed on all the tangential entry wheel dovetails. The wheel bore ultrasonic test revealed no indications in any of the wheels. A magnetic particle inspection was performed on the exposed surfaces of each wheel and no indications were fcund. The ultrasonic inspection of the tangential entry dovetails on the wheels for stages 1 through 6 on both the turbine and generator ends of the shaft revealed no indications.
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Question III Provide the nominal water chemistry conditions for each LP turbine and describe any condenser inleakages or other significant changes in water
-chemistry to this point in its operating life.
Response
The design of Browns Ferry Nuclear Plant did not include provisions for obtaining representative samples of steam to the low pressure turbines.
Therefore, no information on low pressure steam gurity is available.
Unlike fossil plants or pressurized water reactors, chemical additives are not utilized in the primary cycles of the three boiling water reactors at Browns Ferry Nuclear Plant. In.the Browns Ferry Nuclear Plant boiling water reactors, the primary coolant steam circulates between the reactor and the turbine. The conductivity of the ultra-pure reactor coolant is continuously monitored to ensure that applicable technical specification and GE fuel warranty limits are not exceeded. Nominal reactor coolant conductivity varies between 0.15 - 0.45 umho/cm with no detectable chloride concentration (<50 ppb).
Significant e'cursions in reactor coolant quality x
are summarized on a yearly basis according to technical specification and GE fuel warranty requirements in Tables II and III.
Steam produced in a boiling water reactor results from the distillation of the ultra-pure reactor coolant. The distillation. process further purifies the' steam routed to the turbines. Any feedwater impurities are concentrated approximately 100 times in the reactor coolant because of this distillation process. This fact aids in the quick identification of small inputs of impurities into the primary cycle. The condensed steam is continuously domineralized before its return to the reactor as feedwater. Because the condensate demineralizers at Browns Ferry Nuclear Plant use expendable powdered resins, it ic cost prohibitive to operate with any significant condenser tube leaks. All suspected condenser tube leaks are investigated.
Once-through river water is used for condensate cooling. For this reason,i combined with full-flow condensate demineralization, the influence of condenser tube leaks on primary coolant quality is low compared to sea water cooled plants. Therefore, excessive chloride concentrations in the primary coolant have not been a significant problem at Browns Ferry Nuclear Plant-(refer to Table III).
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.' Question IV
.If your plant has not been inspected, describe your proposed schedule and approach to ensure that turbine cracking does not exist in your turbine.
Response
All of the Browns Ferry LP turbines have been inspected at least once except No. 2-C.
One' turbine, No. 1-C, has had an ultrasonic inspection of the wheel disc bores. All other inspections included but were not limited to complete magnetic particle (MP) inspection of all exposed areas of the' shaft, MP inspection of all exposed areas of the wheel discs, MP inspection of all buckets and their covers, dye penetrant inspection of all stellite erosion shields, dye penetrant inspection of all bucket tie wires and sleeves, ultrasonic inspection of all bucket retaining pins, and MP inspection of all diaphragms (stationary blades).
All future inspections will include ultrasonic inspection of all wheel disc bores. The schedule of planned inspections is provided in Table I.
-Question V If your plant has been inspected and plans to return or has returned to power with cracks or other defects, provide your proposed schedule for the next turbine inspection and the basis for this inspection schedule, including postulated defect growth rate.
Response
The schedule _of planned inspections is provided in Table I.
Previous inspections have found no indication of cracking.
Question VI Indicate whether.an analysis and evaluation regarding turbine missiles have been performed for your plant and provided to the staff.
If such an analysis and evaluation has been performed and reported, please provide appropriate references to the available documentation.
In the event that such studies have not been made, consideration should be given to scheduling such an action.
Response
An analysis and evaluation of the possibility of turbine missiles have been performed and provided to the staff. The appropriate references and further details are provided in TVA's response to the NRC's Question 11.2 and was Jncluded in the Browns Ferry FSAR by Amendment 18.
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-5 GENERIC QUESTIONS Question I Describe what quality control and inspection procedures are used for the disc bore and keyway areas.
Response
After the rough machined wheel / disc forging has been tempered, material is removed from surface locations to measure mechanical properties. The forging is then subjected to a 100% volumetric ultrasonic inspection.
If the test results meet stringent acceptance standards, the forging is released for final machining, and attention is continually paid to the linish and dimensions of every surface. For instance, the keyway depth, width, location, radii, and surface finish for every wheel is checked for conformance to drawings.
Quality control personnel ensure that tolerances are maintained. Any deviation from accepted tolerances are reported to engineering for disposition.
Only coolants'and lubricants approved by engineering are used in the manu-facturing and assembly process. These coolants and lubricants have undergone extensive laboratory corrosion testing to ensure their acceptability before their approval for use in manufacturing. Periodic sampling is done on all such fluids to verify that their chemistry is within limits.
After finish machining, each wheel is th r.?hly cleaned and given a magnetic particle inspection of all surfaces.
If.
cptable, the buckets are assembled and the wheel is static balanceu. After assembly on the shaft, each wheel is inspected and measurements are made to ensure its proper location. The assembled rotor is then spun to 20% overspeed following a high speed balance. Finally, after a magnetic particle inspection of the buckets, the rotor is cleaned to prepare for shipment.
l Question II Provide details of the GE repair / replacement procedures for faulty discs.
Resnonst Stress corrosion cracks have not been observed to date in nuclear wheels manufactured by GE, and we do not anticipate that removal or replacement of whccis will be required because of this phenomenon. The water erosion which has been observed in the keyways of wheels on several nonreheat machines is being studied intensively. We currently believe that the erosion process is self-limiting and should not require the replacement of j
any wheels.
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- Question III What immediate and long term actions are being taken by GE to minimize future " water cutting" problems with turbine disks? What actions are being recommended to utilities to minimize " water cutting" of disks?
Response
No immediate actions are required to minimize water erosion because of the apparent self-limiting nature of the phenomenon.
However, if future inspections show an unexpected progression of the water erosicn, appropriate operating restrictions and/or modifications will be recommended.
Question IV Describe fabrication and heat treatment sequence for disks, including thermal exposure during shrinking operations..
Response
The wheel / disc forgings are heat treated in the rough machined condition.
The heat treatment consists of soaking at a temperature above the upper critical temperature with the time and temperature sufficient to ensure complete austenitization throughout the forging, followed by a cuench in cold, vigorously circulated water for a sufficient time to ensut~ complete transformation throughout the section. The forgings are heated uniformly to a tempering temperature below the lower critical temperature and held for a sufficient time to soften to the desired tensile range.- After teepering, the forgings are still-air cooled to room temperature.
After final machining, the wheels (discs) are uniformly heated in an electric furnace to a temperature below the embrittling range, but sufficiently high to increase the wheel diameter enough to assemble on the shaft with the requf. red shrink fit.
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l TABLE 1 Browns Ferry Wuclear Plant Low-Pressure Turbine Inspections Last Inspection Next Inspection Projected Operating Operating Turbine Date Hours
- Date Hours
- 1-A 9/77 17,275 9/82 53,393 e
1-B 11/77 24,320 3/84 65,073 (1) 1-C 1/80 32,313 9/85 77,419 i
7-A 3/78 14,818 3/82 43.676 2-B 4/79 21,899 9/83 55,356 4
2-C 9/80 32,012 3-A 9/78 15.331 9/81 36,743 3-B 8/79 21,320 9/81 36,743
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3-C 8/79 21,320 3/83 47,668 (1) Ultrasonic inspection of disc bores performed.
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- Since initial operation.
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TABLE II CONDUCTIVITY
-Hours of operating time above 1 umho/cm (GE Fuel Warranty Limit)
Year Unit 1-Unit 2-Unit 3 (1) 1974 139 6
(2)
(2)
(1) 1975 (2)
(2) 1976 32.5
'1977 11 0
16.5
.1978 90.82-47.72 137 1979 17 12.5 167.9
- ( } Unit'not operational
( ) Shutdown due to cable tray fire of March 22, 1975 s
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i TABLE III CHLORIDES
' Hours of operating time above 0.2 ppm Year
' Unit 1 Unit 2 Unit 3 (1) 1974I
' 21 '
O (2)
(2)
(1) 1975 0
(2)
(2)
(1) 1976 1977-0 0
0 1978 0
9.5 0
1979 0
0 0
- (1) Unit not operational Shutdown due to cable tray fire of March 22, 1975 t
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