ML19221B077
| ML19221B077 | |
| Person / Time | |
|---|---|
| Issue date: | 11/24/1975 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| References | |
| NUREG-75-087, NUREG-75-087-10.2.3, NUREG-75-87, NUREG-75-87-10.2.3, SRP-10.02.03, NUDOCS 7907120363 | |
| Download: ML19221B077 (7) | |
Text
NU REG-75/087 fj.g%
) U.S. NUCLEAR REGULATORY N['hh't
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OFFICE Or flUCLEAR REAClOR REGULATION
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SECTION 10.2.3 TURBINE DISK INTEGRITY REVIEW RLSPCNSIBILITIES Primary - Materials Engineering Branch (MTEB)
Secondary - None I.
AREAS OF REVIEW General Design Criterion 4 requires that structures, systems, and compor.ents of nuclear power plants important to safety be protected against the effects of missiles that might result from equipment failures. Because turbine disks have large masses ar.d rotate at relatively high speeds during normal reactor operation, failure of a disk could result in high energy missiles and excessive vibration of the turbine rotor assembly.
The following areas of the applicant's safety analysis report (SAR) relating to turbine disk integrity are reviewed:
1.
Materials Selection The high pressure turbine rotor is generally a one piece forging. Stresses at norral operating speeds are relatively low. The low pressure turbir.e rotor assembly usual v consist, of a rotor shaft with shrunk-on disks. Low pressure disk stresses are due to thermal gradients, the interference fit, and centrifugal forces. These stresses are relatively high. The low pressure turbine also operates at lower temperatures than the nigh pressure turbine. Thus, it is particularly important that low pressure disks be made of a tough material. The use of suitable material, adequate design, and inservice nspection can greatly reduce the probability of a turbine rotor or disk f ailure.
i The materials properties, including descriptions of the procedures to minimize flaws and improve fracture toughness, are reviewed to establish that sufficient information is provided to pernit an evaluation of the adequacy of the low pressure disk materials The materials properties such as creep, stress rupture, and toughness are reviewed to est hlish th't sufficient information is provided to permit an evaluation of the ade-quacy of the high pressure turbine rotor materials.
Included in this information are:
A discussion of the ductile-brittle transition temperatures (FATT or NDT) of the a.
materials and the tests and standards used to determine them.
USNRC STANDARD REVIEW PLAN
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b.
The Charpy V-notch test program used to establish minimum upper shelf energies of the disk materials.
The fracture toughness test program used to establish minimum upper shelf tough-c.
ness of the disk materials.
2.
Fracture Toughness The fracture toughness of the materials and the materials tests or correlations of Charpy and tensile data to toughness properties are reviewed to establish that the rotor and disk materials exhibit adequate fracture toughness at normal operating tem-perature and during startup, 3.
High Temperat_ure Paperties The creep si stress-rupture properties of the high pressure rotor materials are reviewed to establish that these materials exhibit adequate high-terrperature, long-term properties.
4.
Preservice Inspection The preservice inspection program information is reviewed to verify that the disk forgings are first machined with minimum excess stock prior to heat treatrent, that visual and surface inspections are performed on all finished machined surfaces, and that a 100; volumetric (ultrasonic) examination is performed.
5.
Turbine Disk Dasign The nigh and low pressure turbine rotor design i: f o rra tion, including allowable stresses, temperature distributions, and design overspeed considerations, is reviewed.
6.
Inservice Inspection Descriptions of the baseline and inservice chases of the inservice inspection program, incluJing types of inspections, areas to be inspec <J, frequencies of ir spection, and acceptance criteria, are reviewed.
II.
ACCEPTANCE CRITERIA The acceptance criteria for the areas of review described in Section I of this plan are as follows:
1.
Materials Selection The applicant's selection of a disk or rotor mdterial is acceptable if in accordance with the following:
The turbire disk or rotor should be made from a material and by a process that tends to minimize flaw occurrence and maximize fracture toughness properties, such as a NiCrMoV alloy processed by vacuum melting or vacuum degassing. The raterial should be examined and tested to iceet the following criteria:
10.2.3-2 0
a.
Chenical analysis should ta made for each forging. Elements that have a delete-rious ef fect on toughness, such as sulfur and phosphorus, should be controlled to low levels.
b.
The fracture appearance transition temperature (50; FATT) as obtained from Charpy tests perforred in accordance with specification ASTM A-370 should be no higher than 0 F for low pressure disks and 50*F for high pressure rotors. Nil-ductility transition (NDT) temperature obtained in accordance with specification ASTM E-208 may be used in lieu of FATT. NDT temperatures should be no higher than -30 and 20"F, respectively.
c.
The Charpy V-notch (C ) energy at the minimum operating temperature of each low prcssure disk in the tangential direction should be at least 60 ft-lbs.
The C y energy of high pressure rotor naterials at minimum operating terrperature should be at least 50 f t-lbs.
1 minimum of three C specimens should be tested in accordance with specification ASTM A-370.
2.
Fracture Toughness The low pressure turbine disk and high pressure rotor fracture toughness properties are acceptable if in compliance with the following criteria:
The ratio of the fracture toughness (Kk) of the disk and rotor materials to the maxi-mum tangential stress at speeds from normal to design overspeed should be at least two 9
/Tii, at minimum operating temperature. Bore stress calculations should include com-ponents due to centrifugal loads, interference
., and thermal gradients. Sufficient wdrmup time should be specified in the turbine operating instructions to assure that toughness will be adequate to prevent Mittle fracture during startup. Fracture tough-ness properties can be obtained by any of the following methods:
value at a.
Testing of the actual material of the turbine disk to establish the Kk normal operating temperature.
b.
Testing of the actual material of the turbine disk with an instrumented Charpy machine and a fatigue precracked specimen to establish the KIc (dynamic) value at normal operating temperature. If this method is used, Kk (dynamic) shall be used in lieu of Kk (static) in meeting the tocS ness criter ia above.
h c.
Estimating of K values at various temperatures from conventional Charpy and k
tensile data on the disk material usinc methra.;s presented by J. A. Begley and W. A. Logsdon in Westinghouse Scientific Pacer 71-1E7-MSLRF-Pl (Ref. 5).
This method of obtaining K should be used only on r.aterials which exhibit a well-g defined Charpy energy and fracture appearance transition curve and are strain-rate insensitive. The test data and the calculated toughness curve should be 14 0(>9 submitted to the staff for review.
10.2.3-3
d.
Estircating " lower bound" values of K at various temperatures using the equiva-k lent energy concept of F. J. Witt and T. R. Mager, ORNL-TM-3894 (Ref. 6).
Load-displacement data from the compact tension specimens and the calculated toughness data should be submitted to the staff for review.
3.
High Temperature Properties The stress-rupture propertics of the high pressure rotor r"aterial are acceptable if they provide sufficient assurance of rotor integrity for the lifetime of the turbine.
The applicart can demonstrate compliance by submitting stress-rupture data of an equiva-lent material with similar properties to the staf f for evaluation.
4.
Preservice Inspection The applicant's preservice inspection program is acceptable if in compliance with the following criteria:
Disk forgings should be rough machined prior to heat treatment.
a.
t,.
Each finished disk should be subjected to 1001 volumetric (ultrasonic), surface, and visual examinations using procedures and acceptance criteria equivalent to those specified for C: ass components in the ASME Eoiler and pressure Vessel Code, Sections I!! and V Finish machined bores, keyways, and drilled holes should be subjected to magnetic c.
particle or liquid penetrant exac ination. No f'aw indications in kep,ay or hole regions are allowable.
d.
Each turbine rotor assembly should be spin tested at the maximum speed anticipated during a tuibine trip following loss of full load.
5.
Turbine Disk Desijn The applicant's design is acceptable if in cocpliance with the following:
The turbine assembly should be designed to withstand nornal cunditions, anticipated transients, and accidents r?culting in a turbine trip without loss of structural integ-rity. The design of the turbine assembly should rect the following criteria:
The design overspeed of the turbine should be 5' above the hi@est anticipated a.
speed resulting from a loss of load. The basis for the assreo design overspeed should be submitted to the staff for review.
b.
The combined stresses of low pressure disks cr high pressure rotors at design overspeed due to centrifugal forces, interference fit, and thernal gradients should not exceed 0.75 of the minimum specified yield strength of the material, or 0.75 of the measured yield strength in the weak direction of the raterials if appropriate tensile tests have been performed on the actual disk uterial.
}k 10.2.3-4
The turbine shaft bearings should be able to withstand any combination of the normal operating loads, anticipated transients, and accidents resulting in turbine trip.
d.
The natural critical f requencies of the turbine shaf t assemblies existin' between ze"o speed and 20, overspeed should 7e controlled in the design and operation so as to cause no distress to the unit ouring operation, e.
The turbine rotor and disk design shout' Scilitats inservice inspection of all high stress regions, including bores and keyways, with the need for re oving the disks from the shaft.
6.
Inservice Insp_ection The applicant's inservice inspection program is acceptable if in compliance with the following criteria:
The inservice inspection program for the steam turbine assembly should provide assur-ante that disk flaws that might lead to brittle failure of a disk at speeds up to design speed will be detected. The inservice inspection program for the turbine assembly should include the following:
Disasserbly of the turbine at appruxinately 10-jear intervals, during plant shut-a.
down coinciaing with the inservice inspection schedule as required by A5MF Boiler and Pressure Vessel Code,Section XI, and complete inspection of all normally inaccessible parts, such as couplings, coupling bolts, turbine shafts, low pres-sure turbine blades, low pressure disks, and high pressure rotors. This inspection should consist of visu3l, surface, and volucetric examinations, as required.
The applicant should keep abreast of technological advances in volumetric examina-tion techniques so that when improved e9 0ds for inspection of turbine disks are developed they can ba incorporated into the inservice inspection progra b.
An in-place visual exanination of the turbine assembly at accessible locatiori should be conducted during refueling shutdowns at intervals not exceeding three years.
III.
REVIEW PROCEDURES The reviewer will select and erphasize naterial from the procedJres described below, as may be appropriate for a particular case.
For each area of review, the following review procedures are followed:
1.
Materials Selection The materials properties and the procedures to minimize flaws and improve fracture toughness, as described by the applicant, are reviened and co pared with the require-rents of Section II. I of this plan. If a new raterial not used in prior licensed cases 07i 10.2.3-S t
is utilized, the applicant's materials selection is reviewed and evaluated to establist its acceptability. Such an evaluation is based on the acceptance criteria of Section II of this review plan.
2.
Fracture Toughness The fracture toughness properties of the low pressure disk and high pressure rotor materials, including materials specimen test data, where applicable, are reviewed and compared with the requirements of Section II.2 of this plan. The applicant is per-mitted any of three alternates for deriving the fracture toughness of the disk materials.
3.
High Temperature Properties The high temperature properties of the high pressure rotor materials, including speci-men test data, where applicable, are reviewed and compared with the requirements of Section II.3 of this plan.
4.
Preservice Inspection The preservice inspectic"1 program, including finish machining, ultrasonic inspection, surface inspection, visual inspection, and spin testing, is reviewed and compared with the requirements of Section II.4 of this plan. The extent to which the ultrasonic inspections and the acceptance criteria in the SAR agree with ASME Boiler and Pressure Vessel Code,Section III, NS-2530 for plate materials or NB-2540 for forgings, is reviewed.
5.
Turbine Disk Design The design and stress analysis procedures used for the high and low pressure turbine disks are reviewed including the following areas:
a.
Load combinations at normal operating speed and allowable stresses.
b.
Design overspeed and basis for selection of design overspeed.
c.
Load combinations at design overspeed and allowable stresses.
The SAR data are compared and evaluated against Section II.5 of this plan.
6.
Inservice Inspection The inservice inspection program described by the applicant, including areas to be inspected, methods of inspection, frequency of inspection, and acceptance criteria, is reviewed and compared with the requirements of Section II.6 of this plan.
IV.
EVALUATION FINDINGS The reviewer verifies that sufficient information has been provided in accordance with the requirerents of this review plan and that his evaluation supports conclusions cf the follow-ing type, to be included in the staff's safety evaluation report:
149 0..2
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10.2.3-6
"The probability of failure of a turbine disk or rotor can be minimized by the use of suitable naterials, adequate design, and preservice and inservice inspections. The applicant has described his program for assuring the integrity of low pressure turbine disks and high pressure turbine rotors by use of suitable materials of adequate fracture taughness, conservative design practices, and preservice and inservice inspections.
The staff concurs that these provisions, as described in the SAR, provide reasonable assurance that the turbine disks will not fail during normal operation, including transients up to design overspeed."
V.
REFERENCES 1.
10 CFR Part 50, Appendix A, Generai Design Criterion 4, " Environmental and Missile Design Bases."
2.
ASME Boiler and Pressure Vessel Code, Sections III, V, and XI, American Society of Mechanical Engineers.
3.
ASTM E-208, " Standard Method for Conducting Drop-Weight Test to Determine Nil-Ductility Transition Temperature of Ferritic Steels," Annual Book of ASTM Standards, Part 31, American Society for Testing Materials.
4.
ASTM A-370, " Standard Methods and Definitions for Mechanical Testing of Steel Products,"
Annual Book of ASTM Standards, Parts 1, 2, 3, 4, or 31, American Society for Testing Materials.
5.
J. A. Begley and W. A. Logsdon, Scientific Paps 71-lE7-MSLRF-P1, Westinghouse Electric Corp., July 26, 1971.
6.
F. J. Witt and T. R. Mager, ORNL-TM-3894, Oak Ridge National Laboratory (1972).
10.2.3-7