Regulatory Guide 1.14

Reactor Coolant Pump Flywheel Integrity

ML003739936
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Issue date:	08/31/1975
From:	Office of Nuclear Regulatory Research
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RG-1.14, Rev 1
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Revision 1 U.S. NUCLEAR REGULATORY COMMISSION Au"ust 1975 REGULATORY GUIDE

OFFICE OF STANDARDS DEVELOPMENT

REGULATORY GUIDE 1.14 REACTOR COOLANT PUMP FLYWHEEL INTEGRITY

A. INTRODUCTION

conditions that would cause such overspeed. Methods of limiting potential pump overspeed are also under investi General Design Criterion 4, "Environmental and gation.

Missile Design Bases," of Appendix A, "General Design Criteria for Nuclear Power Plants," to 10 CFR Part 50, If the flywheel of the reactor coolant pump is

"Licensing of Production and Utilization Facilities," conservatively designed and made from suitable mate requires that nuclear power plant structures, systems, rials with closely controlled quality, if adequate design and components important to safety be protected review of new configurations is provided, and if ade against the effects of missiles that might result from quate inservice inspection is provided, the probability of equipment failures. This guide describes a method a flywheel failure is sufficiently small that the conse acceptable to the NRC staff of implementing this quences of failure need not be protected against.

requirement with regard to minimizing the potential for failures of the flywheels of reactor coolant pump motors Materials for pump flywheels should be manufac in light-water-cooled power reactors. tured by processes that minimize flaws and result in adequate fracture toughness in both the transverse and

B. DISCUSSION

longitudinal rolling directions. Materials produced by vacuum melting and degassing or the electroslag remelt The flywheels on reactor coolant pump motors ing process are known to have improved cleanliness and provide inertia to ensure a slow decrease in coolant flow toughness. Plate material should be cross rolled to a ratio in order to prevent fuel damage as a result of a loss of of at least I to 3, sufficient to achieve acceptable power to the pump motors. During operation at normal isotropy. Fracture toughness is achieved more readily in speed, a flywheel has sufficient kinetic energy to thinner plates, and fabrication of laminated flywheels by produce high-energy missiles and excessive vibration of assembling them from several plates is acceptable.

the reactor coolant pump assembly if the flywheel should fail. Overspeed of the pump rotor assembly As an example, past evaluations have shown that during a transient increases both the potential for failure ASME SA-533-B Class 1 and SA-508 Classes 2 and 3 and the kinetic energ3T of the flywheel. The safety materials generally have suitable toughness for typical consequences could be significant because of possible flywheel applications provided stress concentrations are damage to the reactor coolant system, the containment, kept within reasonable limits and the reference tempera or other equipment or systems important to safety. ture RTNDT, determined in accordance with Article NB-2331(a) of Section HI of the ASME Code,' is at Methods of predicting the loss-of-coolant accident least 50 0 C (900F) below the lowest temperature at (LOCA) overspeed conditions are under continuing which operating speed is achieved. For other materials investigation. The limit on predicted pump overspeed in that may be considered for flywheels, the strength and the event of a LOCA should be less than the calculated toughness properties should be evaluated and justified critical speed for failure of the flywheel. The conserva for this application.

tism inherent in the latter calculation, coupled with a realistic prediction of maximum rotational speed, is 'Copies may be obbtined from the American Society of considered to provide adequate margin because of the Mechanical Engineers, United Engineering Center, 345 East low probability of occurrence of the specific LOCA 47th Street, New York, New York 10017.

USNRC REGULATORY GUIDES Comments should be sent to the Secretary of the Commission, U.S. Nciler Regulatory Guides are issued to describe and make available to the public Regulatory Commission. Washongton. D.C. 2 , Attention: Dockeling end methods acceptable to the NRC staff of implementing specific parts of the Commission's regulations, to delineate techniques used by the staff In evalu- The guides are issued in the following ten broad divisions:

sting specific problems or postulated accidents. or to provide guidance to appli cents. Regulatory Guides are not substitutes for regulations, end compliance 1: Power Reactors S. Products with them is not required. Methods and solutions different from those set out in 2. Research end Test Reactors 7. Transportation the guides will be acceptable if they provide a basis for the findings requisite to 3' Fuels and Materiasi Facilities "8. Occupational Health the issuance or continuance of a permit or license by the Commission. 4. Environmental end Siting 9. Antitrust Review Comments and suggestions for improvements in these guides are encouraged 5. Materials and Plant Protection 10. General at all times, and guides will be revised. as appropriate, to accommodate com ments and to reflect new information or experience. However. comments on Copies of published guides may be obtained by written requeat indicating the this guide, if received within about two months after its issuance, will be par. divisions desired to the U.S. Nuclear Regulatory Commission. Washington. D.C.

ticularly useful in evaluating the need for an early revision. 21, Attention: Director, Office of Standards Development.

The non-ductile fracture analysis called for in The desired results of the analyses described in regulatory position C.2.d should be based on appropriate regulatory positions C.2.c, d, and e are quantitative conservative assumptions for stress level, flaw size, estimates of the margins against fracture or excessive temperature, and fracture toughness at the location of deformation during overspeed because such estimates, interest. The non-ductile fracture criterion used to coupled with adequate provisions against overspeed, predict the critical fracture speed should be based on provide the best basis for assurance that the probability initial instability of the flaw as defined in ASTM E-399. of failure under normal and transient conditions is The justification for the stress analysis method used in sufficiently small that the consequences of failure need the fracture analysis should describe the treatment of not be protected against.

stresses arising from interference fits and thermal stresses when they are superimposed on the stresses caused by

C. REGULATORY POSITION

rotational forces. Justification for the flaw size estimate should consider it to be the maximum expected size of 1. Material and Fabrication flaw that could conceivably escape detection, and should consider material thickness, method and frequency of a. The flywheel material should be of closely nondestructive inspection, and analysis of flaw growth in controlled quality. Plates' should conform to ASTM A20

fatigue if that is significant. The effect of cracks and should be produced by the vacuum-melting and emanating from such structural discontinuities as key degassing process or the electroslag remelting process.

ways and bolt holes should be evaluated. Justification Plate material should be cross-rolled to a ratio of at least for the fracture toughness assumed for the material 1 to 3.

should describe the properties to be measured transverse to the rolling direction in the tests of each plate of b. Fracture toughness and tensile properties of material. The range of fracture toughness test tempera each plate of flywheel material should be checked by tures should include the lowest service temperature at tests that yield results2 suitable to confirm the applica which overspeed could occur. If not, the basis used for bility to that flywheel of the properties used in the any extrapolation should be justified. fracture analyses called for in regulatory positions C.2.c, d, and e.

In doing the fracture analysis described in regulatory position C.2.d, engineering judgment should be used to c. All flame-cut surfaces should be removed by select for analysis only those locations that appear to machining to a depth at least 12 mm (1/2 inch) below have the most severe sets of conditions. Severity is a the flame-cut surface.

function of stress level, flaw size, and fracture toughness at the location of interest. Comparison of perhaps three d. Welding, including tack welding and repair or four cases in terms of KI/KIC, the ratio of the welding, should not be permitted in the finished flywheel imposed stress intensity factor at some nominal speed to unless the welds are inspectable and considered as the material toughness, should locate to most severe sets potential sources of flaws in the fracture analysis.

of conditions. Evaluation of the critical speed for fracture, which may require techniques that go beyond 2. Design linear elastic fracture mechanics, may then focus on one critical location. a. The flywheel assembly, including any speed limiting and antirotation devices, the shaft, and the Excessive deformation during overspeed of the bearings, should be designed to withstand normal condi flywheel is of concern because damage could be caused tions, anticipated transients, the design basis loss-of by separation of the flywheel from the shaft. For the coolant accident, and the Safe Shutdown Earthquake purpose of this guide, excessive deformation means any loads without loss of structural integrity.

deformation such as an enlargement of the bore that could cause such separation directly or could cause an b. Design speed should be at least 125% of normal unbalance of the flywheel leading to structural failure or speed but not less than the speed that could be attained separation of the flywheel from the shaft. The calcula during a turbine overspeed transient. Normal speed is tion of deformation should employ elastic-plastic meth defined as the synchronous speed of the a.c. drive motor ods unless it can be shown that stresses remain within at 60 hertz.

the elastic range.

c. An analysis should be conducted to predict the The geometry of the flywheel and pump motor critical speed for ductile fracture of the flywheel. The design should facilitate preservice and inservice inspec methods and limits of paragraph F-1323.1(b) in Section tion of all high-stress regions (bore, keyway, and bolt III of the ASME Code are acceptable. If another method hole regions) without the need for removal of the flywheel from its shaft and preferably without the need

2 for removing the rotor from the motor assembly. These results should be included as part of the'FSAR.

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is used, justification should be provided. The anal ,sis b. Inservice inspection should be performed for should be submitted to the NRC staff for evaluation.7 each flywheel as follows:

d. An analysis should be conducted to predict the

(1) An in-place ultrasonic volumetric examina critical speed for nonductile fracture of the flywheel.

tion of the areas of higher stress concentration at the Justification should be given for the stress analysis bore and: keyway at approximately 3-year intervals, method, the estimate of flaw size and location, which during the refueling or maintenance shutdown coin should take into account initial size and flaw growth in service, and the values of fracture toughness assumed for ciding with the inservice inspection schedule as required the material. The analysis should be submitted to the by Section XI of the ASME Code.

NRC staff for evaluation.3

(2) A surface examination of all exposed sur e. An analysis should be conducted to predict the faces and complete ultrasonic volumetric examination at critical speed for excessive 4 deformation of the fly wheel. The analysis should be submitted to the NRC approximately 10-year intervals, during the plant shut staff for evaluation.3 down coinciding with the inservice inspection schedule as required by Section XI of the ASME Code.

f. The normal speed should be less than one-half of the lowest of the critical speeds calculated in

(3) Examination procedures should be in regulatory positions C.2.c, d, and e above.

accordance with the requirements of Subarticle IWA-2200 of Section XI of the ASME Code.

g. The predicted LOCA overspeed should be less than the lowest of the critical speeds calculated in

(4) Acceptance criteria should conform to the regulatory positions C.2.c., d, and e.

recommendations of regulatory position C.2.f.

3. Testing

(5) If the examination and evaluation indicate Each flywheel assembly should be spin tested at the an increase in flaw size or growth rate greater than predicted for the service life of the flywheel, the results design speed of the flywheel.

of the examination and evaluation should be submitted,

4. Inspection to the staff for evaluation.

D. IMPLEMENTATION

a. Following the spin test described in regulatory position C.3, each finished flywheel should receive a The purpose of this section is to provide informa check of critical dimensions and a nondestructive exam ination as follows: tion to applicants and licensees regarding the staff's plans for utilizing this regulatory guide.

(1) Areas of higher stress concentrations, e.g.

Except in those cases in which the applicant bores, keyways, splines, and drilled holes, and surfaces adjacent to these areas on the finished flywheel should proposes an acceptable alternative method for com be examined for surface defects in accordance with plying with specified portions' of the Commission's paragraph NB-2545 or NB-2546 of Section III of the regulations, the positions of this guide will be used by ASME Code using the procedures of paragraph NB-2540. the NRC staff as follows.

No linear indications more than 1.6 mm (1/16 inch)

long, other than laminations, should be permitted. 1. The recommendations of regulatory positions C.A, C.2, C.3, and C.4.a will be used in evaluating submittals for construction permit applications docketed

(2) Each finished flywheel should be subjected on or after January 1, 1976. If an applicant wishes to to a 100% volumetric examination by ultrasonic meth use the recommendations of regulatory positions C.1, ods using procedures and acceptance criteria specified in C.2, C.3, and C.4.a of this regulatory guide in developing paragraph NB-2530 (for plates) or paragraph NB-2540

submittals for an application docketed before January 1, (for forgings) of Section III of the ASME Code.

1976, the pertinent portions of the application will be evaluated on the basis of this guide.

'The analyses outlined in regulatory positions C.2.c, d, and e 2. The recommendations of regulatory position should preferably be submitted in topical reports rather than on a case-by-case basis for those flywheel designs that will have C.4.b will be used in evaluating procedures used in multiple applications. inservice inspections conducted on all plants after January 1, 1976. If a licensee wishes to use the

4 As defined in the Discussion. recommendations of regulatory position C.

4. b of this

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regulatory guide in performing the inspection before quently become effective per paragraph (b) of § 50.55a January 1, 1976, the pertinent portions of the inspec. for any portion of the inspection, the pertinent portions tid procedures will be evaluated on the bosb of this of the inspection procedures will be evaluated on the guide. Where requirements of Section X) are recom basis of those editions and addenda.

mended, examinations conducted during each 40-month inspection period should meet the code edition and all addenda that were in effect per paragraph (b) of 10 CFR 3. The recommendations of this guide will be used

§ 50.55a 6 months prior to the inspection period. If a in evaluating all topical reports on flywheel integrity licensee wishes to use editions and addenda that subse after January 1, 1976.

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