Regulatory Guide 1.83

Inservice Inspection of Pressurized Water Reactor Steam Generator Tubes

ML031470630
Person / Time
Issue date:	07/31/1975
From:	NRC/OSD
To:
References
RG-1.083, Rev. 1
Download: ML031470630 (5)

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U.S. NUCLEAR REGULATORY COMMISSION

REGU LA TORY GUIDE

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.REGULATORY GUIDE 1.83 INSERVICE INSPECTION OF PRESSURIZED

WATER REACTOR STEAM GENERATOR

TUBES

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A. INTRODUCTION

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GeneralDesign Criteria 14, "Reactor Coolant Pressure Boundary,' and,31, "Fracture Prevention of Reactor Coolant;Pressure.Boundary," of Appendix A, "General Design Criteria for Nuclear Power Plants," to 10 CFR

Part -50' "Licensing..,of Production and Utilization

!Facilities,"' require.,that the reactor coolant pressure boundary- -have.- an extremely low probability of abnorrnal leakage, of rapidly propagating failure, and of

-gross rupture:1General Design Criterion 15, "Reactor Coolan1'.System.:Design,"

requires that the reactor coolant system and associated auxiliary, control,.and protection systems be designed with sufficient margin to

• ensure;.that.the design conditions of the reactor coolant

-pressure boundary'are not exceeded during any condi-

'tion of '-normal ;operation, including anticipated opera- ltional.ioccurrences. Furthermore, General Design Criter-

-ibn 32,i "Inspection :of Reactor Coolant Pressure

Boundary,"i-requires that components'that are part of rthe reactor coolant.pressure .boundary be designed to i',pernit;periodic-inspection and testing of'critical areas to assess their structural and leaktight integrity.

• !~tiFaiure1 6of t'teaam generator tubes,' which can be

'caused;by cr!ackoig} wastage and fretting, will release radioa'ctive. materials to the secondary coolant system.

Farthermro:r ,serious weakening of these tubes from msimiar causes could, in the' event of a loss-of-coolant accident (LOCA), result in tube' failures that would release the energy of the secondary system into the

-Failure is defined as full penetration of the pressure boundary with subsequent leakage containment. This guide describes a method acceptable to the NRC staff for implementing these General Design Criteria by reducing the probability and consequences of steam generator tube failures through periodic inservice inspection for early detection of defects and deteriora- tion. This guide applies only to pressurized water reactors (PWRs). The Advisory Committee on Reactor Safeguards has been consulted concerning this guide and has concurred in the regulatory position.

B. DISCUSSION

The' heat transfer area of the steam generators in pressurized water reactors can comprise well over 50% of the area of the total primary system pressure-retaining boundary. The thin-walled -steam generator tubing is an important part of a major barrier against fission product release to the environment. The steam generator tubing also acts as a barrier against steam release to the containment in the event of a LOCA. To act as an effective barrier, this tubing must be free of cracks, perforations, and general deterioration. The design criteria used to establish the structural integrity of the steam generator tubing should also define the ninimum tube wall thickness required to sustain the pressure and thermal loading caused by the worst postulated LOCA in combination with a safe shutdown earthquake.

Inadequate control of the secondary coolant chem- istry has been identified as one of the principal sources As defined in Appendix A, "Seismic and Geologic Siting Criteria for Nuclear Power Plants," to 10 CFR Part 100,

"Reactor Site Criteria."

USNRC REGULATORY GUIDES

Comments should be ent to he Secretary of the Com,ission U S Nuclear R us l d

inCIte sIra'bbl to the P-bis Regulatory Commission. Washington. D C. 20656. Attention: Docketing and Regulatory Guides are issued to describe and mavaailable totepublic methods acctplable o the NRC staff of implementing specific paris of the Service Section Comniss,on's reg.leions lo delineate echniques used by tho staff in etru.

The guidesae issued in the following len broad diiusions ating spec.fic problems 0, postulated accdents. ot to provide guidance to appli.

cants. Regulatory Guides are not substutes for egulations, and compliance

1. Power Reactor,

6 Poducts with them is not required Methods anJ solutions different from those set out in

2. Research and Test Reactors

7 Transportation the guides will be acceptable I they pro,ide a basis lor the findings requisite to

2 Fuels nd MaterialsF Fcilitie

8 Occupational Health the issuance or continuance of a permit or license by the Commission

4. Environmental and Siting

9 Antitrust Review Comments end suggestions for mprocements in these guides are encouraged S. Materials end Plant Protection

10 General at all tames and guidss wll be evised as appropriate. to accommodate com Monts and to reflect new information or esperience This guide was revised as a Copies o published guides may be obtained b written request indicating the result of substantive comments received bow the public and additional staff divisions desired to the U S Nuclear Regulatory Commission. Washington. D C

review.

20X,5. Attention 0iector. Office of Standards Deeslopment Revision 1 July 1975

of steam generator tube degradation and failure. There is During reactor operation, steam generator tube leaks evidence that excessive steam-side corrosion attack 'are dtected by?

s occurs in restricted fow areas tha

t. permit highlocal

-radioactivity and.the.presence of bo,rogthae insru- concentration of free caustic, 'phosphates, and i punies n

mtenanalysis of steam and bq'dWnza

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s that rnay enter the steam gerator though- coiden'ser S are piesent, ,heycaniisiially Xeb&

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0d4 irgt inleakage. Therefore, secondary water cheristry specifi- examination of suspect tubing. Eddy current examina- cations -must reflect the limitation of the materials in the don 'is ebffective' because ' it-d'tetst)p?e c%f secondary system, and the supporting auxiliary chemical defect-caused variations in effective electrical conduc- feed system must be designed to maintain desired tivity and/or magnetic permeability of the material being feedwater quality to each steam generator. Effective tested. Because the eddy current probing technique has monitoring of water chemistry with in-line; coriitiuous'

excelleht sensitivity in nonmagnetic materials, decreases analytical instrumentation supplemented by plant in effective conductivity due to a discontinuity in a tube laboratory sampling analysis 'of stea'; condensate!'

wall can ie'measured directly by increases in coil voltage return, and feedwater is necessary' at 'all. iimes during '

in the' probe. Special eddy current probes designed for operation to ensure that water quality is not degraded_ -scanning tubing from the inside have proved very below acceptable lirits by such events as condenser effective in locating defect areas in steam generator inleakage or chemical feed system maloperation.

tubes and for assessing the overall condition of ihe tubing in numerous operating PWRs.

Mechanical or flow-induced vibration can cause fret- ting or fatigue damage to stear generator'tubes, which could also lead to tube failures.

A program of periodic inservice inspection of steam generators is essential to monitor the'integrity of the tubing, particularly if there is evidence of mechanical damage or progressive deterioration caused by inade- quate design, mianufacturng eriors, or chemical imbal- ance. Inservice inspection of steam generator tubing can also provide useful information regarding the nature and cause of any tube degradation, thereby assisting the operator in taking proper and timely corrective measures.

Inspection and repairs of steam generator tubing in operating plants cause some radiation. exposure to personnel. Careful pre-job planning can assist in main- taining radiation exposures as-.low as is reasonably achievable.

Temporary shielding, decontamination, special tooling, jigs and fixtures for remote inspection and repair, and other design and procedural considera- tions such as are outlined in Regulatory Guide 8.8,

"Information Relevant to Maintaining Occupational Radiation Exposure as -Low as Practicable (Nuclear Reactors)," should be used to the extent practical.

The recommendations in this guide are applicable to current "typical"

once-through and U-bend- steam generators that have Ni-Cr-Fe or stainless steel tubing.

The steam, generator tubing is usually seamless, cold drawn, and annealed and is manufactured and tested in accordance with specifications of the American Soaety of Mechanical Engineers and the American Society for Testing and Materials.

The initial quality of manufactured tubing' is deter- mined by hydrostatic, eddy current, and ultrasonic tests.

The tube-to-tube-sheet welds are inspected visually and by dye penetrant, then finally leak tested.

Radiography is a supplemerital miethod for inservice inspection of steam generator tubing. Although radi- ography does not provide the'3peed and lexibility of eddy 'current 'methods, it can supplemient eddyrctrret testing for defect characterization o a limited biAi';

Leaking tubes, defective tubes,'and tubes that exce'ed the 'plugging limit should be ta'kendiu'of service by plugging both ends of the'tube at the'tUbe hsbeertwith welded plugs. Various methods ire'used fofliindghd welding. Plugs' r'ay be installed"iniechaniclllydr explo- sively, and welding nay be perforied'r an'ually',auto- matically, or explosively.

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t Experience has indicated thatdea'ch steamfgenerator design has critical areas (e.g.', crevices,'-low-flow areas, and regions that allow'steam blanketing) where attack and degradation of the steam generatortubes rnaya- occur even if secondary water chemistry'is:pr6peily main- tained. Mechanical darage to steam generator(tubesnmay also occur'in areas subject to floWiriduced&vibrations.

Typically, the number of tubesinAthese'critical!areasEis less than 20% of the total. '

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The usual shop examination of tubing can be,consid- ered to serve as an adequate baseline examination.,An onsite preservice inspecton of the,,steami generator tubing should be performed in,; the .absence of- a documented shop or field examination. For.plants now operating, the initial inspection should sample .tubes on a random basis unless experience with.similar-designs and chemistry indicate critical areas: Subsequent inspec- tions should concentrate on any critical areas identified so that most defective tubes will be found.-This'selection method can be expected to resultin' the-ratio'of tube defects found to 'total tubes inspected being consider-

'ably higher than -the ratio of-defective tubes -to -total tubes in the steam generator.

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Lines indicate substantive changes from previous issue.

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C. REGULATORY POSITiON

A program for inservice inspection of steam generator tubing should be established and should include the following:

1. Access for'Inspection a. Steam generators of pressurized water reactors should be designed to facilitate inspection of all tubes.

b. Sufficient access should be provided to perform these inspections and to plug tubes as required.

c. Pre-job planning should be undertaken to make provisions for inspections that ensure that personnel radiation exposure is maintained as low as is reasonably achievable.,

2. Inspection Equipment and Procedures a. Inservice inspection should include nondestruc- tive examination by eddy current testing or equivalent techniques. The equipment should be capable of locating and identifying stress corrosion cracks and tube wall thinning by chemical wastage, mechanical damage, or other causes.

b. The inspection equipment should be sensitive enough to detect imperfections 20% or more through the tube wall.

c. A suitable eddy current inspection system could consist of () an intemal sensing probe, (2) a two-channel eddy curent tester, (3) a viewing oscillo- scope, (4) a conventional two-channel strip chart recorder, and (5) a magnetic tape-data recorder.

d. Examination results and reports should be stored and maintained for the operating life of the facility.

e. Standards consisting of sirnilar as-manufactured steam generator tubing with known imperfections should be used to establish sensitivity and to calibrate the equipment. Where practical, these standards should include reference flaws that simulate the length, depth, and shape of actual imperfections that are characteristic of past experience.

f. 'Me equipment should be capable of examining the entire length of the tubes.3

'For U-bend designs, entry for the hot-leg side with examination from the point of entry completely around the U-bend to the top support of the cold leg is considered sufficient to constitute a tube inspection.

g. The equipment used for eddy current testing should be designed so that operators may bc`hielded or the equipment. may be. operated remotely to linit operator exposure to radiation.

h. Personnel engaged in data taking and interpret- ing the results of the eddy current inspection should be tested and qualified in accordance with American Society for Nondestructive Testing Standard SNT-TC-IA and supplements.4 i. The ex'aminations should be performed accord- ing to written procedures.

3. Baseline Inspection a. All tubes in the steam generators should be inspected by eddy current or alternative techniques prior to service to establish a baseline condition of the tubing.

b. For operating plants without an initial baseline inspection, the first inservice inspection performed according to regulatory positions CA and C.5 will define the baseline condition for subsequent inspections.

c. Operating plants institu'ting a major-change in their secondary water chemistry (e.g., phosphate to volatile treatment) should conduct a baseline inspection before resumption of power operation.

4. Sampk Selection and Testing Selection and testing of steam should be made on the following basis:

generator tubes a. The preservice inspection should include all the tubes in the steam generators.

b. Tubes for the ispect6n of operating plants should be selected on a random basis except where experience in similar plants with similar secondary water chemistry indicates critical areas to be inspected.

c. At least 3% of the total number of tubes in each steam generator to be inspected should be tested during each inspection (see regulatory positions C.3 and C.6).

d. All of the steam generators in a given plant should be inspected at the first inservice ispection.

Subsequent inspections may be limited to one steam generator on a rotating schedule encompassing 3% of the total tubes of the steam generators in the plant if the

4SNT-TC-IA and Supplements, "Recommended Practice for Nondestructive Testing Personnel Qualification and Certifica- tion." Copies may be obtained from the American Society for Nondestructive Testing, 914 Chicago Avenue, Evanston, Illinois 60202.

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results of the first inspection indicate that all steam generators are performing in a like manner. (Note:

Under some circumstances, the operating conditions in one or 'ore specific steam generators may be found to be more severe than those in the other generators. Under such circumstances, the sample sequence should be

,modified to inspect the steam generator with the most

'severe conditions.)

e. Every inspection subsequent to the preservice inspection should include all nonplugged tubes 'that previously had detectable wall penetrations (>20o) and should also include tubes in those areas where experi- ence has indicated potential problems.

S. Supplementary Sampling Requirements a. If the eddy current inspection pursuant to regulatory position C.4.d indicates any tubes with previously undetected imperfections of 20% or greater depth, additional'steam 'generators, if any, should be inspected. If previously degraded tubes exhibit signifi- cant (>10%) 'further willi penetration, additional steam generators should be inspected.

b. If the eddy current inspection pursuant to regulatory, position C.4.c indicates that more than 10%5 of the inspected tubes have detectable wall penetration

(>20%) or that'one' or more of the inspected tubes have an indication in excess of the plugging limit (see regulatory position C.7.a), an additional 3% of the tubes should be inspected, concentrating on tubes in those areas of the tube sheet array where tubes with Imperfec- tions were found. In addition, the rest of the steam generators should be inspected according to regulatory position CA.c.

c. If this additional inspection indicates that more than 10% of these additionally inspected tubes have detectable wall penetration (>20%) or one or more of these additiona1y' inspected tubes has an indication in excess of the plugging limit, additional tubes (no less than 6% of the total tubes in the steam generator) in the area of the tube sheet array where tubes with inperfec- tions were found should be inspected.

6.' Inspection Intervals a. The first inservice inspection of steam genera- tors should be performed after 6 effective full power months but before 24 calendar months.

b. Subsequent inservice iispections should be' not less than 2 nor more than 24 calendar months after the previous inspection.

In au inspections,- previously degraded tubes that exhibit significant (>10%)further wall penetration must be included in the 10%.;

c. Inspections may be made coincident with refueling outages or any shutdown for plant repair and maintenance'in accordance with the American Society of Mechanical Engineers Boiler and Pressure Vessel Code,Section XI.'

d. If two consecutive inspections, not including.

the preservice inspection, result in less than 10% of the tubes with detectable wall penetration (>20o) znd no significant (>10%) further penetration of tubes with previous indications, the inspection frequency should be extended to 40-month intervals. If it can be demon- strated through two consecutive inspections that previously observed degradation has not continued and no additional degradation has occurred, a 40-month inspection interval may be initiated.

e. Unscheduled inspections should be conducted in the event of primary-to-secondary leaks exceeding technical specifications, a seismic occurrence greater than an operating basis earthquake,2 a loss-of-coolant accident requiring actuation of engineered safeguards, or a major steam line or feedwater line break.

7. Acceptance Limits a. As used in this regulatory guide:

(I) Imperfection means an exception to the dimensions, finish, or contour required by drawing or specification.

(2) Defect means an imperfection of such severity that the tube is unacceptable for continued service.

(3)

ugging limit means the imperfection depth at or beyond which plugging of the tube must be performed. (Note that the plugging limit is not a depth of penetration within the defect range but rather an imperfection depth with conservative allowances. These allowances include such considerations as general corro- sion and neasurement error.)

(4) Plugging criteria means those calculational and analytical procedures used to arrive at the plugging limit. These currently may be submitted by a licensee for approval by NRC.

b. If, in the inspection performed under regula- tory position C.4, less than 10% of the tubes inspected have detectable wall pentration (>20%) and no tube has imperfections that exceed the plugging limit defect, plant operation may resume.

Ccpies may be obtained from the American Society of Mechanical Engineers, United Engineering Center. 345 East

47th Street, New York, New York 10017.

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c. If, in the inspections performed under regula- tory position C.5, less than 10% of the total tubes inspected have detectable wall penetration (>20o) and no more than three tubes exceed the plugging limit, plant operation may resume after required corrective measures have been taken.

d. If, in the inspections performed under regula- tory position C.5, more than 10% of the total tubes inspected have detectable wall penetration (>20o) or more than three of the tubes inspected exceed the plugging limit, the situation should be immediately reported to the Commission in accordance with the facility license for resolution and approval of the proposed remedial action. Additional sampling and more frequent inspections may be required.

D. IMPLEMENTATION

The purpose of this section is to provide information to applicants and licensees reprding the NRC staffs plans for utlizing this regulatory guide.

This guide reflects current regulatory practice. There- fore, except in those cases in which the applicant proposes an acceptable alternative method for comply- ing with specified portions of the Commission's regula- tions, the methods described herein will be used by the NRC staff in evaluating an applicant's program for inspection of steam generator tubes.

8. Conective Measures All leaking tubes, defective tubes, and tubes with imperfections exceeding the plugging limit should be Iplugged.

Technical specifications for ensuring inspection as recommended in regulatory position C should be incor- porated in operating licenses.

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