Regulatory Guide 1.90

Inservice Inspection of Prestressed Concrete Containment Structures with Grouted Tendons

ML13350A298
Person / Time
Issue date:	11/30/1974
From:	Office of Nuclear Regulatory Research
To:
References
RG-1.090
Download: ML13350A298 (5)

November

1974U.S. ATOMIC ENERGY COMMISSION

REGULATORY

GDIRECTORATE

OF REGULATORY

STANDARDS

REGULATORY

GUIDE 1.90INSERVICE

INSPECTION

OF PRESTRESSED

CONCRETECONTAINMENT

STRUCTURES

WITH GROUTED TENDONSUIDE

A. INTRODUCTION

General Design Criterion 53, "Provisions for Contain.ment Testing and Inspection,"

of Appendix A, "GeneralDesign Criteria for Nuclear Power Plants,"

to 10 CFRPart 50, "Licensing of Production and Utilization Facil.ities," requires, in part, that the containment be de-signed to permit (I) appropriate periodic inspection ofall important areas and (2) an appropriate surveillance program.

This guide describes a basis acceptable to theRegulatory staff for developing an appropriate surveil-lance program for prestressed concrete containment structures of light-water-coolcd r~actors with groutedtendons made up of parallel wires or strands (bar-type tendons arc not covered).

B. DISCUSSION

This guide is applicable to current "typical"

pre-stressed concrete containments having a shallow-domed roof on cylindrical walls about 150 feet in diameter andan overall height of about 200 feet and for which thenumber of tendons is approximately as follows:

200 inthe dome (either three families of tendons 600 apart ortwo families of tendons 900 apart). 200 vertical (inwall), and 500 complete hoops (in wail).For containment that differ from the "typical"

de-scribed above, the model program presented in this guideshould serve as the basis, for development of a compara-ble inservice inspection program which the Regulatory staff will evaluate on a case-by-case basis.This guide covers inservice inspection of contain-ments using grouted wire tendons of all sizes (up to anultimate strength of approximately

1300 tons) and alltypes, for example, tendons with parallel wires, with oneor several strands, and with different systems ol" anchors.The inservice inspection program should cover thetendons, the anchor hardware, and protection featuresintended for corrosion prevention including grout. Bat-type tendons are not covered in this guide, and, irused,will be reviewed by the Commission's Regulatory staffon a case-by-case basis to determinhe inservice inspection requirement s.In service inspection of the structural integrity of pre-stressed concrete containment structures with groutedtendons is needed because any deterioration of the pre-stressing tendons may not become evident until the con-taininent is loaded as a result of a loss-of-coolant acci-dent. Even though grouted tendons are a proven technol-ogy in other types of structures, there is as yet no realexperience to adequately define the long-term character- istics of containment structures with grouted pre-stressing systems.

Various types of corrosion may occurin the tendon, depending on age, temperature variation, degree of exposure, and other environmental factors, aswell as the quality of workmanship.

Of particular impor-tance is the quality of the grouting.

The prestressing force in a tendon can be indirectly checked by measuring the level of prestress in the struc-ture. Any eventual decrease in the tendon prestressing force is due to the interaction of several time-dependent factors such as:I. Stress relaxation in the wire;2. Shrinkage and creep in concrete;

3. Differential thermal expansion or contraction between the tendon, grout, and concrete;

and4. Reduction in cross section uf the wires due tocorrosion, including possible fracture of the wire

s. USAEC REGULATORY

GUIDES Copies of published guides may be obtimned by request indicating the divisions deitird to the US. Atomic Energv Commistion, Washinglon, D.C. 20545.Regulatory Guides ote Issued to describe end make available to the public Atlention:

Director of Regulatory Comments and sug9gtions formethods acceptable to ihe AEC Regulatory stafIf of Implementing specific paris of in theat guide" are encouraged and should be sent to the Secretary the Commission's regulatlons.

to delineate technlques

.,eýd by the 1t1ll in of the Cornmision, US. Atomit Energy Commistion.

Wathiinglon.

O.C. 2055,.evaluating

"clidfic problamts or postulated accldents, or to provide guidance to Attention:

Dockelingr nd Service Section.applicants.

Regulatory Guides ar not substitutes for regulalions and compliance with them is not required.

Methods and tolutlons different from those set out in The guides are issued in the following ten broad divisions:

the gtuldet will be If they provide a batis for the findings requisite tothe Isuanca or continumnce of a permit or license by the Commlision.

1. Power Reactors

6. Products2. Research end Test Reactors

7. Transportation

3. Fuels and Materials Facilities

8. Occupational HealthPublished guldan will be tevisad periodically, as appropriate, to accommodlte

4. Environmental and SitIng 9. Antitrust Reviewcomments and to reflect new Information or experience.

S. Matirisls and Plant Protection t0. Gencral The effects of corrosion on the tendons are ofgreatest concern, but they cannot be isolated from othereffects.

Therefore, tolerance limits for the loss of pre.stressing force which arc established to monitor corro-sion must also take into account all prestress losses. Aninservice inspection program is needed to ensure thatthese limits are not exceeded.

It should be noted, how-ever, that this program will not detect minor losses intendon prestress due to corrosion.

but will insteadprovide a means of tracking changes in the containment prestress level which will initiate investigative actions ifthe prestress losses become significantly greater than theestimated losses.Many hoop tendons are anchored on buttresses located partially inside the building adjacent to the con-tainment.

Unless the anchors are installed with consider.

ation for inspection, they will not be easily accessible forinspection, especially during operation.

The originallayout of tendons should address itself specifically tothis accessibility problem.

Any architectural treatment or environmental protection provided for the anchorsshould not preclude access for inspection purposes.

The recommendations outlined in this guide are appli-cable to all containments with grouted wire (parallel orstranded)

prestressing systems regardless of plant geo-graphical location, but the following factors warrantspecial attention:

1. The tendons may need protection from moisture andsalt intrusion at coastal sites and other sites having highmoisture levels and significant temperature cycles ofshort duration.

2. For sites in indus!rial areas, tendons should beguarded against fume releases containing SO2, li2S,NO or chlorides.

3. 6hemical constituents of grou! and placement methods can influence the vulnerabifity of groutedtendons to corrosive attack.4. Where environmental conditions make electro-chemical phenomena a consideration, grounding ofgrouted tendons against stray electrical currents, andpossibly cathodic protection of the tendons, could beneeded. It should be recognized, however, that cathodicprotection can, under some circumstances, be detri-mental to the tendons.The inservice inspection program outlined in thisguide consists of three major parts. Some test tendonsare left ungrouted and are environmentally protected with a grease. The effects on these test tendons are notintended to represent the environmental or physical.effects (with respect to corrosion)

on the groutedtendons.

Instead, acting as compensating gauges, thesetendons will be used to evaluate the extent of concretecreep and shrinkage as well as relaxation of the tendonsteel. This information will then assist in interpreting gross changes in the readings obtained from the instru-mentation which is measuring the available level ofprestressing in the structure.

This instrumentationj composed of either strain gauges or stress meters, willprovide prestress level readings in representative areas ofthe structure.

The instrumentation can be cithe," em-bedded permanently in the structure as it is being builtor else installed so that it is possible to remove andreplace it. The combined evaluation of the test tendonsand instrumentation readings will be supported by avisual examination of the overall structure specifically including sonic representative critical locations (such asanchorages).

Information from the test tendons, instru-mentation, and visual examination will be used toevaluate the overall structural condition of the contain-ment.Because of the nature of the program described above, decisions must be made early in the designprocess as to the nature and acceptability of the systemto be used and the components to be installed as notedbelow. In order to ensure timely review, the proposedinservice inspection program should be presented in thepreliminary safety analysis report (PSAR); it shouldinclude:1. A description of the instruments that will be installed in the structure arid the data collecting system that willbe used;2. A description of the planned erection procedure ofthe system, including the instrument calibration proce-dure to be used and also the locations of the instru-1ments, the data collecting system, and the ungrouted tendons;3. Identification of which tendons will not be groutedand how these tendons will be protected against corro-sion;4. Discussion on the accessibility of the end anchorages;

and5. A description of the overall inservice inspection program utilizing instruments, ungrouted tendons, andvisual observations.

Later, at the time of submittal of the final safetyanalysis report (FSAR), with construction well ad-vanced, sufficient information will be available to submita correct and expanded study. The FSAR shouldincorporate all changes that occurred during construc- tion as well as:1. A description of the provisions made to ensure thatonly properly calibrated gauges have been used;2. A numerical estimate of the expected theoretical indication level of the gauges presented as a function oftime for the entire life of the plant. This estimate shouldinclude all necessary estimated corrections, including concrete creep and shrinkage and tendon relaxation which will be checked by the ungrouted test tendons;3. An indication of the reasons and tolerances forpossible discrepancies between the measurements and Ithe actual prestress;

1.90-2 U-4. An evaluation of the maximum probable error in the* results and the accuracy expected:

5. A discussion of the probable influences of tempera-lure on the results due to changes in the length of thewires, in the size of the structure, and in friction values;6. A description of actions that should be taken as aresult of anomalous gauge readings or indications thatnumerous gauges are defective;

and7. The visual observations to be made, the procedures for checking the ungrouted tendons, and the integration of these data with gauge data to form inservice in;spec-lion conclusions regarding continued structural integrity.

The FSAR should also contain a certification that theinstallation and the calibration of the instruments arecorrect.

If the installation of the instrumentation is notyet completed, this certification may be submitted later,but not less than 3 months before issuance of an* operating license.The use of the Regulatory Positton described belowdoes not eliminate the requirement for compliance with"Capability for Containment Leakage Rate Testing,"

ofAppendix A to 10 CFR Part 50, General Design Crite-rion 52, which requires tha the containment be de-* signed so that periodic integratcd leakage rate testing canbe conducted at containment dtsign pressure.

C. REGULATORY

POSITIONW 1. Inservice Inspection Program-General Each "typical"

prestressed concrete containment structure with grouted tendons,

4s described in SectionB, should be subjected to mn inservice inspection program that includes:

a. iftoff tests ofungrouted test tendons;b. Periodic reading of instrumentation for deter-mining concrete prestress level; andc. Visual examination.

2. Ungrouted Test Tendonsa. The following ungrouted test tendons'

should beinstalled:

(1) Three vertical tendons.(2) Three hoop tendons, and(3) Two dome tendons if the design utilizes two900 families of tendons or three dome tendons if the.design utilizes three 600 families of tendons.b. At the intervals given for visual examinations inC.4.a below, the ungrouted test tendons should be sub-.3 For the purposes of this guide, a tendon is defined as aseparate continuous tensioned element consisting of wires orstrands anchored at eacl. end to an end anchorage assembly.

jected to liftoff testing to measure the effects of con.crete shrinkage and creep and relaxation of the tendonsteel. These data should be evaluated in conjunction with concurrent instrumentation readings and visualexaminations.

If instrumentation readings indicate aneed for further checking, additional liftoff tests of theungrouted test tendons may be needed.3. Instrumentation a. Characteristics (I) Instrumentation provided for the determina- lion of concrete prestress level should be capable ofeffective use over the life span of the containment structure within specified operational limits under thefollowing conditions, unless othenvise defliaed by thedesigner and approved by the Regulatory staff:(a) Humidity;

0% to 100%;(b) Temperature:

00F to 200'F; and(c) Cyclic loading:

500 cycles of 600 psistress variation in compression.

(2) The instruments should be protected againstadverse effects of' the expected environment in whichthey will be located, e.g., electrolytic attack, including the effects of stray electric currents of a magnitude thatmay be encountered at the particular site and structure.

They should be protected against temperature extremesto which they may be exposed while the containment isunder construction.

(3) The snsitivity of strain gauges should bespecified, and the drift or stability under the conditions in C.3.a.(l)

and (2) above should be accounted for in thespecified limits, or the gauges should be subject torecalibration in service.(4) The range of stress meters shuuld be from 500psi in teasion to 2500 psi in compression.

(5) A numerical estimate of the expected theoret-ical indication level of the gauges or meters. including permissible deviations of readings, presented as afunction of time, should be incorporated in the designspecifications and the FSAR.b. Installation The prestressed cylindrical wall and the domeshould be instrumented.

The base mat need be instru-merited only if it is prestressed.

This instrumentation may be either embedded in the concrete or inserted intothe structure so that it can be maintained and/orreplaced.

Instrument types, locations, and quantities should be selected to provide the best representation ofprestress levels in the structure.

Generally, these loca-tions are presumed to be it the mid-depth of thethickness of the wall and dome, unless specified other-wisc by the designer, at locations around the structure that match the locations at which deflection readings (ina prototype structure, deflection and strain readings)

aretaken during the structural acceptance test.1.90-3 If redundancy is required to achieve rcliability at ameasurement point, six strain gauges or six stress metersshould be installed.

Three galiges should measure theprestress in the direction of the meridian and three theprestress in the hoop direction.

This ,vould permitevaluation of anomalous readings and isolation of amalfunctioning gauge.c. Reading Frequency Every month for the first six months following thestructural integrity test, all strain gauges or stress metersshould be read. At the option of the designer, earlierreadings may be initiated following completion ofprestressing, but such readings are supplementary tothose necessary following the structural integrity testand should not be substituted for them. Each gaugewhose indication deviates from its initially predicted level by more than the preestablished amount contained in the design specifications should be listed in a specialtable with an indication of its location and all additional pertinent.

information.

After the first six months, thereading frequency can be changed to reflect the devia-tion from the predicted readings.

Those points whosemeasured strains have not deviated more than the pre-established amount from their initially predicted levelsmay be read once a year for the rest of plant life if theirreadings continue to approximate the predicted levels.Gauges whose strains have deviated from their predicted levels by more than the preestablished amount shouldcontinue to be measured once each month until, duringsix'month span of monthly readings, a pattern of noexcessive deviations develops.

These measurement pointsmay then be read once a year. However, local conditions or special circumstances may dictate a continuation ofonce a month readouts.

All gauges should be read during the periodic TypeA leakage tests required by Appendix J to 10 CFR Part50, and the results should be evaluated against otherdata gathered during the overall inservice inspection program.When the number of gauges listed in the specialtable of deviations described above reaches the predeter- mined fraction of the total contained in the designspecifications or if there are other indications of possibleloss of prestress, this event should be considered as anabnormal occurrence and reported in accordance withC.5 below.If anomalous readings are received, it should bedetermined whether they result from defective gauges,and the basis for such a determination should bejustified.

4. Visual Examination a. A visual examination of the entire concrete con-tainment structure should be performed

.1, 3, and syears after the initial containment structural integrity test and every 5 years thereafter.'As a part of this visualexamination, the tendon anchorage assembly hardware(such as bearing plates, stressing washers, shims, wedges,and buttonheads)

of 21 selected tendons should bevisually examined to the extent practical without dis-mantling load-bearing components of the anchorage.

These selected tendons'

should include:(1) Six dome tendons;

two located in each 600group (three families of tendons)

and randomly dis-tributed to provide representative sampling, or threelocated in each 900 group (two families of tendons),

(2) Five vertical tendons, randomly but repre-sentatively distributed.

(3) Ten hoop tendons, randomly but represen- tatively distributed.

For each succeeding examination, the tendonsshould again be selected on a random but representative basis, so the sample group will change somewhat eachtime.b., The inservice inspection program should define thedefects the inspector should look for during visualexamination of the anchorage system and should estab-lish the corresponding limits and tolerances.

Specialattention should be given to the concrete supporting theanchor assemblies, and the crack patterns at these pointsshould be observed, analyzed, and reported.

c. A visual examination of concrete cracking anddeformations should be scheduled during integrated leakage testing while the containment is at its maximumtest pressure, even if visual examinations have beenconducted at other times.d. Regulatory practice is to consider groutedtendons as unbonded for load-carrying purposes, and theanchor hardware is therefore considered to be a principal load carrying element requiring periodic visual examina-tion. Consequently, containments should be designed sothat the prestressing anchor hardware is accessible forperiodic examination.

S. Reporting If the specified limits of the inservice inspection program are exceeded, a possible abnormal degradation of the containment structure (a boundary designed tocontain radioactive materials)

is indicated.

In such cases,the reporting program of Regulatory Guide 1.16,"Reporting on Operating Information-Appendix ATechnical Specifications,"

should apply. A description should be furnished of the condition of the concrete(especially at tendon anchorages)

and all examinedtendon hardware, the inspection procedures, the toler-ances on concrete cracking and hardware corrosion, themeasures to be used when the specified limits or1.90.4

0tolerances are exceeded, and a decription of procedures to be used following cumpletion of dorrective measuresto verify the satisfactory condition of the structure.

D. IMPLEMENTATION

For applicants choosing to implement the Com-mission's regulations by the methods described in thisguide, the following guidance is provided:

1. Construction permit reviews for applications dock-eted after July 1, 1975, will be evaluated on the basis ofthis guide.2. Construction permit and operating license reviews forplants whose construction permit applications weredocketed prior to July 1, 1975, will be evaluated on acase-by-case basis. If practical, the applicant and designerin such cases may choose to follow the recommenda- tions of this guide.1.90-5I