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 1974 U.S. ATOMIC ENERGY COMMISSION

REGULATORY

G DIRECTORATE

OF REGULATORY

STANDARDS REGULATORY

GUIDE 1.90 INSERVICE

INSPECTION

OF PRESTRESSED

CONCRETE CONTAINMENT

STRUCTURES

WITH GROUTED TENDONS UIDE

A. INTRODUCTION

General Design Criterion 53, "Provisions for Contain.ment Testing and Inspection," of Appendix A, "General Design Criteria for Nuclear Power Plants," to 10 CFR Part 50, "Licensing of Production and Utilization Facil.ities," requires, in part, that the containment be de-signed to permit (I) appropriate periodic inspection of all important areas and (2) an appropriate surveillance program. This guide describes a basis acceptable to the Regulatory staff for developing an appropriate surveil-lance program for prestressed concrete containment structures of light-water-coolcd r~actors with grouted tendons 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 and an overall height of about 200 feet and for which the number of tendons is approximately as follows: 200 in the dome (either three families of tendons 600 apart or two families of tendons 900 apart). 200 vertical (in wall), and 500 complete hoops (in wail).For containment that differ from the "typical" de-scribed above, the model program presented in this guide should 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 an ultimate strength of approximately

1300 tons) and all types, for example, tendons with parallel wires, with one or several strands, and with different systems ol" anchors.The inservice inspection program should cover the tendons, the anchor hardware, and protection features intended for corrosion prevention including grout. Bat-type tendons are not covered in this guide, and, irused, will be reviewed by the Commission's Regulatory staff on 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 grouted tendons 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 real experience to adequately define the long-term character- istics of containment structures with grouted pre-stressing systems. Various types of corrosion may occur in the tendon, depending on age, temperature variation, degree of exposure, and other environmental factors, as well 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;

and 4. Reduction in cross section uf the wires due to corrosion, 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 for methods 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 to the Isuanca or continumnce of a permit or license by the Commlision.

1. Power Reactors 6. Products 2. Research end Test Reactors

7. Transportation

3. Fuels and Materials Facilities

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

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

S. Matirisls and Plant Protection t0. Gencral The effects of corrosion on the tendons are of greatest concern, but they cannot be isolated from other effects. 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. An inservice inspection program is needed to ensure that these limits are not exceeded.

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

but will instead provide a means of tracking changes in the containment prestress level which will initiate investigative actions if the prestress losses become significantly greater than the estimated 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 for inspection, especially during operation.

The original layout of tendons should address itself specifically to this accessibility problem. Any architectural treatment or environmental protection provided for the anchors should not preclude access for inspection purposes.The recommendations outlined in this guide are appli-cable to all containments with grouted wire (parallel or stranded)

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

1. The tendons may need protection from moisture and salt intrusion at coastal sites and other sites having high moisture levels and significant temperature cycles of short duration.2. For sites in indus!rial areas, tendons should be guarded against fume releases containing SO 2 , li 2 S, NO or chlorides.

3. 6hemical constituents of grou! and placement methods can influence the vulnerabifity of grouted tendons to corrosive attack.4. Where environmental conditions make electro-chemical phenomena a consideration, grounding of grouted tendons against stray electrical currents, and possibly cathodic protection of the tendons, could be needed. It should be recognized, however, that cathodic protection can, under some circumstances, be detri-mental to the tendons.The inservice inspection program outlined in this guide consists of three major parts. Some test tendons are left ungrouted and are environmentally protected with a grease. The effects on these test tendons are not intended to represent the environmental or physical.effects (with respect to corrosion)

on the grouted tendons. Instead, acting as compensating gauges, these tendons will be used to evaluate the extent of concrete creep and shrinkage as well as relaxation of the tendon steel. This information will then assist in interpreting gross changes in the readings obtained from the instru-mentation which is measuring the available level of prestressing in the structure.

This instrumentationj composed of either strain gauges or stress meters, will provide prestress level readings in representative areas of the structure.

The instrumentation can be cithe," em-bedded permanently in the structure as it is being built or else installed so that it is possible to remove and replace it. The combined evaluation of the test tendons and instrumentation readings will be supported by a visual examination of the overall structure specifically including sonic representative critical locations (such as anchorages).

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

and 5. A description of the overall inservice inspection program utilizing instruments, ungrouted tendons, and visual observations.

Later, at the time of submittal of the final safety analysis report (FSAR), with construction well ad-vanced, sufficient information will be available to submit a correct and expanded study. The FSAR should incorporate all changes that occurred during construc-tion as well as: 1. A description of the provisions made to ensure that only properly calibrated gauges have been used;2. A numerical estimate of the expected theoretical indication level of the gauges presented as a function of time for the entire life of the plant. This estimate should include 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 for possible discrepancies between the measurements and I the 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 the wires, in the size of the structure, and in friction values;6. A description of actions that should be taken as a result of anomalous gauge readings or indications that numerous gauges are defective;

and 7. 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 the installation and the calibration of the instruments are correct. If the installation of the instrumentation is not yet 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 below does not eliminate the requirement for compliance with"Capability for Containment Leakage Rate Testing," of Appendix 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 can be conducted at containment dtsign pressure.C. REGULATORY

POSITION W 1. Inservice Inspection Program-General Each "typical" prestressed concrete containment structure with grouted tendons, 4s described in Section B, 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; and c. Visual examination.

2. Ungrouted Test Tendons a. The following ungrouted test tendons' should be installed:

(1) Three vertical tendons.(2) Three hoop tendons, and (3) Two dome tendons if the design utilizes two 900 families of tendons or three dome tendons if the.design utilizes three 600 families of tendons.b. At the intervals given for visual examinations in C.4.a below, the ungrouted test tendons should be sub-.3 For the purposes of this guide, a tendon is defined as a separate continuous tensioned element consisting of wires or strands 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 tendon steel. These data should be evaluated in conjunction with concurrent instrumentation readings and visual examinations.

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

0% to 100%;(b) Temperature:

0 0 F to 200'F; and (c) Cyclic loading: 500 cycles of 600 psi stress variation in compression.

(2) The instruments should be protected against adverse effects of' the expected environment in which they will be located, e.g., electrolytic attack, including the effects of stray electric currents of a magnitude that may be encountered at the particular site and structure.

They should be protected against temperature extremes to which they may be exposed while the containment is under construction.

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

and (2) above should be accounted for in the specified limits, or the gauges should be subject to recalibration in service.(4) The range of stress meters shuuld be from 500 psi 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 a function of time, should be incorporated in the design specifications and the FSAR.b. Installation The prestressed cylindrical wall and the dome should 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 into the structure so that it can be maintained and/or replaced.

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

Generally, these loca-tions are presumed to be it the mid-depth of the thickness 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 (in a prototype structure, deflection and strain readings)

are taken during the structural acceptance test.1.90-3 If redundancy is required to achieve rcliability at a measurement point, six strain gauges or six stress meters should be installed.

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

This ,vould permit evaluation of anomalous readings and isolation of a malfunctioning gauge.c. Reading Frequency Every month for the first six months following the structural integrity test, all strain gauges or stress meters should be read. At the option of the designer, earlier readings may be initiated following completion of prestressing, but such readings are supplementary to those necessary following the structural integrity test and should not be substituted for them. Each gauge whose indication deviates from its initially predicted level by more than the preestablished amount contained in the design specifications should be listed in a special table with an indication of its location and all additional pertinent.

information.

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

Those points whose measured strains have not deviated more than the pre-established amount from their initially predicted levels may be read once a year for the rest of plant life if their readings continue to approximate the predicted levels.Gauges whose strains have deviated from their predicted levels by more than the preestablished amount should continue to be measured once each month until, during six'month span of monthly readings, a pattern of no excessive deviations develops.

These measurement points may then be read once a year. However, local conditions or special circumstances may dictate a continuation of once a month readouts.All gauges should be read during the periodic Type A leakage tests required by Appendix J to 10 CFR Part 50, and the results should be evaluated against other data gathered during the overall inservice inspection program.When the number of gauges listed in the special table of deviations described above reaches the predeter-mined fraction of the total contained in the design specifications or if there are other indications of possible loss of prestress, this event should be considered as an abnormal occurrence and reported in accordance with C.5 below.If anomalous readings are received, it should be determined whether they result from defective gauges, and the basis for such a determination should be justified.

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

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

of 21 selected tendons should be visually 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 600 group (three families of tendons) and randomly dis-tributed to provide representative sampling, or three located 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 tendons should again be selected on a random but representative basis, so the sample group will change somewhat each time.b., The inservice inspection program should define the defects the inspector should look for during visual examination of the anchorage system and should estab-lish the corresponding limits and tolerances.

Special attention should be given to the concrete supporting the anchor assemblies, and the crack patterns at these points should be observed, analyzed, and reported.c. A visual examination of concrete cracking and deformations should be scheduled during integrated leakage testing while the containment is at its maximum test pressure, even if visual examinations have been conducted at other times.d. Regulatory practice is to consider grouted tendons as unbonded for load-carrying purposes, and the anchor hardware is therefore considered to be a principal load carrying element requiring periodic visual examina-tion. Consequently, containments should be designed so that the prestressing anchor hardware is accessible for periodic 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 to contain radioactive materials)

is indicated.

In such cases, the reporting program of Regulatory Guide 1.16,"Reporting on Operating Information-Appendix A Technical Specifications," should apply. A description should be furnished of the condition of the concrete (especially at tendon anchorages)

and all examined tendon hardware, the inspection procedures, the toler-ances on concrete cracking and hardware corrosion, the measures to be used when the specified limits or 1.90.4

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

D. IMPLEMENTATION

For applicants choosing to implement the Com-mission's regulations by the methods described in this guide, the following guidance is provided: 1. Construction permit reviews for applications dock-eted after July 1, 1975, will be evaluated on the basis of this guide.2. Construction permit and operating license reviews for plants whose construction permit applications were docketed prior to July 1, 1975, will be evaluated on a case-by-case basis. If practical, the applicant and designer in such cases may choose to follow the recommenda- tions of this guide.1.90-5 I