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

DIRECTORATE OF REGULATORY STANDARDS

G UIDE

REGULATORY GUIDE 1.90

INSERVICE INSPECTION OF PRESTRESSED CONCRETE

CONTAINMENT STRUCTURES WITH GROUTED TENDONS

A. INTRODUCTION

or several strands, and with different systems ol" anchors.

The inservice inspection program should cover the General Design Criterion 53, "Provisions for Contain. tendons, the anchor hardware, and protection features ment Testing and Inspection," of Appendix A, "General intended for corrosion prevention including grout. Bat- Design Criteria for Nuclear Power Plants," to 10 CFR type tendons are not covered in this guide, and, irused, Part 50, "Licensing of Production and Utilization Facil. will be reviewed by the Commission's Regulatory staff ities," requires, in part, that the containment be de- on a case-by-case basis to determinhe inservice inspection signed to permit (I) appropriate periodic inspection of requirement s.

all important areas and (2) an appropriate surveillance program. This guide describes a basis acceptable to the Regulatory staff for developing an appropriate surveil- In service inspection of the structural integrity of pre- lance program for prestressed concrete containment stressed concrete containment structures with grouted structures of light-water-coolcd r~actors with grouted tendons is needed because any deterioration of the pre- tendons made up of parallel wires or strands (bar-type stressing tendons may not become evident until the con- tendons arc not covered). 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

B. DISCUSSION

experience to adequately define the long-term character- This guide is applicable to current "typical" pre- istics of containment structures with grouted pre- stressing systems. Various types of corrosion may occur stressed concrete containments having a shallow-domed roof on cylindrical walls about 150 feet in diameter and in the tendon, depending on age, temperature variation, an overall height of about 200 feet and for which the degree of exposure, and other environmental factors, as number of tendons is approximately as follows: 200 in well as the quality of workmanship. Of particular impor- tance is the quality of the grouting.

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). The prestressing force in a tendon can be indirectly checked by measuring the level of prestress in the struc- For containment that differ from the "typical" de- ture. Any eventual decrease in the tendon prestressing scribed above, the model program presented in this guide force is due to the interaction of several time-dependent should serve as the basis, for development of a compara- factors such as:

ble inservice inspection program which the Regulatory staff will evaluate on a case-by-case basis. I. Stress relaxation in the wire;

2. Shrinkage and creep in concrete;

This guide covers inservice inspection of contain- 3. Differential thermal expansion or contraction ments using grouted wire tendons of all sizes (up to an between the tendon, grout, and concrete; and ultimate strength of approximately 1300 tons) and all 4. Reduction in cross section uf the wires due to types, for example, tendons with parallel wires, with one corrosion, including possible fracture of the wires.

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The effects of corrosion on the tendons are of gross changes in the readings obtained from the instru- greatest concern, but they cannot be isolated from other mentation which is measuring the available level of effects. Therefore, tolerance limits for the loss of pre. prestressing in the structure. This instrumentationj stressing force which arc established to monitor corro- composed of either strain gauges or stress meters, will sion must also take into account all prestress losses. An provide prestress level readings in representative areas of inservice inspection program is needed to ensure that the structure. The instrumentation can be cithe," em- these limits are not exceeded. It should be noted, how- bedded permanently in the structure as it is being built ever, that this program will not detect minor losses in or else installed so that it is possible to remove and tendon prestress due to corrosion. but will instead replace it. The combined evaluation of the test tendons provide a means of tracking changes in the containment and instrumentation readings will be supported by a prestress level which will initiate investigative actions if visual examination of the overall structure specifically the prestress losses become significantly greater than the including sonic representative critical locations (such as estimated losses. anchorages). Information from the test tendons, instru- mentation, and visual examination will be used to evaluate the overall structural condition of the contain- Many hoop tendons are anchored on buttresses ment.

located partially inside the building adjacent to the con- tainment. Unless the anchors are installed with consider. Because of the nature of the program described ation for inspection, they will not be easily accessible for above, decisions must be made early in the design inspection, especially during operation. The original process as to the nature and acceptability of the system layout of tendons should address itself specifically to to be used and the components to be installed as noted this accessibility problem. Any architectural treatment below. In order to ensure timely review, the proposed or environmental protection provided for the anchors inservice inspection program should be presented in the should not preclude access for inspection purposes. preliminary safety analysis report (PSAR); it should include:

The recommendations outlined in this guide are appli- 1. A description of the instruments that will be installed cable to all containments with grouted wire (parallel or in the structure arid the data collecting system that will stranded) prestressing systems regardless of plant geo- be used;

graphical location, but the following factors warrant 2. A description of the planned erection procedure of special attention: 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

1. The tendons may need protection from moisture and tendons;

salt intrusion at coastal sites and other sites having high 3. Identification of which tendons will not be grouted moisture levels and significant temperature cycles of and how these tendons will be protected against corro- short duration. sion;

2. For sites in indus!rial areas, tendons should be 4. Discussion on the accessibility of the end anchorages;

guarded against fume releases containing SO2 , li 2 S, and NO or chlorides. 5. A description of the overall inservice inspection

3. 6hemical constituents of grou! and placement program utilizing instruments, ungrouted tendons, and methods can influence the vulnerabifity of grouted visual observations.

tendons to corrosive attack.

4. Where environmental conditions make electro- Later, at the time of submittal of the final safety chemical phenomena a consideration, grounding of analysis report (FSAR), with construction well ad- grouted tendons against stray electrical currents, and vanced, sufficient information will be available to submit possibly cathodic protection of the tendons, could be a correct and expanded study. The FSAR should needed. It should be recognized, however, that cathodic incorporate all changes that occurred during construc- protection can, under some circumstances, be detri- tion as well as:

mental to the tendons.

1. A description of the provisions made to ensure that The inservice inspection program outlined in this only properly calibrated gauges have been used;

guide consists of three major parts. Some test tendons 2. A numerical estimate of the expected theoretical are left ungrouted and are environmentally protected indication level of the gauges presented as a function of with a grease. The effects on these test tendons are not time for the entire life of the plant. This estimate should intended to represent the environmental or physical include all necessary estimated corrections, including

.effects (with respect to corrosion) on the grouted concrete creep and shrinkage and tendon relaxation tendons. Instead, acting as compensating gauges, these which will be checked by the ungrouted test tendons;

tendons will be used to evaluate the extent of concrete 3. An indication of the reasons and tolerances for creep and shrinkage as well as relaxation of the tendon possible discrepancies between the measurements and I

steel. This information will then assist in interpreting the actual prestress;

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4. An evaluation of the maximum probable error in the jected to liftoff testing to measure the effects of con.

• results and the accuracy expected: crete shrinkage and creep and relaxation of the tendon

5. A discussion of the probable influences of tempera- steel. These data should be evaluated in conjunction lure on the results due to changes in the length of the with concurrent instrumentation readings and visual wires, in the size of the structure, and in friction values; examinations. If instrumentation readings indicate a

6. A description of actions that should be taken as a need for further checking, additional liftoff tests of the result of anomalous gauge readings or indications that ungrouted test tendons may be needed.

numerous gauges are defective; and

7. The visual observations to be made, the procedures 3. Instrumentation for checking the ungrouted tendons, and the integration of these data with gauge data to form inservice in;spec- a. Characteristics lion conclusions regarding continued structural integrity.

(I) Instrumentation provided for the determina- lion of concrete prestress level should be capable of The FSAR should also contain a certification that the effective use over the life span of the containment installation and the calibration of the instruments are structure within specified operational limits under the correct. If the installation of the instrumentation is not following conditions, unless othenvise defliaed by the yet completed, this certification may be submitted later, designer and approved by the Regulatory staff:

but not less than 3 months before issuance of an (a) Humidity; 0% to 100%;

• operating license. (b) Temperature: 00 F to 200'F; and (c) Cyclic loading: 500 cycles of 600 psi The use of the Regulatory Positton described below stress variation in compression.

does not eliminate the requirement for compliance with (2) The instruments should be protected against

"Capability for Containment Leakage Rate Testing," of adverse effects of' the expected environment in which Appendix A to 10 CFR Part 50, General Design Crite- they will be located, e.g., electrolytic attack, including rion 52, which requires tha the containment be de- the effects of stray electric currents of a magnitude that

• signed so that periodic integratcd leakage rate testing can may be encountered at the particular site and structure.

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

C. REGULATORY POSITION

(3) The snsitivity of strain gauges should be W 1. Inservice Inspection Program-General specified, and the drift or stability under the conditions in C.3.a.(l) and (2) above should be accounted for in the Each "typical" prestressed concrete containment specified limits, or the gauges should be subject to recalibration in service.

structure with grouted tendons, 4s described in Section

(4) The range of stress meters shuuld be from 500

B, should be subjected to mn inservice inspection psi in teasion to 2500 psi in compression.

program that includes:

(5) A numerical estimate of the expected theoret- ical indication level of the gauges or meters. including a. iftoff tests ofungrouted test tendons;

permissible deviations of readings, presented as a b. Periodic reading of instrumentation for deter- function of time, should be incorporated in the design mining concrete prestress level; and specifications and the FSAR.

c. Visual examination.

2. Ungrouted Test Tendons b. Installation a. The following ungrouted test tendons' should be The prestressed cylindrical wall and the dome installed: should be instrumented. The base mat need be instru-

(1) Three vertical tendons. merited only if it is prestresse

d. This instrumentation

(2) Three hoop tendons, and may be either embedded in the concrete or inserted into

(3) Two dome tendons if the design utilizes two the structure so that it can be maintained and/or

900 families of tendons or three dome tendons if the. replaced. Instrument types, locations, and quantities design utilizes three 600 families of tendons. should be selected to provide the best representation of b. At the intervals given for visual examinations in prestress levels in the structure. Generally, these loca- C.4.a below, the ungrouted test tendons should be sub- tions are presumed to be it the mid-depth of the

. 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.

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.

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If redundancy is required to achieve rcliability at a years after the initial containment structural integrity measurement point, six strain gauges or six stress meters test and every 5 years thereafter.'As a part of this visual should be installed. Three galiges should measure the examination, the tendon anchorage assembly hardware prestress in the direction of the meridian and three the (such as bearing plates, stressing washers, shims, wedges, prestress in the hoop direction. This ,vould permit and buttonheads) of 21 selected tendons should be evaluation of anomalous readings and isolation of a visually examined to the extent practical without dis- malfunctioning gauge. mantling load-bearing components of the anchorage.

These selected tendons' should include:

c. Reading Frequency

(1) Six dome tendons; two located in each 600

group (three families of tendons) and randomly dis- Every month for the first six months following the tributed to provide representative sampling, or three structural integrity test, all strain gauges or stress meters should be read. At the option of the designer, earlier located in each 900 group (two families of tendons),

(2) Five vertical tendons, randomly but repre- readings may be initiated following completion of sentatively distributed.

prestressing, but such readings are supplementary to those necessary following the structural integrity test (3) Ten hoop tendons, randomly but represen- tatively distributed.

and should not be substituted for them. Each gauge whose indication deviates from its initially predicted For each succeeding examination, the tendons level by more than the preestablished amount contained should again be selected on a random but representative in the design specifications should be listed in a special basis, so the sample group will change somewhat each table with an indication of its location and all additional time.

pertinent. information. After the first six months, the reading frequency can be changed to reflect the devia- b., The inservice inspection program should define the tion from the predicted readings. Those points whose defects the inspector should look for during visual measured strains have not deviated more than the pre- examination of the anchorage system and should estab- established amount from their initially predicted levels lish the corresponding limits and tolerances. Special may be read once a year for the rest of plant life if their attention should be given to the concrete supporting the readings continue to approximate the predicted levels.

anchor assemblies, and the crack patterns at these points Gauges whose strains have deviated from their predicted should be observed, analyzed, and reported.

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 c. A visual examination of concrete cracking and excessive deviations develops. These measurement points deformations should be scheduled during integrated may then be read once a year. However, local conditions leakage testing while the containment is at its maximum or special circumstances may dictate a continuation of test pressure, even if visual examinations have been once a month readouts. conducted at other times.

All gauges should be read during the periodic Type A leakage tests required by Appendix J to 10 CFR Part d. Regulatory practice is to consider grouted

50, and the results should be evaluated against other tendons as unbonded for load-carrying purposes, and the data gathered during the overall inservice inspection anchor hardware is therefore considered to be a principal load carrying element requiring periodic visual examina- program.

tion. Consequently, containments should be designed so that the prestressing anchor hardware is accessible for When the number of gauges listed in the special table of deviations described above reaches the predeter- periodic examination.

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 S. Reporting abnormal occurrence and reported in accordance with C.5 below. If the specified limits of the inservice inspection program are exceeded, a possible abnormal degradation If anomalous readings are received, it should be of the containment structure (a boundary designed to determined whether they result from defective gauges, contain radioactive materials) is indicated. In such cases, and the basis for such a determination should be the reporting program of Regulatory Guide 1.16, justified. "Reporting on Operating Information-Appendix A

Technical Specifications," should apply. A description should be furnished of the condition of the concrete

4. Visual Examination (especially at tendon anchorages) and all examined tendon hardware, the inspection procedures, the toler- a. A visual examination of the entire concrete con- ances on concrete cracking and hardware corrosion, the tainment structure should be performed .1, 3, and s measures to be used when the specified limits or

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tolerances are exceeded, and a decription of procedures 1. Construction permit reviews for applications dock- to be used following cumpletion of dorrective measures eted after July 1, 1975, will be evaluated on the basis of to verify the satisfactory condition of the structure. this guide.

2. Construction permit and operating license reviews for

D. IMPLEMENTATION

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

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