Regulatory Guide 1.90: Difference between revisions

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{{Adams
{{Adams
| number = ML003740281
| number = ML13350A298
| issue date = 08/31/1977
| issue date = 11/30/1974
| title = Inservice Inspection of Prestressed Concrete Containment Structures with Grouted Tendons
| title = Inservice Inspection of Prestressed Concrete Containment Structures with Grouted Tendons
| author name =  
| author name =  
Line 10: Line 10:
| license number =  
| license number =  
| contact person =  
| contact person =  
| document report number = RG-1.90, Rev 1
| document report number = RG-1.090
| document type = Regulatory Guide
| document type = Regulatory Guide
| page count = 12
| page count = 5
}}
}}
{{#Wiki_filter:Revision i *
{{#Wiki_filter:November 1974 U.S. ATOMIC ENERGY COMMISSION
                                      U.S. NUCLEAR REGULATORY COMMISSION                                                                                       August 1977 REGULATORY GUIDE
REGULATORY G
                                      OFFICE OF STANDARDS DEVELOPMENT
DIRECTORATE OF REGULATORY STANDARDS
                                                                      REGULATORY GUIDE 1.90
REGULATORY GUIDE 1.90
                                          INSERVICE INSPECTION OF PRESTRESSED CONCRETE
INSERVICE INSPECTION OF PRESTRESSED CONCRETE
                                      CONTAINMENT STRUCTURES WITH GROUTED TENDONSt
CONTAINMENT STRUCTURES WITH GROUTED TENDONS
UIDE


==A. INTRODUCTION==
==A. INTRODUCTION==
deleterious environment, (3) the extent of temperature variations, and (4) the quality of the General Design Criterion 53, "Provisions for Con                                      grout and its installation. Following the recommen tainment Testing and. Inspection," of Appendix A,                                        dations of Regulatory Guide 1.107, "Qualifications
General Design Criterion 53, "Provisions for Contain.
  "General Design Criteria for Nuclear Power Plants,"                                      for Cement Grouting for Prestressing Tendons in to 10 CFR Part 50, "Licensing of Production and                                          Containment Structures," could significantly reduce Utilization Facilities," requires, in part, that the con                                  the danger of widespread corrosion. However, the tainment be designed to permit (1) appropriate                                            mechanism of corrosion in all conditions and situa periodic inspection of all important areas and (2) an                                    tions is not fully understood. Because many appropriate surveillance program. This guide                                              parameters can influence the development of corro describes bases acceptable to the NRC staff for                                          sion or stress corrosion, there is always an area of un developing an appropriate surveillance program for                                        certainty with regard to the corrosion of tendon steel, prestressed concrete containment structures with                                          and it is necessary to monitor the structure in a man grouted tendons. The Advisory Committee on Reac                                            ner that would reveal the existence of widespread cor tor Safeguards has been consulted concerning this                                        rosion.


guide and has concurred in the regulatory position This guide outlines the recommendations for inser
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==
==B. DISCUSSION==
vice inspection of containments having grouted Inservice inspection of prestressed concrete con                                      tendons of sizes up to an ultimate strength of approx tainment structures with grouted tendons is needed to                                    imately 1300 tons (11,000 kN) and consisting either verify at specific intervals that the safety margins                                      of parallel wires or of one or several strands. The provided in the design of containment structures have                                    detailed recommendations of the guide are not direct not been reduced as a result of operating and en                                        ly applicable to grouted tendon containments having vironmental conditions. Grouting of tendons to                                          bar tendons. However, the inservice inspection protect them against corrosion is a proven                                              program for grouted tendon containments with bar technology in other types of structures. However,                                        tendons may be developed using the principles in this there is as yet no real experience to adequately define                                  guide and will be reviewed by the NRC staff on a the long-term characteristics of containment struc                                      case-by-case basis. This guide does not address the in tures with grouted tendons. The major concern in                                        service inspection of prestressing foundation anchors.
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).
containment structures with grouted tendons is the                                      If they are used, the inservice inspection program will possibility that widespread corrosion of the. tendon                                    be reviewed by the NRC staff on a case-by-case basis.
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.
 
steel may occur and remain undetected. The major                                        Inservice inspection of the containment liner and factors influencing the occurrence of corrosion are (1)                                  penetrations is also not addressed in this guide.


the susceptibility of the tendon steel to corrosion, (2)
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 degree of exposure of the tendon steel to a                                              The simplest means of monitoring these prestres sed concrete structures would be to ascertain the


* The substantial number of changes in this revision has made it                        amount of prestress at certain strategically located impractical to indicate the changes with lines in the margin.                             sections in the structure. However, it is generally felt t For the purpose of this guide, a tendon is defined as a tensioned                      that available instrumentation for concrete, i.e.,
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.
steel element consisting of wires, strands, or bars anchored at each                    strain gages, stress meters, and strain meters, is not end to an end anchorage assembly.                                                        reliable enough to provide such information. When USNRC REGULATORY GUIDES                                          Comments should be sent to the Secretary of the Commission, US. Nuclear Regu Regulatory Guides are issued to describe and make available to the public methods      latory Commission, Washington, D.C. 20555, Attention: Docketing and Service Branch.


acceptable to the NRC staff of implementing specific parts of the Commission's regulations, to delineate techniques used by the staff in evaluating specific problems The guides are issued in the following ten broad divisions:
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.
or postulated accidents, or to provide guidance to applicants. Regulatory Guides are not substitutes for regulations, and compliance with them is not required.


t. Power Reactors                          6. Products Methods and solutions different from those set out in the guides will be accept
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:
                                                                                        2.   Research and Test Reactors              7. Transportation able if they provide ovidens a ba basis for the fidings requisite to the issuance or continuance the    findin.                                         3.  Fuels and Materials Facilities         
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 wires.


===8. Occupational Health===
USAEC REGULATORY GUIDES
                                                                                        4.   Environmental and Siting               
Copies of published guides may be obtimned by request indicating the divisions deitird to the US. Atomic Energv Commistion, Washinglon, D.C. 20545.


===9. Antitrust Review===
Regulatory Guides ote Issued to describe end make available to the public Atlention: Director of Regulatory Standard*. Comments and sug9gtions for methods acceptable to ihe AEC Regulatory stafIf of Implementing specific paris of Irnpr*vements 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,.
                                                                                        5.  Materials and Plant Protection
evaluating "clidfic problamts or postulated accldents, or to provide guidance to Attention: Dockelingr nd Service Section.
                                                                                                                                    10. General Comments and suggestions for improvements in these guides are encouraged at all Request for single copies of issued guides which may by reproduced; or for place times, and guides will be revised, as appropriate, to accommodate comments and mest onsan automatic distribution list for single copies of future guides iii specific to reflect new information or experience. This guide was revised as a result of divisions should be made in writing to the US. Nuclear Regulatory Commission, substantive comments received from the public and additional staff review.


Washington, D.C. 20555, Attention          Director, Division of Document Control.
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 ac* pt*lle If they provide a batis for the findings requisite to the Isuanca or continumnce of a permit or license by the Commlision.


instrumentation that either can be recalibrated or            concrete creep and shrinkage and relaxation of the replaced in case of a malfunction or is proven to be          tendon steel.
===1. Power Reactors ===


sufficiently reliable is developed, monitoring the The measurement of forces in ungrouted test prestress level would be a desirable means of assess ing the continuing integrity of prestressed concrete          tendons would provide a quantitative means of structures with grouted tendons.                             verifying the design assumptions regarding the volumetric changes in concrete and the relaxation of Another means of monitoring the functionality of          prestressing steel. If some lift-off readings (or load the containment structure would be to subject it to a        cell readings) indicate values lower than the expected pressure test and measure its behavior under pres            low values, checks should be made to determine if sure. Industry comments indicate that an inservice in        such values are due to corrosion of wires of un spection program based on the test of overall func            grouted tendons or to underestimation of prestress tionality is preferable.                                      ing losses. The plant need not be shut down or main tained in a shutdown condition during such an This regulatory guide provides two acceptable              evaluation period. These tendons may also serve as alternative methods of inspecting containment struc            an investigative tool for assessing the structural con tures with grouted tendons: (1) an inservice inspec          dition after certain incidents that could affect the tion program based on monitoring the prestress level          containment.
===6. Products===
2. Research end Test Reactors


by means of instrumentation, and (2) an inservice in          2. MONITORING ALTERNATIVES FOR
===7. Transportation===
spection program based on pressure-testing the con                  GROUTED TENDONS
3. Fuels and Materials Facilities
tainment structure.                                             a. Monitoring of Prestress Level (Alternative A)
8. Occupational Health Published guldan will be tevisad periodically, as appropriate, to accommodlte
    The detailed inspection program outlined in this              After the application of prestress, the prestressing guide is applicable to a sphere-torus dome contain            force in a tendon decreases owing to the interaction ment having cylindrical walls about 130 feet (40 m) in        of such factors as:
4. Environmental and SitIng
diameter and an overall height of about 200 feet (61 m) with three groups of tendons, i.e., hoop, vertical,          (1) Stress relaxation of the prestressing steel;
9. Antitrust Review comments and to reflect new Information or experience.
and dome. For the purpose of this guide, such a con tainment is termed the "reference containment." The              (2) Volumetric changes in concrete;
recommendations in the guide may be used for similar containments with cylindrical walls up to 140            (3) Differential thermal expansion or contraction feet (43 m) in diameter and an overall height up to          between the tendon, grout, and concrete; and
210 feet (64 m).
                                                                  (4) Possible reduction in cross section of the wires For containments that differ from the reference            due to corrosion, including possible fracture of the containment or are under a controlled environment,            wires.


the inservice inspection program may be developed using the concepts evolved in this guide and the                  In this alternative, the prestress level is monitored guidelines in Appendix A.                                      at certain strategically located sections in the contain ment. Thus it is a sampling procedure in which degradation in the vicinity of the instrumented sec The inservice inspection program recommended in tion will be detected by evaluation of the instrumen this guide consists of:                                      tation readings. However, if corrosion occurs at loca
S. Matirisls and Plant Protection t
    1. Force monitoring of ungrouted test tendons;            tions away from the instrumented sections, it would
    2. Monitoring performance of grouted tendons by            have to produce gross degradation before the in strumentation readings would be affected.


a. Monitoring of prestress level, or b. Monitoring of deformation under pressure;              The prestressing force imparted to the structure by and                                                  a grouted tendon system could be monitored by an appropriate combination of the following methods:
===0. Gencral===
    3. Visual examination.


1. FORCE MONITORING OF UNGROUTED                                (1) Monitoring the tensile strains in the wires of a TEST TENDONS                                            tendon;
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.
    Some tendons (otherwise identical) are left un                (2) Evaluating the prestress level at a section in the grouted and are protected from corrosion with                structure from readings of appropriately located grease. The changes observed in these tendons are not        strain gages or strain or stress meters at the section intended to represent the changes due to environmen          (see Refs. 1 through 7).
  tal or physical effects (with respect to corrosion) in the grouted tendons. Instead, these test tendons will            Method (1) above is useful for direct monitoring of be used as reference tendons to evaluate the extent of       prestressing force in a tendon. However, the installa-
                                                      1.90-2


tion of the instrumentation required for this method              anchorage takeup, and friction. The 8% bandwidth needs careful attention during installation and grouting of the tendons. Moreover, strain gages in               would amount to between 40% and 70% of the total time-dependent losses.
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.


%talledon the prestressing wires of a tendon will not detect the loss of force due to relaxation of prestress              Alternative A is based on the use of instrumenta ing steel. Allowance for this can be based on relaxa              tion. Many of these instruments have to be built into tion data for the prestressing steel used.                        the structure in such a manner that they can be neither replaced nor recalibrated. It is quite likely Evaluation of strain gage and stress meter readings requires a full understanding of what makes up the                that such built-in instrumentation may not remain readings, e.g., elastic, creep, and thermal strain or            reliably operable throughout the life of the structure.
Many hoop tendons are anchored on buttresses located partially inside the building adjacent to the con- tainment. Unless the anchors are installed with consider.


stress components. Strain gage readings will consist              Recognizing such a possibility, the guide provides for an alternative of pressure testing (Alternative B)
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.
    of elastic strains corresponding to the prestressing stress in concrete and strains due to creep and                  when the data obtained from instrumentation readings are found to be questionable.


shrinkage of concrete. Strains from creep and shrinkage of concrete can vary between 1.5 and 2.5                    b. Monitoring of Deformation Under Pressure times the elastic strains in concrete. However, there                    (Alternative B)
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:
  are methods that can be used to isolate these effects.
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.


Testing the containment under pressure and Three such methods are:                                          evaluating its elastic response has been proposed as a
2. For sites in indus!rial areas, tendons should be guarded against fume releases containing SO2, li2S,
      (1) Calculate average creep and shrinkage strains            means of assessing the integrity of the containment.
NO
or chlorides.


The elastic response under pressure testing is primari from the time-dependent losses measured on the un ly a function of the stiffness of the structure. Any grouted tendons.
3. 6hemical constituents of grou! and placement methods can influence the vulnerabifity of grouted tendons to corrosive attack.


significant decrease in the stiffness of the structure
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.
      (2) Use stress meters at sections where strain gages          due to loss of prestress would be the result of crack are used.                                                         ing of the structure. Because of the insensitive and in direct relationship between the prestressing force and
      (3) Use special strain meters that respond only to            the elastic response of the structure, such a method volumetric and temperature changes in concrete                    cannot be used to establish the existing prestress level (Ref. 7).                                                          at various sections. However, comparison of the con dition and deformation of the structure during the A sufficient number of temperature sensors instal            ISI (Inservice Inspection) pressure testing with those led at the sections where instrumentation is located              during the ISIT (Initial Structural Integrity Testing)
  can be useful in isolating the thermal effects. It is            pressure testing could provide a basis for evaluating recognized that the raw instrumentation readings can             the functionality of the structure. This method has be deceptive, and adjustments may be necessary to                been accepted* previously by the NRC staff on the account for the calibration constants and                        condition that the containment be designed conser temperature effects. The interpretation and evalua                vatively so that there will be no cracking (or only tion of the results will be simplified if the instrumen            slight cracking at the discontinuities) under the peak tation is provided at sections away from structural                test pressure. Section III, Division 2, of the ASME
discontinuities. The applicant should provide suf                Code (Ref. 8) allows a 33-1/3% increase in the al ficient redundancy in the instrumentation to permit              lowable stress in tensile reinforcement under a test the evaluation of anomalous readings and the isola                condition. The NRC staff has accepted this al tion of a malfunctioning gage. One such combination              lowance on the assumption that it is only a one-time would be two strain gages and one stress meter at                loading (i.e., during the ISIT). However, if such each face of a section.                                          testing is to be performed a number of times during the life of the containment structure, it is prudent not After appropriate use has been made of the                    to use this allowance in order to avoid or minimize methods and instruments available, an average stress            gradual propagation of cracking during subsequent and an average prestressing force at a section can be            pressure tests.


evaluated. Even though the predicted prestressing force corresponding to a specific time may include                    The locations for measuring the deformations un adequate consideration for creep of concrete and                 der pressure should be based on the recommenda relaxation of prestressing steel, the chance that the             tions of this guide. For a meaningful comparison of value based on measurements will compare well with                the deformations, it is recommended that the loca the predicted value is small. Hence it is recommended            tions where the deformations are to be recorded have that an applicant establish a band of acceptable                  deformations larger than 0.06 inch (1.5mm) under the prestress level similar to that illustrated in Figure 1. It      calculated peak containment internal pressure as is also recommended that the bandwidth not exceed                sociated with the design basis accident and that these
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
8% of the initial prestressing force at a section after considering the loss due to elastic shortening,               
.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.
* Three Mile Island Nuclear Power Station Unit 2 and Forked River Nuclear Power Station.


1.90-3
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.


Fi - Initial prestressing force at a section considering the losses due to elastic shortening, anchorage takeup, and friction.
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


PREDICTED PRESTRESS FORCE
U-
                (CONSIDERING HIGH TIME-DEPENDENT LOSSES)
4. An evaluation of the maximum probable error in the
4*
*  
                                                                  PREDICTED PRESTRESS FORCE
results and the accuracy expected:
                                                                  (CONSIDERING LOW TIME-DEPENDENT LOSSES)
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;
  w
6. A description of actions that should be taken as a result of anomalous gauge readings or indications that numerous gauges are defective; and
        0.9Fi
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.
        0
  LIb a,M
  I-
  C,,J
  U0
  K O.8F1
        0.7Fi
                                        5                10            15        20      25  30    35 40
              1            3 TIME IN YEARS
                    Figure 1. Typical Band of Acceptable Prestress Level


locations be approximately the same during the ISIT              3. The inservice inspection program should consist and the subsequent ISIs. This will require these loca        of:
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
tions to be away from the areas of structural discon tinuities. Thus the number of locations for measure                a. Force monitoring of ungrouted test tendons;
*
ment of deformations in typical cylinder and dome b. Periodic reading of instrumentation for deter areas wili be in excess of those recommended in mining prestress level (Alternative A) or deforma Regulatory Guide 1.18, "Structural Acceptance Test for Concrete Primary Reactor Containments."                  tions under pressure (Alternative B) at preestablished sections; and If an analysis of the effects of such parameters as normal losses in prestressing force, increase in                    c. Visual examination.
operating license.


modulus of elasticity of concrete with age, and dif ferences in temperatures during various pressure tests          4. The inservice inspection should be performed at indicates that they could affect the deformations of           approximately 1, 3, and 5 years after the initial struc the selected points, these parameters should be con          tural integrity test and every 5 years thereafter.
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-
sidered in comparing the deformations during                  However, when an applicant chooses pressure testing various pressure tests.                                        (Alternative B) as a part of the inspection, the fre quency of inspections should be as indicated in
*
3. VISUAL EXAMINATION                                          Figure 2.
signed so that periodic integratcd leakage rate testing can be conducted at containment dtsign pressure.
 
Visual examination of structurally critical areas consisting of the areas of structural discontinuities            5. Alternative B may be substituted for Alternative and the areas of heavy stress concentration is recom          A by the applicant if, at some time during the life of mended. Reference 9 provides excellent guidance for          the structure, the inspection based on Alternative A
reporting the condition of concrete and should be            does not provide satisfactory data. The details of used whenever applicable for reporting the condition          such a substitution will be reviewed by the NRC staff of examined areas.                                            on a case-by-case basis.
 
There are numerous examples of the use of pulse velocity technique to obtain information concerning              6. If the containment base mat is prestressed, its the general quality level of concrete. Based on ex            proposed inspection program will be evaluated by the perience and experimental data (Refs. 10, 11, 12), a          NRC staff on a case-by-case basis.
 
pulse velocity of 14,000 ft/sec (4300 m/sec) or higher indicates a good to excellent quality of concrete. For normal weight concrete, a pulse velocity of 11,000            2. UNGROUTED TEST TENDONS
ft/sec (3400 m/sec) or lower indicates concrete of questionable quality. Thus the technique can be used              1. The following ungrouted test tendons should be as part of the inspection of concrete containments            installed in a representative manner:
when the visual examination reveals a high density of wide (>0.01 in. or 0.25 mm) cracks or otherwise                    a. Three vertical tendons, heavy degradation. The detailed procedure and                      b. Three hoop tendons, and limitations of the techniques are described in Reference 13.                                                      c. Three dome tendons for the design utilizing three 600 families of tendons.


==C. REGULATORY POSITION==
==C. REGULATORY POSITION==
2. The ungrouted test tendons need not be in addi
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.


===1. GENERAL===
iftoff tests ofungrouted test tendons;
                                                              tion to the design requirements.
b. Periodic reading of instrumentation for deter- mining concrete prestress level; and c. Visual examination.


1. All prestressed concrete containment structures with grouted tendons should be subjected to an inser            3. The ungrouted test tendons and their vice inspection (ISI) program. The specific guidelines        anchorage hardware should be identical to the provided herein are for the reference containment            grouted tendons and their hardware.
2. Ungrouted Test Tendons a. The following ungrouted test tendons' should be installed:
(1) Three vertical tendons.


described in Section B.
(2) Three hoop tendons, and
(3) Two dome tendons if the design utilizes two
900 families of tendons or three dome tendons if the.


4. The ungrouted test tendons should be subjected
design utilizes three 600 families of tendons.
    2. For containments that differ from the reference        to force measurement by lift-off testing or load cells containment, the program described herein should              to assess the effects of concrete shrinkage and creep serve as the basis for developing a comparable inser          and relaxation of the tendon steel. These data should vice inspection program. Guidelines for the develop          be evaluated in conjunction with the overall struc ment of such a program are given in Appendix A to            tural condition of the containment evident from the this guide.                                                  other examinations.


1.90-5
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.


I LRT
jected to liftoff testing to measure the effects of con.
  SCHEDULE                  -A                                              -                        -    a    -1
  (10 CFR Part 50,
  APP. J)
  ISI SCH.                                                    -      =                                    --
                                          1 5  D
  PRESSURE                                                                                                    PA    PA
                            1 15                                  PA                    PA
  LEVELS              pN    " PPD
                                                                                                                  30    35
                                                                                          20            25
                                                        10              15
                    0 1              5
*P        -TIME                                                                AFTER ISIT - YEARS
                    KEY
                    PN  - Normal Operating Pressure or Zero PD)  - Containment Design Pressure PA  - Calculated Peak Internal Pressure Associated with the Design Basis Accident ILRT - Integrated Leak Rate Testing ISIT - Initial Structural Integrity Testing ISI  - Inservice Inspection Figure 2.       Schedule for Inservice Inspections (Alternative B)


3. MONITORING ALTERNATIVES                        FOR              c. Cyclic loading: 500 cycles of 600 psi (4.2 GROUTED TENDONS                                          MPa) stress variation in compression.
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.


3.1 Instrumentation for Monitoring the Prestress                  2. The instruments should be protected against adverse effects of the expected environment in which Level (Alternative A)                                    they will be located, e.g., electrolytic attack, including the effects of stray electric currents of a magnitude
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:
    3.1.1 Installation                                        that may be encountered at the particular site and I. The prestressed cylindrical wall and dome              structure. They should be protected against should be instrumented. This instrumentation may be          temperature extremes to which they may be exposed either embedded in the concrete or inserted into the          while the containment is under construction.
(a) Humidity; 0% to 100%;
(b) Temperature: 00F to 200'F; and (c) Cyclic loading: 500 cycles of 600 psi stress variation in compression.


structure so that it can be maintained or replaced.              3. The sensitivity of strain gages should be Instrument types, locations, and quantities should be          specified; the drift or stability under the conditions in selected to provide the best representation of                I and 2 above should be accounted for in the prestress level in the structure. A sufficient number of      specified limits, or the gages should be subject to temperature sensors should be installed to isolate and         rec:libration in service.
(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.


evaluate the effects of variations in temperature gradients on the instrument readings and observa                  4. The stress meters should be able to measure tions. Redundancy of the embedded instrumentation              compressive stresses up to 2500 psi (17.2 MPa).
They should be protected against temperature extremes to which they may be exposed while the containment is under construction.
should be based on a conservative estimate of the                3.1.3 Monitoring Instrumentation Operability probability of malfunction of the instrumentation to be installed.                                                    After the installation of the instrumentation, all embedded strain gages and stress meters should be
    2. The instrumentation in the concrete should be          read every two months until the initial structural in arranged and distributed in such a manner as to per          tegrity test (ISIT) is performed. The response of the mit evaluation of the prestressing levels and should          instrumentation during prestressing and pressure be located:                                                  testing (ISIT) should be used to confirm their operability. After the ISIT, the monitoring of the in a. At six horizontal planes to measure the hoop        strumentation should be continued every two months prestressing levels;                                        to confirm operability of the instrumentation until the first inservice inspection. The monitoring fre b. Along three vertical tendons to measure ver        quency may be reduced to once every six months tical prestress levels;                                      thereafter unless local conditions or special circum stances dictate more frequent readouts. The c. Along three dome tendons for the design us          operability of the instrumentation should also be ing three families of 600 tendons.                            confirmed during subsequent pressure tests. If anomalous readings are obtained, the reason for such
    3. Sections through the structure should be              readings should be determined. If it is determined selected- at a minimum of four locations in each              that they result from defective gages, the basis for horizontal plane, three locations along each vertical        such a determination should be justified.


tendon, and two locations along each dome tendon (see Figure 3). At these sections, the prestress level        3.2 Monitoring Deformation Under Pressure (Alter should be monitored by (a) a combination of stress                  native B)
(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.
meters or strain gages in concrete or on rebar at a minimum of two points through the section or (b)                  When it is planned to use this alternative as a part strain gages directly on tendon wires with a minimum          of the total inservice inspection program, it is recom of 3% of the tendon wires instrumented.                       mended that the design of the containment structure include the following considerations:
    3.1.2 Characteristics
                                                                  1. Membrane compression should be maintained
    1. Instrumentation provided for the determination        under the peak pressure expected during the ISI tests.


of concrete prestress level should be capable of effec tive use over the life span of the containment struc              2. The maximum stress in the tensile reinforcing ture within specified operational limits under the fol        under the peak pressure expected during the ISI test lowing conditions, unless otherwise defined by the            should not exceed one-half the yield strength of the designer and approved by the NRC staff:                      reinforcing steel (0.5fy).
(4) The range of stress meters shuuld be from 500
      a. Humidity: 0% to 100%;                                  3.2.1 Pressurization b. Temperature: 0°F (-18°C) to 200 0 F (93 0 C);          1. During the first inspecticn, the containment and                                                          structure need not be pressurized.
psi in teasion to 2500 psi in compression.


1.90-7
(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.


DT-1 DT-2 DI-2 L                          T-3 DOME TENDONS AT 600
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.
00 VI-i    VT-1              VI-2            VT-2    VI-3            VT-3KEY
                    HI-1i                                                                      HT, VT, DT - HOOP, Vertical, Dome
                                          _T-i                                                  Ungrouted Test Tendons.


J      HI-2            '                                _                        HI - Horizontal Planes to be Selected
1.90-3
        1-         HI-            I  -I                                                      for Instrumentation.


T      _I  H__                                                                        VI & DI - Vertical & Dome Tendons
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.
      ,               I                  -1-                                        HT-2      to be Identified for Instrumentation.


HI-4            IFour                                                          Sections Along HI Planes, Three
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.
        'I            _11                                                                    Sections Along VI Tendons, Two Sections Along Dl Tendons to be Selected for HI-5                                  -     -Monitoring                              Prestress Level.


-            -I
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.
        -I                                                                          HT-3      0- Shows Selection of Sections Along HI-6                                                                      One Horizontal Plane, One Vertical Tendon,
                            _-                                      -                            and One Dome Tendon.


I
All gauges should be read during the periodic Type A leakage tests required by Appendix J to 10 CFR Part
        I                                                      I
50, and the results should be evaluated against other data gathered during the overall inservice inspection program.
        I                              I
      300                          1500                        2700
                    CONTAINMENT CYLINDER - DEVELOPED
                            Figure 3.         Containment Diagram Showing Typical Locations of Test Tendonrr        Instrumentation


2. During the second and third inspections, the                 3. Local areas around penetrations that transfer containment structure should be subjected to a max              high loads to the containment structure (e.g., around imum internal pressure of 1.15 times the containment            high-energy fluid system lines).
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.
design pressure.


4. Other areas where heavy loads are transferred
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.
  3. During the fourth and subsequent inspections,             to the containment structure (crane supports, etc.).
the containment structure should be subjected to a maximum internal pressure equal to the calculated                  A visual examination of structurally critical areas peak internal pressure associated with the postulated          should be scheduled during all pressure tests while design basis accident.                                          the containment is at its maximum test pressure, even if visual examinations of these areas have been con ducted at other times.


3.2.2 Instrumentation and Deformations
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.
                                                                4.2 Anchorage Assemblies
  1. Instrumentation similar to that used during the ISIT should be installed prior to the pressure testing            Exposed portions of the tendon anchorage as for measurement of overall deformations at the                  sembly hardware or the permanent protection selected points.                                                thereon (whether it be concrete, grout, or steel cap)
                                                                should be visually examined by sampling in the fol
  2. The limit of accuracy of readings of the instru          lowing manner:
ments to be used should be specified by means of an error band so that a meaningful comparison of defor                1. A minimum of six dome tendons, two located in mations measured during the ISIT and ISI can be                each 60* group (three families of tendons) and ran made.                                                          domly distributed to provide representative sampl ing,
  3. The points to be instrumented for the measure ment of radial displacements should be determined in              2. A minimum of five vertical tendons, randomly six horizontal planes in the cylindrical portion of the        but representatively distributed, shell, with a minimum of four points in each plane (see Figure 3).                                                    3. A minimum of ten hoop tendons, randomly but representatively distributed.


4. The points to be instrumented for the measure ment of vertical (or radial) displacements should be              For each succeeding examination, the tendon determined as follows:                                          anchorage areas to be examined should be selected on a random but representative basis so that the sample a. At the top of the cylinder relative to the base,       group will change each time.
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.


at a minimum of four approximately equally spaced azimuths.                                                          The inservice inspection program should define the defects the inspector should look for during visual ex b. At the apex of the dome and one intermediate          amination of the exposed anchor hardware and point between the apex and the springline, on at least          protection medium and should establish the cor three equally spaced azimuths.                                  responding limits and tolerances. Special attention should be given to the concrete supporting the anchor
(3) Ten hoop tendons, randomly but represen- tatively distributed.
  5. The intermediate pressure levels at which the            assemblies, and any crack patterns at these points deformations at the selected points are to be                  should be observed and analyzed.


measured should correspond to those for the ISIT.
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.


5. REPORTABLE CONDITIONS
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.
                                                                5.1 Inspection Using Alternative A


===4. VISUAL EXAMINATION===
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.
                                                                  If the average prestress force along any tendon falls
4.1 Structurally Critical Areas                                below the acceptable band (see Figure 1), the condi tion should be considered as reportable.


A visual examination should be performed on the following exposed structurally critical areas:                    If the prestress force determined at any section falls below the design prestress force, the condition should
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.
  1. Areas at structural discontinuities (e.g., junction      be considered as reportable.


of dome and, cylindrical wall or wall and base mat).
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,
                                                                5.2 Inspection Using Alternative B
"Reporting on Operating Information-Appendix A
  2. Areas around large penetrations (e.g., equip ment hatch and air locks) or a cluster of small                    If the deformation measured under the maximum penetrations.                                                  test pressure at any location is found to have in-
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
                                                        1.90-9
1.90.4


creased by more than 5% of that measured during the        6. REPORTING TO THE COMMISSION
0
ISIT under the same pressure, the condition should be considered as reportable.                                  The reportable conditions of Regulatory Position C.5 could be indicative of a possible abnormal de
tolerances are exceeded, and a decription of procedures to be used following cumpletion of dorrective measures to verify the satisfactory condition of the structure.
5.3 Reportable Conditions for Visual Examinations          gradation of the containment structure (a boundary designed to contain radioactive materials). Any such If the crack patterns observed at the structurally      condition should be reported to the Commission.*
critical areas indicate a significant decrease in the spacing or an increase in the widths of cracks com                         


==D. IMPLEMENTATION==
==D. IMPLEMENTATION==
pared to those observed during the ISIT at zero pres sure after depressurization, the condition should be          The purpose of this section is to provide informa considered as reportable.                                  tion to applicants and licensees regarding the NRC
For applicants choosing to implement the Com- mission's regulations by the methods described in this guide, the following guidance is provided:
                                                          staff's plans for using this regulatory guide.
1. Construction permit reviews for applications dock- eted after July 1, 1975, will be evaluated on the basis of this guide.
 
If the visual examination of the anchor hardware indicates obvious movements or degradation of the            Except in those cases in which the applicant anchor hardware, the condition should be considered        proposes an acceptable alternative method for com as reportable.                                            plying with specified portions of the Commission's regulations, the method described herein will be used If the anchor hardware is covered by permanent          in the evaluation of submittals in connection with protection and the visual examination reveals a            construction permit applications docketed after degradation (e.g., extensive cracks or corrosion          October 1, 1977.
 
stains) that could bring into question the integrity and effectiveness of the protection medium, the con          If an applicant wishes to use this regulatory guide dition should be considered-as reportable.                in developing submittals for applications docketed on or before October 1, 1977, the pertinent portions of
5.4 Reportable    Conditions for Ungrouted      Test      the application will be evaluated on the basis of this Tendons                                              guide.
 
When the force monitoring (by liftoff or load cell)
 
* The report to the Commission should be made in accordance of ungrouted test tendons indicates a prestress force      with the recommended reporting program of Regulatory Guide below the acceptable band (see Figure 1), the condi        1.16, "Reporting of Operating Information-Appendix A
tion should be considered as reportable.                  Technical Specifications."
                                                  1.90-10
 
APPENDIX A
            GUIDELINES FOR DEVELOPING THE INSERVICE INSPECTION
            CONTAINMENTS (OTHER THAN REFERENCE CONTAINMENT PROGRAM FOR
                                                                                      DISCUSSED IN
                                  THE GUIDE) WITH GROUTED TENDONS
Ungrouted Tendons Monitoring Deformations Under Pressure (Alternative B)
    Three ungrouted tendons should be provided in each group of tendons (e.g.,vertical, hoop, dome, in          The number of locations (N) to be selected for verted U).                                                  measuring the deformations under pressure should be determined as follows:
Instrumentation (Alternative A)
                                                            For radial deformations of cylinder, The following criteria should be used to determine the number of sections (N) to be monitored for each              Surface Area of Cylinder infsquare feet group of tendons:                                                            (square meters)I
                                                            N =
                                                                                2700 (250)
N = Actual Area Prestressed by a Group of Tendons K x Area Monitored by a Set of Instruments          but not less than 12.
 
at a Section (determined as SxL)
where                                                      For vertical deformations. of cylinder, S = spacing of tendons in feet (meters)                    N=4 L = length of a tendon monitored by a set of instruments- may be considered as 12 ft (3.66m)      For radial or vertical deformations of dome, and K is determined as follows:
  For containments under uncontrolled environment              Surface Area of Dome in square feet and having continuous tendon curvature,                    N =              (square meters)
                                                                              2700 (250)
K !SlO0
                                                          but not less than 4 For containments under uncontrolled environment and having essentially straight tendons, K: 160
  For containments under controlled environment and having either straight or curved tendons.
 
K.200
                                                  1.90-11
 
APPENDIX B
                                                      REFERENCES
  1. Jones, K., "Calculation of Stress from Strain in          6. Carlson, R. W., "Manual for the Use of Stress Concrete," U.S. Department of Interior, Bureau of              Meters, Strain Meters, and Joint Meters in Mass Reclamation, Oct. 1961. Copies may be obtained                Concrete." Copies may be obtained from Ter from the Bureau of Reclamation, Denver Federal                rametrics, A Teledyne Company, 16027 West 5th Center, Denver, Colorado.                                      Avenue, Golden, Colorado 80401.
 
2. Irving, J., "Experience of In-service Surveillance        7. Raphael, J. M., Carlson, R. W., "Measurement and Monitoring of Prestressed Concrete Pressure              of Structural Action in Dams," 1965. Copies may be Vessels for Nuclear Reactors," a paper presented at          obtained from Terrametrics, A Teledyne Company, International Conference on Experience in the                16027 West 5th Avenue, Golden, Colorado 80401.
 
Design, Construction and Operation of Prestressed Concrete Pressure Vessels and Containments for                  8. "Code for Concrete Reactor Vessels and Con Nuclear Reactors, University of York, England,                tainments," American Concrete Institute Committee Sept. 1975. Copies may be obtained from J. C.                359 and American Society of Mechanical Engineers Mundy, Publication Liaison Officer, Mechanical                Subcommittee on Nuclear Power, 1975. Copies may Engineering Publications Limited, P.O. Box 24,                be obtained from the American Society of Northgate Avenue, Bury St. Edmunds, Suffolk,                  Mechanical Engineers, 345 E. 47th St., New York, IP326BW.                                                      N.Y. 10017 or from the American Concrete Institute, P.O. Box 19150, Redford Station, Detroit, Michigan
    3. Hill, H. T., Durchen, N. B., Brittle, W. F.,            48219.
 
"Structural Integrity Test of Prestressed Concrete Containments," a paper presented at International              9. "Guide for Making a Condition Survey of Conference on Experience in the Design, Construc              Concrete in Service," Reported by ACI Committee tion and Operation of Prestressed Concrete Pressure            201. Copies may be obtained from the American Vessels and Containments, University of York,                Concrete Institute, P.O. Box 19150, Redford Station, England, Sept. 1975. Copies may be obtained from J.          Detroit, Michigan 48219.
 
C. Mundy, Publication Liaison Officer, Mechanical Engineering Publications Limited, P.O. Box 24,                10. Whitehurst, E. A., "Evaluation of Concrete Northgate Avenue, Bury St. Edmunds, Suffolk,                  Properties from Sonic Tests," ACI Monograph No.
 
IP326BW.                                                      2. Copies may be obtained from the American Concrete Institute, P.O. Box 19150, Redford Station,
    4. Browne, R. D., Bainforth, P. B., Welch, A. K.,          Detroit, Michigan 48219.
 
"The Value of Instrumentation in the Assessment of Vessel Performance During Construction and Ser                11. Leslie, J. R., Cheesman, W. J., "An Ultrasonic vice," a paper presented at International Conference          Method of Studying Deterioration and Cracking in on Experience in the Design, Construction and                Concrete Structures," ACI Journal, Proceedings V.
 
Operation of Prestressed Concrete Pressure Vessels            46, No. 1, Sept. 1949. Copies may be obtained from and Containments for Nuclear Reactors, University            the American Concrete Institute, P;O. Box 19150,
  of York, England, September 1975. Copies may be              Redford Station, Detroit, Michigan 48219.
 
obtained from J. C. Mundy, Publication Liaison Of ficer, Mechanical Engineering Publications Limited,        12. Van Zelst, T. W., "Concrete Quality Control P.O. Box 24, Northgate Avenue, Bury St. Edmunds,            Instruments," ACI Journal, June 1975. Copies may Suffolk, IP326BW.                                          be obtained from the American Concrete Institute, P.O. Box 19150, Redford Station, Detroit, Michigan
    5. Arthauari, S., Yu, C. W., "An Analysis of the          48219.
 
Creep and Shrinkage Effects Upon Prestressed Concrete Members Under Temperature Gradient                13. "Standard Method of Test for Pulse Velocity and Its Application," Magazine of Concrete                  Through Concrete," ASTM Designation C597-71.


Research, Volume 19, Number 60, Sept. 1967. Copies          Copies may be obtained from the American Society may be obtained from the Cement and Concrete As            for Testing and Materials, 1916 Race Street, sociation, Wexham Springs, SLOUGH SL 3 6 PL.               Philadelphia, Pennsylvania 19103.
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.


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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)
v • d • e


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 wires.

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 Standard*. Comments and sug9gtions for methods acceptable to ihe AEC Regulatory stafIf of Implementing specific paris of Irnpr*vements 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 ac* pt*lle 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 t

0. 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 SO2, li2S,

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;

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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: 00F 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.

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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

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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.

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