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:U.S. NUCLEAR REGULATORY
{{#Wiki_filter:November 1974 U.S. ATOMIC ENERGY COMMISSION
COMMISSION
Revision i
* August 1977 REGULATORY
GUIDE OFFICE OF STANDARDS
DEVELOPMENT
REGULATORY  
REGULATORY  
G DIRECTORATE
OF REGULATORY
STANDARDS REGULATORY
GUIDE 1.90 INSERVICE  
GUIDE 1.90 INSERVICE  
INSPECTION  
INSPECTION  
Line 26: Line 24:
CONCRETE CONTAINMENT  
CONCRETE CONTAINMENT  
STRUCTURES  
STRUCTURES  
WITH GROUTED TENDONSt
WITH GROUTED TENDONS UIDE


==A. INTRODUCTION==
==A. INTRODUCTION==
General Design Criterion  
General Design Criterion  
53, "Provisions for Con tainment Testing and. Inspection," of Appendix A, "General Design Criteria for Nuclear Power Plants," to 10 CFR Part 50, "Licensing of Production and Utilization Facilities," requires, in part, that the con tainment be designed to permit (1) appropriate periodic inspection of all important areas and (2) an appropriate surveillance program. This guide describes bases acceptable to the NRC staff for developing an appropriate surveillance program for prestressed concrete containment structures with grouted tendons. The Advisory Committee on Reac tor Safeguards has been consulted concerning this guide and has concurred in the regulatory position
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==
==B. DISCUSSION==
Inservice inspection of prestressed concrete con tainment structures with grouted tendons is needed to verify at specific intervals that the safety margins provided in the design of containment structures have not been reduced as a result of operating and en vironmental conditions.
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.


Grouting of tendons to protect them against corrosion is a proven technology in other types of structures.
Of particular impor-tance is the quality of the grouting.The prestressing force in a tendon can be indirectly checked by measuring the level of prestress in the struc-ture. Any eventual decrease in the tendon prestressing force is due to the interaction of several time-dependent factors such as: I. Stress relaxation in the wire;2. Shrinkage and creep in concrete;3. Differential thermal expansion or contraction between the tendon, grout, and concrete;
and 4. Reduction in cross section uf the wires due to corrosion, including possible fracture of the wire


However, there is as yet no real experience to adequately define the long-term characteristics of containment struc tures with grouted tendons. The major concern in containment structures with grouted tendons is the possibility that widespread corrosion of the. tendon steel may occur and remain undetected.
====s. USAEC REGULATORY ====
GUIDES Copies of published guides may be obtimned by request indicating the divisions deitird to the US. Atomic Energv Commistion, Washinglon, D.C. 20545.Regulatory Guides ote Issued to describe end make available to the public Atlention:
Director of Regulatory Comments and sug9gtions for methods acceptable to ihe AEC Regulatory stafIf of Implementing specific paris of in theat guide" are encouraged and should be sent to the Secretary the Commission's regulatlons.


The major factors influencing the occurrence of corrosion are (1) the susceptibility of the tendon steel to corrosion, (2) the degree of exposure of the tendon steel to a
to delineate technlques
* The substantial number of changes in this revision has made it impractical to indicate the changes with lines in the margin.  t For the purpose of this guide, a tendon is defined as a tensioned steel element consisting of wires, strands, or bars anchored at each end to an end anchorage assembly.deleterious environment, (3) the extent of temperature variations, and (4) the quality of the grout and its installation.
.,eýd by the 1t1ll in of the Cornmision, US. Atomit Energy Commistion.


Following the recommen dations of Regulatory Guide 1.107, "Qualifications for Cement Grouting for Prestressing Tendons in Containment Structures," could significantly reduce the danger of widespread corrosion.
Wathiinglon.


However, the mechanism of corrosion in all conditions and situa tions is not fully understood.
O.C. 2055,.evaluating "clidfic problamts or postulated accldents, or to provide guidance to Attention:
Dockelingr nd Service Section.applicants.


Because many parameters can influence the development of corro sion or stress corrosion, there is always an area of un certainty with regard to the corrosion of tendon steel, and it is necessary to monitor the structure in a man ner that would reveal the existence of widespread cor rosion.  This guide outlines the recommendations for inser vice inspection of containments having grouted tendons of sizes up to an ultimate strength of approx imately 1300 tons (11,000 kN) and consisting either of parallel wires or of one or several strands. The detailed recommendations of the guide are not direct ly applicable to grouted tendon containments having bar tendons. However, the inservice inspection program for grouted tendon containments with bar tendons may be developed using the principles in this guide and will be reviewed by the NRC staff on a case-by-case basis. This guide does not address the in service inspection of prestressing foundation anchors.
Regulatory Guides ar not substitutes for regulalions and compliance with them is not required.


If they are used, the inservice inspection program will be reviewed by the NRC staff on a case-by-case basis.  Inservice inspection of the containment liner and penetrations is also not addressed in this guide.  The simplest means of monitoring these prestres sed concrete structures would be to ascertain the amount of prestress at certain strategically located sections in the structure.
Methods and tolutlons different from those set out in The guides are issued in the following ten broad divisions:
the gtuldet will be If they provide a batis for the findings requisite to the Isuanca or continumnce of a permit or license by the Commlision.


However, it is generally felt that available instrumentation for concrete, i.e., strain gages, stress meters, and strain meters, is not reliable enough to provide such information.
1. Power Reactors 6. Products 2. Research end Test Reactors


When USNRC REGULATORY
===7. Transportation===
GUIDES Comments should be sent to the Secretary of the Commission, US. Nuclear Regu latory Commission, Washington, D.C. 20555, Attention:
Docketing and Service Regulatory Guides are issued to describe and make available to the public methods 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:
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 2. Research and Test Reactors 7. Transportation if they provide a basis for the fidings requisite to the issuance or continuance
3. Fuels and Materials Facilities  
3. Fuels and Materials Facilities  
8. Occupational Health able ovidens ba the findin. 4. Environmental and Siting 9. Antitrust Review 5. Materials and Plant Protection
8. Occupational Health Published guldan will be tevisad periodically, as appropriate, to accommodlte
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;
4. Environmental and SitIng 9. Antitrust Review comments and to reflect new Information or experience.
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.
 
instrumentation that either can be recalibrated or replaced in case of a malfunction or is proven to be sufficiently reliable is developed, monitoring the prestress level would be a desirable means of assess ing the continuing integrity of prestressed concrete structures with grouted tendons.
 
Another means of monitoring the functionality of the containment structure would be to subject it to a pressure test and measure its behavior under pres sure. Industry comments indicate that an inservice in spection program based on the test of overall func tionality is preferable.
 
This regulatory guide provides two acceptable alternative methods of inspecting containment struc tures with grouted tendons: (1) an inservice inspec tion program based on monitoring the prestress level by means of instrumentation, and (2) an inservice in spection program based on pressure-testing the con tainment structure.
 
The detailed inspection program outlined in this guide is applicable to a sphere-torus dome contain ment having cylindrical walls about 130 feet (40 m) in diameter and an overall height of about 200 feet (61 m) with three groups of tendons, i.e., hoop, vertical, and dome. For the purpose of this guide, such a con tainment is termed the "reference containment." The recommendations in the guide may be used for similar containments with cylindrical walls up to 140 feet (43 m) in diameter and an overall height up to 210 feet (64 m).  For containments that differ from the reference containment or are under a controlled environment, the inservice inspection program may be developed using the concepts evolved in this guide and the guidelines in Appendix A.  The inservice inspection program recommended in this guide consists of: 1. Force monitoring of ungrouted test tendons; 2. Monitoring performance of grouted tendons by a. Monitoring of prestress level, or b. Monitoring of deformation under pressure;
and 3. Visual examination.


===1. FORCE MONITORING ===
S. Matirisls and Plant Protection t0. Gencral The effects of corrosion on the tendons are of greatest concern, but they cannot be isolated from other effects. Therefore, tolerance limits for the loss of pre.stressing force which arc established to monitor corro-sion must also take into account all prestress losses. An inservice inspection program is needed to ensure that these limits are not exceeded.
OF UNGROUTED
TEST TENDONS Some tendons (otherwise identical)
are left un grouted and are protected from corrosion with grease. The changes observed in these tendons are not intended to represent the changes due to environmen tal or physical effects (with respect to corrosion)
in the grouted tendons. Instead, these test tendons will be used as reference tendons to evaluate the extent of concrete creep and shrinkage and relaxation of the tendon steel. The measurement of forces in ungrouted test tendons would provide a quantitative means of verifying the design assumptions regarding the volumetric changes in concrete and the relaxation of prestressing steel. If some lift-off readings (or load cell readings)
indicate values lower than the expected low values, checks should be made to determine if such values are due to corrosion of wires of un grouted tendons or to underestimation of prestress ing losses. The plant need not be shut down or main tained in a shutdown condition during such an evaluation period. These tendons may also serve as an investigative tool for assessing the structural con dition after certain incidents that could affect the containment.


===2. MONITORING ===
It should be noted, how-ever, that this program will not detect minor losses in tendon prestress due to corrosion.
ALTERNATIVES
FOR GROUTED TENDONS a. Monitoring of Prestress Level (Alternative A) After the application of prestress, the prestressing force in a tendon decreases owing to the interaction of such factors as: (1) Stress relaxation of the prestressing steel; (2) Volumetric changes in concrete;
(3) Differential thermal expansion or contraction between the tendon, grout, and concrete;
and (4) Possible reduction in cross section of the wires due to corrosion, including possible fracture of the wires.  In this alternative, the prestress level is monitored 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 tion will be detected by evaluation of the instrumen tation readings.


However, if corrosion occurs at loca tions away from the instrumented sections, it would have to produce gross degradation before the in strumentation readings would be affected.
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.


The prestressing force imparted to the structure by a grouted tendon system could be monitored by an appropriate combination of the following methods: (1) Monitoring the tensile strains in the wires of a tendon; (2) Evaluating the prestress level at a section in the structure from readings of appropriately located strain gages or strain or stress meters at the section (see Refs. 1 through 7).  Method (1) above is useful for direct monitoring of prestressing force in a tendon. However, the installa-1.90-2 tion of the instrumentation required for this method needs careful attention during installation and grouting of the tendons. Moreover, strain gages in%talled on the prestressing wires of a tendon will not detect the loss of force due to relaxation of prestress ing steel. Allowance for this can be based on relaxa tion data for the prestressing steel used.  Evaluation of strain gage and stress meter readings requires a full understanding of what makes up the readings, e.g., elastic, creep, and thermal strain or stress components.
Unless the anchors are installed with consider.ation for inspection, they will not be easily accessible for inspection, especially during operation.


Strain gage readings will consist of elastic strains corresponding to the prestressing stress in concrete and strains due to creep and shrinkage of concrete.
The original layout of tendons should address itself specifically to this accessibility problem. Any architectural treatment or environmental protection provided for the anchors should not preclude access for inspection purposes.The recommendations outlined in this guide are appli-cable to all containments with grouted wire (parallel or stranded)
prestressing systems regardless of plant geo-graphical location, but the following factors warrant special attention:
1. The tendons may need protection from moisture and salt intrusion at coastal sites and other sites having high moisture levels and significant temperature cycles of short duration.2. For sites in indus!rial areas, tendons should be guarded against fume releases containing SO 2 , li 2 S, NO or chlorides.


Strains from creep and shrinkage of concrete can vary between 1.5 and 2.5 times the elastic strains in concrete.
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.


However, there are methods that can be used to isolate these effects.
This instrumentationj composed of either strain gauges or stress meters, will provide prestress level readings in representative areas of the structure.


Three such methods are: (1) Calculate average creep and shrinkage strains from the time-dependent losses measured on the un grouted tendons.
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.


(2) Use stress meters at sections where strain gages are used.  (3) Use special strain meters that respond only to volumetric and temperature changes in concrete (Ref. 7). A sufficient number of temperature sensors instal led at the sections where instrumentation is located can be useful in isolating the thermal effects. It is recognized that the raw instrumentation readings can be deceptive, and adjustments may be necessary to account for the calibration constants and temperature effects. The interpretation and evalua tion of the results will be simplified if the instrumen tation is provided at sections away from structural discontinuities.
Later, at the time of submittal of the final safety analysis report (FSAR), with construction well ad-vanced, sufficient information will be available to submit a correct and expanded study. The FSAR should incorporate all changes that occurred during construc-tion as well as: 1. A description of the provisions made to ensure that only properly calibrated gauges have been used;2. A numerical estimate of the expected theoretical indication level of the gauges presented as a function of time for the entire life of the plant. This estimate should include all necessary estimated corrections, including concrete creep and shrinkage and tendon relaxation which will be checked by the ungrouted test tendons;3. An indication of the reasons and tolerances for possible discrepancies between the measurements and I the actual prestress;
1.90-2 U-4. An evaluation of the maximum probable error in the* results and the accuracy expected: 5. A discussion of the probable influences of tempera-lure on the results due to changes in the length of the wires, in the size of the structure, and in friction values;6. A description of actions that should be taken as a result of anomalous gauge readings or indications that numerous gauges are defective;
and 7. The visual observations to be made, the procedures for checking the ungrouted tendons, and the integration of these data with gauge data to form inservice in;spec-lion conclusions regarding continued structural integrity.


The applicant should provide suf ficient redundancy in the instrumentation to permit the evaluation of anomalous readings and the isola tion of a malfunctioning gage. One such combination would be two strain gages and one stress meter at each face of a section.
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.


After appropriate use has been made of the methods and instruments available, an average stress and an average prestressing force at a section can be evaluated.
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.


Even though the predicted prestressing force corresponding to a specific time may include adequate consideration for creep of concrete and relaxation of prestressing steel, the chance that the value based on measurements will compare well with the predicted value is small. Hence it is recommended that an applicant establish a band of acceptable prestress level similar to that illustrated in Figure 1. It is also recommended that the bandwidth not exceed 8% of the initial prestressing force at a section after considering the loss due to elastic shortening, anchorage takeup, and friction.
If instrumentation readings indicate a need for further checking, additional liftoff tests of the ungrouted test tendons may be needed.3. Instrumentation a. Characteristics (I) Instrumentation provided for the determina- lion of concrete prestress level should be capable of effective use over the life span of the containment structure within specified operational limits under the following conditions, unless othenvise defliaed by the designer and approved by the Regulatory staff: (a) Humidity;
0% to 100%;(b) Temperature:
0 0 F to 200'F; and (c) Cyclic loading: 500 cycles of 600 psi stress variation in compression.


The 8% bandwidth would amount to between 40% and 70% of the total time-dependent losses.  Alternative A is based on the use of instrumenta tion. Many of these instruments have to be built into the structure in such a manner that they can be neither replaced nor recalibrated.
(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.
 
It is quite likely that such built-in instrumentation may not remain reliably operable throughout the life of the structure.
 
Recognizing such a possibility, the guide provides for an alternative of pressure testing (Alternative B) when the data obtained from instrumentation readings are found to be questionable.
 
b. Monitoring of Deformation Under Pressure (Alternative B) Testing the containment under pressure and evaluating its elastic response has been proposed as a means of assessing the integrity of the containment.
 
The elastic response under pressure testing is primari ly a function of the stiffness of the structure.
 
Any significant decrease in the stiffness of the structure due to loss of prestress would be the result of crack ing of the structure.
 
Because of the insensitive and in direct relationship between the prestressing force and the elastic response of the structure, such a method cannot be used to establish the existing prestress level at various sections.
 
However, comparison of the con dition and deformation of the structure during the ISI (Inservice Inspection)
pressure testing with those during the ISIT (Initial Structural Integrity Testing) pressure testing could provide a basis for evaluating the functionality of the structure.
 
This method has been accepted*
previously by the NRC staff on the condition that the containment be designed conser vatively so that there will be no cracking (or only slight cracking at the discontinuities)
under the peak test pressure.
 
Section III, Division 2, of the ASME Code (Ref. 8) allows a 33-1/3% increase in the al lowable stress in tensile reinforcement under a test condition.
 
The NRC staff has accepted this al lowance on the assumption that it is only a one-time loading (i.e., during the ISIT). However, if such testing is to be performed a number of times during the life of the containment structure, it is prudent not to use this allowance in order to avoid or minimize gradual propagation of cracking during subsequent pressure tests.  The locations for measuring the deformations un der pressure should be based on the recommenda tions of this guide. For a meaningful comparison of the deformations, it is recommended that the loca tions where the deformations are to be recorded have deformations larger than 0.06 inch (1.5mm) under the calculated peak containment internal pressure as sociated with the design basis accident and that these
* Three Mile Island Nuclear Power Station Unit 2 and Forked River Nuclear Power Station.1.90-3 Fi -Initial prestressing force at a section considering the losses due to elastic shortening, anchorage takeup, and frictio
 
====n. PREDICTED ====
PRESTRESS
FORCE (CONSIDERING
HIGH TIME-DEPENDENT
LOSSES)PREDICTED
PRESTRESS
FORCE (CONSIDERING
LOW TIME-DEPENDENT
LOSSES)Figure 1. Typical Band of Acceptable Prestress Level w 0 0.9Fi LIb a,M I-C,,J U0 K O.8F 1 0.7Fi 1 3 5 10 15 20 25 30 35 40 TIME IN YEARS
locations be approximately the same during the ISIT and the subsequent ISIs. This will require these loca tions to be away from the areas of structural discon tinuities.
 
Thus the number of locations for measure ment of deformations in typical cylinder and dome areas wili be in excess of those recommended in Regulatory Guide 1.18, "Structural Acceptance Test for Concrete Primary Reactor Containments." If an analysis of the effects of such parameters as normal losses in prestressing force, increase in modulus of elasticity of concrete with age, and dif ferences in temperatures during various pressure tests indicates that they could affect the deformations of the selected points, these parameters should be con sidered in comparing the deformations during various pressure tests.
 
===3. VISUAL EXAMINATION ===
Visual examination of structurally critical areas consisting of the areas of structural discontinuities and the areas of heavy stress concentration is recom mende
 
====d. Reference ====
9 provides excellent guidance for reporting the condition of concrete and should be used whenever applicable for reporting the condition of examined areas.  There are numerous examples of the use of pulse velocity technique to obtain information concerning the general quality level of concrete.
 
Based on ex perience and experimental data (Refs. 10, 11, 12), a 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 ft/sec (3400 m/sec) or lower indicates concrete of questionable quality. Thus the technique can be used as part of the inspection of concrete containments when the visual examination reveals a high density of wide (>0.01 in. or 0.25 mm) cracks or otherwise heavy degradation.
 
The detailed procedure and limitations of the techniques are described in Reference
13.C. REGULATORY
POSITION 1. GENERAL 1. All prestressed concrete containment structures with grouted tendons should be subjected to an inser vice inspection (ISI) program. The specific guidelines provided herein are for the reference containment described in Section B.  2. For containments that differ from the reference containment, the program described herein should serve as the basis for developing a comparable inser vice inspection program. Guidelines for the develop ment of such a program are given in Appendix A to this guide.3. The inservice inspection program should consist of: a. Force monitoring of ungrouted test tendons; b. Periodic reading of instrumentation for deter mining prestress level (Alternative A) or deforma tions under pressure (Alternative B) at preestablished sections;
and c. Visual examination.
 
4. The inservice inspection should be performed at approximately
1, 3, and 5 years after the initial struc tural integrity test and every 5 years thereafter.
 
However, when an applicant chooses pressure testing (Alternative B) as a part of the inspection, the fre quency of inspections should be as indicated in Figure 2.  5. Alternative B may be substituted for Alternative A by the applicant if, at some time during the life of the structure, the inspection based on Alternative A does not provide satisfactory data. The details of such a substitution will be reviewed by the NRC staff on a case-by-case basis.  6. If the containment base mat is prestressed, its proposed inspection program will be evaluated by the NRC staff on a case-by-case basis.
 
===2. UNGROUTED ===
TEST TENDONS 1. The following ungrouted test tendons should be installed in a representative manner: a. Three vertical tendons, b. Three hoop tendons, and c. Three dome tendons for the design utilizing three 600 families of tendons.
 
2. The ungrouted test tendons need not be in addi tion to the design requirements.
 
3. The ungrouted test tendons and their anchorage hardware should be identical to the grouted tendons and their hardware.
 
4. The ungrouted test tendons should be subjected to force measurement by lift-off testing or load cells to assess the effects of concrete shrinkage and creep and relaxation of the tendon steel. These data should be evaluated in conjunction with the overall struc tural condition of the containment evident from the other examinations.
 
1.90-5 I LRT SCHEDULE -A --a -1 (10 CFR Part 50, APP. J) ISI SCH. -= --PRESSURE 1 5 D LEVELS pN 1" 1 5 PPD PA PA PA PA 0 1 5 10 15 20 25 30 35 *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 I LRT -Integrated Leak Rate Testing ISIT -Initial Structural Integrity Testing ISI -Inservice Inspection Figure 2. Schedule for Inservice Inspections (Alternative B)
 
===3. MONITORING ===
ALTERNATIVES
FOR GROUTED TENDONS 3.1 Instrumentation for Monitoring the Prestress Level (Alternative A) 3.1.1 Installation I. The prestressed cylindrical wall and dome should be instrumented.
 
This instrumentation may be either embedded in the concrete or inserted into the structure so that it can be maintained or replaced.
 
Instrument types, locations, and quantities should be selected to provide the best representation of prestress level in the structure.
 
A sufficient number of temperature sensors should be installed to isolate and evaluate the effects of variations in temperature gradients on the instrument readings and observa tions. Redundancy of the embedded instrumentation should be based on a conservative estimate of the probability of malfunction of the instrumentation to be installed.
 
2. The instrumentation in the concrete should be arranged and distributed in such a manner as to per mit evaluation of the prestressing levels and should be located: a. At six horizontal planes to measure the hoop prestressing levels; b. Along three vertical tendons to measure ver tical prestress levels; c. Along three dome tendons for the design us ing three families of 600 tendons.
 
3. Sections through the structure should be selected- at a minimum of four locations in each horizontal plane, three locations along each vertical tendon, and two locations along each dome tendon (see Figure 3). At these sections, the prestress level should be monitored by (a) a combination of stress meters or strain gages in concrete or on rebar at a minimum of two points through the section or (b) strain gages directly on tendon wires with a minimum of 3% of the tendon wires instrumented.
 
3.1.2 Characteristics
1. Instrumentation provided for the determination of concrete prestress level should be capable of effec tive use over the life span of the containment struc ture within specified operational limits under the fol lowing conditions, unless otherwise defined by the designer and approved by the NRC staff: a. Humidity:
0% to 100%; b. Temperature:
0°F (-18°C) to 200 0 F (93 0 C);and c. Cyclic loading: 500 cycles of 600 psi (4.2 MPa) 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.
They should be protected against temperature extremes to which they may be exposed while the containment is under construction.


3. The sensitivity of strain gages should be specified;
(3) The snsitivity of strain gauges should be specified, and the drift or stability under the conditions in C.3.a.(l)
the drift or stability under the conditions in I and 2 above should be accounted for in the specified limits, or the gages should be subject to rec:libration in service.
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.
 
4. The stress meters should be able to measure compressive stresses up to 2500 psi (17.2 MPa).  3.1.3 Monitoring Instrumentation Operability After the installation of the instrumentation, all embedded strain gages and stress meters should be read every two months until the initial structural in tegrity test (ISIT) is performed.
 
The response of the instrumentation during prestressing and pressure testing (ISIT) should be used to confirm their operability.
 
After the ISIT, the monitoring of the in strumentation should be continued every two months to confirm operability of the instrumentation until the first inservice inspection.
 
The monitoring fre quency may be reduced to once every six months thereafter unless local conditions or special circum stances dictate more frequent readouts.
 
The operability of the instrumentation should also be confirmed during subsequent pressure tests. If anomalous readings are obtained, the reason for such readings should be determined.
 
If it is determined that they result from defective gages, the basis for such a determination should be justified.
 
3.2 Monitoring Deformation Under Pressure (Alter native B) When it is planned to use this alternative as a part of the total inservice inspection program, it is recom mended that the design of the containment structure include the following considerations:
1. Membrane compression should be maintained under the peak pressure expected during the ISI tests.  2. The maximum stress in the tensile reinforcing under the peak pressure expected during the ISI test should not exceed one-half the yield strength of the reinforcing steel (0.5fy). 
3.2.1 Pressurization
1. During the first inspecticn, the containment structure need not be pressurized.


1.90-7 DT-1 DT-2 DI-2 L T-3 DOME TENDONS AT 600 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.
(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.


J HI-2 ' _ HI -Horizontal Planes to be Selected 1- HI- I -I for Instrumentation.
The base mat need be instru-merited only if it is prestressed.


T _I H__ VI & DI -Vertical & Dome Tendons , I -1- HT-2 to be Identified for Instrumentation.
This instrumentation may be either embedded in the concrete or inserted into the structure so that it can be maintained and/or replaced.


HI-4 IFour Sections Along HI Planes, Three 'I _11 Sections Along VI Tendons, Two Sections HI-5 Along Dl Tendons to be Selected for --I --Monitoring Prestress Level.  -I HT-3 0- Shows Selection of Sections Along HI-6 One Horizontal Plane, One Vertical Tendon, _- -and One Dome Tendon.  I I I I I 300 1500 2700 CONTAINMENT
Instrument types, locations, and quantities should be selected to provide the best representation of prestress levels in the structure.
CYLINDER -DEVELOPED
Figure 3. Containment Diagram Showing Typical Locations of Test Tendonrr Instrumentation
2. During the second and third inspections, the containment structure should be subjected to a max imum internal pressure of 1.15 times the containment design pressure.


3. During the fourth and subsequent inspections, the containment structure should be subjected to a maximum internal pressure equal to the calculated peak internal pressure associated with the postulated design basis accident.
Generally, these loca-tions are presumed to be it the mid-depth of the thickness of the wall and dome, unless specified other-wisc by the designer, at locations around the structure that match the locations at which deflection readings (in a prototype structure, deflection and strain readings)
are taken during the structural acceptance test.1.90-3 If redundancy is required to achieve rcliability at a measurement point, six strain gauges or six stress meters should be installed.


3.2.2 Instrumentation and Deformations
Three galiges should measure the prestress in the direction of the meridian and three the prestress in the hoop direction.
1. Instrumentation similar to that used during the ISIT should be installed prior to the pressure testing for measurement of overall deformations at the selected points.  2. The limit of accuracy of readings of the instru ments to be used should be specified by means of an error band so that a meaningful comparison of defor mations measured during the ISIT and ISI can be made.  3. The points to be instrumented for the measure ment of radial displacements should be determined in six horizontal planes in the cylindrical portion of the shell, with a minimum of four points in each plane (see Figure 3).  4. The points to be instrumented for the measure ment of vertical (or radial) displacements should be determined as follows: a. At the top of the cylinder relative to the base, at a minimum of four approximately equally spaced azimuths.


b. At the apex of the dome and one intermediate point between the apex and the springline, on at least three equally spaced azimuths.
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.


5. The intermediate pressure levels at which the deformations at the selected points are to be measured should correspond to those for the ISIT.
information.


===4. VISUAL EXAMINATION ===
After the first six months, the reading frequency can be changed to reflect the devia-tion from the predicted readings.
4.1 Structurally Critical Areas A visual examination should be performed on the following exposed structurally critical areas: 1. Areas at structural discontinuities (e.g., junction of dome and, cylindrical wall or wall and base mat).  2. Areas around large penetrations (e.g., equip ment hatch and air locks) or a cluster of small penetrations.


3. Local areas around penetrations that transfer high loads to the containment structure (e.g., around high-energy fluid system lines).  4. Other areas where heavy loads are transferred to the containment structure (crane supports, etc.).  A visual examination of structurally critical areas should be scheduled during all pressure tests while the containment is at its maximum test pressure, even if visual examinations of these areas have been con ducted at other times.  4.2 Anchorage Assemblies Exposed portions of the tendon anchorage as sembly hardware or the permanent protection thereon (whether it be concrete, grout, or steel cap) should be visually examined by sampling in the fol lowing manner: 1. A minimum of six dome tendons, two located in each 60* group (three families of tendons) and ran domly distributed to provide representative sampl ing, 2. A minimum of five vertical tendons, randomly but representatively distributed, 3. A minimum of ten hoop tendons, randomly but representatively distributed.
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.


For each succeeding examination, the tendon anchorage areas to be examined should be selected on a random but representative basis so that the sample group will change each time.  The inservice inspection program should define the defects the inspector should look for during visual ex amination of the exposed anchor hardware and protection medium and should establish the cor responding limits and tolerances.
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.


Special attention should be given to the concrete supporting the anchor assemblies, and any crack patterns at these points should be observed and analyzed.
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.


===5. REPORTABLE ===
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.
CONDITIONS
5.1 Inspection Using Alternative A If the average prestress force along any tendon falls below the acceptable band (see Figure 1), the condi tion should be considered as reportable.


If the prestress force determined at any section falls below the design prestress force, the condition should be considered as reportable.
(3) Ten hoop tendons, randomly but represen-tatively distributed.


5.2 Inspection Using Alternative B If the deformation measured under the maximum test pressure at any location is found to have in-1.90-9 creased by more than 5% of that measured during the ISIT under the same pressure, the condition should be considered as reportable.
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.


5.3 Reportable Conditions for Visual Examinations If the crack patterns observed at the structurally critical areas indicate a significant decrease in the spacing or an increase in the widths of cracks com pared to those observed during the ISIT at zero pres sure after depressurization, the condition should be considered as reportable.
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.


If the visual examination of the anchor hardware indicates obvious movements or degradation of the anchor hardware, the condition should be considered as reportable.
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.


If the anchor hardware is covered by permanent protection and the visual examination reveals a degradation (e.g., extensive cracks or corrosion stains) that could bring into question the integrity and effectiveness of the protection medium, the con dition should be considered-as reportable.
In such cases, the reporting program of Regulatory Guide 1.16,"Reporting on Operating Information-Appendix A Technical Specifications," should apply. A description should be furnished of the condition of the concrete (especially at tendon anchorages)  
 
and all examined tendon hardware, the inspection procedures, the toler-ances on concrete cracking and hardware corrosion, the measures to be used when the specified limits or 1.90.4
5.4 Reportable Conditions for Ungrouted Test Tendons When the force monitoring (by liftoff or load cell) of ungrouted test tendons indicates a prestress force below the acceptable band (see Figure 1), the condi tion should be considered as reportable.
0 tolerances are exceeded, and a decription of procedures to be used following cumpletion of dorrective measures to verify the satisfactory condition of the structure.
 
===6. REPORTING ===
TO THE COMMISSION
The reportable conditions of Regulatory Position C.5 could be indicative of a possible abnormal de gradation of the containment structure (a boundary designed to contain radioactive materials).
Any such condition should be reported to the Commission.*


==D. IMPLEMENTATION==
==D. IMPLEMENTATION==
The purpose of this section is to provide informa tion to applicants and licensees regarding the NRC staff's plans for using this regulatory guide.  Except in those cases in which the applicant proposes an acceptable alternative method for com plying with specified portions of the Commission's regulations, the method described herein will be used in the evaluation of submittals in connection with construction permit applications docketed after October 1, 1977. If an applicant wishes to use this regulatory guide in developing submittals for applications docketed on or before October 1, 1977, the pertinent portions of the application will be evaluated on the basis of this guide.
For applicants choosing to implement the Com-mission's regulations by the methods described in this guide, the following guidance is provided: 1. Construction permit reviews for applications dock-eted after July 1, 1975, will be evaluated on the basis of this guide.2. Construction permit and operating license reviews for plants whose construction permit applications were docketed prior to July 1, 1975, will be evaluated on a case-by-case basis. If practical, the applicant and designer in such cases may choose to follow the recommenda- tions of this guide.1.90-5 I}}
 
* The report to the Commission should be made in accordance with the recommended reporting program of Regulatory Guide 1.16, "Reporting of Operating Information-Appendix A Technical Specifications." 1.90-10
APPENDIX A GUIDELINES
FOR DEVELOPING
THE INSERVICE
INSPECTION
PROGRAM FOR CONTAINMENTS (OTHER THAN REFERENCE
CONTAINMENT
DISCUSSED
IN THE GUIDE) WITH GROUTED TENDONS Ungrouted Tendons Three ungrouted tendons should be provided in each group of tendons (e.g.,vertical, hoop, dome, in verted U).  Instrumentation (Alternative A) The following criteria should be used to determine the number of sections (N) to be monitored for each group of tendons: N = Actual Area Prestressed by a Group of Tendons K x Area Monitored by a Set of Instruments at a Section (determined as SxL) where S = spacing of tendons in feet (meters) L = length of a tendon monitored by a set of instruments- may be considered as 12 ft (3.66m) and K is determined as follows: For containments under uncontrolled environment and having continuous tendon curvature, K !SlO0 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 Monitoring Deformations Under Pressure (Alternative B) The number of locations (N) to be selected for measuring the deformations under pressure should be determined as follows: For radial deformations of cylinder, Surface Area of Cylinder infsquare feet N = (square meters)I 2700 (250) but not less than 12.For vertical deformations.
 
of cylinder, N=4 For radial or vertical deformations of dome, Surface Area of Dome in square feet N = (square meters) 2700 (250) but not less than 4 1.90-11 APPENDIX B REFERENCES
1. Jones, K., "Calculation of Stress from Strain in Concrete," U.S. Department of Interior, Bureau of Reclamation, Oct. 1961. Copies may be obtained from the Bureau of Reclamation, Denver Federal Center, Denver, Colorado.
 
2. Irving, J., "Experience of In-service Surveillance and Monitoring of Prestressed Concrete Pressure Vessels for Nuclear Reactors," a paper presented at International Conference on Experience in the Design, Construction and Operation of Prestressed Concrete Pressure Vessels and Containments for Nuclear Reactors, University of York, England, Sept. 1975. Copies may be obtained from J. C.  Mundy, Publication Liaison Officer, Mechanical Engineering Publications Limited, P.O. Box 24, Northgate Avenue, Bury St. Edmunds, Suffolk, IP326BW.
 
3. Hill, H. T., Durchen, N. B., Brittle, W. F., "Structural Integrity Test of Prestressed Concrete Containments," a paper presented at International Conference on Experience in the Design, Construc tion and Operation of Prestressed Concrete Pressure Vessels and Containments, University of York, England, Sept. 1975. Copies may be obtained from J.  C. Mundy, Publication Liaison Officer, Mechanical Engineering Publications Limited, P.O. Box 24, Northgate Avenue, Bury St. Edmunds, Suffolk, IP326BW.
 
4. Browne, R. D., Bainforth, P. B., Welch, A. K., "The Value of Instrumentation in the Assessment of Vessel Performance During Construction and Ser vice," a paper presented at International Conference on Experience in the Design, Construction and Operation of Prestressed Concrete Pressure Vessels and Containments for Nuclear Reactors, University of York, England, September
1975. Copies may be obtained from J. C. Mundy, Publication Liaison Of ficer, Mechanical Engineering Publications Limited, P.O. Box 24, Northgate Avenue, Bury St. Edmunds, Suffolk, IP326BW.
 
5. Arthauari, S., Yu, C. W., "An Analysis of the Creep and Shrinkage Effects Upon Prestressed Concrete Members Under Temperature Gradient and Its Application," Magazine of Concrete Research, Volume 19, Number 60, Sept. 1967. Copies may be obtained from the Cement and Concrete As sociation, Wexham Springs, SLOUGH SL 3 6 PL.6. Carlson, R. W., "Manual for the Use of Stress Meters, Strain Meters, and Joint Meters in Mass Concrete." Copies may be obtained from Ter rametrics, A Teledyne Company, 16027 West 5th Avenue, Golden, Colorado 80401.  7. Raphael, J. M., Carlson, R. W., "Measurement of Structural Action in Dams," 1965. Copies may be obtained from Terrametrics, A Teledyne Company, 16027 West 5th Avenue, Golden, Colorado 80401.  8. "Code for Concrete Reactor Vessels and Con tainments," American Concrete Institute Committee
359 and American Society of Mechanical Engineers Subcommittee on Nuclear Power, 1975. Copies may be obtained from the American Society of Mechanical Engineers, 345 E. 47th St., New York, N.Y. 10017 or from the American Concrete Institute, P.O. Box 19150, Redford Station, Detroit, Michigan 48219.  9. "Guide for Making a Condition Survey of Concrete in Service," Reported by ACI Committee
201. Copies may be obtained from the American Concrete Institute, P.O. Box 19150, Redford Station, Detroit, Michigan 48219.  10. Whitehurst, E. A., "Evaluation of Concrete Properties from Sonic Tests," ACI Monograph No.  2. Copies may be obtained from the American Concrete Institute, P.O. Box 19150, Redford Station, Detroit, Michigan 48219.  11. Leslie, J. R., Cheesman, W. J., "An Ultrasonic Method of Studying Deterioration and Cracking in Concrete Structures," ACI Journal, Proceedings V.  46, No. 1, Sept. 1949. Copies may be obtained from the American Concrete Institute, P;O. Box 19150, Redford Station, Detroit, Michigan 48219.  12. Van Zelst, T. W., "Concrete Quality Control Instruments," ACI Journal, June 1975. Copies may be obtained from the American Concrete Institute, P.O. Box 19150, Redford Station, Detroit, Michigan 48219.  13. "Standard Method of Test for Pulse Velocity Through Concrete," ASTM Designation C597-71.
 
Copies may be obtained from the American Society for Testing and Materials, 1916 Race Street, Philadelphia, Pennsylvania
19103.1.90-12}}


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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 wire

s. USAEC REGULATORY

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

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

to delineate technlques

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

Wathiinglon.

O.C. 2055,.evaluating "clidfic problamts or postulated accldents, or to provide guidance to Attention:

Dockelingr nd Service Section.applicants.

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

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

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

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

7. Transportation

3. Fuels and Materials Facilities

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

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

S. Matirisls and Plant Protection t0. Gencral The effects of corrosion on the tendons are of greatest concern, but they cannot be isolated from other effects. Therefore, tolerance limits for the loss of pre.stressing force which arc established to monitor corro-sion must also take into account all prestress losses. An inservice inspection program is needed to ensure that these limits are not exceeded.

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

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

Unless the anchors are installed with consider.ation for inspection, they will not be easily accessible for inspection, especially during operation.

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

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

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

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

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

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

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

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

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

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

1.90-2 U-4. An evaluation of the maximum probable error in the* results and the accuracy expected: 5. A discussion of the probable influences of tempera-lure on the results due to changes in the length of the wires, in the size of the structure, and in friction values;6. A description of actions that should be taken as a result of anomalous gauge readings or indications that numerous gauges are defective;

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

The FSAR should also contain a certification that the installation and the calibration of the instruments are correct. If the installation of the instrumentation is not yet completed, this certification may be submitted later, but not less than 3 months before issuance of an* operating license.The use of the Regulatory Positton described below does not eliminate the requirement for compliance with"Capability for Containment Leakage Rate Testing," of Appendix A to 10 CFR Part 50, General Design Crite-rion 52, which requires tha the containment be de-* signed so that periodic integratcd leakage rate testing can be conducted at containment dtsign pressure.C. REGULATORY

POSITION W 1. Inservice Inspection Program-General Each "typical" prestressed concrete containment structure with grouted tendons, 4s described in Section B, should be subjected to mn inservice inspection program that includes: a. iftoff tests ofungrouted test tendons;b. Periodic reading of instrumentation for deter-mining concrete prestress level; and c. Visual examination.

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

(1) Three vertical tendons.(2) Three hoop tendons, and (3) Two dome tendons if the design utilizes two 900 families of tendons or three dome tendons if the.design utilizes three 600 families of tendons.b. At the intervals given for visual examinations in C.4.a below, the ungrouted test tendons should be sub-.3 For the purposes of this guide, a tendon is defined as a separate continuous tensioned element consisting of wires or strands anchored at eacl. end to an end anchorage assembly.jected to liftoff testing to measure the effects of con.crete shrinkage and creep and relaxation of the tendon steel. These data should be evaluated in conjunction with concurrent instrumentation readings and visual examinations.

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

0% to 100%;(b) Temperature:

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

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

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

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

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

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

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

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

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

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

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

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

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

information.

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

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

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

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

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

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

These selected tendons' should include: (1) Six dome tendons; two located in each 600 group (three families of tendons) and randomly dis-tributed to provide representative sampling, or three located in each 900 group (two families of tendons), (2) Five vertical tendons, randomly but repre-sentatively distributed.

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

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

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

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

is indicated.

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

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

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

D. IMPLEMENTATION

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


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