Regulatory Guide 1.35

Inservice Surveillance of Ungrouted Tendons In Prestressed Concrete Containment Structures.

ML12305A260
Person / Time
Issue date:	02/05/1973
Revision:	0
From:	Office of Nuclear Regulatory Research
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References
RG-1.035
Download: ML12305A260 (3)

2/5/73U.S. ATOMIC ENERGY COMMISSIONREGULATORY GIDIRECTORATE OF REGULATORY STANDARDSREGULATORY GUIDE 1.35INSERVICE SURVEILLANCE OF UNGROUTED TENDONSIN PRESTRESSED CONCRETE CONTAINMENT STRUCTURESJIDEA. INTRODUCTIONGeneral Design Criterion 53, "Provisions forContainment Testing and Inspection" of Appendix Ato 10 CFR Part 50, "General Design Criteria forNuclear Power Plants," requires, in part, that thereactor containment be designed to permit (1) periodicinspection of all important areas and (2) 'anappropriate surveillance program. This guide describesan acceptable basis for developing an appropriatesurveillance program for ungrouted tendons inprestressed concrete containment structures oflight-water-cooled reactors. The Advisory Committeeon Reactor Safeguards has been consulted concerningthis guide and has concurred in the regulatory position.B. DISCUSSIONThis guide is applicable to "typical" prestressedconcrete containments with ungrouted tendons only, forwhich the number of tendons does not exceed: 200 inthe dome (either three families of tendons 600 apart ortwo families of tendons 900 apart), 200 vertical (inwall), and 500 complete hoops (in wall).For containments that differ from the "typical"containment described above, the model programpresented in this guide should serve as the basis fordevelopment of a comparable surveillance program.Surveillance of ungrouted wire and strand tendonsof all sizes (up to an ultimate strength of approximately1300 tons) and types should be considered (e.g., tendonswith parallel wires, with one or several strands, and withdifferent systems of anchors). Materials for allcomponents should satisfy the requirements ofapplicable American Society for Testing and Materials(ASTM) material standards. The surveillance programshould cover the anchor hardware and the corrosion-preventing filler (grease). To the fullest extent practical,it should also cover the ducts that contain the tendons.Such a surveillance program is necessary becausegenerally there is no permanent instrumentationinstalled in the containment that could continuouslymonitor its structural behavior.When developing a surveillance program, the totalcontainment tendon population should be divided intohomogeneous subgroups, i.e., tendons havingapproximately the same probability of corrosion and asimilar function in the overall structural capabilities andproperties of the structure. Thus, for each structure thesurveillance program. should consider separately thegroups of vertical, hoop, and dome tendons.Consideration of homogeneous tendon subgroups(i.e., vertical, hoop, and dome) establishes a samplingbase for determining loss of prestress, the maincharacteristic checked by the surveillance program.If some tendons are expected to be subject togreater prestress losses than the rest, this should be takeninto account in selecting samples..The prestressing force in a tendon may :be 'checkedby a liftoff or other equivalent test., One of the mainobjectives of the test is to discover any brittle, damaged,or broken wires. Any eventual decrease in theprestressing force is due to the simultaneous interactionof several time-dependent factors such as:a. Stress relaxation in the wire;b. Temperature variation of the wire;c. Shrinkage, creep, and temperature stresses inconcrete;d. Differential thermal expansion ' or contractionbetween the concrete and the tendon; ande. -Eventual deterioration of the wires (corrosion).USAEC REGULATORY GUIDES Copies of published guides may be obtained by request indicating the divisionsdesired to the US. Atomic Energy Commission, Washington, D.C. 20545,Regulatory Guides are issued to describe and make available to the public Attention: Director of Regulatory Standards. Comments and suggestions formethods acceptable to the AEC Regulatory staff of implementing specific parts of improvements in these guides are encouraged and should be sent to the Secretarythe Commission's regulations, to delineate techniques used by the staff in of the Commission, U.S. Atomic Energy Commission, Washington, D.C. 20545,evaluating specific problems or postulated accidents, or to provide guidance to Attention: Chief, Public Proceedings Staff.applicants. Regulatory Guides are not substitutes for regulations and compliancewith them is not required. Methods and solutions different from those set out in The guides are issued in the following ten broad divisions:the guides will be acceptable if they provide a basis for the findings requisite tothe issuance or continuance of a permit or license by the Commission. 1,. Power Reactors 6. Products2. Research and Test Reactors 7. Transportation3. Fuels and Materials Facilities 8. Occupational HealthPublished guides will be revised periodically, as apprupriate, to accommodate 4. Environmental and Siting 9. Antitrust Reviewcomments and to reflect new information or experience. 5. Materials and Plant Protection 10. General A liftoff test does not separate the effects of thesefactors, and corrosion, the factor of greatest concern,cannot be isolated. Therefore, tolerance limits for theloss of prestressing force, including the effects ofpossible corrosion, should be established, and thesurveillance procedure oriented toward verifying thatthese limits are not exceeded. However, it should benoted that only gross deterioration of the prestressingsystem can be detected.Many hoop tendons are anchored on buttressespartially located inside the auxiliary building adjacent tothe containment. Since these anchors are not easilyaccessible, especially during operation of the facility,they present a special problem for liftoff tests. Theoriginal layout of tendons should address itselfspecifically to this problem. Any anchor architecturaltreatment or environmental protection should beremovable without damage to the anchor.Defects that an inspector might uncover duringvisual inspection of the anchorage assembly should beseparated into three groups:a. Defects that can be found when the tendon is in itsnormally stressed condition;b. Defects that can be found only after the tendon istensioned to a higher value than the existing prestressingforce; andc. Defects that can be found only after the tendon isdetensioned.If the limits provided in C.5. and C.6. are exceededor if abnormal material behavior is detected pursuant toinspection in accordance with C.7., then abnormaldegradation of the containment structure, a boundarydesigned to contain radioactive materials, is indicated. Insuch cases, the reporting provisions of Safety Guide 16,"Reporting of Operating Information," should apply.Included in the report should be a description of thecondition of the concrete (especially at tendonanchorages), the surveillance procedure, the toleranceson cracking, and the measures to be used whentolerances are exceeded.C. REGULATORY POSITION1. This guide should be applied to "typical"prestressed concrete containments having ashallow-domed roof on cyclindrical walls about 150 feetin diameter, an overall height of about 200 feet, and forwhich the number of tendons does not exceed: 200 inthe dome (either three families of tendons 600 apart ortwo families of tendons 90' apart), 200 vertical (inwall), and 500 complete hoops (in wall). Forcontainments that differ from the "typical"containment described above, this guide should serve asthe basis for development of a comparable surveillanceprogram, which will be evaluated on a case-by-case basis.2. Each containment structure should be inspected inaccordance with this guide independently fromcontainments at any other site. Where identicalcontainment structures are located on one site, where noenvironmental or other differences are apparent, andwhere they were constructed by the same contractor inthe same manner at the same time (continuousconstruction), then every second containment structureneed only be visually inspected in accordance with C.7.3. Containments should be designed so that theprestressing anchor hardware is accessible for periodicinspection.4. The surveillance measures identified in C.5., C.6.and C.7. should be performed 1, 2, and 3 years after theinitial containment structural integrity test and every 5years thereafter.5. Selected tendons should be periodically subjected toliftoff or other equivalent tests to monitor loss ofprestress. These tests should include the following:a. Properly calibrated jacks and the simultaneousmeasurement of elongation and jacking force. Allowableelongations and jacking loads, allowable tolerances, andthe effects of influences such as temperature should beestablished prior to the tests.b. A maximum test liftoff force greater than themaximum inservice prestressing force. The liftoff testshould include an unloading cycle going down toessentially complete detensioning of the tendon toidentify broken or damaged wires or strands.c. Selected numbers and types of tendonsperiodically tested for loss of prestress:(1) Six dome tendons; two located in each 600group (i.e.., three families of tendons) and distributed toprovide representative, sampling, or three located in each900 group (i.e., two families of tendons), *(2) Five vertical tendons, randomly butrepresentatively distributed,(3) Ten hoop tendons (where more than onetendon comprises the total hoop, one tendon mayrepresent the hoop), randomly but representativelydistributed.d. A measurement of the prestress force for eachtendon tested in C.5.c., with acceptable limits beingdefined as not less than the predicted lower bound norgreater than the predicted upper bound forces at thetime of the test.e. An allowable limit of not more than onedefective tendon out of the total sample population. Ifone sample tendon is defective, an adjacent tendon oneach side of the defective tendon should also bechecked. If both of these tendons are acceptable asdefined in C.5.d., then the surveillance program shouldproceed considering the single deficiency as unique andacceptable. However, if either adjacent tendon isdefective or if more than one tendon out of the originalsample population is defective, abnormal degradation ofthe containment structure is indicated, and theCommission should be notified in accordance with C.8.1.35-2 6. The physical condition of the tendon materialshould be checked as noted below.a. Previously stressed tendon wires or strandsfrom one dome tendon and two wall tendons (one froma vertical tendon and one from a hoop tendon) shouldbe removed for testing and examination over the entirelength to determine if evidence of corrosion or otherdeleterious effects are present. At each successiveinspection the samples should be selected from differenttendons.b. Tensile tests should be made on at least threesamples cut from each removed wire or strand (one ateach end and one at mid-length; the samples being of amaximum length practical for testing). If frequent stresscycling is suspected, tests simulating his conditionshould be conducted. Similarly, where as a result of thesurveillance program a potentially corrosive atmosphereis suspected, accelerated corrosion tests should be made.c. Failure below the guaranteed ultimate strengthof any one of the three tendon material sample testsshould be considered an indication of abnormaldegradation of the containment structure, and theCommission should be notified in accordance with C.8.7. Tendon anchorage assembly hardware (such asbearing plates, stressing washers, shims, wedges, andbuttonheads) of all tendons inspected pursuant to C.5.and C.6. should be visually inspected. For thosecontainments for which only visual inspections need beperformed, as noted in C.2., the same numbers and typesof tendons as noted in C.5.c. should be visuallyinspected to the extent practical without dismantlingload-bearing components of the anchorage. Thesurrounding concrete should also be checked visually forindications of abnormal material behavior. If the entirecontainment is pressurized for leak testing purposes, thevisual inspection should be scheduled, if possible, tocoincide with the leak test.The method used for checking the presence ofsheathing filler grease should account for: (1) theminimum grease coverage needed for different parts ofthe anchorage system including, for example,buttonheads; (2) the influence of temperature variations,especially the lowest temperature likely to occurbetween two successive inspections; (3) the procedureused to uncover possible voids in grease in the trumpet;and (4) requirements imposed by grease specifications,qualification tests, and acceptability tolera'nces. Themethod used for removing grease in order to permitvisual inspection of the stressing washers, shims, wedges,and bearing plates should neither increase the effects ofcorrosion nor damage the steel (for instance, scratch it)and should be usable even under unfavorable conditionsso as not to conflict with operational requirements.8. Any significant or critical deterioration of thecontainment revealed by the inservice surveillanceprogram should be reported to the Commission as anabnormal occurrence in accordance with Safety Guide16, "Reporting of Operating Information," except thatthe initial report may be made within 10 days of thecompletion of the tests, and the detailed report mayfollow within 90 days of the completion of the tests.1.35-3