Regulatory Guide 1.35

Inservice Inspection of Ungrouted Tendons in Prestressed Concrete Containment Structures

ML031500241
Person / Time
Issue date:	01/31/1976
From:	NRC/OSD
To:
References
RG-1.035, Rev. 2
Download: ML031500241 (4)

._. ._-. U.S. NUCLEAR REGULATORY

COMMISSION

j REGULATORY

GUIDE Revision 2 January 1976 OFFICE OF STANDARDS

DEVELOPMENT

REGULATORY

GUIDE 1.35 INSERVICE

INSPECTION

OF UNGROUTED

TENDONS IN PRESTRESSED

CONCRETE CONTAINMENT

STRUCTURES

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 Facilities," requires in part that the reactor containment be designed to permit (1) periodic inspection of all important areas and (2) an appropriate surveillance program. This guide describes a basis acceptable to the.NRC staff for developing an' appropriate inservice inspection and surveillance program for ungrouted ten-dons in prestressed concrete containment structures of light-water-cooled reactors.

The Advisory Committee on Reactor Safeguards has been consulted concerning this guide and has concurred in the regulatory position.

B. DISCUSSION

• l This revision is the result of comments received on Revision 1, June 1974, and additional staff review.The recommendations of this guide are applicable to"typical" prestressed concrete containnents having a shallow-domed roof on cylindrical walls about 150 feet in diameter, an overall height of about 200 feet, and the following tendons: approximately

200 in the dome (either three families of tendons 600 apart or two families of tendons 90° apart), 200 vertical in the wall, and 500 hoop tendons in the wall. In addition, these recommendations are applicable to containments having a hemispherical dome-shaped roof on cylindrical walls about 150 feet in diameter, an overall height ranging from 200 to 240 feet, and the following tendons: 70 to*Lines indicate substantive changes from previous issue.90 inverted U tendons' arranged in two families of tendons 900 apart and 150 to 180 hoop tendons in the cylinder and dome.Inservice inspection of ungrouted wire and strand tendons of all sizes (up to an ultimate strength of approximately

1300 tons) and all types should be performed (e.g., tendons with parallel wires, with one or several strands, and with different systems of anchors).Materials for all components should satisfy the require-ments of applicable American Society for Testing and Materials (ASTM) material standards.

The inservice in-spection program should 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 an inservice inspection pro-gram is necessary because generally there is no perma-nent instrumentation installed in the containment that could continuously monitor its structural behavior.When an inservice inspection program is being devel-oped, the total containment tendon population should be divided into homogeneous subgroups consisting of tendons having approximately the same probability of corrosion and similar functions in the overall structural capabilities and properties of the structure.

Thus, for each structure the inservice inspection program should consider separately the groups of vertical, inverted U, hoop, and dome tendons. This will permit a sampling.base to be established for determining loss of prestress, the main characteristic checked by the inservice inspec-tion program.IA tendon, both ends of which are anchored at the bottom of the base of the cylindrical walls and which approximately follows the configuration of the containment in the vertical plane passing through the anchor point

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If some tendons are expected to be subject to greater 3. Defec prestress losses than the rest, this should be taken into detensionec account in selecting samples.The inservice inspection programs outlined in this guide are applicable to all containments with ungrouted prestressing systems regardless of plant geographical

1 Gene location.The prestressing force in a tendon may be checked by 1.1 The a liftoff or other equivalent tests. One of the main this guide objectives of the test is to discover any brittle, damaged, prestressed or broken wires. Any eventual decrease in the pre-stressing force is due to the simultaneous interaction of 1.1.1 several time-dependent factors such as: shallow-doi in diameter 1. Stress relaxation in the wire; following

1 (either thr 2. Temperature variation of the wire; families of and 500 h 3. Shrinkage, creep, and temperature deformations in ("typical")

concrete;1.1.2 4. Differential thermal expansion or contraction hemispheric between the concrete and the tendon; and about 150 from 200 t 5. Reduction in cross section of the wires, including

90 inverte possible fracture, due to corrosion.

tendons 90 cylinder ar A liftoff test does not separate the effects of these dome").-factors, and corrosion, the factor of greatest concern, cannot be isolated.

Therefore, tolerance limits for the 1.2 For loss of prestressing force, including the effects of types, the possible corrosion, should be established, and the inser- for the dew vice inspection program should be oriented toward tion prograr determining whether these limits are exceeded.

However, it should be noted that only gross deterioration of the 1.3 All prestressing system can be detected.

dons should Many hoop tendons are anchored on buttresses partially located inside the auxiliary building adjacent to the containment.

Since these anchors are not easily accessible, especially during operation of the facility, they present a special problem for liftoff tests. In the original layout of tendons, this problem should be specifically considered.

Any architectural treatment or environmental protection of the anchors should be removable without damage to the anchor.Defects that an inspector might uncover during visual inspection of the anchorage assembly should be sepa-rated into three groups: 1. Defects that can be found when the tendon is in its normally stressed condition;

2. Defects that can be found only after the tendon is the existing prestressing

~~tensioned to a igher value than force; and l

'..-; -.~~~~~cts that can be found only after the tendon is 1.C. REGULATORY

POSITION inservice inspection program described in is applicable to the following types of concrete containment structures:

Prestressed concrete containments having a ned roof on cylindrical walls about 150 feet , an overall height of about 200 feet, and the tendons: 2 approximately

200 in the dome ee families of tendons 60° apart or two tendons 900 apart), 200 vertical in the wall, oop tendons in the wall (herein designated and Prestressed concrete containments having a ial dome-shaped roof on cylindrical walls feet in diameter, an overall height ranging o 240 feet, and the following tendons: 70 to I U tendons' arranged in two families of°apart and 150 to 180 hoop tendons in the id dome (herein designated "hemispherical containments that differ from these two program described should serve as the basis relopment of a comparable inservice inspec-iM.containment structures with ungrouted ten-I be inspected in accordance with this guide.However, if it can be shown by the applicant that identical containment structures are located on one site, that no environmental or other differences are apparent, and that they were constructed by the same contractor in the same manner at the same time (continuous construction), every second containment structure need only be visually inspected as described in regulatory position C.3.1.4 Containments should be designed so that the prestressing anchor hardware is accessible for periodic examination.

1.5 The inservice inspection should be performed

1, 3, and 5 years after the initial containment structural integrity test and every 5 years thereafter.

2 For the purpose of this guide, a tendon is defined as a separate continuous multiwire or multistrand tensioned element anchored at both ends to an end anchorage assembly.1.35-2 Q

2. Sample Selection 2.1 Samples for the inspection at 1, 3, and 5 years should be selected as follows: 2.1.1 "Typical" containments:

2.1.1.1 Six dome tendons, two located in each 60° group (i.e., three families of tendons) and randomly distributed to provide representative sampling, or three located in each 900 group (i.e., two families of tendons).2.1.1.2 Five vertical tendons, randomly but representatively distributed.

2.1.1.3 Ten hoop tendons randomly but repre-sentatively distributed.

2.1.2 "Hemispherical dome" containments:

2.1.2.1 4% of the U tendon population with the result rounded off to the nearest integral number of tendons, but no less than four.2.1.2.2 4% of the hoop tendon population with the result rounded off to the nearest integral number of tendons, but no less than nine.2.2 If the inspections described in regulatory posi-tion C.2.1 indicate that there are no problems with prestressing tendons in containment structures, the samples for the subsequent inspections may be selected as follows: 2.2.1 "Typical" containments:

2.2.1.1 If there are three dome groups, one from each group; if there are two dome groups, one from each dome group plus one additional dome tendon selected at random: 2.2.1.2 Three vertical tendons randomly but representatively distributed.

2.2.1.3 Three hoop tendons randomly but representatively distributed.

2.2.2 "Hemispherical dome" containments:

2.2.2.1 2% of the U tendon population with the result rounded off to the nearest integral number of tendons, but no less than two.2.2.2.2 2% of ie hoop tendon population with the result rounded off to the nearest integral number of tendons, but no less than three.2.3 If some tendons are subject to greater prestress losses than others, this should be considered in the sample selection.

For each inspection, the tendons should again be selected on a random but representative basis so the sample group will change somewhat each time. However, to develop a history and for correlating the observed data, one tendon from each group may be kept unchanged after the initial selection.

3. Visual Inspection Tendon anchorage assembly hardware (such as bearing plates, stressing washers, sims, wedges, and buttonheads)

of all tendons selected as described in regulatory position C.2 should be visually examined.

For those containments for which only visual inspections need be performed, tendons selected as described in regulatory position C.2 should be visually examined to the extent practical without dismantling load-bearing components of the anchorage.

The surrounding concrete should also be checked visually for indications of abnormal material behavior.

The visual examination of the concrete should be scheduled during integrated leakage testing while the containment is at its maximum test pressure.The method used for removing grease in order to permit visual examination of the stressing washers, shims, wedges, and bearing plates should neither increase the effects of corrosion nor damage the steel (for instance, scratch it) and should be usable under oper-ating conditions.

4. Prestress Monitoring Tests Tendons selected as described in regulatory position C.2 should be subjected to liftoff or other equivalent tests to monitor loss of prestress during each inspection.

These tests should include the following:

4.1 The simultaneous measurement of elongation and jacking force with properly calibrated jacks. Allow-able elongations, jacking loads, allowable tolerances, and the effects of influences such as temperature should be established prior to the tests.4.2 The maximum test liftoff force should be greater than the maximum inservice prestressing force. The liftoff test should include an unloading cycle going down to essentially complete detensioning of the tendon to identify broken or damaged wires or strands.5. Tendon Material Tests and Inspections

5.1 Previously stressed tendon wires or strands from one tendon of each type (i.e., for "typical" contain-ments, one dome, one vertical, and one hoop tendon; for"hemispherical dome" containments, one U tendon and one hoop tendon) should be removed for testing and examination over the entire length to determine if evidence of corrosion or other deleterious effects is 1.35-3 0 I.I

present. At each successive inspection, the samples should be selected from different tendons.5.2 Tensile tests should be made on at least three samples cut from each removed wire or strand (one at each end and one at mid-length;

the samples should be the maximum.length practical for testing).

If frequent stress cycling is suspected, tests simulating this condition should be conducted.

Similarly, where the inservice inspection program indicates the possibility of a poten-tially corrosive atmosphere, accelerated corrosion tests should be made.6. Inspection of Filler Grease The method used for checking the presence of sheathing filler grease should account for (1) the minimum grease coverage needed for different parts of the anchorage system including, for example, button-heads; (2) the influence of temperature variations, especially the lowest temperature likely to occur between two successive inspections;

(3) the procedure used to uncover possible voids in grease in the trumpet;and (4) requirements imposed by grease specifications, qualification tests, and acceptability tolerances.

7. Acceptance Criteria 7.1 The prestress force measured for each tendon in the tests described in regulatory position C.4 should be within the limits predicted for the time of the test.7.2 There should be no more than one defective tendon in the total sample population.

If one sample tendon is defective, an adjacent tendon on each side of the defective tendon should also be checked. If both of these tendons are acceptable as defined in regulatory position C.7.1, the inservice inspection program should proceed considering the single deficiency as unique and acceptable.

However, if efither adjacent tendon is defec-tive or if more than one tendon out of the original sample population is defective, the occurrence should be considered as unacceptable.

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WASHINGTON, D. C. 20555 OFFiCIAL BUSINESS PENALTY FOR PRIVATE USE. 300 7.3 Failure in the tensile test should not occur at a strength value less than the guaranteed ultimate strength of the tendon material.

Failure below this value in any tendon material sample should be considerea as unaccep-table.8. Reporting to the Commission If the acceptance criteria of regulatory position C.7 are not met or if abnormal material behavior is detected as described in regulatory positions C.3 and C.6, a possible abnormal degradation of the containment struc-ture (a boundary designed to contain radioactive mate-rials) is indicated.

Such an occurrence should be reported to the Commission.

The'report should include a description of the tendon condition, the condition of the concrete (especially at tendon anchorages), the I inspection procedure, the tolerances on cracking, and the measures to be used when tolerances are exceeded.

D. IMPLEMENTATION

The purpose of this section is to provide information to applicants and licensees regarding the NRC staff's plans for utilizing this regulatory guide.This guide reflects current NRC practice.

Therefore, except in those cases in which the applicant proposes an acceptable alternative method for complying with speci-fied portions of the Commission's regulations, this guide will be used by the NRC staff in evaluating construction permit and operating license applications for plants whose construction permits are docketed after the date of publication of the guide.3The report to the Commission should be made in accordance with the reporting program summarized in Regulatory Guide 1.16, "Reporting of Operating Information

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