ML20058K097
| ML20058K097 | |
| Person / Time | |
|---|---|
| Issue date: | 07/28/1989 |
| From: | Beckjord E NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES) |
| To: | Jordan E Committee To Review Generic Requirements |
| Shared Package | |
| ML20058A334 | List: |
| References | |
| RTR-NUREG-CR-2719, RTR-REGGD-01.035 NUDOCS 8908100273 | |
| Download: ML20058K097 (52) | |
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FEMORANDtf FOR:
Edetrc L. Jordan. Chairman Cerrittee to Review Generic Fequirements FROM:
Eric 5. Beckjerd, Director Office of liuclear Fegulatory Research l
St$JFCT:
r' REVIEW Of:
3.
F.EGULAT0ki GUIDE 1.35, P.EY. 3, "!NSERVICE INSPECTION OF UNGR0l'TED TEND 0l.S Ili PRESTPESSED CONCRETE CONTAINWENTS" l
LLWLATUM 6010E 1.35.1, DETERHillING PRESTRESSING FORCE!
TOR
!NSr00710N OF FRESTRESSED CONLRETE CONTAINMENTS" Tit enclosec perkeoe is it,t.nitted it. support of this request for the CRGR re-vieh dr+ appr0yal it Jt,tlish the subject ruides.
Though the revised guides do HT contain try Lasic provisions that were not contained in the previous re-visions, they oo reflect edjustments in various-espects of tendon surveillance.
some reli f to the utilities in Certain areas where 1htse ddjustrents proViol f
n telien it i: warrantet 6nd slight increases in other aspects where exFeri-ente has previdec a better understancing of tendon behavior.
More specific St.idance it tiso proviced where clarification is needed to avoid ambiguity.
ihe regulttery analysis (Enclosure 5) perfortaed on Draft 2, Rev. 3 of the guide (P.G. 1,35) inc;1 cates thet the impact on public ritt cannot be quantified with any cerscinty.
The cifference of using one version of the guide over the other could be wel' within the uncertainty level associated w'th the estimate of i
conteitirner t capacity Enc the failure modes.
However we strongly feel that the proposed revisicn will enhance reliat'ility of prestressed cencrete cor,ta:nments with ungrouted tendons.
BACKGROUND ON THE DEVELOPMEN1 0F R.G. 1.35 AND R.G. 1.35.1 A netc to inspect the prestressing components of prestressed concrete contain-ment (PCCs) was recognized by the AEC staff in 1968.
Inservice inspection reovirements fer plants licensed before 1972 were formulated on a case-by-case.
basis.
In 1972, e draf t guice was issued, which was consnented upon by the public, and was revised in 1974 as Rev.1 of Regulatory Guide 1.35.
With the advent of inverted U type of tendon configurat'ons, Rev.1 of the guide was r.odified to acconnodate that type of design as Rev. 2 of the guide.
Revision 2 c' the guiot was issued in January 1970.
In May 1976. NRC received a com-rent letter from Bechtel Power Corporation reouesting a relaxation cf the ten-don monitnrirg guio(lines ' of Rev. I of the guide.
NRC staff did not agree with the corrut and responded, indicating concerns with the tendon force monitoring aspect of tLe letter.
In 1977, in evaluating technical specifica-ticrs for a nutter of plar ts. the Engineering Branch of DOR encountered prcb-lems witt various interpretaticr.s of. Rev. E of the guide's tendon monitoring l
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Utde occurrerces indicated that thtre existed a need to provide de-16i:(c guidanet to the utilities for a rtthod of predicting tendon prestressing 1orce tt any tine, tr.c' f or the dtvelopment of a tolerance band concept as men-tienec in ht,. T of the tuice.
The proposed Regulatory Guide 1.35.1 was de-s elopt.d to ptevice the r. ceded guidance.
Drafts of Revision 3 of Regulatory Wde 1.3E er.c supplen.entel Guide 1.35.1 were issued for comraents in April 1979.
Iri the metr. tire, the equivalent of approximately 250 years of experience was accurrr16tec tri irspecting are t>aminirs greased tendons in prestressed concrete tcchnical essistance cer.trect to Dat Ridge National Laboratory (pirent awarded a contt ir.n ents.
'r November IgED, the Office of Standards Develo ORNL)toevalu-ate the recorcs of 50th inspectier.s.
Due to restrictions in requiring such ex-perience recorft ' rom the utilities, the Eivision of Licensing, 6t the request of t h( Office cf Stendards Development, issued a letter to the applicable uti H iies rect.u :ing ther tc submit the inspection record to the NRC on a volun-tary t uis, in aceition to reviewing the dcte received, the contractor (ORNL) sisitec c #er plerti during actuti inspections and talked with the utilities,
/,/Et, corrosier.-tr.hibitil; trease vendors and prestressing system vendors, The research reptrt was published in August 1982 as NUREG/CR-2719 Evaluation of Inse rv 4 rt inspectier.s of Greaset' Prestressing Tendons (Enclosurc 7).
Appropricte publir corcr..ents (Loclosures ? I 4), and suggestions froir. NUREG/
Cf ?719 are it.corporated ir the proposed Revisior. ? of Regulatory Guide 1.35 ar.c ae proposrr Etsuietory Guide 1.35.1 (Enclosuics 1 & 2),
p.ELEhi pFVini !!J15 ANL IMPLEMENTATION ('et le 4) stews the number cf PCCs using various revisions of R.6.
1.H. anc thc.se revie tc on a case by-case basis.
Some plants have voluntarily edopted the clat if tet suidance of the draf t Res. 3 of R.G.1.30, and of R.G.
1.3E.1 ir develeririg their irspection r(thods and schedules.
NIM corrent letter (S. hanauer to L. Shao, dated December 3,1982) on korking Paper i of the guides recomrrerded backfit of the guides to all PCCs with greascc' tendcr.s.
IE corunt letter (E. Jordan to L. Shao, dated hovember 9,1982) made the observation, "the guides will help to unify the approach to tendon surveillarce."
However, lE did not recommend backfit, but recommended that the liccnsees be riven a choice to use the ruides and err.phesized that, if so choser, the guices be adopted in their entirety and not just a portion of them.
RES agreed with NRL's intent of taving consistency in review and implementa-tion.
However, p.ES had difficulty in justifying the backfit froir the stand-poir.t of cost ard sefety improvements.
F.ES f elt that the clarity and relaxa-tion previded in the revised guides _would be adequate incentive for licensees and applicents to acort the recorrendations of the revised guides voluntarily.
Nr.L telt th6t it vould gin rise to fragrented inspection programs. To resolve this issut, RES awardet e contract to Oak Ridge Fational Laboratory to perform e regulatory arialysis cf draft 2 of the proposed revision of Regulatory Guide 1.35.
The report conteining the enalysis is attached as Enclosure 5.
The ane ?) sis aoot e'.ses the nine backfit clittria stated in 10 CFR 50.109.
Based on the artly sis it cer te summarizcc that it is possible to teckfit the guide (s)
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L. L. Jerde-3 JLil ! 6 1983 t' i ro6,)crity cf the affected containtarts of operating reactors without signi<
d'cbut herowerE modificttions or cost impact.
Therefore, the implementation rections ct Revisior. 3 to R.G.
1.35 and R.G.1.35.1 recommend use by all nuclear power plants having prestressed concrete containments with ungrouted tenccos.
Thtre ere a few reactors which are not adaptable to any of the guide l
ro 151unc.
These tre the reactors which were licensed before publication of Levision 1 of F:.G.1.35.
Hence, application of guides to these reactors should i
be ruiuatec on e case-by-case basis as indicated in a cover letter to be issuec with the propcsed regulatory guides (Enclosurc 8).
EllATICf. TO TECHNICAL STECIFICATION At indicatto in Table 4 (Enclosure 5), the technical specificatinns of eighteen (crtainmertt are basec on the draf t versions of these guides (published in 4ril 1H5).
Enclotute 6 points out that a copy of sample technical specificetiou en availab4 upun request.
IMrtC 0F llc del,' /* FARLEY I In Februar) 3L0, when this guide package was about to be sent to CRGR, an incident of vertical tendor enchor heao failures occurred at Unit 2 of Joseph M. Farley huclear Fower Plant, it was decided to postpone further processing ci the packace ur til the incident was eveluated and considered in Revision 3 cf the cuide.
The deteils of possible causes of the occurrence and the actions trhn (including the guide revision) to alleviate such occurrences in the future are oiscussed in Enclosure 6.
REL ATI0f: 'D INDUSTLY STANDARD
- r Lccember Sff, the Subsection lWL of ASME Section XI Subgroup on " Inservice inspectich of huclear Power Flant Components" was published.
Subsection IWL ceals with the inservic( inspection of prestrested concrete containmcrts with greased tendons.
With minor exceptions, its requirements parallel the positions in tbe proposed Lev. 3 of R.C. 1.35.
The requirements of Subsection lWL will be addrest (c: by the NRL staff through their incorporation in 10 CFR 50.55(a).
However, the IWL requirements will not be incorporated into 10 CFR 50.55(a) until all nuclear power plants with prestressed concrete containments have conferred to the seine positior: in revised R.G. 1.35.
This will provide a period of experience rith the voluntary use of these positions before they become mandatory in 10 CFR 50.55(a).
CONCLUSION As previously stated the guides art basically clarificatiens and improvements n' the previous FosItient, and they co not include any new generic require-rents.
The guides were reviewed by ACRS Subcomrrittee on Regulatory Activi-ties en June 12, 1984 The ACRS concurred in the regulatory positions of the guices.
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JUL 2 s 1999 E... :crcer 4
Pcr ibrthei 1rif t tratior, cr. it.e revier reckage, contact H. Graves, Task Leader, structural and Soisr.;c Ergir.eerir.g branch (492-3613).
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c Eric S. Beckjord, rector Office of f.uclear gelatory Research Enclosurtt:
1.
Lev. 3 of I.C.1.35 -
Iriservice inspection of Ungrcuted Tendens 2.
R.C. 1.35.1 -
Dett rrining Frestressint Forces 1.
Pct 411c Cerrents Lettert en l'raf t of I..C.1.35 - Rev. 3 and R..G. 1.3L.1 t.
f.esclutici t' Public Conments on R.C. 1.35 Rev. 3 end R.G. 1.35.1 E.
Draf t HUREG/Ck /*1? "Regulttery Analysis of f,.C. 1.35" 6.
Irciart of Tencon / nchor th:ac' f tilures ut Farley-?
l'UPEG/CI:-1719. "Eva1Letion cf insersice Inspection of Greased Ir(stressing Tencons" 6.
P((Llotory Glide Cover Lttter cc:
- 0. Cctren, AE00 F. Gii',erpie, NPP
Euclosure 3 REVISION 3 TO REGULATORY GUIDE 1.35 INSERVICE INSPECTION OF UNGROUTED TENDONS 1 IN PRESTRESSED CONCRETE CONTAINMENTS A.
INTRODUCTION General Design Criterion 53, " Provisions for Containment Testing and Inspection," of Appendix A, " General Design Criteria for Nuclear Power Plants,"
to 10 CFR Part 50, " Domestic Licensing of Production and Utilization Facil-ities," requires in part that the reactor containment be designed to permit (1) periodic inspection of all important areas and (2) an appropriate surveil-lance program.
This guide describes ~a basis acceptable to the NRC staff for I
develeping an appropriate inservice inspection and surveillance program for ungrouted tendons in prestressed concrete containment structures of lioht-water-cooled reactors.
Tne Advisory Committee on Reactor Safeguards has been consulted concerning this guide and has concurred in the regulatory position.
B.
DISCUSSION Following the issuance for public comment of the draft Rev. 3 of this regulatory guide and of the accompanying regulatory guide 1.35.1 in April 1979, the NRC Office of Research awarded a contract to Oak Ridge National Laboratory (ORNL).
The work scope included the evaluation of actual inspections performed by licensees and the-methods of implementing the Revision 2 of this guide, and understanding the opinions and problems of utilities, A/Es, vendors, etc., relating to the prior regulatory guide.
The contractor also considered the pertinent portion of the Jan. 1982 drsft version of " Inservice Inspection of Concrete Pressure Components" developed by a 1For the purpose of this guide, a tendon is defined as a separate continuous multiwire or multistrand tensioned element anchored at bcth ends to an end anchorage assembly.
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RG 1.35-
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Working Group of ASME Section XI in making his final suggestions for modifying the guide.
These suggestions are published in NUREG/CR 2719.2 Revision 3 of the guide has been revised to reflect public comments, suggestions from ORNL, and additional staff review.
The following discussion e> plains and clarifies the regulatory positions in this guide.
Regulatory Position 1 - This provides a general description as to the applicability of the guide, frequency of inservice inspections, and inspections when there are two containment $ at a site.
Regulatory Position 2 - This delineates the mathed of determining sample size and emphasizes random sampling.
If random sampling can not be assured, it is acceptable to select representative samples from between the pairs of buttresses and from various heights.
However, the samples for each inspection may be selected any time prior to the inspection.
Since inspections can bo performed when the plant is operating, there may be certain areas where inspec-tion of a randomly selected tendon might result in some radiological exposure to the inspecting personnel.
The position provides for substituting a readily accessible tendon for such a tendon.
Regulatory Position 3 - Describes the areas ard extent of visual examina-tions during each inspection.
Regulatory Position 4 - This position delineates the criteria for performing prestress monitoring tests.
Regulatory Position 5 - This states the extent and scope of tendon mate-rial testing.
Regulatory Position 6 - Items are listed that should be considered in the inspection of sheathing filler grease.
In order to assess the potential grease leakage, a recommendation is made to compare the amount of sheathing filler grease removed with that being replaced.
Regulatory Position 7 - The individual criteria for evaluating inspection results are discussed as follow:
2 NUREG/CR 2719 " Evaluation of Inservice Inspections of Greased Prestressing Tendons," by J. R. Dougan, Oak Ridge National Laboratory, September,1982...
Available from the Division of Technical Information and Document Control, U.S. Nuclear Regulatory Commission, Washington, DC 20555.
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7.1 Pre', tress monitoring criteria are developed to ensure that any signs of systematic tendon force degradation are detected and investigated.
Acceptance of 95% of the predicted force for two tendons out of three f
in 7.1.3 is a slightly relaxed criterion from the previous issue of the guide.
It should be recognized, however, that the primary objective is to compare the treasured tendon forces against the predicted forces at the time of the lift off testing.
Regulatory Guide 1.35.1 provides guidance in establishing the predicted forces.
A provision is added to check the average of measured forces against the minimum required force in an average (hypothetical) tendon in a group.
This provision is added as a result of a suggestion in NUREG/CR 2719 and in public comments.
It should be recognized that each individual tendon i
force (measured) will have to be modified to reflect the condition of an f
everage tendon.
The contributing modifying factors would be the difference in installation forces and in the elastic shortening losses, assuming the tirse dependent characteristics to remain essentially the same for the group of tendons.
The loss of prestress due to creep and shrinkage of concrete and stress relaxat4on of the tendon steel are time dependent and are predicted on such a basis.
The predicted tendon force is represented by a sloped line in a semi-logarithmic graph.
The trend of the actual effective tendon force is obtained by joining the points on the graph representing the measured ten-don forces in two or more surveillances of the same tendon or tendons in a group.
By extending the trend line, one can determine when the effective tendon force will be below the minimum required.
7.2 The position provides a means of tracking elongations during lift off test-ing.
The 10% tolerance in elongations at specific loads of retensioned tendons should include the effect of differential friction (due to fully greased vs. coated tendons), and errors attributed to calibration, measure-ment procedures and equipment, t
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RG 1.35 L
1 7.4 Detailec guioance for acceptability of the results of the grease examina-tion 11 provided.
The incident of tendon anchor need failures at Farley demonstrated that the water (free) in grease was the main source of hydrogen for hydrogen stress cracking of high hardness anchor heads.
High hardness anchor heads are used in large size tendon systems (i.e., 1750 tons).
The small size
(<750 tons) tendons have not exhibited such characteristics.
Hence two limits for water are provided.
It should be recognized that the limits are not the threshold limits for providing distress in anchor heads.
When these limits are exceeded, it is advisable to detension the tendon and l
look for cracts on the shim side of the anchor heads.
An assessment of a base number for filler grease has been proposed for new l
grease in ASME Section Ill, Div. 2, and for new and old grease in ASME Sec-tion XI.
The grease used in many operating plants tends to have a low base number (:5).
The newer grease formulations tend to have base numbers in excess of 20.
Hence. two acceptance limits have been provided.
At least two plants that implemented the detailed grease examination cri-teria experienced problems with the void limit of 5%.
Further inquiry into the matter revealed that when the injection pressure was very high (twice the pressure used during installation of grease) the amount of grease re-placed was 10 to 15*, higher than that removed.
The staff discourages this practice, as there is a likelihood of tearing the sheathing joints at such pressures, opening a way for grease to seep into the concrete.
- Hence, regulatory position 7.4 has been revised to reflect this consideration.
The staff will use the provisions of the gui M
vt 2d in Section D of the guide.
The staff encourages the liceti.
- ating plants to review their existing tendon inservice inspet.....
sms Cod evaluate-i them from the standpoint of operating convenience,.
/ improvements, and cost reduction potential.
Licensees should ado; Juide revision in their entirety, not just segments, whtn formulating i.neir inservice 03/30/89 4
inspection programs.
Tne staff recognizes that in some older plants (plants operating before initial issuance of R.G. 1.35,1974) complete adoption of all provisions of the revised guides may not be feasible withot.: extensive retrofitting.
In those cases, the licensees are aavised to present their revised inservice inspection programs with any necessary e>emptions from the specific provisions of the guides.
r C.
REGULATORY POSITION 1.
GENERAL
- .1.
ine intervice inspection program described in this guide is appli-ceri t tc tN fo'iowing types of prestressed concrete containment structures:
1.1.1.
Prestressed contr0te containments having a shallow-dome to:< on cylindrics1. alls witn tne cylinder prestressed in hoop and vertical airections and the come prestressed by three families of tendons at 60.
1.1.2.
Prestressed concrete containments having.a hemispherical-roof en cylincrical walls with two f amilies of inverted U tendons placed come at 90' to each cther and hoop tendons located in the cylinder and dome, 1.E.
For containments that differ from these two types, the program de-scrit.ed should serve as the basis for the development of a comparable inservice inspection program.
- 1. 3.
The inservice inspection should be performed I, 3, and 5 years after the iritial structural integrity test (ISIT) and every 5 years thereaf ter.
1.4.
Containments should be designed and constructed so that the prestress-ing anchor hardware is accessible for inservice inspection.
- 1. 5.
All containment structures with ungrouted tendons should be inspected in accordance with this guide.
However, the liftoff force comparison may be performed as shown in Figure 1 if any two containments at the same site are shown to satisfy all three of the following conditions:
a.
The containments are identical in all aspects such as size, tendon system. design. materials of construction, and method of construction.
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.i b.
If their ISITs are performed within two years of each other.
c.
.If there is no unique situation that may subject either containment to a different potential for structural or tendon-deterioration.
The visual and filler grease inspection of both containments should be performed according to regulatory position C.3 and C.6 respectively at frequencies described in regulatory position C.I.3.
2.
SAMPLE SELECTION l
2.1.
For the inspections at 1, 3, and 5 years, four percent of the population of each group (vertical, hoop, dome, and inverted V) of tendons should be selected randomly with a minimum of four tendons'from each group.
The sample si:e f rom any group need not exceed ten.
- 2. E If the inspections performed at 1, 3, and 5 years indicate no abnormal cerracat'o" o' int post-tensioning system, two percent of the population of each group (ver ical, hoop, dome, and inverted U) of tendons or five tendons, which--
evt' is less. ray t4 selected for the subsequent inspection with e minimum of three tendant for each group.
l 2.3.
The fraction obtained as a percentage of a tendon population thould be rounced off to the nearest integer.-
2.4.
The tendons for inspection should'be randomly selected from each group during each inspection.
However, to develop a history and to correlate the observed data, one tendon from each group should be kept unchanged after the initial selection, and these should be identified as control tendons.
- 2. 5.
If, owing to plant operating conditions, a randomly selected tendon from a group cannot be inspected during a scheduled inspection-another sample from the grc,up should be randomly selected.
The tendon that was selected but not inspected should be inspected during the following plant _ shutdown and accepted (or rejected) on an individual _ tendon basis.
- 2. 6.
lendons, except the control tendons, that had been inspected and found intact curing previous inspections should be excluded from the group population during subsequent inspections.
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2.
VISUAL INSPECTION j
3.1.
The exterior surf ace of the containment should be visually examined te cetect areas of large spall,3 severe scaling, D-cracking in an area of 25 sq.
ft, or more, other surface deterioration or disintegration, or grease leakage.
3.2.
Tendon anchorage assembly hardware (such as bearing plates, stressing wasners, shims, 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, or removal of grease caps.
- 2. 3.
Bott on: grease caps of all vertical tendons should be visually inspec-te to ottect grease leakage or grease cap deformations.
Removal of grease caps is not necessary for this inspection.
3.4.
Concrete surrounding visually inspected tendon anchorages should also be enetted visually f or indications of abnormal material behavior, 4.
PRESTRE55 M3NITORING TESTS Tencons selected as described in regulatory position C.2 should be subjected to liftoff or other equivalent tests to monitor their prestress.
Additionally, the tests should include the following:
4.1.
One tendon, randomly selected from each group of tendons during each inspection, should be subjected to necessary detensioning in order to identify broken or damaged wires or strands.
4.2.
The simultaneous measurement of elongation and jacking force during retensioning should be made at a minimum of three approximately equally spaced levels of force between zero and the lock-off force.
3The terms "large spall," " severe scaling," "D-cracking," " deterioration" and
" disintegration" are as defined in the American Concrete Institude Publication, ACI 201.1R-6E, " Guide for Making a Condition Survey of Concrete in Service."
The publication can be obtained from the American Concrete Institute, Redford Station, Detroit, Michigan 48219.
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e 5.
TENDON W 'EPIAL TESTS AND INSPECTIONS E.2.
A previously stressed tendon wire or strand from one tendon of each ge r.:: thoulc be remo'.ed for testing a.)d examination over the entire length to ceter.mine if evidence of corrosion or other doleterious effects is present.
At each successive inspection, the samples should be selected from different tendons.
The tendon selected for the purpose may be the same as that selected for the purpose of detensioning.
In addition, all wires or strands identified as broken should be removed for tensile testing and visual examination.
5.2.
Tensile tests should be made on at least three samples cut from each removed wire or strand one a' each end and one at mid-length.
The samples should be the maximum length practical for testing and the gage length for the measure-mert of elongetier sbo dc; be in accordance with the relevant ASTM specification.
N ic H oving id ermstier should be obtained from each test:
6.
Tie'c strengtt' O.
Ultimate tensile strength c.
Elongation at ultimate tensile strength E.
INSPECTION Or r1LLER GREASE A sample of sheathing filler grease from each of the sample tendons should be taken and analyzed to determine water content (ASTM D95),4 reserve alkalinity (ASTM 0974).5 and the concentrations of water-soluble chlorides (ASTM D512),
. nitrates (ASTM D992), and sulfides (APHA 428).6 Additionally, the amount of sheathing filler grease removed and replaced should be compared to make an assessment of grease leakage within the structure.
4 ASTM Standards can be obtained from the American Society of Testing and Materials, 1916 Race Street, Philadelphia, PA 19103 5 Modified by Note 3 of Table CC-2422-1 of the ASME B&PV,Section III, Div. 2, 1982 Winter Addenda.
6 APHA Standard can be obtained from American Public Health Association, 1015 Eighteenth Street, NW, Washington, DC 20036 1
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RG 1.35 i
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7 EVALUATION Or INSDECTION RESL'LTS 7.1.
The prestressing force measured for each tendon in the tests described i
ir regulatcry potition C.4 should be compared with the limits predicted for the time of the test.
Regulatory Guide 1.35.1 provides further information on the determination of these limits.
7.2.1.
If the measured prestressing force of the selected tendon in a group lies above the prescribed lower limit, the liftoff test is considered to be a positive indication of the sample tendon's acceptability.
7.1.2.
If the measured prestressing force of a selected tendon in a i
proup lies between 95% of the prescribed lower limit and 90% of the prescribed lower limit, two additional tendons, one on each side of the first tendon should be checked for their prestressing forces.
If the prestressing forces of esth cf the se ond and third tested tendons are above 95% of the prescribed 1cter lif ts fc: the tendons, all three tendons should be restored to the reovired level et integrity and the tendon group should be considered as acceotable.
7.1.3.
In regulatory position 7.1.2, if the prestressing force of any twc adjoining tendons falls below 95% of the prescribed lower limits of the tencons, auditional lift-off testing should be done to detect the cause and e derit of such occurrence, The condition should be considered as reportable.
7.1.4.
If the measured prestressing force of the selected tendon lies below 90% of the prescribed lower limit, the defective tendon should be completely detensioned and a determination should be mau, as to the extent and cause of such occurrence.
Such an occurrence should be u ns11ered as a report-able condition.
l 7.1.5 If the averape of all measured tendon forces for each group (corrected for average condition) is found to be less than the minimum require'd prestress level at anchorage location for that group, the condition should be considered as reportable.
i 7.1.6 If from consecutive surveillances the measured prestressing i
forces for the same tendon or tendons in a group indicate-a trend of prestress-L loss larger than expected and the resulting prestressing forces will be less than the minimum recuired for the group before the next scheduled surveillance.
I 03/.10/89 9
5:::i t i er.L1 Mf t-off testing should be done so as to determine the cause and
( dent of sucn occurrence.
The condition should be considered as reportable.
- 7. 2.
During dttensioning and retensioning of tencons (regulatory position 4.2), if the elongation correbponding to a specific load differs by more than 20?. f ron that recorded during installation of tendons, an investigation should be maae to ensure that such difference is not related to wire failures or slip of wires in anchorages.
Such a condition should be considered as reportable.
7.3.
Failure in the tensile test at a strength or elongation value less than the minimum requirements of the tendon material should be con-sidered as reportable.
Other conditions found by visual examination of wire P
or strand which wou ) indicate corrosion (metal reduction) should be considered as reportabh i
7.4,
- eportat.le conditions f or sample sheathing filler grease include
a.
Water content exceeding 10% by wt.
t.
Chlorices exceeding 10 ppm c.
Mtrates exceeding 10 ppm c.
Sulfides exceeding 10 ppm Reserve Alkalinity less than 50% of the installed e.
(Base Numbers) value or less than zero when the installed value was less than 5 f.
Amount of grease replaced exceeds 5% of the net duct volume, when injected at the original installation pressure.
g.
Grease leakage aetected during general visual examination of the containment exterior surface.
h.
Presence of free water.
8.
REPORT]NG TO THE COMMISSION t
The reportable conditions of regulatory position C.7.1.3, C.7.1.4, C.7.1.5, C.7.3 or C.7.4 could indicate a possible abnormal degradation of the contain-ment' structure (a boundary designed to contain radioactive materials).
Any such condition should be reported to the Commission in accordance with the recommended reporting program of Regulatory Guide 1.16, " Reporting of Operating Information - Appendix A Technical Specifications."
03/30/99 10 RG 1.35
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'D.
IMPLEMENTATION-The' purpose of this section is to. provide.information:to' applicants'and licensees regarding the NRC staff's!planc for using this regulatory. guide.
Exceptinthosecases~inwhichLtheapplicantor: licensee:prdposesan
~
acceptable alternative methodLfor, complyingLwith specified portions of the Commission's regulation, the methods! described herein should be used in the evaluation-of all nuclear power plantsfusing prestressed concrete containments with ungr6uted_ tendons!
1
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s08/26/88 Ell?
RGl1.35N
i I
o RM N
e-SAMJLESIZECRITERVA(SEEREGULATORYPOSIT10N.C.2) 4%
2%
01 5
1,0 2p 30 TIME AFTER INITIAL STRUCTURAL INTEGRITY TESTING OF CONTAINMENT, YEARS l
(Liftoff Testing Schedule, Containment No. 1) i 4
1 2 YEARS (MAXIMUM)
-+
l ma-01 5
15 25 35 i
e a e
a i
3 TIME AFTER INITIAL STRUCTURAL INTEGRITY TESTING OF CONTAINMENT, YEARS.
(Liftoff Testing Schedule, Containment No. 2) i l
i i
E l
3 Figure 1.
Schedule of Lfftoff Testing for Two Containments at a Site (See Regulatory Position 1.5) i j
l
Regulatory Analysis A separate regulatory analysis was prepared for the revision to this regulatory guice.
The regulatory analysis is contained in NUREG/CR-4712 " Regulatory Analy-sis of Regulatory Guide 1.35 (Revision 3, Draft 2) - In-Service Inspection of Ungrouted Tendons in Prestressed Concrete Containments," and is available in the Commmission's Public Document Room, 2120 L Street, NW., Washington, DC.
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03/30/89 13 RG 1.35
i f
Do r nn.ep
.;3me..
f hG 1,35 hequestor's ID:
FDNNIE i
Author's Netne:
}!!LL/GRAiT.5 Document Comments:
Pil ECS 5/12/F9 please keep sheet with document s
i 4
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Docum*nt flame; RG 1.35A Ee000tt0r'L 10:
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Author's fian,e:
)
HILL /GEAVES Document Comments:
PH ECS 8/26/88 mim D1D'd to NRCRES_POMS 10/4/88 4
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Enclosure,2 i
i REGULATORY GUIDE 1.35.1 DETERMINING PRESTRESSING FORCES FOR INSPECTION OF PRESTRESSED CONCRETE CONTAINMENTS-A.
INTRODUCTION General Design Criterion $3, " Provisions for Containment Testing and Inspection," of Appendix A, " General Design Criteria for Nuclear Power Plants,"
to 10 CFR Part 50, " Domestic Licensing of Production and Utilization Facil-ities," r,equires, in part, that the reactor containment be designed to permit (1) periodic inspection of all important areas and (2) an appropriate surveil-t lance program.
Regulatory Guide 1.35, " Inservice Inspection of Ungrouted Tendons in Prestressed Concrete Containment Structures," describes a basis acceptable to the NRC staff for developing an appropriate inservice inspection and surveillance program for ungrouted tendons in prestressed concrete con-tainment structures of light-water-cooled reactors, This guido expands and 1
clarifies the NRC staff position on determining prestressing forces to be used for inservice inspections of prestressed concrete containment' structure.
The Advisory Committee on Reactor Safeguards has been consulted concerning this guide and has concurred in the regulatory position.
B.
DISCUSSION The inspections of prestressed concrete containment structures (with l
greased or grouted tendons) are performed with the objective of ensuring l
that the safety margins postulated in the design of containment structures are not reduced under operat4ng and environmental conditions.
Of particular j
concern in the case of prestressed concrete containment structures is the possible degradation of the prestressing tendon system due to corrosion.
09/07/88 1
t r
The recommended inservice inspection programs of Regulatory Guides 1.35 and I. E are formulated to achieve this basic objective.
The extent to which the orograms can perform their intended function depends on the method of their-implementation.
Review of reports of some of the inspections performed by licensees on greased tendons indicates that there are various ways (simple but imprecise) of combining the losses in prestressing forces, giving a wide band of toler-ante in comparing the measured results.
Such a practice is not acceptable to the NRC staff because a real and substantial degradation of the tendon system may remain undetected.
Regulatory Guide 1.35 recommends the comparison of measured prestressing forces with the predicted forces of randomly selected tendons.
The predicted forces at a given time are based on the measbrement of prestressing forces during installation rrinut the losses in the prestressing forces that were predicted to have occurred since that time because of material and structural characteristics.
As various complex interacting phenomena are involved in the predic-tion of these losses, the chance is small that the measured prestressing force will agree quite closely with the predicted value.
Hence Regulatory Guice 1.35 recommends the determination of bounds (upper and lower) of pre-stressing force as a function of time.
Revision 1 of Regulatory Guide.l.90 ciscusses this aspect briefly, as it is also relevant to the recommended inspection alternatives in that guide.
This supplementary guide is intended to clarify the NRC staff's posi-tion on the construction of tolerance bands for groups and subgroups of tendons so tnat the small-sample inspection program of Regulatory Guide 1.35 can provide better confidence in the integrity of prestressing tendons.
The regulatory position of this guide recommends the factors that need te be evaluated and a method of using these factors in the construction of a l
tolerance band for a group of tendons having approximately the same time-dependent characteristics.
The methods for evaluating the effects of these L
factors are discussed in this section of the guide.
l The " Code for Concrete Reactor Vessels and Containments" (Ref. 1) enu-9$h merates the factc*! to be considered in determining the effective prestress 1
l 09,07/65 2
(see Section CC-3542 of Ref. 1).
However, it does not provide detailed consiceration of these factors.
The methods suggested here are based on a sea *ch of relevant literature and on information provided to the NRC staf f by applicants and their contractors.
A list of relevant references is pro-viced in Appendix A.
However, the listing of these references does not constitute a blanket endorsement by the staff of their content.
1.
MEASUREMENT OF PRESTRESSIN3 FORCE In general, the requirements of Section CC-4464 of the Code (Ref. 1) are adequate for measuring and verifying the seating force.
However, the allowable discrepancy of.110% of the force calculated from the measured elongation and that obtained by a dynamometer or a pressure gage is excessive.
If the load / elongation curve for the tendon system is based on a thorough evaluation of the prior tests using tensioning and measuring equipment similar to that proposed for use in construction, such a high discrepancy level is un arranted.
The NRC staff believes that this discrepancy level should not exceed tSt.
This recommendation is in agreement with the practice adopted by the American Concrete Institute (Ref, 2) and the Post-Tensioning Institute (Ref. 3).
During an inservice inspection, the lif toff (or load cell) measurements are compared against the initially measured forces.
If the equipment used to make the measurements during the tensioning operation and during an inservice inspection have identical characteristics, the errors introduced by contributing factors such as reading accuracy or friction in the jacking system can be reduced to a minimum.
The objective should be to use well-calibrated, accurate measuring equipment with sufficient sensitivity during both construction and inservice inspections to reduce the comparative errors
]
due to measurement to a negligible amount.
2.
DETERMINATION OF PRESTRESSING LOSSES The losses in prestressing force after the application cv the force can be classified as follows:
l 1
09/07/88 3
i a.
Initial losses due to:
Slip at anchorages Friction between the tendon and the tendon duct at areas of contact Elastic shortening and effect of sequence of stressing the various tendons.
b.
Time-dependent losses due to:
Shrinkage of concrete Creep of concrete Relaxation of prestressing steel, c.
Other losses due to:
Failure of tendon elements due to corrosion or material deficiency.
Effects of variations in temperature.
These losses are discussed briefly in the following paragraphs together with the methods of determining their magnitude.
The discussion pertains only to the prestressed concrete containment structures typically used for i
light-water reactors.
For containments that operate at sustained high temper-atures, the time-dependent characteristics need.to be evaluated at corres-pondingly high temperatures.
2.1 Initial Losses 4
Loss due to slip at anchorages should be determined based on the prior experience and the testing history of the prestressing system to be used.
The influence of slip at anchorages should be allowed for in the computation of initial prestressing forces.
Coef ficients for determining the losses due to friction should be deter-mined before the start of the installation and should be verified'and modified l
(if necessary) during the construction.
In comparing the liftoff (or load cell) forces for ungrouted tendons, friction loss need be considered only for the fixed ends of tendons that have been tensioned from one end.
For the purpose of inspection (or monitoring) of ungrouted tendons, consideration of this loss.can be avoided by comparing forces at tensioned ends.
09/07/88 4
i If all tendons in a specific direction (hoop, vertical, etc.) are prestressed simultaneously, the loss of prestressing force due to elastic shortening (Fg g) can be given by:
F I LES
- l E + A,E,
- A
+ A)E) + Add EE en g pp where F,
is the initial seating force A
is the net concrete area cn A,A,A),Ad are the areas of reinforcing steel, prestressing 3 p steel, liner, and duct, respectively E.E,E,E),Ed are the moduli of elasticity of concrete, reinforcing e 3 p steel, prestressing steel, liner, and duct, respectively.
However, the number of tendons to be prestressed is large, and the prestressing operation is performed in a systematic sequence so that the structure is more or less symmetrically prestressed during the process.
Thus the first tendons that are tensioned undergo a full loss due to the subsequent elastic shortening of the structure, while the tendons that are tensioned last undergo almost no loss due to elastic shortening.
For all practical purposes, the loss of prestressing force due to elastic shortening can be estimated and accounted for by using the following linear relationship:
n "r
ILES = 7 F LES where N represents the total number of tendons in a particul6r direction, n represents tne sequential number of a randomly selected tendon to be tensioned in that direction, and n represents the number of tendons to be tensioned i
r l
after the n tendon, i.e., n = N - n.
r l
If the sequences of tensioning tendons in different directions are intermingled, the stresses produced in one direction by the tendons tensioned in the other directions must be considered.
09/07/88 5
Thus it is essential that the complete history of tensioning a tendon be receroed, including its seating force F,, the number of tendons tensioned before and after it, and any provision to account for the slip at anchorages.
The modified initial prestressing force F at the tensi med end can be calcu-4 lated and receroed as:
F"=F,"-T}3 -F ggg where F is the loss of prestressing force due to slip at anchorages.
ggg 2.2 Time-Dependent losses 2.2.1 Effect of Shrinkace of Concrete The schedule of construction of a typical prestressed concrete containment is such that a substantial portion of the expected long-term shrinkage will have taken place befort the structure is prestressed.
Reference 4 develops formulas for precicting the long-term shrinkage based on the assumption that the shrinkage approximately follows the laws of diffusion and supports the formulas by experimental investigation.
An appropriate extrapolation of these formular (for the volume to surface ratio of the structure in excess of 24 in. (60 cm) and the contributing shrinkage as that occurring 100 days after the average time of construction of the structure) would
-6 yield a value of 100 x 10
, which is considered to be a reasonable value at a temperature of 70 F (21 C) and a relative humidity of 50%.
The safety 1
analysis reports of several plants indicate that a 40 year shrinkage value 0
of 100 x 10 has been used by the applicants.
l l
This value, however, needs to be modified to account for the signif-icantly higher shrinkage in a low-humidity environment and the significantly lower shrinkage in a high-humidity environment.
Table 1 provides typical l
shrinkage values that could be used for computation of prestressing losses due to shrinkage.
11urkey Point, Midland, Bellefonte, Three Mile Island.
09/07/Bo 6
s 2.2.2 Effect of Concrete Creep One of the most significant and variable factors in the computation of time-dependent losses in prestressed concrete = containment structures is the influence of concrete creep.
Creep is thought to consist of two components:
basic cre6p and drying creep.
Drying creep, also sometimes termed stress-iacuted shrinkage, is thought to be due to the exchange of moisture between
'the structure and its environment.
Its characteristics are considered to be similar to those of shrinkage, except that they represent an additional moisture movement resulting from the stressed condition of a structure.
The amount of drying creep depends mainly-on the volume to surface ratio of '
the structure and the mean relative humidity of the environment.
For pre-stressed concrete containment structures having a volume to surface ratio in excess of 24 in. (60 cm), the relative influence of drying creep (compared te basic creep) is negugible as indicated by Figure 9 of Reference 4.
The significant parameters influencing the magnitude of basic creep can be summarized as follows:
1.
Concrete mix:
cement and aggregate type;. proportion of cement,.
water, and aggregates; and the influence of admixtures.
2.
Age at loading.
The basic creep value ir e fb.. tion ]f the degree of hydration that has taken place at the time of it,!ing.
3.
The magnitude of the average sustained stress.
j 4.
Temperature.
Almost all investigators support the assumption that basic creep varies.
linearly with the intensity of sustained stress, as long as the average stress level in the concrete is not greater than 40% of the ultimate strength of the concrete.
The specific creep is thus defined as the ratio of total creep to the average stress intensity.
A literature review of the effect of temperature on. basic creep-(sealed or water-stored concrete specimens) is compiled in Reference 6.' The average y
temperature of a prestressed concrete containment structure could ' vary between 4
40 F (5 C) and 100 F (38 C).
Basic creep is shown to vary linearly with tem-perature in this range of temperatures.
Hence if the basic creep is evaluated at approximately 70 F (21 C), it should represent overall deformation due to creep of concrete.
09/07/88 7
An acceptable method of determining basic creep at various times for a giver. concrete mix as a function of age at loading is provided in Appendix A to this guide.
The method is based on concepts and equations derived by
]
Hansen (Ref. 7) from a rheological model representing creep of concrete.
Referents 8 uses the method of Reference 7 in determining long-term creep for a given concrete mix.
Most investigators agree that there is no one formula that can be generally applicable in determining the long-term creep for various concrete mixes.
Hence Appendix A recommends a method of predict-ing the long-term basic creep from the results of short-term creep tests.
Other methods such as those described in References 9, 10, and 11 may be used if demonstrated to-be appropriate -for predicting long-term basic creep.
Short-term creep tests are generally performed during the construction of e nuclear power plant.
The extrapoleted treep values consistent with -
the average time of the loading of the structure may not be available during the preliminary design. stages.
A ronservative estimate of creep values may be obtained from previous experience or from. creep tests on similar concretes.
However, these values should be modified to estimate the tolerance band for the prestressing force to.be used fer comparison of the measured prestressing forces during inservice inspections.
The' modifications should include the extrapolated creep values in light of the actual averaDe age of the concrete at 1.ne Lime the containment is ' prestressed.
2.2.3 Effect of Relaxation of Prestressing Steel The stress relaxatien properties of prestressing steel vary with its chemical composition and thermal / mechanical treatment. Manufacturers should be able to supply the long-term loss in prestressing steel stress due to pure relaxation for the steel supplied.. Stction CC-2424 of Reference 3 requires a minimum of three 1000-hour relaxation tests for the prestressing steel proposed for use. There should be a:sufficietitmumber of data points in each of the three tests to extrapolate the '1000-hour pure relaxation j
data to the life of the structure. /o appropriate model (Refs. 12, 13, 14) should be selected for the determiration of the "best-fitting" line for the l
purpose of extrapolation, i
1 g
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09/07/8e E
2.3 Losses Due to Te Non Degradation Most applicants make allowance for breakge of wires on an overall basis as well as on a localized basis.
Such an alicvance in the design of the 1
containment would allow a breakage of few wires during construction without the-need for replacing these wires.
For a tendon with a few broken wires, care should be taken not to overstress intact' wires t' bring _the tendtn force to a prescribed value. -Instead, the tendon should be extended to the same
. level as other similar tendons (without broken wires).
The procedure will leave the tendon at a prestress level lower than the prescribed-(generally 70% of GUTS) level.
This is acceptable provided the desigr, includes an allow-ante for the breakage of wires,.
2.4 Effects of variations in Temperature Of particular importance for the purpose of comparing the prestress forces is the effect of differences between the average temperature of the structure during installation and that during inspections.
Localized hot-spots and temperature variations along the_ length of a tendon can cause variations in the force along the length of the tendon.
The differences between the coefficients of expansion or contraction of concrete and steel can also cause modifications of tendon forces.
These effects, as appropriate, should be considered in comparing the measured prestressing forces with the predicted forces.
3.
GROUPING OF TENM NE AND CONSTRUCTION OF TOLERANCE BAND l
The significant variable affecting the time-dependent prestressing force of tendons would be the effect'of concrete creep.
If the concrete mix characteristics and the curing conditions are assumed to be about the same during the entire period of construction of a containment structure, the parameters introducing variations in creep are (1) average compressive stress and (2) age of concrete at the time of prestressing.
For example, in a shallow-dome containment structure, if the design requires that the l.y l
l 09/07/85 9
meridional compressive-stresses.in the cylinder be half those in the hoop direction, the creep strains affecting the losses in prestressing would be proportional to their compressive stresses.
Similarly, at the time of pre-stressing, the dome concrete might have aged three months, while the cylinder 1
con: rete might have aged six months or more.
These parameters would affect the losses in prestressing forces in tendons and should be considered in grouping the tendons according to the similarity of their time-dependent characteristics and in prescribing the tolerance band for prestressing forces in these tendons.
These groups may be further subdivided into subgroups to account for the dif ferences in initial prestressing forces (f )-due to differences in i
j instantaneous elastic shortening during transfer.
To account for the differ-ences in initial prestressing forces F, a tabulation of F for each tendon j
in a group may serve the same purpose as subgrouping.
In short, the-intent cf any adopted procedure should be to track the individual prestressing forces as preciselv as possible with the current state of the art in predict-ine these forces, so that when a tendon is selected randomly during an inscection its measured values can be compared with its prescribed tolerance band.
a.
CONSTRUCTION OF TOLERANCE BANDS It is recognized that each of the factors affecting the time-dependent-i characteristics of tendon forces are subject to. variations.
To account for-these variations in prescribing the tolerance band, the following method is recommended:
Shrinkage.
Table 1 provides the 40 year shrinkage strains in relation to the humidity level at the location of the structure.
To allow for the as-sociated uncertainty in the assumed values, strain should be varied'by 120%.
The shrinkage strains at any time between the time of prestressing (consider zero shrinkage at t = 10 days) and 40 years can be estimated by considering l
shrinkage strain to vary linearly with the logarithm of time.
j Creep.
The creep strains at any time efter prestressing can be deter-mined !>y the method of Appendix A.
The high and low creep strains can be determined by increasing the extrapolated creep values by 25% and decreasing them by 15%, respectively (see Appendix B for illustrative example).
09/07/88 10 RG 1.35.1
l 4
Relaxation of Prestressing Steel.
Provide a A15%_ variation in relaxa-tion values obtained by extrapolation of 1000-hour tests.
The first inservice inspection-needs_to be performed one year after the Initial Structural Integrity Testing (ISIT) of the containment.
- Hence, the period of interest from the point of view of inservice _ inspection is nominally between one year and 40 years af ter. prestressing.
The upper and. lower bounds for prestressing forces at one year and _40 years after prestressing can be found by adding up the low and high. losses and subtracting them from.F.
For the purpose of constructing tolerance bands for various groups 'of tendons, it is sufficiently accurate to consider prestressing force to vary linearly with the logarithm of' time.
In lieu of the variations indicated above, the designer may use the con-servatively estimated design value as the base values for the time dependent factors.
In that case, the individual predicted tendon prestressing force at 1 year and 40 years can be determined using the base value as illustrated in-Appendix B.
The line drawn using these values should be considered as the lower bound.
The upper bound can be arbitrarily drawn by plotting a line parallel to the lower bound and starting at 0.93F$ at 1 year.
This method can be used for the operating plants.
The upper line of the tolerance band is not critical from a safety point.
of view.
However, this line allows the designer to establish a. maximum-variation line.
If the prestressing of a tendon lies above this line, it is prudent to investigate the measurement technique and the pattern of-losses in adjoining tendons.
C.
REGULATORY POSITION The following minimum standards should be followed'in design and construc-tion of prestressed concrete containment structures to ensure the appropriate.
implementation of inspection programs of Regulatory Guide,1.35 (revision 3).
1 l
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09/07/88 11 RG 1.35.1 w
1.
MEASUREPENT OF PRESTRESSING FORCE-l 1
The procedure of Code (Ref. 1) Section CC-4464 should be followed in measuring loads and extensions during tensioning, as supplemented by the following:
a.
A minimum of three readings of loads and extensions at approxi-mately equally spaced levels of load should be recorded before the final seating of the tendon, b.
If'the discrepancy between the measured extension at the final seating. force and-the extension determined from the average tendon force along the length of a tendon exceeds 5%, the cause of such discrepancy:and l
the corrective actions taken should be recorded.
The extension corresponding to the-average tendon force may be determined by calculation or from a tendon loac-extension diagram provided by.the tendon manufacturer.
2.
DETERMINATION OF PRESTRESSING LOSSES s
f 2.1.
The initial seating force (F,) should be modified to allow for the following influences:
A known amount of slip at anchorage (if any) a.
-b.
.A loss due to elastic shortening of the structure, including.the effects of sequence of tensioning by the method discussed in Section B or by any other appropriate method.
c.
Influence of. wire breakage during construction.
The extent of wire breakage should not exceed the allowance'made in the design.
2.2.
A range (high and low) of expected time-dependent. losses at the end of the service life of the structure (generally 40 years), as well as those at one year after prestressing, should be established considering the
. variations in the following factors:
-The extent of shrinkage of the structure contributing to the a.
prestress losses.
Table 1 may be used for that purpose in the absence of specific data.
L l
09/07/88 12 RG 1.35.1 L
e t
f
~
b.
The effect of creep deformation'on~prestressing force. The method-of Appendix A or a similar method may be used to determine the creep I
deformation.
c.
The effect of relaxation of stress in prestressing tendons.
See Section B.2.2.3 for a recommended procedure, 3.
GROUPlflG OF TENDONS 3.1..The basic grouping of tendons for the purpose.of developing tolerance bands should consider:
qr 6.
the geonetric configuration of tendons with respect to the structure, e.g., vertical, hoop, dome, inverted U, and
- b..
the similarity in time-cependent= characteristics.
This may involve' divi. ding the above configuration groups into additional groups, 3.2. The basic groups may be' divided further into subgroups to account for the differences in instantaneous elastic shortening during the-transfer of prestressing force.
4
=C0ll5TRUCTION OF TOLERANCE BAND i
Tolerance bands for groups and subgroups of tendons should be constructed as discussed in Section B, q
These tolerance bands should be used for comparison of measured prestressing forces with the forces predicted for the time of-inspection.
i i
i 06/28/89 13 RG 1.35.1A-
D.
IMPLEMENTATION The-purpose of this section is to provide:information t9 applicants and licensees regarding the NRC staff's plans for'using this regulatory guide.
Except in those cases in which the applicant or! licensee proposes an acceptable' alternative method.for complying with specified portions-of the
-l r
Commission's regulation,-the methods-described herein should be used;in the evaluation of all nuclear power plants using prestressed concrete containments with ungrouted tendons.
06/2E/E9 14 RG 1.35.1A
J TABLE I P
VARIATION OF SHRINKAGE STRAIN WITH. RELATIVE HUMIDITY r
b-Mean Daily 40-Year Shrinkage Strain E
Relative Humidity -
Annual, %
Under 40 130-x 1076 i
-6 40 to 80 100 x 10 j
-6 Above EO 50 x 10 aMean Daily Reletive Humidities for various areas in the U.S. can be found from Map 46 of Reference 5.
bThese values are applicable to containments in which inside operating.
temperatures do not exceed 120'F (49 C) and that arg6 subject to the. ambient outside environment.
The maximum value of 130'x 10 may.be'substantially increased if the containment is exposed to a controlled dry high-temperatures environment after completion of prestressing.
t 09/07/88 15 RG 1.35.1
I t
APPENDIX A
~ DETERMINATION OF BASIC CREEP STRAINS FOR PRESTR'55ED CONCRETE-CONTAINMENT' STRUCTURES
~
Recommended creep formula
-h(t-t'),.
n t
- [,.
-)+Blog10[o
=.A(1 e
c whe.e r
I t=
time _(after average time of concrete placement) when creep value-is desired, days i
time of loading after average time of concrete placement, days t =
g i
f =
average sustained concrete stress
~t c
'c = creep strain at time t-when the age'of concrete at' loading is t o A,B are coefficients to be determined from tests To determine the value of constants A and B, the following_short-term creep tests are recommended:
Age at loading Minimum Observations at t
t 1
1 -
.t t
t o
0 1
2L 3
4 5-30 30 31
.45 - 90 150. 210 90 90 92 110 150 210 270 180 180 185 210 240 300 360 m
'i
}
1 i
?
09/07/88 16 RG 1.35.1
4 The coefficients A and B should be determined from creep _ strains at t,
i y
2' t, 1. an:: t for each t by plotting the measured' specific creep (c )
1 i
4 5
0 e
C
-against t on a semi-logarithmic paper (see Fig. 1).-
The value of B would i
essentially remain the same for all values of t.
The v'alue of A for various i
0 values of t0 can be determined as shown in Fig. 1.-
For t0 values greater than 365 days, the A value determined at 365 days should be used.
The short-term creep tests should be performed according to the test 1 method of Ref. 15.
To make the creep test results representative of creep deformations in a containment structure,-the referenced test method should be used with the following specific provisions:
a.
Section 3.1:
The length of, specimens should be 16 1 1/16 in.
(40 : 0.36 ct).
b.
Section 3.2:
The concrete mix should.be the same as that proposed for use in the construction of the containment, c.
Section 3.3:
Companion identical specimens corresponding to each t may be used to observe the deformations'of. unloaded specimens.
o d.
Section 4,2:
Mass curing (sealed specimen) conditions should be i
used during storage and testing.
(The method used for the "a's' cast" condi-tion in Reference 16 is a good example.)
I e.
Section-5.1:
Load the specimens to maintain a sustained stress of 30% of the design compressive strength of concrete.-
f.
Section 6,1:
Subtract the instantaneous elastic strain taken at q
time t and the strain on the unloaded' specimen'from-the' subsequent total o
strain measurements to arrive at creep strain (c )*
c i
1 i
09/07/88 17 RG 1.35.1
4 f
APPENDIX B CONSTRU,CTION OF TOLERANCE BAND (EXAMPLE)
Consicer the-following values as obtained for time-dependent influences:
Time-Dependent Base Value at 1 Year 40 Years Factors 40 Years High-Low High Low Shrinkage (t ) @ 70%
RelativeHumidity x 106 100' 72 50 120 80 Variation:
120%
e Creep (T }
- 30(
C for t = 180 days g
per psi 0.3 0.193 0.073 0,375 0.255 per LPa 2,05 1.32' O 50
.2.56 1.75 Variation:
+25%
-15%
Stress Reiaxation of Prestressing Steel in % of F 7
- 5. 8 4.2 8.1.
5.9-j Variation:
215%
I i
i l'
l 09/07/88 18 RG 1.35.1
APPENDIX B (Cont'd)
Prestressing Losses in % of F 4
Assume Eps = 26 x 103 ksi'(193 x 103 MPa) fps = 168 ksi (1.158 x 108 HPa)
Time-Dependent Base Value at 1 Year 40 Years Factors 40 Years High.
Low High Low Shrinkage i
xhx100 1.7 1.2 0;8 2.0
'1.3 c 3 Creep for f = 1500 psi I
C (10350 kPa) xf x
.x 100 7.5 4.8 1.8 9.4 6.4 c
C Stress-Relaxation of Prestressing Steel 7
5.8 4.2 8.1 5.9 Total Losses 16.2 11.8 6.8 19.5 13.6 Remaining Prestres-sing Force.in Tendon 1 0.84 F 0.88 F 0.93 F :
0.8 F 0.86 F 4
4 4
4 These values are used for constructing the tolerance ~ band-in Figure 1.
- l i
09/07/8S 19 RG 1.35.1 6
m
.c-F. = Initial Prestressing Force at an Anchorage Considering losses Due to Anchorage Takeup. Instantaneous Elastic Shortening, and Friction F
Predicted Prestressing Force g
.C
/ onsidering High Time-Dependent lossas Predicted Prestressing Force u,g
/
If
,Considering Low Time-Dependent losses E
~
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Tolerance Band?
g i
/
/
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- 0 O 9'r r
Maximum C
g volerance Band v>
~
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Design Prestressing' Force I
at an Anchorage Allowance for Breakage
. g 0.7F I
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10 15-20 25 30 35 40 TIME AFTER PRESTRESSING, YEARS _
Figure 1.
. Tolerance Band of MM s.,,_-
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4 t
REFERENCES 1.'
" Code f or Concrete Reactor Vessels and Containments," American Concrete Institute Committee 359 and American Society of Mechanical Engineers.
-Subcommittee on Nuclear Power, 1996.
Copies may be obtained f rom 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.
1 2.
" Building Code Requirements for Reinforced Concrete," American Concrete Institute Committee 318,.1983.
Copies may be obtained from the American' Concrete Institute, P.O.
Box 19150, RedfordLStation, Detroit, Michigan 48219.
3.
Post-Tensioning Manual, Published by the Post-Tensioning Institute, 1956.
Copies may be obtained from the Post-Tensioning Institute,'301 West Osborn, Suite 3500, Phoenix, Arizona-85013,:
-l 4.
Hansen, T. C., Mattock, A. H., " Influence'of Size andtShape of. Member-on the Shrinkage and Creep of Concrete," Journal of the American Concrete Institute, February 1966, Proceedings Vol. 63.
AlsoLpublished as PCA Development Bulletin D103.
k.
Copies may be obtained from the-American Concrete Institute,-P.O. Box-l 19150, Redford Station,' Detroit, Michigan 48219,Jor from' Portland Cement 3
l Association, 5420 Old Orchard Road, Skokie, Ill.
60077.
l
)
l l
S.
Baldwin, J. L., " Climates of the United States," published by the U.S.
i l
E Department of Commerce, Washington, D.C., December 1974, i
Copies may be obtained from the Superintendent of Documents, U.S. Govern-rent Printing Office, Washington, D.C.
20402.
09/07/88 22 RG 1.35.1 1
t L
l-REFERENCES (Continued) 6.
Geymayer, H. G., "Effect of Temperature on Creep ~of Concrete, A Literature 4
Review," Paper 31 of ACI SP-34, " Concrete for Nuclear Reactors," Vol. 1.
Copies may be obtained from the American Concrete Institute, P.O. Box 19150, Redford Station, Detroit, Michigan 48219 '
7.
Hansen, T. C., " Creep and Stress Relaxation of. Concrete," Swedish Cement and Concrete Research Institute, Stockholm,1960.
Copies may be obtained.from the Swedish Cement and Concrete.Research-Institute, Royal Institute of Technology, Stockholm, Sweden.
8.
" Report on Recommended Concrete Creep and Shrinkage Values;for Computing Prestressing Losses," by Schupack and Associates.
This non proprietary report is filed in the NRC Public Document Room as Appendix:5J of the Preliminary Safety Analysis Report for-the Three File Island Nuclear Power Station, Unit 2, Docket No '50-320.
A copy may be obtained from the Public Document Room,'U.S.' Nuclear.
Regulatory Commission, 1717 H Street, NW,, Washington, D.'C.
9.
Jordann, I.
J., England, C. L., Khalifa, M M. A;, " Creep'of-Concrete:
l A Consistent Engineering Approach," Journal of the Structural Division l-of the American Society of Civil Engineers, March 1977.~
l Copies may be obtained from the Publications.0ffice~, American Society I
5 of Civil Engineers, 345 E. 47th St...New York, N.Y.
10017.
10.
Cinlar, E,, Bazant, 2. P., Osman, E., " Stochastic Process for Extrapolating g
Concrete Creep," Journal of the Engineering Mechanics Division of the American Society of Civil Engineers, December 1977..
o l
09/07/88 23 RG.1.35.1 l-
REFERENCES.(Continued)
Copies may be obtained from the address in Reference 9.
II.
Chaung, J.
W., Kenaedy, T. W., Perry, E. S., "An Approach to Estimating Long-Term Multiaxial~ Creep Behavior from Short-Term Uniaxial Creep i
Results'," Union Carbide Report #2864-3, Department of Civil Engineering, '
University of Texas at Austin, June 1970, TID 25795.
Copies may be obtained from t'he National Technical Information Service ~,
U.S. Department of Commerce, Springfield, Virginia 22161.
IL Magura, D. D., Sozen, M. A., Siess, C. P., "A study of Stress Relaxa-tion in Prestressing Reinforcement," Prestressed Concrete Institute Journai, April 1964.
E Copies may be obtained from the Prestressed Concrete Institute, 20-North Wacker Drive, Chicago, Illinois 60606.
13.
Cahill, T., Branch, C. D., "Long-Term Relaxation Behavior of Stabilized Prestressing Wires and Strands," Group'D, Paper 19 of Conference Papers on Prestressed Concrete Pressure Vessels','the Institution of Civil Engineers, 1968.
Copies may be obtained from the Institution of Civil Engineers, Thomas Telford Ltd., 26-34 Old Street, London, ECIV, 9AD, England.
l 14.
Batal, R.
J., Huang, T., Relaxation Losses in Stress-Relieved Special Grade Prestressing Strands, Fr.itz' Engineering Laboratory Report L
No. 339.5, NTI5 PB200668, April 1971.
I L
Copies may be obtained from the-National Technical Information Servici U.S. Department of Commerce, Springfield, Virginia 22161.
l
-.09/07/89 24
REFERENCES (Continued) 15.
ANSI /A5TM C512-76, " Standard Test Method for Creep of Concrete in Compression."
Copies may be obtained from the American' Society for Testing and Materials, 1916 Race Street, Philadelphia, PA 19103, 16.
Hijazi, A., Kennedy, T. W., " Creep Recovery of Concrete Subjected to-Multiaxial Compressive Stresses and' Elevated Temperatures," Research-i Report 3661-1, Department of Civil Engineering, The Univeristy ofLTexas-at Austin, March 1972 - TID-26102.
Copies may be obtained from the Nationa1> Technical Information Service, U.S. Department cf Commerce, Springfield, Virginia 22161.
.a
.]
l I
a
'.)
4 09/07/8B 25 RG 1.35.1
.i
-VALUE/ IMPACT STATEMENT 1.
ACTION t
1.1 ' Description Inspectionsoof prestressed concrete containment structures are performed usi'ng Regulatory Guides 1.35 and 1.90.
The proposed action is directed toward providing guidance for determining the prestress forces in prestressing tendons l
that can be. compared with the measured liftoff force during:each inspection.
1.2 Need In implementing' Regulatory Guide 1.?'
it was found'that licensees are:not?
. interpreting' the acceptance criteria of that guide in an' appropriate manner.
This was evidenced by a comment letter from Bechtel Corporation.
Also, discus-sions with various applicants and licensees during the' review of their technical specification requirements indicated the need to clarify the acceptance; criteria and to provide guidance in methods of constructing a tolerance band became apparent.
The concept has also been discussed with the ASME Section XI Working Group on Inspection of Concrete Pressure Components:on various occasions.-
i 1.3 Value/ Impact 1.3.1 NRC The. guide will provide a consistent basis for review of applications for plants containing prestressed concrete containment structures, primarily
)
in the area of technical specification requirements for inspection of those i
containments.
It will help clarify the intent of-some of.the provisions' of Regulatory Guides 1.35 and 1.90.
The guide should facilitate the review:
q
.1 09/07/88.
26 RG 1.35.1 1
,.9-
-and evaluation of the' pertinent inspection programs and reduce the time for these efforts in the affected NRC offices.
1.3.2 Industry
.1 It is expected that the guidance provided will help licensees to monitor the tendon forces with better accuracy and thus increase the effectiveness of the inspection programs.
It will help keep licensees' records of. tendon forces in order.
The overall cost impact (increase / decrease) should be
' negligible.
1.3.3 Public The action will result in better control of the inspection program.
Thus it will provide more confidence in the, integrity of prestressed concrete =
containment structures.
l 1.- 3. 4 Occupational Exposure The action will not increase the occupational' exposure.
1.4 Decision f
Guidance should be provided on determining the prestress forces to be used for-comparing -the measured lif tof f' forces during each inspection.
2.
TECHNICAL APPROACH 2.1 Technical Alternatives An alternative proposed (and presumably-used) 1.n lieu of the method-described in the proposed action is as follows:
I 1.
Based on the average instantaneous elastic-shortening losses, time-dependent losses, and friction losses, establish an average required prestress at 40 years in kips /ft.
l 09/07/88 27 RG 1.35.1 L
i
2.
Depending on the' tendon spacing, establish the minimum required
.prestres5 per tendon and subsequently per wire at the jacking end.
3.
When a~ tendon.is randomly selected for liftoff testing, adjust its measured liftof f force to transfer its' actual elastic-shortening loss-and actual number.of effective wires to the condition of the average (hypo-thetical) tendon.
The adjustment (or normalization) factors would vary from inspection to inspection.
4.
On an individual tendon basis, the adjusted _(normalized) wire force should be compared with the minimum required prestress per wire.
2.2 Discussion and Comparison of Technical Alternatives The proposed position assumes that the containment (including its pre-stressing) is designed to the minimum requirements of the Code (ASME Section III, Division 2) as well as to other additional criteria set up by.the jurisdic-tional and regulatory agencies.
Once.the tendons are installed, the inservice j
inspection program should monitor their integrity and reliability.and-detect tendencies toward degradation.
The proposed alternative, on the other hand, is directly design related.
I If the prestressing force provided is (say) 20%. greater than the minimum required prestress, its acceptance criteria.would allow at least'20%Ldegradation of the tendon system before any evaluations or investigations are undertaken.
L Also, the procedure assumes that the average prestressing force of randomly i
selected tencons'always represents the average tendon force of the group k
population.
Moreover, the variation of the tendon force with' time is not considered in the proposed alternative.
I l
2.3 Decision on Technical Approach 3
The proposed alternative is likely to give a wide band of tolerance for comparing the measured prestressing force.
Thus it could result in the 1
acceptance of tendons that are not performing adequately or are degraded.
i 09/07/89 28 RG 1.35.1 L
p The method outlined in Regulatory Guide 1.35.1 alleviates the deficiencies of tne proposed alternative and provides guidance as to the methods of predict-ing the time-dependent parameters and-in constructing a reasonably narrow tolerance band for comparing the measured prestressing force.
The position l
is keyed to the acceptance criteria of _ Regulatory Guide 1.35 in such a way
[
that improper performance of the tendon system can be detected earlier in the life of the structure.
li 3.
PROCEDURAL APPROACH i
3.1 Procedural Alternatives Potential RES procedures that may be used to promulgate the proposed
-j action are:
Regulation Regulatory guide AN51' standard endorsed by a regulatory guide Branch position NUREG report 3.2 Value/ Impact of Procedural Alternatives The matter is not of sufficient importance to-justify _ issuance of a regulation.
There is no ANSI standard prepared or proposed at this time.
No branch position exists on this subject.
A NUREG report and a regulatory guide are the two viable alternatives.
As a NUREG report, the content would be perceived as informational, rather than as a statement of an NRC position.
3.3 Decision on Procedural Approach A regulatory guide supplementary to Regulatory Guide 1.35 should be prepared.
09/07/88 29 RG 1.35.1
e a
4 STATUTORY CONSIDERATIONS The guide will be numbered as Regulatory Guide 1.35.1 an'd will princi-pally supplement the regulatory positions of Regulatory _ Guide 1.35.
Hence the statutory considerations discussed in the regulatory analysis for revision 3 of that' guide are applicable to this guide.
5.
RELATIONSHIP TO OTHER EXISTING OR PROPOSED REGULATIONS OR POLICIES Regulatory Guides 1.35 and 1.90 are related to verifying the continued-structural integrity of prestressed concrete containment structures.
The-proposed action (Regulatory Guide 1.35.1) clarifies and expands the regu-latory positions of these guides, thus making the implementation of these l-guices more effective, j
6.
SUMMARY
AND CONCLUSION A regulatory guide (numbered 1.35.1) should be_ prepared to provide
- guidan:e for constructing a tolerance band for prestressing levels in prestressed concrete containment structures, i
7.
IMPLEMENTATION l
Implementation is recommended for new applications' only.
However, Sec-tion D discusses ways to implement the positions for' operating plants and for i
plants under construction.
I t
i 09/07/88 30 RG 1.35.1 I
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. Document Name:
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E ;uertor's ID:
PROG OR Author's Name:
i Hill / Graves t
Document Comments:
I ECS.9/7/bb' PLEASE KEEP THIS SHEET WITH DOCUMENT j
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' Document liene:
RETYPED'PG_13 RG 1.35.1A rteauestor's ID:
3 M' t.L E R Author'sllame:
GRAVES Document Comments:
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-l PUBLIC COMMENT LETTERS Og
- 1.
R.G. 1.3b - Inserv1:a inspection of engrouted. tendons in prestressed concrete containments Determining prestressing forces for inspection of
- 2.
R. G.. 3 5.1
-orestressed concrete containments i
l#
The-comment letters were received from theifollowing organizations:
i
(
0 gani:ations Date i
A.
Construction Technology Laboratory (PCA)
May 22, 1979 l
5.
Inryce June 15,1979 C.
Visccsity 011 Cc.
June 21 1979 3.
Bechtel Power Corporation
- June 22, 1979 E.
Sargent & Lundy Engineers June 28,- 1979 F.
Consumers' Power Compu1y October 3, 1979 G.
Tennessee Valley Authority November'19, 1979 j
H.
Gilbert / Commonwealth October 31, 1980 i
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5420 ole ore arc Road, Sktkie, ll;rtris 60077 o Area Code 312F G20:
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May 22, 1979
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Secretary of the' Co=ission U. S. Nuclear Regulatory Commission, o=*= % g i
D.C.
20555 y
' Attention:
Docketing and Service Branch NW CONCERNS :
Proposed Regulatory Guide 1.35.1.
Gentlemen :
I The Portland Cement Association reviewed the above document L
entitled "Deterrtining Prestressing Forces for Inspection of Prestressed Concrete Containments.". Accordingly, we submit the following coments.
The first paragraph on Page 17 states that "The constants A and B should be determined from' creep strains at t t
This results in three equations with two unP3c,wnb, and t."
By sblving the equations in pairs, three values for A 'and B can be obtained.
Does the second line of the-first paragraph on Page 17 mean that these three values. should be averaged?
With three ages 'of loading, values for A and B' can be.obtain-ed corresponding to each age of loading.
Does' the second line of the first paragraph on - Page 17' mean that these three ~
values should be averaged?
On Page 17, Item g, the following should be inserted, time t "and the strain on the unloaded specimen" from the 0 Reference No. 4 of the Guide, togethergwith an Ap-pendix containing detailed data, was. reprinted as Portland l
Cement Association Development Bulletin D103.
Figure Al of the Appendix shows that some shrinkage strain can occur in sealed specimens.
There is a typographical error in " University" on the fourth line of Reference 16.
Sincerely yours, Y
Mandger,*
%sg,.., ly q.,
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Structural Development Section H..G.
Russell / amp 3
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riey h.
sberner t
a,
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.c (NRYCC Inc.-
Post Teneenes cimen -
1960 Norm 25m A /enue. 8:n 1066 Moreas Pern, tilinos 60161 M.E R'J.':ltR )
1 31 5USED IULI
]
, 2 379 9600 AL>Am M Inryco June 15,1979 Secretary of The. Commission U. S.' Nuclear Regulatory Commission 3
~
Wa shington, D. C.
20555 A tt enticas.-
Docketing & Service Branch jj 1
Subj ect:
Comments on Draft of l
Regulatory Guide 1. 35 01973 >
Revision 3, Cated Acril'1979
"/ 7 g -
h 4
88 Gentlemen:
After reviewing the Draft of Revision 3 of NRC Regulatory Guide 1. 35 issed for Comments, we offer. our comments as follow below.
4-As a means of introduction, Inryeo,' Inc...- Post Tensicaing Division, has been a supplier firm for post-tensioning srystems for the majority of post-tensioned containment structures built in the U. S.
Our company has also bee = involved in several surveillance inspections of.contain-mest post-tensioning systems and we feel that we have first hand experience in the subject matter.
Comments Page 3, lines 19 through 24.
This paragraph is not quite clear. It.would appear that it implies that wedge-anchored tendons need not to be detensionable, by using words such as "could" and "would". Also, it is not clear how the use of a shi= (or shims) under de anchorhead would ensure that the previously gripped porton of 6e prestressing steel will not form a part of de L
retensiemed tendon. Since de wedge-anchor will remain in the 'ss,me qqg-yg
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' Secretary of The Commission Jcne !!, 1979 Page Two i
position relative to the strand,- any notches or damage to se pre.
stressing steel will remain in the same location as it was when the tandon was originauy instaned, and that is a liart of the reteasioned tendon.
Page 4, lines 14 through 24.
i When removing the grease cap from an anchorage for surveinance purposes, a certaia amount of grease wiu flow out of the trumpet and conduit. This amount wiu depend on the orientation of the tendon and the average temperature of the grease, Normal experience has i
been that the amount of outflow is rather limited (5 to 10 ganoas),
unless the containment is very wann.
The refilling ci a tendon duct, by pumpsg grease under pressure
+
attempting w displace grease already in the duct is not possible, i
unless the "old" grease had been drained out alzaost completely, f
Cn the othet hand, it is expected that voids wiu fort a in the body of the grease as a resu' et aperature variations. These voids act as l
s expansion reseWoirs and sheidd he at a miMmw 4 when the contain-t ment is at operating temperatures. The importa.at iseue is th'; whef i
voids form, ne prestressing stael ls exposed to corrosiva n.ack.
Through tests it has been demonstrated that when the grease contracts at lower temperatursa 't wiu form voids in the body of the grease itself, leaving a heavy coat.ag on the wires and tendon duct. Whether these volds form la the duct or in the trumpet is immaterial, as long as the co rosion protection designed for. is being provided. In the practical world, past and present practice !s to cool the grease in the vicinity of the cap down as much as possible prior to removing the grease cap, I
thus miaimlzing the outflew e a =46um. Prior to reinstalung the cap, as much as peasible of the grease removed is replaced, realizing that it is usuauy not possible to replace grease inside the trumpet. Any void inside the trumpet that could be left amfined is no different from l-voids inside the duct itself.
Based en the above, we recommend to delete the requirements of lines l
17 through 24, sisce they es.nnot to accomplished.
i e
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f INRYCC, Inc.
)
- Secretary of The Commission June 15,1979 I
Page Three i-i i
Page 5, C.
Regulatory Position C.1 General i
51 ace it is not mentioned anywhere else in the Regulatory Guide, i
but is necessary to comply with the random selection of surveinance tendons, we recommend the addition of the fonowing after 1. 4.
" Anchor hardware must be so designed as to anow complete de-tunsioning and retensioning of any one tendon in the structure."
i
. age 6, C. 2 Sample Seleetion Add Item 2. E to reads i
"2.5 Except as noted in C. 2. 4, the selecdon of surveinance tendons must be at random. Pre-selection of surveillance tendons at the time of Laitial instaustion is not permitted. "
It is obvious that the purpose of random sampling is e14=4aated if it is known beforehand which tendons will be subject-d to a surveluance inspection.
Pa g e 7, C. 4 Prestress Monitoring Tests Item 4,1 Tendons should be totally detensioned to identify broken or damaged wires or strand. The wording "essentituy completely de-tensioned" is very confuslag.
Page 9, C. 7 Evaluation of Inspection Results l
Item 7. 4, Line 9: As outlined above, the presence of voids in the grease finer material is expected and necessary to provi& for thermal expansion of the grease. This is not a condition of degradation and, therefore, should not be a reportable condition.
Also, what is the definition of "significant void" for an Inspector to use when he has to decide whether to reper or not? Should the level of significsnce not be temperature related?
0 Y
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Secretary of The Commission June 15,1979 Page Tour i
We recommend that the condition "significant voids withia the grease fL11er material" he deleted.
i We appreciate the opportur3ty of providing our comments to you, j
and hope they are of benefit to the N. R. C.
j very truly years, lbf Peter Reinhardt V
Manager, Business Development 4
j 9
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