ML19210B357
| ML19210B357 | |
| Person / Time | |
|---|---|
| Site: | Three Mile Island  |
| Issue date: | 01/21/1972 |
| From: | METROPOLITAN EDISON CO. |
| To: | |
| Shared Package | |
| ML19210B356 | List: |
| References | |
| NUDOCS 7911070684 | |
| Download: ML19210B357 (13) | |
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ADDDEUM TO REPORT ON CONTAIID'ENT BUILDING RING GIRDER CCNSTRUCTION AND REPAIR THREE MILE ISLAND HUCLEAR S*u1 TION UNIT No. 1 METROPOLITMi EDISON COMPANY Janua.m/ 21, 1CJ72 o
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ErIRODUCTION On Dece=ber 3,1971 Metropolitan Edison Company filed with the AEC a document entitled " Report on Contaireent Building Ring Girder Con-struction and Repair". ' Die infor=ation included in this addendum to the aforementioned report was compiled to answer questions and ccm-ments raised by =e=bers of the DRL staff at a meeting held on Decem-ber 28,1971 in Bethesda, bhryland.
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1.0 Visual Instections 3he possibility of using Sonotubes as an aid for visual inspection within the repaired area of the ring girder was reviewed. Sonotubes were rejected since they could only be placed in areas where their usefulness would be narginal, i.e. away from the anchorage zone where the rebar placement would not permit their use. In addition, they would only add to the congestion in the repair area and difficulty of concrete placement.
She Structural Integrity Test is established to verify the design of the containment building. Therefore, during the SIT the contain=ent building is pressurized to 63 3 psig or 1.15 times the design pressure.
At this time selected areas of the rini; girder are inspected, in ac-cordance with the procedures of FSAR Appendix SE and the section on crack inspection in this amendment.
In addition, these sa=e areas will also be inspected for cracks prior to and -
during the initial prestressing, and during tendon surveillance.
Initial prestressing and structural integrity test pressure place the ring girder under the =ost severe load conditions nor'~tily expected and therefore will provide clear indication of the effects of repair on the ring girder behavior. A check for. cracking patterns in the selected areas during the subsequent integrated leak rate tests where the pressure will be 30 psig is considered unwarranted.
However, surveillance of these same areas for any changes in cracking patterns and size of cracks will be carried out along with the tendon surveillance program established by the technical specifications.
Although the building has been conservatively designed for high pres-sure, it is considered undesirable to subject the building to the design pre.tsure nore than necessary. Berefore, fonowing the initial integrated leak rate test at design pressure of 55 psig, subsequent integrated leak rate tests win be done at 30 psig. This lower pressure
- is sufficient to verify leak tightness without subjecting the building
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2.0 Strain Gares Me behavior of the ring girder will be checked during the Structural Integrity Test through strategic location of strain gages.
The gages win indicate the strain in the reinforcing bars around the ring girder including those within the repaired areas. The gages are placed on the same group of reinforcing bars at different azimuths around the ring girder at the chosen elevation so that the strains will be co= parable for each set of gages. The vertical.and hoop strains are expected to be approximately the same for each asi=uth at a given elevation. The corresp'onding stresses are expected to be less than the allowable tensile stress of 20 ksi.'
The strain gage locations are listed in the FSAR Appendix SE Table I.
In addition to those three strain gages listed originally in Appendix 0
SE at azi=uths 108 , 2h5 and 352 for elevatign M ', two additional hoop strain gages will be added to aci=aths 80 and 320 also at eleva-tion W '. These additional gages are located within the double dome tendon anchorage zone or within both the single and double tendon anchorage zones of the ring girder repair area to provide index of effect the repai, red areas have on the function of the ring girder.
The use of strain gages is discussed in FSAR Appendix SE Section V.2.
3he gages are installed in pairs to preclude the loss of strain gage readings in a particular location should one of the pair of gages malfunction. The gages win be utill:ed during the Structural Integrity Test and, therefore, have been waterproofed and protected in such a mn.nner to assure their usefulness at least to that time. Since it is not anticipated that they will be used again, they have not been de-signed for the plant service life. Inspection of cracking patterns in selected zones will be the method of future structural surveillance in the ring girder zone fonowing the Structural Integrity Test.
All test results will be collected, recorded, and evaluated in accordance with the procedures given in Appendix 5E of the FSAR.
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. et 3.o crack Increetion Four strategic locations around the de=e tenden anchorages will be in-spected for crackir4 before and during prestressing, durir4 the struc-tural integrity test, and as part of the in-service tendon surveillance program. Each of the four areas vill be a minimm of 6 ft. wide and 12' high enco=passirg r: ore than the full height of the repair area.
'Ihree of the areas will be located in the north part of the ring girder in the repair area.while the fourth area will be located in the south part. 'Ihe exact locations of the white wash areas will be as stated in Table I .of Appendix SE in the FSAR. All cracks larger than five (5) mils width will be recorded. The initial inspection will be done prior to white washing. 'Ihe area will then be white washed and grid =arked in accordance with FSAR Appendix E 513 prior to prestressing. crac':s will be recorded during and following the prestressing operation. During the Structural Integrity Test, these areas will be inspected again in accordance with the procedures for the SIT given in FSAR Appendix 5E.
And finn 117, these four designated areas will be inspected during each tendon surveilinnce for changes in the crack size or pattern. These re-sults will be compared with earlier results and will be retained as records.
4.0 Electrical Conductivity Across Cadwelds There is no design requirement for the reinforcing bars to serve as any part of the grounding system for the contain=ent building and, therefore, electrical continuity through the cadwelds is not a requirement. 'Ihe containment building has a separate lightening protection and grounding system.
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50 Local Stress Distributien Behind Bearing Plates Be anchorage zone design fulfills the allowable bearing stress require-ments of ACI-318-63 section 2605C. m e bearing stress on the concrete beneath the bearing plates does not exceed the allowable bearing stress in any of the anchorage zones including those in the repair area.
A 30 degree stresa distribution is assumed in each direction beneath the bearing splate where the concrete configuration per=its.* h e design be-neath the plate is similnr to spirally reinforced colu=ns up to and con-servatively beyond the point where the concrete compressive stress does not exceed the allowable compressive stress.
With the above distribution, the allowable ccepressive stress in the con-crete is reached in less than 6 inches behind the bearing plate. Thus, considering the effect of adjacent bearing plates on the ec=pressive stress at a point behind the plates, the design of the lead-in zone similnr to a colu=n conservatively ensures allowable compressive stresses beyond a very short distance behind the plates into the concrete.
The concrete has been excavated =uch more than 6 inches behind the bearing plates in the repair area. Berefore, no problems peculiar to the con-crete in the repaired area are expected with regard to bearing stresses and distribution of prestress force into the ring girder.
6.0 Lap Splices of Reinforcing Inp splicing of reinforcing steel is per=itted in the ring girder in ac-cordance with the requirements of ACI-318, Section 80s.
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7.0 Butt Weld Sulices Butt welding of reinforcing steel in the ring girder will be pered.tted when cadweld splices or lap splices cannot be executed provided the fol-lowing conditions are observed;
- a. Specific splice point and rebar location are identified.
- b. Icw stressed bars are involved or If higher stressed bars are involved, only a low percentage of these bars ray be butt welded in a given area. Classifica-tion of bars (higher vs. lower-stressed) will be by a repre-sentative of Gilbert Associates, Inc. The basis for classifi-cation will be design stress requirements.
- c. Specific approval of a representative of Gilbert Associates, Inc. is obtained on a case basis,
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- d. Welding is accomplished in accordance with a welding procedure prepared for welding rebar in the ring girder area. Welding will be done only by welders qua14 fied to this procedure,
- e. All required inspections and tests are carried out.
8.0 Reinforcine Steel Butt Welding procedure A welding precedure has been prepared for the butt welding of reinforcing steel in the ring girder and the weld repair of an nged rebar. 'Ihe pro-cedure covers base naterial, joint and welding details, weld rod, control of weld rod, velding paraneters, inspections, tests, and qualifications.
'Ihe procedure has been reviewed by the Owner, the Engineer, the Owner's consultant, and for-nlly approved by the Owner.
'Ihe procedure.has been qualified with the rebar ends free and also with the rebar ends restrained.
Because much of the welding will be done in congested areas, welders who will be assigned to this work will have been qualified under space re-stricted conditions.
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s 90 Nondestructive "estine of Butt Welded Rebar Joints Reinforcing steel spliced by butt welding will be nondestructively examined as follows:
(a) Each co=pleted joint - 100% visual examination (b) Each completed joint - 100% =agnetic particle inspection (c) 10% of the co=pleted joints will be radiographed. Joints to be radiographed will be selected on a random basis by LE C QC personnel.
10.0 Renair of Reinforcina Steel Mechanical Defects by Weldine As stated in the report (Section 4.01.2) reinforcing steel containing notches in excess of 3/32" deep v471 be re=oved a.nd replaced. However, in those instances where such re= oval would create significant addition-al damage which =ay be virtually impossible to repair, welded repairs to defects will be per=itted, subject to the same limitations applied tg butt weld splicing (Section 7.0). Separate qualifications of welaers for such repair is required.
It is also anticipated that some larger defects cay be present which obviously will not affect the strength or ductility of the rcpaired or replaced reinforcing. (For exa=ple, notches near the end of the rebar).
Some such oversize defects =ay be allowed to re=11n unrepaired, but only with the spegific prior approval of a representative of the Engineer.
11.0 Control of Weiding Electrode The welding electrode to be used in the butt welding of reinforcing in the ring girder will be of the low hydrogen type (E7018). The issuance and use of the electrode will be controlled in strict accordance with an approved ccustntetion procedure subject to Quality Control surveillance.
Electrodes used in the ring girder repair will be from heats selected and maintained segregated for ring girder repairs.
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12.0 Reinforcing MaYerial Control Reinforcing steel for the Ihree Mlle Island project is purchased and re-ceived on a " heat" basis. After receipt, user samples (for rechanical tests) are selected frem each heat and size received. Following user testing, the heats are " released for construction".
Review of receiving records and documentation show that no heat of Grade 40 rebar has been received with a carbon content in excess of 0.44% based on ladle nrmlysis.
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s 13.o quality control of Rina Girder Repair Repair of the ring girder will be accomplished and controlled, using ap-proved constructied procedures covering all aspects such as excavation of unconsolidated concrete, tests of re=aining concrete, repair of tendon conduit, re= oval and replacement of rebar, and concrete replacement. Be construction procedures wil.1 also identify the construction records to be mintained.
E g Quality Control checklist prepared to cover each applicable construction procedure will list inspection points, tests to be perfor:ed, acceptance criteria, and data to be recorded. Inspection points treated as " hold points" are identified. .
Prior to replacement of concrete and after all excavation and repair is co=pleted in each segment, the U E C Quality Control Group will perform a final review of inspections and records to date prior to release of the segnent for concreting.
Replacement of concrete will be inspected and tests performed under sur-veilhnce of a QC inspector assigned to the location of each repair place-ment.
. 14.0 Reinforcinz Steel-Defect Size Test Procram he defects introduced in the reinforcing steel test progras detailed in the report (Section 4.01.2) were accomplished manually using a wide blunt chisel. Itotographs taken of the test samples are available at the project site for review.
15.0 Ring Girder - South 180 0 Me relocation of construction joints in the South half of the ring girder and the removal of lap spliced reinforcing steel above eacl lift provided complete visual and physical access to South lifts 3, 4, and 5 Serefore, consolidation of concrete and inspection of placing was accomplished with-out interference or unusual placing conditions.
A detailed visual inspection of the surface of the South 1600 will be made prior to tendon installation. Bis inspection will be fully documented.
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16.0 Arolication of Bending Cc=rcund The surface of the concrete rernining after excavation will be somewhat rough and irregular. However, no minimm thickness of the bcnding ec=-
pound to be used is required to effect bond. Likewise excessive thic.besses do not affect the q1mlity of the bond. Therefore, the following conditions governing application will be adhered to:
(a) Both spray and brush application =ay be used. Areas care. W checked for cc=plete coverage according to manufacturers reco==endation.
(b) Epoxy ec= pound cures rapidly and =ust be " live" at the time -
of concrete placement. Application of cc= pound shan proceed as closely ahead of the concrete placing as practical. How-ever, if ec= pound has set prior to placing concrete, it shall be reinstated " live" through application of an additional coat per the manufacturers recc==endations.
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Several editorial comments about the report require clarification and these are as follow:
Table of Contents - omission Add to second page of Table of Contents:
"4.025 - Quality Assurance & Control - Pg 4-7".
Sequence of Major Events - (Pe 1) - erratum The date shown for " Complete entire Ring Cirder Repair" should be changed to 4/15/72.
Page 2 Third paraeraph - clarification ,
The report indicates a heavy concentration of reinforcing steel. It should be noted that rebar spacing is in accordance with the minimum requirements of ACI 318. . ~
Page 2 Last paracraph - clarification The weld of the galvanized tendon conduit to the ungalvanized bearing plate is made on the 0.D. of the conduit to the inside face of.the bearing pinte. These welds were made in the fabricating shop. Galvanize coating was stripped from the O.D. of the conduit, and a galvanize paint applied over the surface of the finished weld.
Pace 2 First Paracraoh - clarification Mention is made of a " joint bonding agent". The material used was an epoxy based bonding agent commonly used and approved for use on the Three Mile Island projec t.
.Page 2 Third paraeraoh - clarification Concrete placing operations for Lift 3, North 180 , were continuous.
During placing operations at night, adequate lighting was employed.
No precipitation occurred during the time of the pour. .
- Page 2 Fourth oaragraoh - clarifiention Mention is made of slow placement rate affecting slump and workability.
It should be noted that all concrete placed, however, had a measured slump, just prior to discharge from the truck, of between 1" to 3%".
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9 Paec 2 First Para. - Section 2.03.4 - clarification Mention is made of rebar removed above each lift. The rebar temporarily removed was that which had been lap spliced. Splices were unwited, bars removed, and when bars were replaced they were again lap spliced using tie wire.
Page 2 First Para. - Section 2.03.4 - clarification Mention is made the South lifts 4 & 5 employed the use of a concrete pump in addition to cranes. It should be noted that a concre te pump was also employed in placing concrete in Lift 3 - South.
Four sets of test cylinders were made representing the 120 cubic 3prds placed in lift 3. The second and third of these sets were made from the same truckload of concrete, one set from the truck discharge and one set from the pump discharge. Slump at pump discharge was 1/2" lower (3" vs.
3 ") and 28 day cylinder compressive strength was 5820 psi (pump discharge) vs. 5750 psi (truck discharge).
A rather extensive correlation has been made on the project between concrete properties at truck discharge vs. those at pump discharge. On the average it has been found that through the pump there is a 1/2" slump loss, a 1%
air content decrease, and an 8% strength increase.
Pace 2 Section 2.04.1 - Second Paracraph - clarification Mention is made of "Cadweld electrical connections". These are better defined as "Cadwelded grounding connections".
Page 2 Section 2.04.3 - Second Paragraph - clarification Mention is made of the " proper mix". The mix employed was identical to that described in report section 4.02.5 (Page 4-8).
Page 4 Section 4.01.2 - Third Paraeraoh - clarification -
Reinforcing bars remaining in the excavated areas will be thoroughly visually inspected for de f,ects. It is not anticipated that the area will be so congested as to prevent direct inspection. However, should they be re, quired, inspection mirrors will be used.
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The inspector checking remaining rebar will be provided with a sketch of the area and as each bar is inspected, he will " color out" that bar on the sketch,,(40r note it is to be removed and then verify removal).
Page 4S5 - Fif th Paracraoh - clarification Mention is made of "1" square hoops". These are better described as *
"1" square stock bent into a circle".
Page 4 Second Parsersch - clarification The air content of the mix described is shown as 4-6%. The air is entrained by use of a vinsol resin type chemical admixture.
Ficure A Elevations The elevation of the lower construction joint shown in the Figure is 443' - Oh". The elevation at the top of the vertical tendon bearing plate is 453' 6".
In figure A-6, A-7, and A-8, the exact elevations of the limits of the replacement concrete pours are unknown at this time and will vary some-what from segment to segment depending on the amount of concrete actually excavated.
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