ML19210A389
| ML19210A389 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 06/03/1977 |
| From: | Herbein J METROPOLITAN EDISON CO. |
| To: | Reid R Office of Nuclear Reactor Regulation |
| References | |
| GQL-0771, GQL-771, NUDOCS 7910290615 | |
| Download: ML19210A389 (13) | |
Text
NRCcon u.s. NUCLEAR REGULATORY COMMISSION CoCKET NUMBE R 50- 127 (2 781 CC DISTRIBUTION PA..T 50 DOCKET M ATERI AL TO:
FROM:
oATE or ooCUMENT Metropolitan Edison Company 6/3/77
_R. W. Reid Reading, Pa.
DATs RECEIVE D 6/6/77 J. G. Herbein
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OESCRIPTION EN CLOSU R E Consists of additional informatioh
.DO NOT. REM 0YE-Pertaining to egglicent s regert b
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-f entitled " Reactor Containment Building Ring Girder Surveillance Tese Two Years After S.I.T.".................,........
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$CKNOWLEDGED (I-P)
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PLANT NAME:
Three Mile Island Unit No. 1 RJL SAFETY FOR ACTION /INFORMATION rwrpn f
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METHOPOLil AN EDISON COMPANY PCST OFFICE BOX 542 READING, PENNSYLVANI A 19603 TELEPuCNE :15 - ?:5. :01 June 3,1977 GQL 0771
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RIGl.ATORY DOCKET Fl.ECOPY S. /hd Director of Nuclear Reactor Regulation kS Attn: R. W. Reid, Chief
,y Operating Reactors Branch No. L s
U. S. Nuclear Regulatory Cct=ission gjg Washington, D. C.
20555
Dear Sir:
Three ?'ile Island Nuclear Station, Unit 1 (T!E-1)
Operating License No. EPR-50 Docket No. 50-289 Enclosed please find an original and 39 copies of additional information pertaining to our report entitled " Reactor Containment Building Ring Girder Surveillance Test Tvc Years After S.I.T. " requested by your letter of May 3,1977 We trust this submittal satisfies your needs while cc=pleting the reviev of our report.
C'ncerely,
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J. G. Herbein j/
Vice President b
JGH:JMC:rk Enclosure 1469 072 1715800'
Tn;ee Mile Island Nuclear Station Unit 1 Reactor Containment Building Ring Girder Surveillance Ref: USNRC Letter May 3, 1977 Request for Additional Information QUESTION 1.
Figure 3 of the referenced report shows areas where the ring girder
" facing" has broken away.
Descrite the function of the " facing".
It is not clear whether it is part of the structural concrete or a fascia.
If the " facing" is not structural, provide assurance that eventual cracks can be uncovered during visual inspection.
If the " facing" is structural address the effect of the spalling on the structural integrity of the ring girder.
Indicate the depth and area of the broken away " facing".
RESPONSE
The " facing" is a surface patch en the outside vertical face of the upter area of the Reactor Containment Building Ring Girder.
There is evidence of surface cracking and/or breaking away of " facing" (scaling) in the region designated as A in Sketch #1 around the entire circumference of the ring girder.
The scaling is more prevalent around the North half of the structure than the South half. An examination of the scaled material indicates that two to four layers of finishing mortar has been applied in the area.
3469 3 0
A visual inspection of a substantial region of the ring girder surface has been conducted using the nomenclature of ACI Co=mittee 201 Report
" Guide for making a Condition Survey of Concrete in Service". The surface cracking of the vertical surface can be described as pattern cracking and does not extend beyond the patching material. The condition of the surface which was exposed by breaking away of material can be described as one of severe scaling with encrustations.
With regard to the function of the " facing", the construction drawings of this area and the FSAR indicate a minimum cover of 2" for reinforcement.
The scaling may have reduced the actual cover to less than specified.
However, exposed reinforcing bars or rust stains which could be attributed to reinforcement corrosion in either the scaled or cracked areas has not been observed.
Any significant corrosion of the reinforcement would be accompanied by increased scaling and discoloration which would be easily detectable. A review of the design calculations indicates that the vertical and circumferential reinforcing near the surface of the affected region is not required for satisfactory structural performance. It serves as minimum reinforcement for shrinkage and te=perature.
In any event the surface condition around the ring girder circumference does not reduce the margin of safety for any design basis load combination.
The condition is a problem of appearance rather than structural adequacy. }kh9
QUESTION 2.
In Table h, Note h, it is indicated that small cavities were found in the vicinity of tendon bearing plates lh9 and 225 Describe these cavities.
Indicate their location with respect to the tendon in a sketch. Present a discussion of their effect on the margin of safety and present a suggested nethod of repair.
RESPONSE
The reported cavities are approximately 1" in diameter, 1" deep and located as illustrated in Sketch #2.
They represent an acceptable as-built condition since they do not extend into the bearing area and do not degrade the structural integrity of the containment.
Therefore, corrective measures are not required. However, they should be treated in the same manner as the other voids.
QUESTION 3
Figures 6 thru 12 present sketches of seven voids which vere found around the dome tendon bearing plates, a.
Explain why these voids were not discovered during previous inspections.
RESPONSE
It nas been surmised that the voids were covered by lens of concrete (see Sketch #1) which resulted in their being undetected during previous inspections. The ise of a reciprocating power wire brush (needle gun) to clean off the surface of bearing plates prior to painting apparently 7 z g9 3 3
broke the covering lens and exposed the voids. The voids were reported the next regular surveillance report.
QUESTION 3 (CONTINUED) b)
Outline the procedure by which the effect of the veids on the structural integrity has been evaluated. Address the fact that the voids vill act as stress raisers and therefore may generate future cracks.
Discuss environ = ental factors that may facilitate local damage.
In light of these concerns, address the effects on the ori 1nal factor 6
of safety of the design. Discuss in detail the approach used to predict losses in tendon force.
RESPONSE
Section 1.0 of Addendum 1 to " Report on Containment Building Ring Girder Construction and Repair" states the following regarding prestressing and structural integrity testing.
" Initial prestressing and structural integrity test pressure place the ring girder under the most severe load conditions normally expected and therefore vill provide clear indication of the effects of repair on the Ring Girder behavior."
Initial prestressing stressed the tendons to 80% of the guaranteed ultimate tensile strength (GUTS) prior to lock off at 70% of GUTS. During the structural integrity test (SIT) the internal pressure of the Contaiment was raised to 63.3 psig. All the tendens have experienced initial prestressing and SIT loads with no signs of structural distress.
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RESPONSE (continued)
The TMI Final Safety Anaysis Report *(Ref. 1) states that the calculated ratio of allovable to actual bearing stress is 1.08 at 705 of GUTS (139h KIPS Tendon Force). Due to predicted losses the tendon force is approximately 1260 KIPS. *(Ref. 2).
Considering the loss in bearing area (approximately L sq. inches for void near tendon bearing plate D-115) the ratio of the allowable to actual bearing stress was calculated to be 1.18.
This indicated a 105 increase in the factor of safety against exceeding allovable stresses.
It should be noted that this factor of Safety was based on the design concrete strength of 5000 psi.
The inplace concrete strength is higher (6590 psi based on 90 day cylinder tests). The Factor of Safety for bearing for tendon bearing plate D 1h1 (loss of 6 sq. inches bearing area and considering the present predicted tendon force) has been calculated to be 1.21 using design concrete strength.
This is 135 higher than the acceptance criteria of 1.08.
Ccnsidering the actual inplace concrete strength of 6590 psi the Factor of Safety is 159 which represents an increase of 515 over the 1.08.
T"I ~urveillance Test No. 1301-9.1 titled " Reactor Building Structural Integrity Tendon Survei'. lance Program datec October Th indicates the predicted reduction in tendon force due to long term losses.
The first Tendon Surveillance test Report, GAI 1880, indicated close agreement between measured and predicted Tenden Forces.
The procedure for computation of Tendon force is discussed in the TMI FSAR.
1469 077 Ref. 1 "Cencrete Bearing", IMI Nuclear Station Unit 1 FSAR Docket No. 50-289 Appendix 53, Part B.
Section 8.1, Metropolitan Edisen Company.
Ref. 2 Data Sheet 6 Tendon Surveillance Test one year after SIT.
GAI Report No. 1880.
RESPONSE (continued)
Although the voids may act as stress raisers the strength of the concrete is continuing to increase and the tendon force is decreasing. The possibility of voids producing further cracks is unlikely.
Inspection of void at tendon D 115 over an 18 month period indicated no detectable c$ange in its conditions.
'dith reference to environmental factors the ther=al cycling which has produced the scaling discussed in response to Question 1 could have influenced the cracking at the voids.
However, there does not appear to be any correlation between the previously reported cracks near the tendon bearing plates and the presence of voids.
There are minor cracks at the Southwest ends of tendon D 115 and D I 2 which also have voids while the I
remaining of the tendon bearing areas with voids are free of cracks.
C:her tendon bearing areas with cracks do not show sigm of voids and none is likely to occur due to environmental or other factors.
Considering the above discussions related to the evaluation of the effects of voids the factor of Safety against exceeding allovable stresses has inproved with time.
QUESTION 3 Present the acceptance criteria used in the evaluation.
c.
RESPONSE
Acceptance criteria is as discussed in paragraph 2, page 5 1469 078
QUESTICN 3
-d.
Provide a timetable for the repair of voids. Outline the repair procedure and discuss the impact of any delay in the repair schedule.
RESPONSE
It is presently planned to repair the voids by the end of the 1978 Refueling Outage. The structure is responding satisfactorily with the voids and there is little likelihoed of environ = ental damage in either the short or long term. Since the voids are not a nuclear safety related problem, there should be no impact if any delay in the repair schedule occurs.
The procedure for repair is as detailed below:
METHOD OF REPAIR MATERIAL The void should be repaired with a nonmetallic, nonshrink, high strength grout such as one of the following:
a.
U. 3. Grout Corpcration, Five Star Grout.
b.
Sauereisen Cements Cc=pany, Sauereisan F-100 Level Fill Grout.
c.
Master Builders, Enbeco 713 Grout.
AREA PREPARATION The void area must be prepared for repair as follows and no repair verk should com=ence until sl1 requirements for successful grouting have been satisfied:
Clean the interior of the void to provide a firm rough surface, free a.
of dust, dirt, oil, grease and paint.
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i469 079
b.
The area to be grouted must be saturated with water four hours prior to placement of the grout.
c.
Any surface water in the repair area must be removed prior to grout placement.
FORM 3 Forms should be constructed of coated vood or metal and should be firmly anchored. They should be of sufficient strength to keep the grout in place and should be leak proof and of sufficient height to contain a
" head" of grout.
MIXING All mixing must be performed in accordance with the published specifications provided by the grout manufacturer to provide a flovable mix.
- Sand, gravel or other additives must not be used.
INSTALLATION The grout is to be poured into the form from only one side to avoid entrapment of air.
Grout is to be placed in a continuous operation to preclade separation and is to be worked into place with suitable tools to ensure that the space is completely filled and is free of air pockets or voids.
Temperature of both grout and concrete must be within the range specified by the grout manufacturer.
CURING Curing must be accomplished in accordance with the published specifications of the grout manufacturer. The " pouring spout" mus; be removed after initial set but prior t.' final curing. \\469 Ob
TESTING Cube specimens should be made and tested in accordance with ASTM C 109 A total of 6 specimens vill be tested:
3 at seven days and 3 at forteen days. Documentation of results will be retained at TMI.
ALTERNATE I?ISTALLATION Variations may be made in the repair procedure to allow the grout to be
" dry packed" in accordance with the published specificatiers of the grout manufacturer.
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