ML20076N279
| ML20076N279 | |
| Person / Time | |
|---|---|
| Site: | Midland |
| Issue date: | 04/30/1983 |
| From: | Corley W CONSTRUCTION TECHNOLOGY LABORATORIES, INC. |
| To: | |
| Shared Package | |
| ML20076N260 | List: |
| References | |
| NUDOCS 8307210271 | |
| Download: ML20076N279 (7) | |
Text
{{#Wiki_filter:1 Report to CONSUMERS POWER COMPANY i Jackson, Michigan VISUAL INSPECTION OF CRACKS IN CONTAINMENTS NEAR ANCHORAGES IN ROOMS 110 and 116 by W. G. Corley 'l Submitted by CONSTRUCTION TECHNOLOGY LABORATORIES
- A Division of the Portland Cement Association 5420 Old Orchard Road
' - Skokie, Illinois 60077
-March 11983 ~
-Revised April 1983 .
9307210271 830719 PDR ADOCK 05000329
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PDR_
VISUAL INSPECTION OF CRACKS IN CONTAINMENTS NEAR ANCHORAGES IN ROOMS 110 AND 116 by W. G. Corley* h gi INTRODUCTION This document reports observations made by W. G. Corley during a visit to the Midland Nuclear Power Plant on February 15, 1983. The report describes observations of reported cracking visible in Rooms 110 and 116 near intersections of buttresses and base mat in the containments. Purpose of the visual inspec-tion was to determine the nature of the cracking and make ; recommendations concerning actions that should be taken. SITE INSPECTION OBSERVATIONS On February 15, 1983, Dr. W. G. Corley inspected cracks in Containment Unit 1 and Unit 2 at the Midland Nuclea'r Power Plant. Cracks inspected were near the buttresses in the walls ! of each unit. Access to cracks in Containment Unit 1 was obtained through < Room 110 at Elevation 584 of the Auxiliary Building. Visual inspection indicated that concrete surfaces had been covered with a coating. Reflection of the cracks through the coating l *W. G. Corley, Divisional Director, Engineering Development i Division, Construction Technology Laboratories, a Division of the Portland Cement Association, 5420 Old Orchard Road, i Skokie, Illinois 60077. t i construction technology laboratories
- could be seen from floor level. Appendix A shows crack mapping records obtained in Room 110 by Bechtel staff.
At two separate locations in Unit 1, the coating had been removed in the vicinity of a crack. Measurements with a 50 power microscope indicated that at one location the crack'sas approximately 0.002-in, wide and at the other location the crack was 0.001-in. wide. Magnification of the crack disclosed that the coating had penetrated and filled the portion of the crack inspected. There were no visible signs that the crack opened after the coating had been applied and the prestressing was completed. Access to the buttress of Containment Unit 2 was obtained through a pipeway designated as Room 116 at Elevation 584 of the Auxiliary Building. In this room, one crack was visible just to the right of a prestressing anchorage. No other cracks were observed. The crack in Unit 2 appeared to be similar to those observed near the anchorage of Containment Unit 1. Due to lack of access, no measurement was made. However, the crack was judged to be extremely narrow. The direction and width of cracks in each containment , suggests that they occurred soon after construction and that they are not currently widening. No pattern was observed that would suggest the cracking was caused by prestressing oper,ations. However, the possibility that cracks are related to prestressing cannot be completely ruled out.
* 'C ll construction technology laboratories
CONCLUDING REMARKS
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Based on a site inspection made on February 15, 1983, the following observations can be made:
- 1. Cracks visually inspected in Containment Unit 1 and Unit 2 were measured to have widths on the order of O.002 in.
- 2. Since coating material was observed to have penetrated the cracks, it is. concluded that they occurred prior to the time the walls were coated.
- 3. Under 50 power magnification, appearance of coating filled cracks disclosed that they had not widened since the coating was applied and prestressing was completed.
- 4. Based on the narrow width of the cracks and the lack of any clear relationship between crack patterns and stress patterns likely to have been caused by pre-stressing, it is my opinion that the cracks can be attributed to volume changes caused by temperature effects, creep, and shrinkage. The observation that the cracks have not widened since the coating was applied and prestressing was completed, suggests that the cracks are now in compression. Consequently, it appears unlikely that they can be attributed to stress conditions under final prestressing.
- 5. It is recommended that the cracks be monitored by
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qualified engineers during the pressure testing of Unit 1 and Unit 2. l construction technology Iskorstories
e APPENDIX A Bechtel Crack Mapping Room 110 of Auxiliary Building e
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I [#'[f ,putt o, UNITED STATES NUCLEAR REGULATORY COMMISSION
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,'. h /. 5 E WASHINGTON. D. C. 20555
%; m Wf' ..'.3 N 1 3 'd C Docket Nos: 50-329/50-330 OM, OL APPLICANT: Consumers Power Company FACILITY: Midland Flant, Units 1 & 2
SUBJECT:
TELEPHONE DISCUSSIONS OF JANUARY 11 & 12, 1983 REGARDING UNDERPINNING SETTLEMENT READINGS On January 11 and 12, 1983, the NRC and its consultant from Geotechnical Engineers, Inc. (GEI) participated in a telephone discussion with Consumers Power Company (CPC) and Bechtel. The call primarily discussed settlement records for deep-seated benchmarks associated with under-pinning construction of the two Electrical Penetration Areas (EPA's) . located at the southern portion of the Midland Auxiliary Building. CPC's plans for underpinning the EPA's and the Service Water Pump Structure (SWPS) are described in Supplement 2 of the Safety Evaluation Report (NUREG-0793, October 1982). Enclosure l-is a record of this telephone conversation. w Darl Hood, Project Manager Licensing Branch No. 4 Division of Licensing
Enclosure:
-As stated cc: 'See next page ,
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,- ENCLO3URE s .
RECORD OF TELEPHONE CONVERSATION DATE: January 11, 1983 0 2:00 PM ' PROJECT: Midland RECORDED BY: Joseph D. Kane TALYED WITH: CPC Bechtel $Ei NRC J. Mooney M. DasGupta S. Poulos R. Landsman . . J. Schaub W. Paris J. Kane T. Thiruvengadam R. Wheeler K. Razdan G. Murray R. Ramanujam B. Cuikl J. Darby B. Adler . M. Lewis B. Crouse ROUTE T0: ~< J. Knight H. Singh, COE G. Lear S. Poulos, GEI L. Heller R. Landsman, Region III ... D. Hood J. Kane MAIN SUBJECT OF CALL: To discuss background settlement readings - Auxiliary Building Underpinning ITEMS DISCUSSED: This call had been arranged at the request of NRC to discuss the background (underpinning had not yet started) settlement records provided to NRC for the
, period from 8/23/82 to 10/14/82. The records provided werc for DSB-AN1, DSB-lE, DSB-2E, DSB-AS4 and DMD-3E and the ambient air temperatures for the same time frame. Region III had requested that HGEB review the background data and provide comments on the apparent upward movement of the EPA which is indicated by.the settlement monitoring program.
- 1. CPC was asked to briefly describe the procedure that was followed to -
establish-the uncorrected and corrected settlement curves which were
' provided for the deep-seated benchmarks (DSB). The uncorrected curves are based on the recorded LVDT readings. The occasional small triangles-plotted on the curves are points estabhshed from the back-up dial gages.
The corrected curves adjust the uncorrected curves for temperature changes measured at ,the deep-seated benchmarks (DSB) since the time of. initial
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%' s: installation. Temperature changes are measured at each DSB location at depths of 3 ft,15 ft and 50 ft through thermocouples which were placed during installation. Minimal changes in temperature are being observed below the upper thermocouple. CPC is to provide the temperature readings with depth to support their position that temperature corrections at - DSB-AN1, DSB-AM2 DSB-1E and DSB-1W are not required in the future. The plot of ambient air temperatures which was provided was not used in correcting f]r temperature variations.
- 2. During this call the following information was provided by CPC on a values (See Drawing C-1493(Q) and prior reports for definition of differentia 1' settlement, a j).
Buildir.c Monitorina location Uncorrected Settlement Corrected Settlement (in mils as of 1/11/83) (in mils as of 1/11/8: DSB-ANI (North Main Auxil.) 68 118 DSB-AS4 (South Main Auxil.) 46 63 DSB-2E (East EPA) 35 43 l DSB-3E (Control Tower) ' 22 44 DSB-2W(WestEPA) 27 39 ' Computed values of A) that were given include: DSB-2E-
- 4) = -18 mils DSB-3E:
a) = -17 mils DSB-2W: a) = -15 mils DSB-3W: a) = -10 mils These values are based on uncor.rected readings for DSB-AN1 and corrected readings for the other loctions. The minus signs reflects a magnitude of settlement at the EPA and Control Towers less than the Main Auxiliary .- Building. -
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- 3. Additional information provided by CFC included:
Building Monitoring Actual Settlement (corrected) Location (in mils as of 1/3/83)
-0SB-2W' 29 OSB-3W 38 , ,
DSB-3E 39 OSB-2E 30 Estimated bearing pressures: EPA = 4.5 ksf, Control Tower = 5.2 ksf and Auxil. Bldg. = 9.5 ksf
- 4. Possible explanations for the lahger amount of settiement occurring at the north end of the Main Auxiliary Building were discussed and included:
- a. The heavier loaded Auxiliary Building which rests on glacial till may be picking up additional load from the EPA and Control Tower through cantilever actim because the more compressible till beneath the EPA and Control Tower is providing little foundation support.
- b. The EPA is affected moe by changes in temperature than the other structures which causes an upward expansion of the EPA. This is-reflected as less settlement than the other structures.
- c. The dewatering for underpinning is causing an uneven immediate settle:ent over a relatively large area in the thick glacial till layer.
- 5. The NRC Staff.and its consultant made the following recommendations for plotting of the settlement data in order. to sort out the many variables affecting the settlement readings.
- a. Plot the uncorrected and corrected readings for each monitor location along one line (North Auxil. Bldg. through to Control Tower) at the noon time interval. (On 1/12/83 this was later agreed to be at the midnight interval). Two settlement history plots on standard ll" by 17" graph papr should be developed for each monitoring location.
One plot would have both horizontal and vertical (suggested 1 inch = 20 or.40 mils) arithmetic scales and the other plot would graph time
- in days (1,10,100,1000) on semi-log paper. The temperatures used to correct the data should be plotted on the same graph at the same time interval (Temperaure. plot needed only on settlement graph plotted to arithmetic scales).
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- 6. CPC indicated the requesed settlement plots would be furnished to NRC in about one week's time. This was noted to be acceptable and will permit staff review prior to any site visit for reviewing underpinning progress (now planned for time when pier load test of Wil is being condacted).
- 7. The staff and its consultant believe the relatively small settlement values and the trends of that data which have been recorded to date are a result of temperature changes. It is felt that if sufficient background data were available, where comparable temperature and seasonal conditions .
were repeated, that the effects of sustained temperature changes would be clearer. It is also felt that the apparent upward movement of the EPA with respect to the other structures will be quickly reversed as underpinning operations progress beneath its foundation slab. The present trend indicated by the settlement readings is favorable with respect to the settlement acceptance criteria which has been established to control underpinning operations.
- 8. At the request of R. Ramanujam, CPC, several other items were discussed and included:
- a. CPC plans to explore for buried utilities in advance of drilling the SWPS dewatering wells and soldier piles by using a jet-wash type boring (3-1/2" diameter water pipe) which would be inspected by the Resident Geotechnical Engineer. R. Landsman and J. Kane, NRC, agreed that this type of boring would be acceptable for attempting to locate utilities when performed in foundattn soils which would eventually I
be removed either in underpinning operations or in replacement of service water piping. There is a concern when using this type of drilling that the jetting and washing action, if not properly controlled, could cause
' development of voids and loosenindgf cohesionless foundation soils. .
The NRC staff expressed preference for other types of exploratory drilling (e.g., augering) in areas where future foundation stability was required. W. Paris of CPC indicated that this position does ' give them problems. At the' staff's' request', CPC is to identify the specific location of proposed borings which will be located in permanent foundation soils required to remain stable. This information will be used to guide the staff in a future response on the use of the jet-wash type boring. .
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R. Landsman indicated that his review of underpinning procedures
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b. developed by CPC has identified a problem. The procedures presently indicate that backpacking behind pit excavation lagging is not required when " neat cut" of.the pit excavation is made. CPC indicated-that the lagging would be essentially in direct contact with the foundation soils when neat cutting was performed. After considerable discussion.the major difference became centered on the interpretation of essential and whether the entire length of lagging is required to be in contet or 3 if short, narrow intermittent voids 1 were acceptable behind lagging. All parties did agree that backpacking should be required, even if neat cutting procedures were used, if sufficient voids behind lagging did exist. It was acknowledgedt that reasonable judgtments will have to be made during construction when faced with widelz differing conditions of voids that may run from several inches toseveral feet in length behind the lagging. It is hoped that the early planned site visit will permit the typical void conditions to be viewed where a consensus of agreement can be reached.
- 9. An additional call from J. Kane to R. Landsman and K. Razdan on 1/12/83 requested that settlement be plotted vertically downward in the conventional engineering manner on the settlement history plots which CPC has agreed to
' provide. In addition CPC agreed to provide the background readings for the extensometers and strah monitoring? devices.
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