ML18058A544
| ML18058A544 | |
| Person / Time | |
|---|---|
| Site: | Palisades  |
| Issue date: | 06/15/1992 |
| From: | Masciantonio A Office of Nuclear Reactor Regulation |
| To: | Slade G CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| References | |
| TAC-M81937, NUDOCS 9206250170 | |
| Download: ML18058A544 (7) | |
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'I UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555 Docket No. 50-255 Mr. Gerald B. Slade Plant General Manager Palisades Plant Consumers Power Company 27780 Blue Star Memorial Highway Covert, Michigan 49043
Dear*Mr. Slade:
June 15, 1992
SUBJECT:
EVALUATION OF PALISADES ANCHOR BOLT DESIGN (TAC NO. M81937)
Reference:
Letter from D. C. Kansal, Bechtel Power Corporation, to B. Holian, NRC dated October 21, 1991, same subject The adequacy of anchor bolt design at Palisades has been at issue since it was identified during NRC inspections from September 1990 through April 1991.
We met with Consumers power Company and Bechtel Power Corporation on April 23, 1991, to discuss the application of the unique methodology used in calculating anchor bolt stress allowables.
Our conclusions and recommendations were provided in letter from B. Holian, NRC to D. C. Kansal, Bechtel dated June 13, 1991.
In that_letter, the NRC staff again advised Consumers Power to verify that anchor bolt allowables were not exceeded by reducing the stress capacities in proportion to the ratio of anchor bolt separation distances in order to arrive at a conservative assessment of bolt capacities. A response to our recommendations was provided by Bechtel Power Corporation in the referenced letter.
We have reviewed the information provided in the October 21, 1991, letter.
Based on our review, we have concluded that, although the approach described is more logical than the previous approach, it is still deficient and unacceptable.
The basis for our conclusions is provided in the enclosed evaluation.
In order to speed up the reevaluation of the adequacy of anchor bolt design at Palisades, we have developed an alternative approach which is consistent with the approach developed by the Seismic Qualification Utility Group for the
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- implementation of USI-46 (verification of seismic adequacy of mechanical and electrical equipment in operating nuclear power plants).
The enclosed evaluation report provides our recommendations.
We request that you inform us of your intended course of action for resolving the anchor bolt design problems.
Enclosure:
As stated cc w/enclosure:
See next page DISTRIBUTION:
- ~ Docket File JZwolinski G. Bagchi EGSB WShafer OFFICE LA:PDIII-1 NAME DATE LPDR & PDR AMasciantonio M. Ring RIII Sincerely, Original signed by Armando Masciantonio, Project Manager Project Directorate III-1 Project Division III/IV/V Office of Nuclear Reactor Regulation PD31 Reading file BBoger MShuttleworth Plant file OGC ACRS(lO)
PM:PDIII-1 ~ PDIII-1 Masciantonio LMarsh h //Z./92 v I r~/92 OFFICIAL RECORD COPY FILENAME: B:\\SLADE.LTR
Mr. Gerald B. Slade Consumers Power Company cc:
M. I. Miller, Esquire Sidley & Austin 54th Floor One First National Plaza Chicago, Illinois 60603 Mr. Thomas A. McNish, Secretary Consumers Power Company 212 West Michigan Avenue Jackson, Michigan 49201 Judd L. Bacon, Esquire 212 West Michigan Avenue Jackson, Michigan 49201 Regional Administrator, Region III U.S. Nuclear Regulatory Commission 799 Roosevelt Road Glen Ellyn, Illinois 60137 Jerry Sarno Township Supervisor Covert Township 36197 M-140 Highway Covert, Michigan 49043 Office of the Governor Room 1 - Capitol Building Lansing, Michigan 48913 Mr. Patrick M. Donnelly Director, Safety and Licensing Palisades Plant 27780 Blue Star Memorial Hwy.
Covert, Michigan 49043 Resident Inspector c/o U.S. Nuclear Regulatory Commission Palisades Plant 27782 Blue Star Memorial Hwy.
Covert, Michigan 49043 Palisades Plant Nuclear Facilities and Environmental Monitoring Section Office Division of Radiological Health Department of Public Health 3423 N. Logan Street P. 0. Box 30195 Lansing, Michigan 30195 Gerald Charnoff, P.C..
Shaw, Pittman, Potts &
Trowbridge 2300 N. Street, N.W.
Washington, D.C.
20037 Mr. David L. Brannen Vice President Palisades Generating Company c/o Bechtel Power Corporation 15740 Shady Grove Road Gaithersburg, Maryland 20877 Roy W. Jones Manager, Strategic Program Development Westinghouse Electric Corporation 4350 Northern Pike Monroeville, Pennsylvania 15146 Mr. David Joos, Vice President Energy Supply Services Consumers Power Company 212 West Michigan Avenue Jackson, Michigan 49201 Mr. Dinesh C. Kansal Manager Quality Assurance Bechtel Power Corporation 9801 Washington Bl v.d.
Gaithersburg, Maryland 20878
ENCLOSURE EVALUATION OF PALISADES ANCHOR BOLT DESIGN BACKGROUND Bechtel submitted a report entitled "Response to June 13, 1991 NRC letter to Bechtel regarding Palisades anchor design", dated October 21, 1991.
Bechtel developed a new approach, called detailed approach in the report, for reevaluation of anchor bolts* tensile capability at Palisades, and illustrated through mathematics that the new approach should yield only minor difference in results from that of the previous approach, called simplified approached in the report.
Furthermore, the report stated that the results of the evaluations using the detailed approach were identical to those using the simplified approach, and in all cases the anchors were determined to have sufficient capacity to sustain the imposed loading without exceeding design limits.
With respect to the extent of application of the simplified approach, the report stated that the approach was uniquely developed by Palisades project personnel solely for Palisades application.
EVALUATION Both the detailed and simplified approaches were developed based on the 45 degree concrete-failure-cone theory put forth in Appendix B of the ACI-349 code without examining the validity of that theory.
The assumed 45 degree concrete-failure-cone is only a hypothesis, and the validity of that assumption has been controversial and challenged by test data.
Test data (see Reference 1) have shown that the concrete-failure-cone is about 30 degrees for a single headed stud em.bedded in concrete and loaded in tension.
Test data for expansion anchors (s~e Reference 2) have also shown the concrete-failure-cone is about 30 degrees.
Test data in References 1 and 2 have shown that the tensile capacity of anchors is affected (reduced) if an anchor is located less than a distance of 1.75 times the em.bedment length of the anchor from a concrete free edge, and if anchors are spaced less than a distance of 3.5 times the em.bedment length of the anchors.
These test data have challenged the validity of design approaches based on the 45 degree concrete-failure-cone theory.
Based on the 45 degree concrete-failure-cone theory, the tensile capacity of any anchors would not be affected (reduced) when anchors are spaced no less than 2.0 times the em.bedment length of the anchors.
Therefore, as far as the anchor spacing effect on the tensile capacity of multi-anchors is concerned,
- which is the case in Palisades anchor design, the use of 45 degree concrete-failure-cone assumption is not only inaccurate but also unconservative.
v 2
The report stated that the two approaches developed by Bechtel were consistent with good structural engineering practice, and had employed the criteria of Appendix B of ACI-349 code.
However, the NRC staff has not endorsed the Appendix B of ACI-349 code, and has rejected its use in a previous license submittal with respect to under-cut anchors. It is the staff's understanding that the ACI-349 and ACI-355 code committee members have been investigating the validity of the 45 degree concrete-cone-failure theory for a period of time and the investigation is still going on.
Based on the available information to the staff, the two approaches developed by Bechtel are unacceptable to the staff.
The anchor problem at Palisades is somewhat complex, because it involves Hilti expansion bolts (classified as non-ductile bolts by Bechtel) closely spaced with Drillco under-cut bolts (classified as ductile anchors by Bechtel), and the two kinds of bolts are embedded at different depths.
Recognizing that the knowledge in anchorage has not advanced to such a stage.
that the complex problem at Palisades can be resolved by the simple application of the ACI code criteria and that there is a need to assess the adequacy of those anchors, the staff has specified its approach and criteria for the evaluation of anchors at Palisades in the next section.
APPROACH AND CRITERIA FOR PALISADES ANCHORS The approach and criteria specified below are consistent with the approach and criteria for anchorage (see Reference 3) developed by the Seismic Qualification Utility Group (SQUG) for the implementation of OSI A-46 (verification of seismic adequacy of mechanical and electrical equipment in operating nuclear power plants).
The approach and criteria have been specified and adjusted in such a way that some of the concepts used by Bechtel, based on the 45 degree concrete-failure-cone theory, can still be used for calculations.
The approach requires three-step verifications:
- 1.
to verify that the allowable tensile force of single Drillco under-cut bolts is greater than the maximum tensile load for these bolts assuming no loads on the Hilti bolts.
The allowable tensile force is one half of the concrete capacity.
The concrete capacity is calculated by multiplying an assumed tensile capacity of the concrete with the projected cone area of a single Drillco bolt based on the 45 degree concrete-failure-cone assumption.
This concrete capacity calculation is identical to the equation 2 in the Bechtel report, or the procedures in Appendix B of ACI-349 code.
This step of verification assumes that the support, which is anchored by Drillco bolts, is subjected to the maximum tensile load, but the adjacent
3 support, which is anchored by Hilti bolts, is subjected to no tensile load.
- 2. to verify that the allowable tensile force of single Hilti expansion bolts is greater than the maximum tensile load for these bolts assuming no loads on the Drillco bolts.
The allowable tensile force is one fd'~th of the average of the ultimate tensile capacity of test bolts.
This step of verification assumes that the support, which is anchored by Hilti bolts, is s:ubjected to the maximum tensile load, but the adjacent support, which is anchored by Drillco bolts, is subjected to no tensile load.
- 3. to verify that the allowable tensile force of the combined anchor system in the concrete is greater than the sum of the load capacity of the Drillco and Hilti boltse The allowable tensile force is the ultimate concrete tensile capacity of the combined anchor system divided by a factor of 1.s.
The ultimate concrete tensile capacity is calculated by multiplying an assumed tensile capacity of the concrete with the combined projected cone area based on the 45 degree concrete-failure-cone assumption.
This concrete capacity calculation is identical to the equation 2 in the Bechtel report, or the procedures of Appendix B of ACI-349 code.
The combined load capacity is the sum of the Drillco bolts*capacity and the Hilti bolts*
capacity within the combined projected cone area.
The Drillco bolts* capacity is calculated by multiplying the total effective areas of bolts with the minimum specified yield stress of the bolt.
The Hilti bolts*
capacity is the average of the ultimate tensile capacity of test bolts.
This step of verification assumes that both supports are imposed with maximum tensile loads.
CONCLUSION AND RECOMMENDATION The staff has reviewed the Bechtel submittal, dated October 21, 1991, and found that both the detailed and simplified approaches are deficient and unacceptable.
The staff has specified its approach and criteria for Palisades anchor bolt reevaluation as an alternative.
The staff's approach and criteria are consistent with that developed by the SQOG for the implementation of OSI A-46 (verification of seismic adequacy of mechanical and electrical equipment in operating nuclear power plants).
4
References:
- 1. Bode, H., and Roik, K., "Headed studs Embedded in Concrete and Loaded in Tension," Anchorage to Concrete, SP-103, American concrete Institute, D*troit, 1987, pp.61-88.
- 2. Eligehausen, R., "Anchorage to Concrete by Metallic Expansion Anchors," Anchorage to Concrete, SP-103, American concrete Institute, Detroit, 1987, pp.181-202.
- 3. Seismic Qualification Utility Group, 11Generic Implementation Procedure (GIP) for seismic Verification of Nuclear Plant Equipment, 11 Section 4, and Appendix c, Revision 2, June 28, 1991.