ML20031C648
| ML20031C648 | |
| Person / Time | |
|---|---|
| Site: | Callaway  |
| Issue date: | 10/01/1981 |
| From: | Sen S BECHTEL GROUP, INC., UNION ELECTRIC CO. |
| To: | |
| Shared Package | |
| ML20031C639 | List: |
| References | |
| ISSUANCES-OL, NUDOCS 8110070396 | |
| Download: ML20031C648 (12) | |
Text
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N UNITED STATES OF AMERICA NULM REGULATORY COMMISSION BEFORE THE ATOMIC SAFETY AND LICENSING BOARD In the Matter of
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UNION ELECTRIC COMPANY
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Docket No. STN 50-483 OL
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(Callaway Plant, Unit 1)
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AFFIDAVIT OF SUBIR K. SEN IN SUPPORT OF APPLICANT'S MOTION FOR
SUMMARY
DISPOSITION OF JOINT INTERVENORS' CONTENTION NO. I. D (CONCRETE COVER)
County of Mentogmery )
- SS State of k ryland
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i SUBIR K. SEN, being duly sworn, deposes and says as follows:
1.
I am an Engineering Specialist assigned to the staff of the Chief Civil Engineer of Bechtel Power Corporation ("Bechtel"). My business address is 1574C Shady Grove Road, Gaithersburg, Maryland 20877. A summary of my professional qualifications and experience is attached hereto as Exhibit "A".
I have personal knowledge of the matters stated herein and believe them to be true and c.orrect. I make this Affidavit in supgrt of Applicant's Motion for Summary Disposition of Joint Intervenors' Contention No. I.D (Concrete Cover) in this proceeding.
2.
Bechtel Power Corporation is the Architect / Engineer for the SNUPPC project, including the Callaway Plant. The Bechtel i
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organizations have been engaged in constructfon and engineering activities since 1898. Bechtel has substantial experience in the design and engineering of electrical power generation projects. For over 25 years, Bechtel has been actively working on auclear projects, including power plant design, engineering and construction.
3.
The function of the Civil Engineering Staff within the Bechtel 2ower Corporation is to provide techical guidance to the Bechtel proj ects. As a member of the Civil Staff, I have advised Bechtel's i
SNUPPS project team concerning concrete cover requirements.
4.
The purpose of this Affidavit is to demonstrate that 1
Applicant's interpretation of the concrete cover requirements was reasonable, and that in any case the concrete cover on the reactor building at the Callaway Plant is adequate to perform its design functions.
5.
Concrete cover is the thickness of the concrete layer j
measured from the concrete surface to the nearest surface of the reinforcing steel ("rebar"). The concrete cover which appears to be of interest in Joint Intervenors' Contention No. I.D is the thickness of the layer of concrete between the outside face of the reactor building wall and the outside edge of the rebar nearest to that face of the wall.
6.
In the construction of the four-foot thick reactor building wall, the prefabricated steel reinforcement bars were first positioned one at a time, in the. annular space bounded by a formwork which served to retain the concrete when it was poured. The rebars, however, were required to be located so as not to interfere with rebars l
already installed or with other items, such as penetration sleeves and anchor bolts, embedded in the concrete.
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Because it is not practical to build to theoretical design dimensions, ce:tain amounts of tolerances are allowed, for example, in the fabrication of the rebars and in the erection of the formvork rebars and otiser embedded items. These tolerances are identified in the construction specifications and constitute limited deviations about a mean value used in the design. Since any variation 1
in the locations of rebar and/or formwork would affect the concrete j
cover, it is standard engineering practice to provide a similar j
tolerance band on the specified concrete cover used in the design.
Consequently, as long as the concrete cover in actual construction is maintained within the specified tolerance band, it is considered to have met the design requirements.
8.
In reinforced concrete members, the concrete cover for i
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rebar serves two specific purposes:
(a) to protect the steel from corrosion in an adverse environment; and, (b) to provide an adequate s
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bond between the rebar and concrete such that the rebar can be effective in helping the concretc structure to support loads imposed upon it.
9.
The degree to which concrete will provide satisfactory
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corrosion protection is a function of the severity of the exposure conditions, the permeability of the concrete, acd the presence of cracks i
in the concrete cover.
10.
Under most conditions concrete, because of its high alkalinity and relatively high electrical resistancy in normal atmospheric exposure, provides adequate protection of rebars against exposure. The environment to which the Callaway Plant reactor building wall will be subjected during the life of the plant is expected to be normal atmospheric conditions which will not be unusually corrosive 4
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m chemically nor abrasive. The exposure conditions at Callaway will not approach those of marine structures to sea water, or of bridge decks to salt laden de-icing agents - the two comon examples of severe exposure situations. Nevertheless, exposure tests conducted in extremely aggressive environments have revealed:
(a) No corrosion that would affect structural performance in reinforcing bars with 3/4 inch cover in prestressed beams exposed to freezing and thawing in sea water for 20 years at the Corps of Engineers severe exposure station in the State of Maine.
(Ref. 1: " Design of Permanent Seawater Structures to Prevent Deterioration," presented by M.
Shupack at the American Concrete Institute Fall Convention in San Juan, Puerto Rico, September 26, 1980).
(b) A minimum cover of 1.7 inches to be adequate for corrosion protection for slabs subjected to a test of 830 daily applications of stit solutions in a test conducted by the Federal Highway Administration.
(Ref. 2:
" Time to Corrosion of Reinforcing Steel in Concrete Slabs," Federal Highway Administration Report No.
FHWA-RD-76-70, Vol. 3, 1976).
- 11. Permeability of concrete is also a factor which affects the process of corrosion of embedded materials. Lower concrete permeability affords a higher degree of corrosion protection. One of the parameters which when properly controlled results in concrete with low permeability is mix proportioning -- i.e., the water-cement ratio.
Severe exposure tests have shown that a water-cement ratio of 0.45 provides good protection against corrosion, and that concrete with a water-cement ratio of 0.4 performed significantly better than concrete with water-cement ratios of 0.5 and 0.6.
(Ref. 3: " Guide to Durable
t Concrete," American Concrete Institute Committee 201 Report - Title No.
74-53). In fact, it has been cer.cluded that a reduction of the water-cement ratio from 0.5 to 0.4 is equivalent to increasing the cover by one inch (Ref. 2). A water-cament ratio of 0.4 was used for the concrete in the Callaway Plant reactor building wall.
- 12. Cracks leading from the surface of the concrete to the reinforcement (i.e., traversing the concrete cover) may provide access for corrosive ingredients to come into contact with th( rebars.
Although it is recommended that in aggressive environments crack widths j
should be minimized to safeguard against corrosion, tests and research have indicated that there is no general relationship between cracking and corrosion.
(Ref. 4: "Corrosien of Reinforcing Steel in Concrete and its Relation to Cracking," by A. W. Beeby in The Structural a'
Engineer / March 1978/ho.3/ Volume 56A).
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- 13. Cracks in concrete cover ara generally controlled by placing rebars as close to the surface as practical. Based upon 4
extensive research studies on cracking behavior, it has been concluded that the cracking mechanism in two-way action slabs and plates is controlled primarily by the steel stress level and the spacing of the reinforcement in the two perpendicular directions, and only to a small extent by the magnitude of the concrete cover.
(Ref. 5: " Control of Cracking in Concrete Structures," American Concrete Institute Committee 224 Report -Title No. 69-69, December 1972). The reactor building wall can be classified as a two-way action plate structure for which, as i
indicated above, a smaller concrete cover will not Leve any detrimental effect from the standpoint of corrosion.
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- 14. The potential for corrosion through cracks in the concrete cover diminishes even more when it is recognized that the reactor building wall is a prestressed concretri structure where the wall i
is la a state of compression under the long-term normal operating coM ition. Because of the prestriassing, the cracks in the wall will close on application of the prestressing, and the applied compressive load will reduc's the tension stress'es in the rebar.
- 15. Adequate bond between the rebar and surrounding concrete, which must be maintained so that the rebar can be effective in carrying i
i tensile stresses, is ensured if there is no failure or disintegration of j
the concrete cover. According to the ACI 318-71 Stai,dard, a minimum design concrete cover of 1-1/2" for walls is deemed adequate where exterior exposure is not encountered. With the allowable construction tolerance of 1/2", this cover can be as small as 1" and yet satisfy the requirements for bond.
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- 16. No approved national standard or code existed i
specifically for the design and construction of reactor buildings at the time the initial design work conunenced and the licensing effort was in t
progress for the SNUPPS project. Consequently, Bechtel prepared a Topical Report, BC-TOP-5, which was approved by the NRC Staff for uas on the SNUPPS project, including the Callaway Plant, and which provides, in part, the techniques and procedures used for the design of the l
prestressed concrete reactor building. The design criteria prer.,ented in j
the Topical Report, issued in June 1974, essentially incorporated the available draft information (January 1971) of a report prepared by a joint ACI-ASME (American Concrete Institute-American Society of
(
l Mechanical Engineers) technical committee. Since the Topical. Report is i
linke, to design considerations only, ACI standard 318-71, along with other applicable codes and standards, were referenced to cover those matters of fabrication and construction not included in the Topical Report. Specifically, ACI 318-71 is utilized in connection with the placing and splicing of reinforcing steel.
- 17. The SNUPPS Preliminary Safety Analysis Report ("PSAR")
references BC-TOP-5 which specifies the minimum and maximum concrete i
i cover to be used in the design. BC-TOP-5 specifies a minimum of two inches and a maximum of 1/5 the section thickness (or about 10 inches for the SNUPPS reactor building wall) of concrete cover for design purposes. The PSAR states that the tolerance on the cover shall be as much as + 1-1/2 inches, but that the cover shall not be reduced by more than 1/3 the specified (i.e., design) cover.
- 18. ACI Standard 318-71 provides that when exposed to the weather, the minimum design concrete cover shall be two inches for reinforced concrete walls, and one inch for prestressed concrete walls.
No specific maximum cover has been prescribed. ACI 318-71 also states char the minimum cover is cubjec: to construction tolerances except that it cannot be reduced by more than 1/3. The recommendations of this ACI Standard, which is the most widely used code for concrete structures, are tempered by years of extensive field experience in many different environmenee.
- 19. The reactor building wall at the Callaway Plant is a prnatressed concrete structure where the wall is in a state of compression undct the long-term, normal operating condition. The effect of this prestressing is two-fold:
(a) concrete cracks in the wall are minimized or eliminated altogether, greatly reducing the potential for
robar corrosion; and, (b) the tension stresses in rebar are lowered, thereby reducing the bond development requirements. As recognized by the ACI Standard discuased above, the net effect of prestressing is to reduce the overall concrete cover requirement. While the ACI standard recommends a minimum concrete cover of one inch, with tolerance, for prestressed concrete walls, the design specification for the SNUPPS PSAR was two inches, with tolerance. Thus, the requirement as applied at the Callaway Plant was more than adequate from a technical standpoint.
- 20. According to the NRC Report, on January 5, 1978, the NRC i
Staff conducted a special announced investigation into anonymous l
allegations regarding, among other things, improper _ concrete cover for reinforcement. The NRC inspectors did not agree with th: Applicant's interpretation of min 4=== :over requirements which wouJ a allow a reduction of the two-inch mini =um cover by one-third. The NRC personnel indicated that their interpretation of the requirement was that the two-inch minimum cover cannot be further reduced. See NRC Inapection Report No. 50-483/77-11, pp. 10,11.
- 21. According to the NRC Inspection Report No. 50-483/78-01, NRC inspectors on January 10-13,1978,1dentified apparent deviations regarding placement of face reinforcement steel where the concrete cover exceeded the design maximum or was found less than the design minimu.
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- 22. Subsequently there was a meeting on January 23, 1978, in l
Bethesda, Maryland between representatives of the Applicant land the NRC l
Staff to discuss, among other things, concrete cover requirements.
The l
NRC staff repeated that their interpretation of the cover requirement I
was that the two-inch =4a4=n= cover could not be further reduced. Also, while the NRC Staff indicc.ted that the 10-inch maximum cover was l
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absolute, local variations to the maximum cover may be considered in special cases where necessary due to wall blockouts. The NRC Staff indicated that it would be acceptable if the cover requirements, as interpreted by the Staff, were fully met in the area of the sixth lif t, utilizing the fif th lif t as a transition area.
(See NRC Inspection Report No. 50-483/78-01). Union Electric Ccmpany subsequently agreed to comply with the NRC Staff's interpretation of the concrete cover requirements starting at the sixth lift. Design documents were revised to reflect this decision.
- 23. For the reasons stated above (paras. 8-15), the design functions of the concrete cover -- corrosion protection and bond development -- are not compromised when the design minimum concrete cover is reduced by allowable construction tolerances. Therefore, application of such a minimum cover requirement in the Callaway Plant reactor building wall below the sixth lift will not affect the integrity of the structure.
- 24. With respect to the maximum cover requirements below the sixth lift, there are only very local areas around two electrical i
i penetrations blockouts where, due to the geometry of the blockout, field tolerances were utilized inwardly so that maximum cover requirements are i
exceeded. However, the purpose of the crack control provisions in BC-TOP-5 is primarily intended to be applicasia for the main body of the shell to control general face cracking. Over local areas a strict adherence to the placing provision was not intended and was not viewed to be technically required. None of the areas affected by increased reinforcing cover are exposed to outside environmental conditions.
Rather, the exterior wall of the reactor building shall in these areas
is enclosed within the environment of the auxiliary building.
Censequently, Bechtel properly dispositioned a Non-Conformance Report (NCR-2-2055-C-A) on these field tolerances on a "use as is" basis.
Considering the fact that the building is prestressed, it is inconceivable that the structural integrity of the containment shell will be compromised in any way where the maximum cover design limits were exceeded in these local areas.
- 25. The issue of concrete cover requirements does not involve any quality assurance problem in connection with the Callaway Plant.
Applicant and its contractors did not grossly misunderstand or ignore the requirements. They were consistently applied through tha fourth lift. Applicant believes today that its interpretation of the requirements was technically correct and sound. The NRC Staff advanced a different interpretation of the requirements, which are subject to more than one reasonable interpretation, and Applicant agreed to,cilize the NRC Staff's interpretation beginning with the sixth lift.
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iubir K. Sen
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Subscribed and sworn to before me t.his 1st day of October, 1981.
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L LloWW Diane W. Carpenter, Notfry Public My Commission Expiree Jbly 1, 1982 4
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EXHIBIT A NAME S. K. SEN POSITION Engineering Specialist EDUCATION BE, University of Calcutta MS, Washington University DSc, Washington University.
Graduate studies in Business Management
SUMMARY
4% Years Staff specialist for nuclear containmerit and shell structures and for wind, tornado, and impact effects on structures 3% Years Engineering and design in nuclear power plant projects 3 Years Research work on finite element analysis, shell structurrs and composite construction 3 Years Engineering and design for fossil s,ower plants projects EXPERIENCE Dr. Sen is a specialist assigned to the staff of the chief civil engineer. His responsibilities include guiding and performing special analyses and design work pertaining to nuclear containment and other complex structures. He is involved in developmental work in the area of wind, tornado, impact and inelastic effects on structures. In addition, he provides expert assistance to various projects on shell structures, finite element analyses, prestressed concrete, testing and design of structural systems and stadstical analyses.
Dr. Sen was a scnior engineer on the PWR Midland Nuclear Power Plant Units 1 and 2 (500 MW and 800 MW, respectively) for the Consumers 4
Power Company and the 1300 MW BWR Grand Gulf Nuclear Power Station Units I and 2 for Mississippi Power & Light Company. He worked on the design of concrete containment shell, stiffened equipment hatch assembly and free-standing large steel containment dome. Dr. Sen was involi ed in the Mark I containment integrity study for the General Electric Company and also participated in the selection cf the containment structure for t'.ie 1300 MW BWR Skagit Units I and 2 for Puget Sound Power & Light Company.
Prior to joining Bechtel, Dr. Sen was associated with Washington University where he performed research work on finite element analysis, shell struc-tures and composite construction. Before his relocation to the U.S.A.,
Dr. Sen was involved in the design of fossil-fueled power plants in India.
Dr. Sen is an active member of the American Concrete Institute Code Committee on Nuclear Safety-Related Concrete Structures (AC1349)
PROFESSIONAL j
MEMBERSHIPS Member, American Society of Civil Engineers Member, American Concrete Institute REGISTRATION Registered Professional Engineer in Michigan 9/81
t PUBLICATIONS
- 1. Sen, S. K.; and Giltmb::s, T. V. "Ccmposite Open Web Jcists,"
Washington University Research Report No. 24,1969.
- 2. Gould, P. L.; and Sen, S. K. " Refined Mixed Method Finite Elements for She!!s of Revolution," Proc. Third Conf. on Matrix Methods in Structural Mechanics, Wright Patterson Air Force Base, Ohio,1971.
- 3. Sen, S. K.; and Gould, P. L. " Criteria for Finite Element Discretization of Shells of Revolution," Int. Journal for Numerical Methods in Engr., Vol. 6, No. 2 (1973).
- 4. Sen, S. K.; and Gould, P. L. " Free Vibration of Shells of Revolution Using FEM," J. Engineering Mech. Div., ASCE, Vol. 100, 283-303 (1974).
- 5. Sen, S. K.; and Gould, P. L. "Hyperboloidal Shells on Discrete Supports," J. Structural Div., ASCE, Vol. 99,595-603 (1973).
- 6. Gould, P. L.; Sen, S. K.; and Suryoutomo, H. " Dynamic Analysis of Column. Support Hyperboloidal Shells," Int. Journal for Earthquake Engineering and Structural Dyn., Vol. 2,269-279,1974
- 7. Gould, P. L.; Sen, S. K.; Wang, R.; Suryouwmo, H.; and Lowrey, R.
" Column Supported Cylindrical Cenical Tanks," J. Structural Div.,
ASCE, Vol.102, Feb.1976.
- 8. Gould, P. L.; Swryoutomo, H.; and Sen, S. K. " Stresses in Column.
Supported Hyperboloidal Shells Subject to Seismic Loading," Int. J.
Earthquake Engr. and Structural Dynamics, Vol. 5, No.1,1977.
- 9. Shah, G.; Sen, S. K.; and Wen, R. " Design Guide for Natural Draft Hyperbolic Cooling Towers" Bechtel Power Corp., Design Guide No.
C-2.40.
- 10. Elgaaly, M.; Sen, S. K.; and Cheung, C. F. "Analy:is of a Prestressed Concrete Containment-Dome with Circular Openings." Presented at the Fourth International Conference on Structural Mechanics in Reactor Technology held at San Frucisec, CA (Aug.1977).
- 11. McMahon, P., Sen, S. K.; Meyers, B. L.; and Buchert, K. P.
" Structural Response of R/C Slabs to Tornado Missiles," Journal of the Structural Division, ASCE, March 1979.
- 12. McMahon, P. M.; Sen, S. K; and Meyers, B. L. " Behavior of Rein-forced Concrete Barriers Subject to the Impact of Turbine Missiles,"
presented at the 5th SMIRT Conference in Berlin, August 1979.
- 13. Buchert, K. P.; and Sen, S. K. " Application of the Split. Rigidity Concept to Concrete Cracking in Reactor Containment Design,"
presented at the 5th SMIRT Conference in Berlin, August 1979.
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- 14. Burdette, E.G.; Sen, S.K.; and Ismen, E. "Effect of Abandoned Holes
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on Pull-out Capacity of Wedge Bolts," to be published in the Journal of the Structural Division ASCE 9/81 l
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