ML20235Z341
| ML20235Z341 | |
| Person / Time | |
|---|---|
| Site: | 05000000, San Onofre |
| Issue date: | 04/11/1971 |
| From: | Hall W, Newmark N NATHAN M. NEWMARK CONSULTING ENGINEERING SERVICES |
| To: | |
| Shared Package | |
| ML20235X376 | List:
|
| References | |
| FOIA-87-462 NUDOCS 8710210093 | |
| Download: ML20235Z341 (11) | |
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Re'gulatory Fite Cy.-
g3.g.d wNr cat:4-DRAFT-REPORT TO AEC REGULATORY STAFF 1
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l ADEQUACY OF. THE STRUCTURAL CRITERIA FOR' SAN ONOFRE. NUCLEAR GENERATING STATION UNITS 2. AND 3 i
l Southern California Edison Company:
San. Diego Gas and Electric Company AEC Docket Nos. 50-361 and 50-362 1.
by i
N. M. Newmark and'
. W. J. Ha l l l
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11 April '1971 g.
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8710210093 871014 PDR -FOIA SCHADRAB7-462' PDR l
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a ADEQUACY OF THE STRUCTURAL CRITERIA FOR SAN ONOFRE NUCLEAR GENERATING STATION UNITS 2 AND 3 Southern Calliornia Edison Company and San Diego Gas 'and Electric Company by N. M. Newmark and W. J. Ha ll INTRODUCTION This report is concerned with the adequacy of the containment structures and components for a 2-unit nuclea r power station, San Onofre Units 2 and 3, for which application for a construction permit has been made to the U.S. Atomic Energy Commission by the Southern California Edison Company and the San Diego j
Gas and Electric Company.
The facility is located on the west coast of Southern California on the Pacific Ocean in San Otego County, approximately 62 miles southeast of Los Angeles and approximately 51 miles northwest of San Diego.
This report is based on information and criteria set forth in the Preliminary Safety Analysis Report (PSAR) and amendments thereto, as ilsted at the end of this report.
Also, we have participated in discussions with the AEC Regulatory Staff concerning the design of this unit.
The two units will be constructed on the existing San Onofre site and will be located immediately south of Onof re Unit 1.
DESCRIPTION OF FACILITY The San Onof re Units 2 and 3 will each consist of nuclear steam supply systems (NSSS) with an associated pressurized water reactor t hat will operate at core power levels up to 3390 MWt.
The core and the NSSS design are similar to that of Hutchinson Island Unit 1, and the reactor coolant system is quite similar to that for Palisades Unit 1.
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f The reactor containment structure, which houses the reactor and steam generators, consists of a concrete vertical right cylinder with a flat base and a' shallow-domed roof.
The planned preliminary dimensions of the containment g
structure are as follows:
inside diameter,130 f t ; inside height,' 185 f t ;
cylindrical wall thickness, 4 f t; and dome thickness, 3.1/2 f t.
The cylindrical portion of the containment structure is post-tensioned with horizontal (hoop) and verticcl tendons.
The hoop tendons are anchored at 3 buttresses equally spaced around the containment structure.
These tendons extend 240 around the l
3 cylinder periphery, bypassing Intermediate buttresses.
The dome has a 3-way post-tensioning system.
The foundation slab is conventicnall', reinforced with high-strength reinforcing steel.
The Interior of the containment shell Is steel-lined with ASTM A-285 carbon steel plate.
Personnel and equipment access hatches are provided to permit access to the facility.
There are a number of additional penetrations for piping and j
q electrical condults.
l Section 2.9 of the PSAR Indicates that major structures will be founded in the San Mateo foundation.
The applicant Indicates that even the heaviest structure can be supported in this material using spread footings or mat f oundat i ons.
SOURCES OF STRESSES IN CONTAINMENT STRUCTURE AND CLASS I C04PONENTS The containment structure is to be designed for the following loads:
dead load, including hydrostatic pressure; live load; acciden,t containment design pressure of 60 psig; proof test pressure at 115 percent cf design pressure; external pressure of 2 psi; thermal load arising f rom the maximum temperature gradient through the concrete shell and mat, based on a raximum design temperature in excess of 250 F; wind load varying with the height and corresponding to a 90~
miles per hour basic wind 30 f t above grade; and seismic loads, as described next.
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3 The applicant, in the PSAR in Section 5, indicates that the design is to be made for a Design Basis Earthquake characterized by a maximum horizontal ground acceleration of 0.50g to insure containment and safe shutdown; the plant is also to be designed for an Operating Basis Earthquake based on a maximum horizontal ground acceleration of 0.25.
The seismic design levels for 9
this facility are still under review by the representatives of NOS, USGS, and AEC and their consul tants. No further comment will be made in this report on the seismic design levels until such time as this review has been completed.
Similarly, no comment is made herein on design against possible fault motions until such time as the review is completed.
COMMENTS ON ADE00 ACY OF DES IGN I
Foundations and Cuts The PSAR presentation indicates that heavy structures will be supported on spread footings or mat foundations, and that for these types of foundations the total and dif ferential settlement will be small.
The foundation scheme proposed by the applicant is acceptable to us.
The applicant indicates that the highly compacted, dense nature of the l
San Mateo formation makes the chance of 1Iquef action of the foundation sands during an earthquake unlikely. We concur in this evaluation.
There is an indication on page ll-17 of Appendix 2B that cuts as deep as 70 f t will be required for the construction of Units 2 and 3.
Slope stability L
analyses have been carried out for earthquake accelerations corresponding to 0.259 and 0.50g.
These analyses are described briefly in Appendix 28.
1 Further elaboration on the excavated slopes for Units 2 and 3 is presented in Section 2.9 beginning on page 2.9-0 ( Amendment 6 f and indicates that the slopes are considered critical or noncritical, depending upon whether l
4 slippage can cause any structural or equipment damage at the plant.
The discussion given indicates that vertical earthquake effects have been considered
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in a preliminary fashion along with the horizontal effects, and that it is estimated that the amount of slippage can be handled by the terraces and other provisions incorporated in the site design.
There is every reason to believe that, with coroful analysis, the possibility of slope failures can be calculated adequately to insure the safety of the plant and critical items of equipment.
On the basis that comprehensive analysis will be carried out for the appropriate j
i levels of earthquake excitation finally agreed upon for the plant design, and that the design criteria will incorporate conservative safety factors against slip, we concur in the general approach adopted for the design of the cut slopes.
The discussion on page 1.8-38 of the PSAR indicates that the containment structure foundation will be located approximately 20 f t below the adj acent finished grade.
The method selected for handling this soil-structure interaction is not presented but it is indicated that the details of the procedure will be based upon the reference material given in Section B1 of Appendix B, and will be submitted af ter a more detailed design.
I On page 1.8-49 at the bottom of the page, there is a statement Indicating that approximate analysis of containment structures for local loading originating j
i f rom the earthquake exci tation will be made.
It is indicated that previous work on similar containments indicates that there is disagreement concerning the actual local effects on the portion of the structure below grade among experts, and that the designers plan to consult with the seismologists and seismic consul tants on the detail s.
l We interpret these various statements to mean that further information l
will be forthcoming as to the cri te ria to be employed in design to account for j
possi bl e soil-s tructure interaction.
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Response Spectra l
l The proposed response spectra for the San Oncfre Nuclear Generating 1
i Station Uni ts 2 and 3 are presented in Figs. 2.10-1 and 2.10-2, and Figs. B' 2-1 and 8.2-2.
The two sets of spectra appear to-be identical.
The horizontal response. spectra for the Operating Basis Ea. thquake is shown-for a base acceleration value of 0.209 and that for the D8E is shown for 0.25 ; it will 9
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be noted that these acceleration levels, corresponding to the bound in the high-frequency region, and used as descriptors,. are not even the same as the j
seismic criteria noted in other places in~ the PSAR (i.e., 0.25g and 0.50g).
The discussion at the bottom of page 8.2-5 indicates that these response spectra were developed by Dames & Moore in consul tation with Dr. G. V.
Housner, and are based on references given in Subsection 8.1.
Unfortunately, reference to Subsection 8.1 does not indicate the source of the development of l
the spectra shown.
It appears that the spectre may be patterned af ter some specific earthquake or earthquakes, al though this is not clear.
There are a j
number of points that remain to be clarified about the spectra, including their j
basis of derivation, and the reasoning leading to the frequencies chosen at which the spectra are f aired into the acceleration bound in the high-frequency region.
Since the seismic design criteria are'still under study, it is expected that the various points noted in this section will be answered in more detail at l
such time as there is agreement on the seismic design levels.
Vertical Seismic Resoonse On page 1.8-51 of the PSAR it'is indicated that the vertical ground acceleration will be' taken as two-thirds the horizontal acceleration except that
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.1 for periods greater than I second, a value of three-quarters the horizontal acceleration will be used.
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b in Section B.2.3.1.1.1 and 8.2.3.1.1.2 in Appendix B of the PSAR,
" gravi ty coef ficients" are presented.
The manner in which these vertical seismic coef ficients are presented suggests that the design for vertical excitation may involve the use of constant acceleration coefficients. Howeve r,. In the material filed with Amendment 4, and par::Icularly that given in Section B.2.3.1.2.1 for structures (Type A) and in Section B.2.3.1.2.2 for structures (Type B), the a
discussion indicates that the vertical excitation will be treated in the sEne rnanner as the horizontal excitation with regard to amplified response.
On the assumption that this is the approach employed in the analysis, we concur.
1 D ampi ng The structural damping to be employed in the design is discussed in several places in the PSAR.
On page 1.8-50 i t is stated that for structural deformation, damping will be taken to be 2 percent of critical for the OBE and 3.5 percent for the DBE; for rocking, the corresponding percentages are 5 percent and 9 percent.
The 9 percent value for the DBE rocking seems to us to be rather j
high and further Justification for this value would seem to be needed, in a form other than merely general reference to 3 or 4 journals, as is currently given on j
page 1.8-50.
The other damping values applicable to the design are given in Appendix B and appear acceptable so long as the response spectra reflect amplification values which are commensurate with the percentages of critical damping listad.
Final decision as to the suitability of the damping values wl.11 await finalization of the seismic hazard and response spectra for this design.
Me thods of Dynamic Analysis The presentation on page 1.8-49 Indicates that the general analytical r odel for the analysis of the containment structure for earthquake motion has not been selected, but that i t will meet the detailed requirements of Appendix B.
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The infonnation presented in Appendix B and updated through knendment 4, and I
particularly that in Section B.2, Indicates that the structures will evidently be categorized into two types- (A and B) and that they will be analyzed by t
generally available computer codes such as SMIS,and STARDYNE.
The general description given suggests that the approach will be ' satisfactory, although l
few detail s~ are given.
In the event that time-history techniques are employed, it is assumed 1
that the response spectra corresponding to the time-histories will exceed or equal throughout the entire frequency range the response spectra employed as l
4 the criteria for design.
Seismic Analysis of Equipment and Pipinq I
The approach to be followed in the seismic analysis 'of equipment is J
described on page B.2-13.
It is indicated that the syste:ns will be analyzed by l
the response spectrum technique.
The description indicates that simplified i
analytical model s will be employed as requi red.
It is also indicated that i
j special attention will be given to the flexibility or rigidity characteristics
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i of pipe networks and that local restraints and hydraulic snubbers will be pieced q
as required.
The analysis of reactor internal s is described on pages B.3-9 and the l
general approach given (although with very little detail) is acceptable.
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Further detail on the design approach for the reactor vessel, steam 1
l generators, and reactor coolant piping-pump assembly is contal.ned in presentation in Section B.3 beginning on page B.3-8.
The approach given for this portion of the equipment and piping appears satisfactory.
It is not clear that this cove rs all of the Class I ' piping in the p~ snt.
Other information concerning piping analysis and design is presented on page 1.8-35.
The details on the piping analysis are extremely general, and although satisfactory in concept, on the
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basis of the information presented little comment can be made about the adequacy i
of the techniques to be employed.
For certain Class I systems and equipment, where analytical models and
.. 1 normal mode theory may not be applicable, the applicant Indicates. that testing may be employed to help insure functional integrity.
This approach appears l
satisf actory for certain specific classes of equipment.
Cranes The discussion on page 1.8-4 indicates that cranes in critical areas of the nuclear facility will be designed to insure that they are adequately tied down and cannot be dislodged from the rails during seismic excitation.
This approach is satisfactory.
Cl ass i Equipment in Class !! Structures j
l The design approach to be followed for Class I equipment items which i
are located in Class 11 structurer., is discussed on page 1.8-37.
The applicant i
indicates that special attention will be directed to insure a conservative design approach for those portions of the structures, and moreover that the response of i
Class I components located thereon nill be examined in detail also.
This approach l
appears satisfactory.
Penetrations and Liner plates The general design approach as outlined for the penetrations and liner pl ates appears satisfactory insofar as the detail s given. A final evaluation of the criteria in this regard will be given by us in this report when the seismic
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design level is established and we reexamine these design criteria in light of j
the seismic criteria.
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General Design Stress Bases The combined load expressions applicable to design are presented in Section B.3 and appear generally acceptable.
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9 A stetement is-made at the top of page. B.3-5 that " Stress in some of the materials may exceed yield strength if an analysis is made and demonstrates that the energy absorption capacity of the structure exceeds the energy input".
The resulting deflection or distortion is to be calcul ated in an elasto-plastic
- analysis, in the event that such an approach is followed, the applicant should document clearly the procedure that is to be followed in assessing such over-stressing, and the basis for assuming that the stress, deformation, and energy criteria are appIIcable and satisfactory to insure proper functioning of-the j
structure or equipment.
On page B.3-6 the re is a statement "For the accident basis design, stress analysis is based upon the ul timate strength and plastic theories".
If Indeed these criteria are to be applicable to the design for the OBE, then the margins of safety must be clearly delineated in all cases.
And the methods of dynamic analysis will have to be handled in such a manner as to reflect nonlinear i
behavior which wilI occur.
So long as a reasonable margin of safety exists and can be demonstrated i
to exist, the approaches considered may be satisfactory but documentation will have to be supplled.
CONCLUSIONS in keeping with the design goal of providing serviceable structures I
and components with a reserve of strength and ductility, and on the basis of the information presented, we believe the design criteria outlined for the containment vessel, Class I piping and equipment items, and other critical componen ts, can provide an adequate margin of safety to resist the seismic effects to tSe extent of insuring safe shutdown and containment.
However, in 1
arriving at this conclusion, we have noted in our report a large number of points which remain to be resolved by the applicant before such a conclusion can be
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ascertained to. be. applicable in its entirety. We trust that the applicant I
. will be able to provide the necessary in/ornation in the near future.
REFERENCES d
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' " Preliminary Safety Analysis Report", Vols.1-5, and Amendments 1 through 4 l-and-6 through 8, San Onofre Nuclear Generating Station Uni ts. 2 and 3, Southern -
- Call fornia Edison Company, San Diego Gas and Electric Company",1970 and 1971.
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