ML20235Z680

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Revised Draft of Adequacy of Structural Criteria for San Onofre Nuclear Generating Station Units 2 & 3
ML20235Z680
Person / Time
Site: San Onofre  Southern California Edison icon.png
Issue date: 07/03/1972
From: Hall W, Newmark N
NATHAN M. NEWMARK CONSULTING ENGINEERING SERVICES
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FOIA-87-462 NUDOCS 8710210257
Download: ML20235Z680 (9)
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REVISED ORAFT

REPORT TO.AEC REGULATORY STAFF ADEQUACY OF THE STRUCTURAL CRITERIA FOR SAN ONOFRE NUCLEAR GENERATING STATION UNITS 2 41D 3

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Southern California Edison Company I

San Diego Gas and Electric Company l

AEC Docket Nos. 50-361 and 50-362 4

by N. M. Newmark 1

and W. J. Hall l

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- t 3 July 1972 37 871014 AB7-462 PDR gg

I ADEQUACY OF THE SD1UCTURAL CRITERIA FOR SAN ONOFRE NUCLEAR GENERATING STATION UNITS 2 AND 3 Southern Cal f fornia Edison Company

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and San Diego Gas and Electric Company by N. M. Newmark and W. J. Ha ll i

INTR ODUCTION This report is concerned with the adequacy of the containment structures and components for a 2-unit nuclea r power station, San Onof re Units 2 and 3, for which application for a construction permit has been made to the U.S. Atomic I

Energy Commission by the Southern California Edison Company and the San Diego 1

Gas and Electric Company.

The facility is located on the west coast of Southern California on the Pacific Ocean in San Diego County, approximately 62 miles q

southeast of Los Angeles and approximately 51 miles northwest of San Diego.

i This report is based on information and criteria set forth in the Preliminary Safety Analysis Report (PSAR) and amendments thereto, as listed 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 N111 be incated immediately south of San Onof re Unit 1.

DESCRI_PTION 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 that 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 1s quite similar to that for Palisades Unit 1.

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2 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 structure are as follows:

Inside diameter,130 f t ; inside height, 185 ft; cylindrical wall thickness, 4 f t; and dome thickness, 31/2 f t.

The cylindrical portion of the containment structure is post-tensioned with horizontal (hoop) and vertical tendens.

The hoop tendons are anchored at 3 buttresses equally spaced around the containment structure.

These tendons extend 240 around the cylinder periphery, bypassing intermediate buttresses. The dome has a 3-way 1

post-tensioning system.

The foundation slab is conventionally reinforced with high-strength reinforcing steel.

The interior of the containment shell is steel-If ned wi th ASTM A-285 carbon steel plate.

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Personnel and equipment access hatches are provided to permit access to the fac!Ilty.

There are a number of additional penetrations for piping and l

l electrical conduits.

Section 2.9 of the PSAR Indicates that major structures will be founded l

l In the San Mateo foundation.

The appIlcant Indicates that even the heaviest structure can be supported in this material using spread footings or mat f oundat i ons.

SOURCES Ce STRESSES IN CONTAINMENT STRUCTURE AND CLASS I C04PONENTS The containment structure is to be designed for the following loads:

dead lead, including hydrostatic pressure; live load; accident containment design pressure of 60 psig; proof test pressure at 115 percent of design pressure; external pressure of 2 ps!; thermal load arising f rom the maximum temperature gradient through the concrete shell and mat, based on a maximum 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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The applicant, in Anendment 14, indicates that the design is to be made for a Design Basis Earthquake characterized by a maximum horizontal ground acceleration of 0.679 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 0.33.

These seismic design levels 9

are adequate.

COMMENTS ON ADEQUACY OF DESIGN 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 differential 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 San Mateo formation makes the chance of liquefaction of the foundation l

sands during an earthquake unlikely. We concur in this evaluation.

There is an indication on page 11-17 of Appendix 28 that cuts as 3

deep as 70 f t will be required for the construction of Units 2 and 3.

1 Slope stability analyses have been carried out for earthquake accelerations corresponding to 0.25g and 0.50, and we understand will be made for the 9

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higher accelerations now indicated in Amendment 14.

Further elaboration on the excavated slopes for Units 2 and 3 is l

l presented in Section 2.9 beginning on page 2.9-9 (Amendment 6) and indicates that the slopes are considered critical er noncritical, depending upon whether slippage can cause any structural or equipment damage at the plant.

The discussion given indicates that vertical earthquake effects have been considered p.

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l 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 careful 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 l

1evels 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 i t is indicated that the details of the procedure will be based upon the reference material given in Section 81 of Appendix B, and will be submitted af ter a more detailed design.

On page 1.8-49 at the bottom of the page, there is a statement l

indicating that approximate analysis of containment structures for local loading originating from the earthquake excitation will be made.

It is indicated that previous work on similar containments indicater that there is disagreement I

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 details.

We interpret these various statements to mean that :further information l

will be forthcoming as to the criteria to be employed in design to account for l

l possible soil-structure interaction at the seismic levels now used.

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1 Response Spectra l

The proposed response spectra for the San Onofre Nuclear Generating Station Units 2 and 3 are presented in Figs. 2.10-1 and 2.10-2, and Fi gs.

l 8.2-1 and 8.2-2.

The horizontal response spectra for the Operating Basis l

Earthquake are shown for a base acceleration value of 0.339 and those for the Design Basis Earthquake are shown for 0.67.

9 The response spectra proposed are generally acceptable in shape and intensity, although they are slightly different from spectra used for plants with a lower level of seismic hazard.

This difference is reflected by slightly lower frequencies of the transition points in the response spectrum (1 hertz instead of 2 for the velocity-acceleration transition, 5 hertz instead of 6 for the drop-off in amplified acceleration, and 20 hertz instead of 30 for the return to the base-acceleration level), but these changes are consistent with the foundation conditions and appear justified by the studies reported in the material following Tab A2, submi tted with Amendment 14, entitled " Estimates of Site Dynamic Response", by Woodward-McNeill and Associates.

It is noted that the acceleration amplification values are consistent with those generally accepted by AEC, with a value of 3.5 for 2 percent damping.

It is also noted that the velocity bounds of the spectra used are somewhat higher than the values normally used.

Hence the spectra are indeed 1

quite conservative for frequencies lower than 1 hertz, and somewhat conservative for frequencies between 1 and 2 hertz.

l 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 for periods greater than I second, a value of approximately three-quarters the horizontal acceleration will be used.

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7 in Amendment i4 it is stated on page 1.8-121aa that the response spectra corresponding to time-histories used in the analysis will not be l

' i available until about August 1972, but are expected to envelope the smoothed i

response spectra employed as the criteria for design.

Seismic Analysis of Equipment and Piping 1

- The approach to be followed in the seismic analysis of equipment is I

described on page 8.2-13.

It is indicated that the systems will be analyzed I

by the response spectrum technique. The description indicates that simplified analytical models will be employed as required.

it is also indicated that special attention will be given to the flexibility or rigidity characteristics 1

of pipe networks and that local restraints and hydraulic snubbers will be j

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l placed as required.

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The analysis of reactor internals is described on page 8.3-11 and the general approach given is acceptable.

Further details on the design approach for the reactor vessel, steam l

generators, and reactor coolant piping-pump assembly are contained in presentation in Section 8.3 beginning on page 8.3-8.

The approach given for this portion of the equipment and piping appears satisfactory.

It is not clear that this covers all of the Class I piping in the plant.

Other information concerning piping l

analysis and design is presented on page 1.8-35.

The details on the piping analysis are satisfactory in concept.

For certain Class I systems and equipment, where analytical models and normal mode theory may not be applicable, the appilcant indicates that testing may be employed to help insure functional in teg ri ty.

This approach appears satisfactory.

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8 Cranes The discussion on page 1.8-48 Indicates that cranes in critical areas of the nuclear fa,cility 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.

Class l Equipment in Class ll St ructu res The destgr. approach to be followed for Class I equipment items which I

are located in Class 11 structures is discussed on page 1.8-37.

The applicant I

indicates that special attention will be directed to insure a conservative design i

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approach for those portions of the structures, and moreover that the response of Class I components located thereon will be examined in detail also.

This approach j

l appears satisf actory.

l Penetrations and Li-er Plates The general design approach for the penetrations and liner plates as outlined in Section 5 appears satisfactory insofar as the details given are concerned. We expect that the final comprehensive seismic design document referred to on page 1.8-163 of Amendment 14 will include consideration of the 1

seismic aspects of the design of these details, and we would expect to review these items when the document is available.

General Desion Stress Bases The combined load expressions applicable to design are presented in 1

Section B.3 and appear generally acceptable.

We understand f rom our discussion with the applicant and AEC l

representatives in Urbana on 8 June 1972 that the design stress criteria are generally such as to limit stresses to less than yield values. We concur in this criterion.

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CONCLUSIONS In keeping with the design goal of providing serviceable structures 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 l

containment vessel, Class I piping and equipment items, and other critical components, can provide an adequate margin of safety to resist the seismic l

effects to the extent of insuring safe shutdown and containment.

Howeve r, i n arriving at this conclusion, we have noted in our report that documentation of the seismic Class I design program will be available at a later date, and needs j

to be reviewed by us to support our tentative conclusions.

REFERENCES 1

" Preliminary Safety Analysis Reporf', Vols.1 -5, and Amendments 1-8 and l

10-14, San Onof re Nuclear Generating Station Units 2 and 3, Southern California Edison Company, San Diego Gas and Electric Company,1970 and 1971.

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" Methods of Of rect Application on Element Damping, San Onofre Units 2 and 3", Bechtel Corporation, Jan. 1972.

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