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L-l N' A T H A N M. N E W M A R K. .
111 'TALBOT L A S O 9 A T O R Y.' URRANA. IL LIN Ol3
. CONSULTING ENGINEERING SERVICES l
DRAFT l
Report to AEC Regulatory Staff I-ADEQUACY OF THE STRUCTURAL CRITERIA FOR THE :
QUAD-CITIES STATION-UNITS 1 AND 2 l COMMONWEALTH EDISON COMPANY z(Dockets No. 50-254 and 50-265) l 1
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N. M. Newmark and W. J. Hall i
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4 ADEQUACY OF THE STRUCTURAL CRITERIA FOR THE QUAD-CITIES' STATION UNITS 1 AND 2 by H. H. Newmark and W. J. Hall INTRODUCTION l
This report is concerned with the adequacy of the containment struc-
'tures and 'compone6ts for the Quad-Ci. ties Units I and 2 of 715 MWe each, for which application for a construction permit and operating license has. been -
made to -the United States Atomic Energy Commission by the Commonwealth Edison C ompa ny . The facility is located on the east bank of the Mississippi River in Rock.lsland County, Illinois, approximately 3 miles north of Cordova and about 20 miles northeast of the Quad Cities (Davenport, Iowa ; Rock Is land, Mol ine ,
and East Moline, Illinois).
Specifically this report is concerned with the design criteria that determine the ability of the primary and secondary containment systems to with-stand a design carthquake of 0.129 maximum transient ground acceleration-simultaneously with the other loads forming the basis of the containment design.
The f acility also is to be designed to withstand a maximum earthquake loading of 0.24g to ,the extent of preserving the ability to maintain the plant in a safe shutdown condition.
This report is based on information and criteria ' set forth in the Plant Design Analysis (PDA) reports and the supplements thereto as listed at the end of this report. Also, we have participated in discussions with the AEC regulatory staf f concerning the design of this unit.
I DESCRIPTION OF FACILITY Quad-Cities Station Units 1 and 2 are described in the PDA as being two complete nuclear power units, each to be licensed for operation at power 1
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l levels up to'approximately 2300 MWt (715 MWe net each). The units are to be single cycle, forced circulation, boiling water reactors that produce steam for direct use in the steam turbine, in most respects the design is essentially identical to that f or Commonwea l th -Edi son's Dresden Unit 2.
The primary containment system which houses the reactor vessel and the recirculation system consists of the drywell, vent pipes, and a structure shaped like a torus, which contains a pool of water for pressure suppression purposes; the center of the torus lies slightly below the bottom of the drywell.
The drywell and all other aspects of the primary containment system appear to be identical to those of Commonwealth Edison's Dresden Unit 2, as described in Ref. 6.
The reactor building provides secondary containment to both units of the system when the primary containment is in service, and also serves as the primary containment structure during periods when the primary containment is open for servicing purposes. The building is described on page V-2-2 of Volume I of the PDA as consisting of cast-in-place reinf orced concrete exterior walls to the refueling floor and of steel f rame with insulated metal siding above this floor. The reactor building, together with the stand-by gas treat-ment system and a 310-f t stack, provide the secondary containment barrier.
The common reactor building for the two units, which is a controlled-leakage structure, appears to be similar in design in terms of the foundation and superstructure to that previously described for Dresden Unit 2 (Ref. 6).
\ Section II-5.0 of Ref. 1 indicates that bedrock is present at or near the planned foundation elevation. We assume this to mean that the founda-tion of the plant will rest on bedrock.
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SOURCES OF STRESSES IN CONTAINMENT STRUCTURE AND TYPE I COMPONENTS The primary containment system, which includes the drywell, vents, torus , and penetrations, is 'to be des igned f or the following conditions', ~ as noted on page V-l-? of Ref.1; pressure suppression chamber internal design pressure, +62 psig, -2 psig; design temperature of drywell and pressure.suppres-I 1
slon chamber, 281*F.
. . I As noted in Section V-3 of the PDA, Volume I, the aseismic design of the primaryLcontainment system, which is classified asi either a' Class I-- !
Critical Structure or Class I--Critical Equipment,.will be based on dynamic i analyses. using response spectrum curves which are based on a ground motion of 0.129. 'I t is further noted that the design is such that a safe shutdown can oc made for an earthquake having a ground' motion of 0.24 9 . As noted later in j the next major secti on of this report, the spectra are not necessarily used in the designeprocess, however.
All structures will be designed to withstand a wind velocity of 110 mph, and where f ailure possibly could af fect the operations and functions of the primary containment and reactor primary system, the design is to be made to assure that safe shutdown can be achieved, considering the effects of possible damage arising f rom a short-term tornado loading. ;
The reactor building, which comprises the secondary containment system, is listed as a Class I--Critical Structure. The reactor building is to be designed to withstand an Internal negative pressure of 0.25 in. of water with respect to the outs ide atmosphere under neutral wind condi tions.
It is also designed to be able to withstand an internal pressure of 7 in. of water (about 1/4 psi) without structural failure and without pressure relief.
The aseismic design of the structure is to be made f or forces (supposedly
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4 coincident with dead load, snow load, and other applicable operating loads) for a design and maximum earthquake as noted above for the primary containment
'!./stem. The structure is to be designed to withstand a wind velocity of 110 mph, and again, for short-term tornadic loadings, saf e shutdown of the plant is assured.
The Class I--Critical Equipment, which includes the nuclear steam supply systems and reactor cooling and stand-by systems as well as a number of other items, as lis ted in Section V-3 of PDA Volume I, are to be designed to withstand the same seismic f orces as noted earlier for the primary and secondary
, ::ontainment systems, in conjunction with other applicable loads.
P l COMMENTS ON ADEQUACY OF DESIGN Seismic Design criteria -- We agree with the approach adopted, which is identical in principle to that adopted for Dresden Unit 2, namely that of a basic design f or a design earthquake of 0.12g with the provision that a safe shutdown can be made for a maximum earthquake of twice this intensity (0.24 9).
These earthquake design values are in agreement with those given by the U.S.
Coast and Geodetic Suivey (Ref. 5).
The design response spectra are presented as Plate 5 in Appendix F of Ref. 2, and aga in as Fig. C-2-1 in Amendment No. 2. The two plots are identical, with the exception that the former plot has been carried to a slightly lower f requency value. According to the answer to Question C2 in Amendment No. 2, these spectra correspond to the 1957 San Francisco Golden Gate Park $80E strong 1 motion earthquake recording. The shape of the spectra are different f rom those l
that have been commonly employed previously. The reasoning for the selection j l
of the Golden Gate Park recording is not provided in the PDA reports or amend-i ments. There is some question in our minds as to the wisdom of this selection; j i
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in general the spectra provide a larger force input ~In the'high. frequency.
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second than would otherwise have occurred with an earthquake patterned af ter the El . Centro earthquake, or even the Helena, Montana strong motion earthquake, which was. recorded on rock. Most structural elements will have a low natural f requency greater than 3 or 4 cycles per second; thus 'the use of the cited
.Gol den Gate spectrum,or the associated earthquake record may be justified in those cases.' The possibility.of lower than expected rusistance might occur for 1 those structures having rather long natural periods, on the order of 0.3 see or j 1
longer, such as might occur for the stack or for certain items of equipment. j in the case of items which have periods of 0.3 sec or greater, we recommend that the designers employ a higher input consistent with that used in previous ;
designs of this type, corresponding to the shape of the El Centro response spectrum scaled to the appropriate acceleration. I On page V-3-5 of the PDA It is noted that the vertical acceleration is assumed equal to two-thirds of the horizontal ground acceleration, and that for the design of Class ! structures and equipment the maximum horizontal i acceleration and the maximum vertical acceleration are considered to occur j
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simultaneously. Where applicable, stresses are added directly. We interpret I this latter statement to mean that the stresses arising from the earthquake in both the vertical and horltontal direction and which occur simultaneously at a particular-location will be added directly to the stresses arising from the other applicable loadings, including pressure arising f rom an accident.
On the assumption that this interpretation is correct, we concur in the approach.
For the 0.249 maximum earthquake, and safe shutdown, it is noted that the functional load stresses probably do not exceed yleid stress; however, where calculations indicate that a structure or piece of equipment is stressed beyond
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the yi..eld point, an-analysis will be made to determine its energy absorption m p capacity,-and a review Will be made to insure that any resu'lting deflections or. distortions.will not prevent. proper' f unctioning.of the structure or piece of; equipment. -This criterion appears reasonable to us as long as- the design leads' to insurance that shutdown can be achieved.
The table of damping;coef ficients given on page V-3-2 of the PDA appears to be identical to that for the Dresden Unit 2 design, and accordingly we concur. In the values: given therein. However, as a result of 'recent consid-
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- erations we suggest for reinforced concrete structures'that' constitute an integral part of the containment and which must . play a signifletnt role in the ability of.the contairiment to function properly in. terms of prevention ~of-leakage, that about 5 percent damping is appropriate for such: structures and components that can have a moderate amount of yielding without impalring safety.
Not more than~2 percent dampinp appears appropriate for structures which must.
stay in the. range below normal' working stresses. Thus in terms of the' primary containment, one should consider a lower value of damping, of about 2 percent, in connection with certain portions of the primary containment and suppression system.
e if the applicant correlates the damping values with the amount of cracking expected in the structure, then under situations where cracks are not considered to remain open, 2 percent would be an appropriate level; under 3 situations where some reasonable amount of cracking would be expected, 5 percent
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would be ace'eptable. Itwouldbehptotheapplicant, however, to demonstrate 1
that if such cracks occur as are consistent with e 5 percent level of damping, they will partly close with only that length of crack remaining which permits neeting the required leakage specifications. Hence, the degree of cracking l
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permissible and the nature'of the damping is dependent on the specified leak.
rates and the internal pressures associated with such' rates.
In connection with-the secondary containment as provided by'the reactor building that covers the two units, the statement on page V-2-2 of the PDA- indicates that the siding is installed with sealed joints. In answer to Question D6e of Amendment No. 2,'the applicant advises, "In the event of a design carthquake causing movement of structural steel f rame, some of the siding connections may be distressed, however, it is expected that the mastic
_ joint sealant will provide suf ficient resilience to prevent the exfiltration.
of air." The insurance provided against leakage is not clear for the case of the design earthquake, and deserves further consideration in the case of the rnaximum earthquake.
With-regard to the use of response spectra in the dynamic-analyses, the applicant makes the following statement in answer to question C2 of Amendment No. 2 : "The purpose of the spectra shun is to provide earthquake response in a dynamic analysis. These are averaged single-mass spectra and
'are usually employed in a modal analysis. These are not generally used in the i
analysis of important critical components, since computer programs are utilized which follow the actual earthquakes, rather than their response curves, and it is -not necessary to combine modes in some approximate manner to arrive at final f
l shears, moments and displacements." in answer to Question C4, dealing with the i 1
310-f t stack, the applicant generally describes the method employed in analyzing )
the stack, which follows more or less along the lines just described, but notes t
that generally five modes are considered and a damping value of 5 percent is 4
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used for all five modes. Our previous comments concerning the level of damping are applicable here as well, and generally one would not expect this higher I
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l oercentage of damping to be operative without some significant yielding and cracking of the concrete structure.
It is not apparent to us whether consideration has been given to the possibility of the stack toppling onto the remainder of the plant < If the ,
toppling of the stack could jeopardize the ability to shut down the reactor safely, this is a factor which should be given careful consideration. Attention should be paid to the possibility of the stack falling at a low elevation unless it is specifically designed not to do so.
We can find no details concerning specific attention to the strength-ening of areas around penetrations of the containment, particularly in the pr ima ry conta inment area. In the case of large penetrations, especially, care should be taken to insure that these details will maintain the required strength and ductility under carthquake and service loadings.
The applicant has discussed the matter of cranes in the report and in Amendment No. 2, and it appears that provisions have been made to insure that the cranes and their trucks cannot fall during an earthquake.
Primary and Secondary Containment S t ruc ture -- Tables of a llowable stresses for the primary and secondary containment design are presented on pages V-3-3 and V-3-4 of PDA Volume I . These tables appear to be essentially similar to the tables presented for Dresden Unit 2 (Ref. 6); the tables appear j to be in agreement with applicable codes, or in other cases appear reasonable to us.
A study of the PDA documents indicates that the piping appears to meet the applicable ASME and ASA code provisions, as in the case of Dresden Un i t 2. and no f u r t he r c ommen t is made herein on this matter. The pipe pene-trations appear to be similar to the previous design also, it is noted elso
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on page V-1-1 in the PDA Volume I that provision will be made to accommodate the jet forces resulting.from postulated rupture of any pipe within the t
containment.-
. CONCLUSIONS In keeoing. 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'beIleve the design eriterla out1ined for the primary conta inment , secondary containment,.and Type I~ piping can' provide an adequate margin of safety for. aseismic resistnace. In reaching this' conclusion we assume that: the applicant will give further consideration to the several
- i tems noted herein concerning' the low f requency end of the earthquake response .
. spectrum, the amount of damping, and the provisions f or safety of the stack.
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' REFERENCES
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- l. " Plant Design Analysis--Volume I," quad-Cities Station Units l and 2,
'Commonwea l th Edi son Company , - 1966.
27 Plant Design Analysis--Volume II," Quad-Cities Station Units 1. and 2 Commonweal th Edison Company .1966.
1 3.. " Plant Des ign Analys Is--Amendment No. I," Quad-Citles Station Units 1
' and 2, Commonwea l th Edi son Company, - 1966.
'4 " Plant Design Ana lys is--Amendment No. '2," Quad-Ci t ics S ta t ion Uni ts 1 J and 2,' Commonwea l th Edison Company, 1966.
5.. "Draf t Report on the: Seismicity of. the Quad-Ci ties, Illinois Reactor.
. Si te Region," U.S. Coast and Geodetic Survey, Rockville,, Maryland, 7 Novembe r .1966.~
- 6. ' Adequacy
" of the- Structural Criteria for the Dresden Nuclear Power
. Sta t ion Un i t - 2," Repor t to the AEC Regulatory Staf f, by N. M.~ Newmark
. a nd W J . Ha l l , S pe t embe r 1965.
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