ML20128A290
| ML20128A290 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 03/31/1967 |
| From: | Newmark N ILLINOIS, UNIV. OF, URBANA, IL |
| To: | |
| Shared Package | |
| ML20128A275 | List: |
| References | |
| NUDOCS 9212030267 | |
| Download: ML20128A290 (6) | |
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March 1967 ADEQUACY OF THE ST3UCTURAL CHITERIA FOR THE MONTICELLO NUCLEAR GENERATING PIANT UNIT 1 by N. Me Newmark and W. J. Hall INTRODUCTION This report is concerned with the adequacy of the containment structures and components for the Monticello Nuclear Generating Plant Unit 1,. designed for a net electrical output of about 4 2 We, for vbich application for a construc-7 tion permit and operating license has been made to the U. S. Atomic Energy Commission by the Northern States Power Company, Minneapolis, Minnesota. The f acility is located 22 miles dovnstream from dt. Cloud, Minnesota, and about-3 miles northwest of the village of Monticello, Minnesota, on the south bank of the Mississippi River.
Specifically, this report is concerned with the design criteria that determine-the ability of the primary and secondary containment systems to withstand a decign earthquake of 0.06g maximum transient ground acceleration simultaneously with the other loads forming the basis of the containment design. The facility also is to be designed to withstand a maximu:n earthquake of 0.12g cround accel-eration to the extent of insuring safe shutdown and containment.
This report is based on information and criteria set forth in.the Facility ~
Deceription and Safety Analysis Report (FDSARJ and supplements thereto as Tisted at the end"of this report. Also, ve have participated in discussions
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with the AEC regulatory staff concerning the design of this unit.
DESCRIPfION OF FACILITY Monticello Unit 1 is described in the AR as a complete nuclear power unit to be licensed for operation at power leycis up to approximately 1469 MWt (472 MWe net). The unit will be a single cycle, forced circulation, boiling water reactor that produces steam for direct use in the steam turbine.
In most respecte the design vill be essentially identical to that for Commonwealth-Edison's Dresden Unit 2 and the Millstone Nuclear Power Station.
The primary containment system, whieb houses the reactor vessel and the recir-culatten system, consists of a dryvell, vent pipes, and a torus shaped structure which cantains a pool of water for Dressure suppression purpores; the center of the toruc lies slightly below the bcttom of the dryvell. The dryvell is a-steel pressure vessel with a lover spherical portion about 62 f t in diameter and a cylindrical upper portion about 30 f t in diameter; the over-all' height is approximately 105 ft.
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-e-The reactor building provides secondary containment for the system vnen the prinary contaircent in in service and cerves as the primary contaitsent struct ure during teriods when the primary containment is open for servicing.
The reactor building together with the standly gas treatment system and a 290 f t stack provide the secondr.ry containment barrier. The recondarY ccntain-cent tuilding is described in Section V-2 of tle FDSAR Vol. I as consisting of poured-in-place reinforced concrete exterior valls up to the refueling s
floor, with a steel structural frame with insulated metal siding located above thic floor. The siding is to be installed with cealed jointo.
Section 11-5 of Ecf.1 and Figo.11+5-3 through 11-5-5 indicate that bedrock exists at about elevation 660 ard 670 at the plant cite, and that about 60-60 f t of predominantly grandular cedimentc with interbedded layers of Incus-trine clay ard glacial till overlie the bedrock. As noted in Amendment 6, on page V-2-2 (Revised 3/8/67I of the PDSAR, the building is founded on a layer of compacted granulated backfill overlying a hardpan which covers a rock formation.
SOUhCES OF SThr2Sr.S IN CONTAINMENT STRUCTUIE AND TYPr; 1 COM10NENTS The containnent cyctem, ubich includes the dryvell, vento, toruc, and pene-trationo, is to be designed for the following conditiono, as noted in Section V-1 of her.1; pressure suppreccion chamber, ir.ternal design preocure, +56 poig, external denign pressure, 42 pais; dryvell internal design pressure, +56 paig, external design pressure, +2 poig; design temperature of dryvell and pressure suppression chauber, 2810F.
An noted in Eection V-3 of the FDSAH, the neicmic design of the primary con-toinment system, which is clacoified as either a Clans I--Critical Structure or Class I--Critical Equipment, la to le based on dynamic analysec.
All structures vill te designed to withstand a vind velocity cf 100 mph with ruats of 110 mph, and where failure poscibly could affect the operation and f unction of the primary centainment and reactor primary cyster., the design.
is to be twie to insure that safe shutdovn can be achieved, considering tre effects of possible damage arising f rom a short-term torando loading with vindc up to 300 mph.
Tre reactcr building, which comprises the secondary containment system along with the stack and gas treatment system, is listed as a Class I--Critical Structure. The reactor building is to be designed to withstand an internal negative preocure of 0.25 in. of water with respect to the outside atmosphere an ncutral vind conditions.
It is also designed to be able to withstand 7 in.
d vc.ter (about 1/k psi) withcut pressure relief. The structure in to be denirned for acicmic loadings ecmbined with the applicable functional loadings (dead load, oterating leads, snov load, vind load, etc. ).
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. Tbc Class I--Critical Equipment, vbich includes the nuclear steam supply system, and reactor cooling and standby systems, as well as a number of other items, as listed in Section V-3 of FDSAR, are to be designed to withstand the same seismic forces and other applicable leadings as noted earlier for tha primary and second-ary containment sys tems.
COMMENTS ON ADEQUACY OF DESIGN Seismic Design Criteria -- We agree with the approach adopted, whieb is identical in principle to that adopted for Dresden Unit 2, namely that of a basic design for a design earthquake with provision that a safe shutdown can be made for a maximum eartbguake somewhat larger than the design earthquake.
Since, as noted in Amendment b, the foundations of Class I structures and equipment rest on sound rock or an otherwise firm basc, ve are in agreement with the 0.06g design earthquake and 0.12g maximum earthquake criteria as given by the applicant in the FD g v The answer to Question 6.4 of Amendment 6 discusses soil-structure interaction.
We aissume that the interaction loadings between the reactor building substructure and the surrounding soil vill be considered in the design of the substructure for both static and dynamic loading conditions.
The response acceleration spect2a for tti design earthquake of 0.06g (as recom-mended by the applicant in the FDSAR) is presented as Fig. II 6-5, and is plotted therein to an arithmetic scalt which makes it difficult to read, especially in i
the high-frequency (low period) regf ons. The applicant indicates his use of l
acceleration response spectra corresponding to a smoothed response spectrum for l
the Taf t earthquake of July 21,1952, N69N, except in terms of amplitude, which has been scaled. A replot of the spectrum with arithmetic scale for both period and response acceleration has been presented in Fig. 8 5-3 in Amendment 6.
A l
plot of t%e spectra on tripartite logarithm paper would facilitate comparison I
of W acceleration, velocity, and displeMr3t J;.g.w spectra, and would give
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more cefinitive valnes in the hWfn dency region, particularly those intended l
for use perio n
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% We seconds.
The discussion on page 11-6.h of the FDSAR Vol. I indicates that if computerized' methods of dynamic ant. lysis are used the mathematical model may be subjected to an excursion through the moiified Taf t earthquake. We recommend that,-if this l
method of analysis is employed, the time-history record be such that it vill bc l
in agreement with the smoothed response spectrum values to be used in design, j
as described above, throughout the entire frequency range.
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In Section V-3 it is noted that the vertical acceleration is assumed to be equal to two-thirds the '.izontal ground acceleration, ani that for the design of Class I structurer 2d equipment the maximum horizontal acceleration and the maximum vertical at 'eration are considered to occur siaultaneously, and, where applicable, stresse.
Te added directly. We concur in this approach as emplified in anever to Questic. 8.6, Amendment 6.
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For the maximum earthquake and safe shutdown, it is noted in Section V-3 that the functional load stresses combined with the earthquake stresses probably do not exceed yield stress; however, vbere calculations indicate that a structure or piece of equipment is stressed beyond yield, an analysis vill be made to determine its energy absorption capacity and a reviev vill be made to insure that any resulting deflections or distortions vill not prevent proper functioning of the structure or piece of equipment. The same type of statement is made for the maximum earthquake. These criteria are reasonable as long as the design leads to assurance that the shutdown can be achieved under the maximum earthquake conditions.
A table of damping coefficients is given on page II-6-5 It is noted therein that for tbc " reactor-building (massive construction with many cross valls and equip-ment and providing only secondary containmeut)" a damping value of 5 percent is specified. Further elaboration on this point is given in answer to Question 2.8 of Amendment 4 and Question 8.7 of Amendment 6.
As a result of recent considera-tions on our part and by others, ve vould be in agreement with this value for cases in vbich working stresses are no more thau about one-balf the yielu point and in vnien there may be considerable cracking associated with the concrete structure.
In the event tnat the concrete is not stressed to that level vbere it is considerably cracked, ve vould recommend a value of 2 or j percent as being more reasonable. In eitber case the degree of cracking affects the amount of leakage and must be consistent with the damping value used, since it affects the design.
1so listed therein is a value of 10 pere-nt critical damping for ground rocking
, Mes of Nbration; the applicant states in reply to Question 8.8 of Amendment 6 2at 5 m cent damping vill be employed in this case, and ve concur with this
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fbe applicant advises in Amendment 6 that the damping factors cited in Table II-6-3 are to be employed for both the design and maximum ea@ quake loading con-ditions. We concur in this approach.
I' connection with the secondary containment as provided by the reactor building, statements in Section V-2 indicate that the siding is to be installed with sealed joints. The insurance provided against leakage is not clear to us for cases in-volving design or maximum earthquake loadings and, we believe, deserves further consideration.
On page 11-6-5 the statement is made that Class II structures and equipmert shall be dec1gned on the basis of a minimum seismic borisontal coefficient of 0.10 vith a one-third allovable increase in basic stress. Furtter amplification on this approach is provided in ansver to Question 8.10 of Amendment 6 wherein the appli-cant indicates that a seismic coefficient of 0.05 vill be used instead, and claims that this approach is conservative when considared in connection with the basic design earthquake proposed by the applicant.
In accordance with the discussion presented in the amendment, ve believe this approach is acceptable.
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5 With reference to cranen, furtber cleboration on the deiscn of the crancs ic presented in ansver to Question 2 9 of Amendment 4.
On the basis of tbc philosophy therein, that clamps and bumpers vill be provided ts prevent the trolley and bridge from being displaced during earthquake excitation, ve believe that the design vill be satisfactory.
The desiem of the stach is described in more detail in answer to Questien 2.10 of Amendment 4, and we are in agreement with the criteria described there con-cerning the pocsibility of damage should the stack fail, and the method of analysis to be followed in the design for possible earthquake loading. We recommend that the danping to be emoloyed in the design be consistent with the ctress levels that are expected, and a damping value on the order of 2 or 3 rercent be used unless significant cracking is envisioned in the response of the stack, which we exnect would not be the case. The apnlicant advises 'in Amendeent 6 that 3 percent damping vill be employed, with which we concur.
We find no detailt concerning specific attention to the strengthening of areas around penetrations or the containment, particularly in the primsry containment area, the dryvell.
In the case of large penetrations especially, care should be taken to insure that these details vill retain the required strength and ductility under carthquake and service loading.
Primary and Secondary Containment Structure -- Tables of allovabic stressco for the primary and secondary containment design are presented on pages V-2-3 and V-3-3 of FDSAR Vol. I.
The values listed in these tables arc cither in agreement with applicable codes or in other respects are reasonable. Clarification of the statements (and footnote) concerning safe shutdown as given in these tables ic provided by the applicant in answer to Question 8.13 of Amendment 6, and is acceptable to us.
A study of the FDSAR documents indicctes that the piping meets the applicable APJC and AEA Code provisions,. and no further comment is made.herein on this matter. The pipe penetrations are similar to the previous Dresden 2 des 10m, ant in accordance with discussion in the FDSAR and Amendment 4, provisions are indicated to accommodate the jet forces resulting from postulated ruptures of any pipes within the containment. We also note and agree with the design approach followed for the main steam isolation valvec an outlinei en paEe 2 7-2 of Amendment 4 vberein the design is enrried out for seismic effects on these values as well as the applicable piping.
CONCLUSIONS In line with the design goal of providing serviceable stru;t ures 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 primary containment, secondary containment, and Type 1 piping can provide an adequate margin of safety for seismic resistence.
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i REFERENCES 1.
" Facility Description and Safety Analysis Report--Volume I," Monticello Nuclear Generating Plant Unit 1, Northern States Pover Company,1966.
2.
" Facility Description and Safety Analysis Report--Volume II," Monticello Nuclear Generating Plant Unit 1, Northern States Power Company,1966.
3
" Facility Description and Safety Analysis Report--Amendments k and 6,"
Monticello Nuclear Generating Plant Unit 1, Northern States Power Company, 1966.
4.
" Adequacy of' the Structural Criteria for the Dresden Nuclear Power Station Unit.2," Report to the AEC Regulatory Staff, by N. M. Newmark and W. J. Hall, September, 1965 5
" Report on the Seismicity of the Monticello Nuclear Generating Plant Unit 1," U. S. Coast and Geodetic Survey, Rockville, Maryland, March 30, 1967 r
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