ML20214G558
| ML20214G558 | |
| Person / Time | |
|---|---|
| Site: | Columbia  |
| Issue date: | 05/26/1972 |
| From: | Gammill W US ATOMIC ENERGY COMMISSION (AEC) |
| To: | Clark R US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| CON-WNP-0124, CON-WNP-124 NUDOCS 8605220276 | |
| Download: ML20214G558 (10) | |
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i ERf 2 i M R. Clark, Chief, Ga.5 Cooled Reactora Branch, L H A'IFORD 2 NUCLI:AR REACIOR SITE - DOC 3T NO. 3 7 1.acloued for yo'er information in the interiva report cowerine th.= :colo;n, neisnelory and fou.idotion enginraering aspecta of the um. ford 2 site.
'J. Gamill, Chir f Site Analysis Branch Directorate of Licensinr Enclocure :
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HN; FORD 2 CEOLOGY, SEISMOLO3Y NID FOUNDATIONS ENGINEERING INTER 111 REPORT The staf f has completed its review of the geology, seismology and foundatiens engineering sections of the PSAR and the pertinent portions of Amendments 1 through 3.
There are still sor.c unresolved iters regarding the site geology and its relationship to the regional struc-tural geology. Little is known about the structural geology beneath the site because no borings vere drilled into basalt bedrock at the site and there arc nany difficulties in accurately interpreting geologic structure in this area using only scismic refraction data. There are also a number of open itens regarding foundation conditions beneath specific safety related structures which are discussed later in this report. Most of the concerns have been made knoun to k'PPSS and he is doing r.Cditioral investigations to provide answers to these questions.
Our NOAA and USGS consultants have not completed their revicu. The following is a discussion of the geology, seismology and site subsurf ace conditions of the Hanford 2 site along with the identification of specific unresolved itces.
CEOLOGY AND PIIYSIOGRAPHY The Hanford 2 nuclear facility is to be constructed on the AEC Hanford Reservation, which is located within the Pasco Basin, a physiographic and
. tectonic subdivision of the Colunbia River Basalt Plateau Geologic Province. The Pasco Basin is bordered on the north by the Saddle Moun-tains; on the west by the Yakina and Uttenun Ridges; on the southwest and south by the Rattlesnake Ilills and the Horse Heaven Hills; and on the cast by the L.'hite Bluf fs, which comprise the local cast bank of the Columbia River. Topographic relief in the basin area varies from naximum elevations exceeding 3,500 feet atop Rattlesnahe Mountain to a mininun elevation of +340 in the Colunbia River channel at Richland where the river flows out of the Basin. The site lies at elevation +440 on flat terrain that slopes gently to the northeast about 3-1/2 miles west of the Columbia River.
Within the Pasco Basin and about 8 to 12 miles north of the site are Cable Mountain and Gabic Butte which are two en echelon, asynnetrical, anticlinal hills. These features represent outliers within the basin of the Umtanun Ridge which plunges beneath the glacio-fluvial soils at the west side of the Basin. The buried extension of this structure lies about 2 niles east of the site in a more subdued form.
The ridges that are present in the Pasco Basin area are long, sinuous, asymmetrical -anticlines that are generally oriented in a northwest-southeasterly direction. Between the anticlines lie the Cold Creek, Wahluke, and the Pasco Synclines. These folds were forned as a result
l-of regional warping. Several of the anticlines, such as Untanum Ridge-f Cable Mountain and Saddle Mountain, are f aulted. The faults, where identifiable, are high angle thrust or normal faults that occurred when t
I folding was inadequate to relieve the regional stresses.
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The Pasco Basin is distinct from most of the Columbia River Plateau, the i
formation of which began by volcanic activity in early Miocene, in that i
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it has undergone continuous subsidence at least since the Miocene. The basalt flows beneath the basin have attained a thickness of at leas t 5,000 feet.
In late Miocene or Pliocene, in addition to the continuing j
subsidence of the basin, the region of which the Pasco Basin is a part 1
becane subjected to folding, thus forming the anticlines and synclines i
described above. Volcanic activity ceased in early Pliocene. The subsiding of the basin and the regional warping are believed to be con-I tinuing to the present time.
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The subsidence of, and the folding around, the Basin have created the setting for a natural reservoir, and the area has been subjected to alternate periods of flooding and erosion. It was this environment that i
allowed for the deposition of the approximately 400 feet of soil I
comprising the glacio-fluvial deposits and the Ringold Formation that i
overlic basalt beneath the site. The Ringold formation was deposited directly on basalt during an extended period of flooding, from Pliocene i
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. to early P]eistocene. In the Pleistocene, as a result of the nelting of glaciers to the north. the Pasco Basin was subjected to short, internittent intervals of flooding and crosion. During periods of flooding, the glacio-fluvial soils overlying the Ringold fornation were formed.
The applicant has adequately evaluated the regional geology based on available infornation; houever, the structural geology beneath the site and its relationship to the regional structural geclogy hcvc not been well enough deff d to demonstrate the conservatism of the recom-cnded carthquake desiga bcscs.
SEISMOLOGY The historic seismicity record of the region is limited to only about 100 years. The two historically recorded macrocarthquakes of greatest significance to the site are the 1918 Corfu carthquake with a Modified Mercalli Intensity V-VI and the 1936 Milton-Freewater Walla Walla event with an FM Intensity of VII. The Corfu carthquake may have been associated with the Saddle Mountain st ructure, and the Pditen-Freewater carthquake has been attributed to the Rattlesnake-Wallula structure.
Since 1967 the USGS has been monitoring microcarthquakes in the Hanford Region. Several patterns of epicenters have been established. The most significant to the llanford 2 site is an east-west oriented elliptical
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. arrangement of nicrocarthquake epicenters about 3-1/2 miles southeast of the site, near Wooded Island. The rderocarthquakes at Wooded Island have bee, at tributed to the continuing basining of the Pasco Basin. The applicant recommends that 0.25g be used as the design acceleration value for the Safe Shutdoun Earthquake. This value is based on the probabic occurrence of a Milton-Freewater type carthquake on the Rattlesnake Wallula structure at its closest approadt to the site (11 miles west).
NOAA's evaluation of the adequacy of this value depends on a more com-s'n /4 c vic i n < f,' o l' plete definition of the structural geology be.weth the site.
4 SITE I;VESTIGATIO:S Eleven borings were drilled at the site, the deepest of which were 250 feet. Thc site was relocated about 400 feet to the south and, there-fore, some of the borings were drilled outside the proposed building areas. Four seisele refraction lines were run at various angles across the site to determine dynamic properties of the soil and to locate the top of basalt bedrock. Uphole tests were performed in two of the b orings. Piezoneters were established in several of the holes to monitor groundwater fluctuations. The following laboratory tests were made on selected sanples: water content, grain size, max / min densities, column, and repetitive triaxial.
FOUNDATIG; ENGINEERING The site area is blanketed by from 1-1/2 to 3 feet of wincblown sand.
. Unconsolidated but very dense glacio-fluvial sands lie beneath the acolian deposits and extend to a, depth of about 40 feet. Beneath the glacio-fluvial soil and extending to bedrock surface at a depth of about 420 feet lie the unconsolidated to semi-consolidated sands, gravels, silts and clays of the Ringold formation. Groundwater beneath the site is at an elevation of +378 (62 foot depth).
The nat foundation for the reactor will lie within the glacio-fluvial deposits at a depth of 31 feet. The other Category 1 structures will be founded as follows:
(1) emergency cooling ponds on nat foundations at elevation +418 or 22 foot depth; (2) auxiliary pump on nat foundativt at elevation +409 or 31 feet icep; (3) Raduaste Building at elevation +429 (11 foot depth) on a cat foundation; (4) Diesel Generator Building on continuous wall footings placed on compacted fill at elevation +436.6 The compacted fill will extend from this level down to elevation +410.
All structures except the reactor building will be founded on either natural soil or soil co=pacted to a minimum relative density of 75%, and
F to an overall average relative density of 85%. Settlerents are expected to be mininal and occur during construction. Lateral pressures at the proposed depths have been evaluated. Additional studies were done assuning a rise in the water tabic of about 40 feet above its present Icvc] as a result of the construction of Ben Franklin Dan.
An analysis of the liquefaction potential of subsurface soils is presented. Our evaluation of these analyses is still underway.
OUTSTANDING ITEMS The follouing itens are still unresolved, and the applicant has been advised of this by telephone:
1.
a nore conplete definition of the geologic structure beneath the site nust be provided ;
2.
the prelininary investigation for the energency cooling pond rust be completed and representative boring logs showing foundation conditions provided; 3.
a boring into the basalt bedrock to confirm the geophysical work and the data extrapolated from qearby borings is required; 4.
a geologic nap of a trench cut across the reactor site should be provided; and
r 8-5.
the results of in-place density tests to confirm the relative density data estinated fren the standard penetration tests nust be provided.
In regard to nost of these iters WPPSS has verbally agreed to do the following additional investigations and to provide the results no later than 27 July:
1.
drill two deep core borings each at dianetrically opposite corners of the reactor conplex.
One boring is to be 150 feet deep and the other is to penetrate basalt bedrock. The depth in basalt to which this boring should be drilled has not been agreed upon. We feel that a positive identification of the upper flew should be nade, and that the hole should be drilled to whatever depth is necessary to do this; 2.
a trench will be excavated across the reactor site between the two deep borings to a depth of 15 feet. Plate bearing and density tests will be perforned at depths of 10 feet and 15 feet in the trench.
The trench will be logged in detail by geologists, and tne logs will be availabic by 17 July; and 3.
three borings to depths of 60 feet will be drilled in the energency cooling pond area and the logs will be availabic by 17 July.
_9-As stated earlier, liSGS and NOAA have not conpleted their review. It is anticipated that these agencies will also have additional questicus concerning their respective disciplines.
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