ML20198G331
| ML20198G331 | |
| Person / Time | |
|---|---|
| Site: | Washington Public Power Supply System |
| Issue date: | 02/24/1975 |
| From: | Harold Denton US ATOMIC ENERGY COMMISSION (AEC) |
| To: | Moore V Office of Nuclear Reactor Regulation |
| References | |
| CON-WNP-1044 NUDOCS 8605290480 | |
| Download: ML20198G331 (11) | |
Text
.
s f
f DISTRIBUTION:
FEB 2419/5
.,,Desket File NRR-RDG SAB i
V. A. Moore. Assistant Director for LWRs i
SEE - SEISMDLOGY & SBOLOGY AND POUNDATION ENGINEERING l
.'WPPSS 1 & 4 PLANT NAME:
i DOCENSING STAGE: CE,g l
DOCKET NUMBER: 50-400/513 RESPONSIBLE BRANCE: LWR 2-3
-j REQUESTED COMPLETION DATE: 1-23-75 APPLICANTS RESPONSE DATE NECESSARY POR l
NEKT ACTION PLANNED ON PROJECT: None t
DESCRIPTION OF RESPONSE: NA REVIEW STATUS: CP j
Enclosed is our input to the Safety Evaluation report regarding the i
geological, seismological, and foundation engineering aspects of the Hanford site. The report was prepared by Dr. L. Heller, S. Coplan, and R. McMullen of the Site Analysis Branch.
. Harold R. Denton, Assistant Director for Site Safety Directorate of Licensing
Enclosure:
As stated ces w/o encicoure A. Ciambuseo W. Mcdonald J. Pansarella ces w/ enclosure S. Hanauer S. Varga F. Schroeder R. Morrise,USGS SS Branch Chiefs S. Brockman, USGS A. Kenneke G. Franklin, C of C A. Schwencer T. Cox If
f-R. McMullen R. Klecker 0605290400 h bbk60 D. Eisenhut J. Carter PDR ADOCK PDR E
TR g TR:SAB O R* [
TRISAB d r(
TRJSAA TR
/SS McMulie pg Coplan hp Heller Y G
k De n
2719775
]717775.
y773
~F{i775'
~27f 75-~~ ~7TpT73
~
r Asc.ne imee.
- 5H AscM ouo
- v.***aa"*aa'"""*a**'""*"*'"
l
E Q
r SER - WPPSS NUCLEAR PROJECT - UNITS 1 AND 4 2.5 Geology and Saismology The staff has completed its review of the geological, seismological, an'd foundation engineering aspects of the site. The applicant has adequately demonstrated by detailed site investigations that there are no geological structures that could cause near surface faulting, or could localize earth-quake activity in the immediate vicinity of the site. The causative mechanisms of the moderate earthquake activity within and around the Pasco Basin remains undetermined; however, the preponderence of available geological information indicates that the Rattlesnake-Wallula lineament is the surface representation of the geological structure most significant to the site. We conclude that the applicant's earthquake design bases are appropriately conservative, the site foundation investigations -
are adequate and the derived design parameters will contain sufficient margins of safety. The following is a discussion of the geology, seismology and site subsurface conditions of the Hanford site. The site had been reviewed previously for the Washington Nuclear 2 - Docket No.30 - 397.
2.5.1 Basic Geologic and Seismie Information 2.5.1.1 Regional Geology The WPPSS Nuclear Project No.1 site is located on the AEC Hanford Reservation, which is within the Pasco Basin, a physiographic and tectonic subdivision of the Columbia River Basalt Plateau Geologic Province. The Pasco Basin is bordered on the north by Saddle !!ountain; on the west by the Yakima and Umtanum Ridges; and the no'Athwest and south by the Rattlesnake Hills and the Horse Heaven Hill. These features are anticlinal folds 4
(JI
. within the upper basalt flow units. The eastern boundary is formed by the White Bluffs, which locally is the east bank of the Columbia River.
Topographic relief in the Pasco Basin varies from maximum elevations exceeding 3,500 feet atop Rattlesnake Mountain to a minimum elevation of
+340 in the Columbia River channel at Richland where the river flows out of the Basin. The site lies at elevation +445 on flat terrain that slopes gently to the northeast about 2 1/2 miles west of Columbia River.
The Pasco Basin has undergone continuous subsidence relative to the Columbia River Plateau since its formation which began with volcanic activity in early Miocene. The basalt flows beneath the Pasco Basin have attained a thickness of at least 5,000 feet.
In late Miocene or Pliocene, in addition to the continuing subsidence of the basin, the region became subjected to folding, ferming anticlines and synclines.
Igneous activity ceased in early Plioc.sne. The subsiding of the basin and the regional warping may be continuing at the present time.
The topography surrounding the Pasco Basin has created the setting for a natural reservoir. Consequently, the area has been subjectsd to alternate periods of flooding and erosion. This environment has been responsible for deposition of the approximately 500 feet of Ringold Formation and glacio-fluvial deposits. The Ringold Formation was deposited directly on basalt during an extended period of flooding, from Pliocene to early Pleistocene.
In the Pleistocene, as a result of the melting of glaciers to the north, the Pasco Basin was subjected to short, intermittent intervals of flooding and erosion.
. During periods of flooding, the glacio-fluvial soils overl ing the Ringold Formation were deposited, o
Cable Mountain and Gable Butte are two.en enchelon, asynunetrical, anticlinal hills which lie within the Pasco Basin and about 8 to 12 miles north of the site. These features represent outliers of Umtanum Ridge which plunges beneath the glacio-fluvial soils at the west side of the Basin. The buried extension of this structure may be present about 2 miles east of the site in a subdued form.
The ridges of the Pasco Basin area are long, sinuous, asymmetrical anticlines which generally trend in an east-west or a northwest-southeast direction. Between these ridges lie the Cold Creek, Wahluke, and the Pasco Synclines. Several anticlines including the Umtanum Ridge-Gable Mountain-Gable Butte complex, and Saddle Mountain, are faulted. The faults, where identifiable, are high angle thrust faults of limited extent which originated where folding was inadequate to relieve the regional stresses.
Some normal faulting has also been identified in'the region.
The faults parallel the anticlinal structures and are generally found on the north, overturned side, however, some such as the thrust fault on the Cable Mountain Anticline are subparallel and cut across the fold axis.
Most of the faults are at least' older than late Pleistocene. Bingham et al (1970) determined that the faults on Cable Mountain Anticline are probably more than 100,000 years old. Faults within the Pasco Basin are associated with steeply overturned assymetrical anticlines. The applicant has demonstrated,
. both in geolgoical investigations for WPPSS-2 and for this investigation
~
that there are no sharply assymetrical anticlines or other geological stru'etures that could localize earthquakes in the immediate site vicinity, or that could cause surface displacement at the site.
The Rattlesnake-Wallula structure west and southwest of the Pasco Basin is a northwest-southeast trending belt approximately~80 miles long of assymetrical-to-the-north anticlines, at least some of which may be faulted. Although it has not been conclusively demonstrated, faulting associated with the Rattlesnake-Wallula lineament, and other mapped faults around and within the Pasco Basin, appear to be related to near surface folding that occurred contemporaneous 1y with the downwarping qf the Columbia River Plateau and the Pasco Basin. Thus, this structure is not likely to be directly related to basement structure nor is it apt to be continuously faulted along its entire length. We conclude that the Rattlesnake-Wallula lineament is the most significant structure for determination of the safe shutdown earthquake.
2.5.1.2 Site Geology The site is a gently undulating, slightly dissected plain with occasional low lying hills and sand dunes. Average relief on the site is about 10 feet and the average elevation is +445.
Drainage is toward the Columbia River located about 2 l'/2 miles to the east.
The site was investigated by 140 drill holes of which seven penetrated several hundred feet into the Yakima basalt, several miles of seismic refraction lines, shallow trenches across the site and in-hole seismic l
refraction and geophysical surveys.
The site is mantled by 10 feet or less of aeolium deposits overlying 50 to 90 feet of Pasco gravels. The glacio-fluvial Pasco gravels consist primarily of medium dense to very dense gravelly sands. Beneath the Pasco gravels is the Ringold formation, which is composed of three units:
~
an upper weakly indurated siltstone and sandstone, a middle conglomerate member, and a lower siltstone and claystone member. The upper unit is absent in the site area and the Category 1 foundations will be founded either directly on the conglomerate or on engineered backfill on the conglomerate.
The Ringold lies unconformably on the relatively thin Ward Gap basalt flow which overlies the Elephant Mountain flow. These units vary from about 90 to 120 feet thick at the site.
The Rattlesnake Ridge member of the Ellensburg formation is beneath the Elephant Mountain basalt and consists of poorly bedded and slightly indurated tuff. The Rattlesnake Ridge is a fine to medium grained tuffeceous sandstone, siltstone and claystone.
Beneath the Rattlesnake Ridge interbed are from 160 to 170 feet of Pomona s
basalt. The Pomona flow is very widespread throughout the region, and was therefore used by the applicant to define the structural geology at the site.
The Pomona basalt overlies several thousand feet of older basalt flows
. and interbeds.
Structurally the site is located on the northeast limb of the Cold Creek Syncline, a structural trough that lies between the east and southeast trending Gable Butte-Gable Mountain anticline to the north and the Rattlesnake Hills antic 11ne to the south. Structural relief on'the syncline is 630 feet within 171/2 miles.
Borings and seismic data indicated a 150 foot bedrock structural high just north of Unit 4.
The steepest gradient is about 15' vertical to 1000' horizontal to the southwest. Although this dip is slightly steeper than the normal local gradient, it is much less than those associated with the major anticlines in the region. The feature is interpreted as being a smalleslightly assymetrical domal anticline similar to 1
many other features exposed around the Pasco Basin, such as domed hills in the Horn Rapids area.
Interpretation of the seismic refraction data indicated the presence of a sinuous buried channel that had been cut about 200 feet into the Ringold formation. The channel trends generally in an east-west direction several hundred feet north of Unit 4.
Available information indicates that the feature is arosional and not related to bedrock structure.
The applicant has adequately demonstrated by the deep borings, extensive seismic refraction survey lines, and mapping of 30 miles along the east bluff of the river, that there are no identifiable structures beneath the site that could pose a hazard by localizing earthquakes or causing surface faulting.
_w.-w-,-
tw-e---+m,.,w--
-e-e-w w w o-%
2.5.2 Vibratory Ground Motion 2.5.2.1 Tectonic Provinces The site is located within the Columbia Basin Tectonic Province which is geographically comprised of the Columbia River Basalt Plateau Geologic Province. The historical seismicity indicates that the province is characterized by the infrequent occurrence of low to moderate intensity earthquakes. The largest event had a maximum intensity of VII and occurred in the Milton-Freewater area of northern Oregon in 1936.
Several smaller events are also geographically clustered in the same area about sixty miles from the site. A second cluster near Ellensburg, Washington consists only of smaller events. The remaining earthquakes have been geographically scattered through the province, the largest being an intensity VI-VII event which occurred near Umatilla Oregon in 1893. We consider it possible that similar earthquakes could occur anywhere in thq province.
Several other provinces lie in part within 200 miles of the site; however, the historical record indicates that carthquakes uhich'could be expected to occur in these provinces would affect the site at lower intensities than would earthquakes originating in the Columbia Basin Tectonic Province.
In the vicinity of the site lie.,several major folded structures some of which are at least discontinuous 1y faulted. These are described in Section 2.5.1.1 above and include the Rattlesnake-Wallula lineament, Saddle Mountain, Cable Mountain and Cable Butte. Cable Mountain and Cable Butte show no evidence of seismic activity; however, both the
Rattlesnake - Wallula lineament and Saddle Mountain may have associated 3
earthquake activity.
By virtue of its greater extent and proximity to the site, the Rattlesnake-Wallula lineament must be considered to be of greater significance.
It appears likely that the intensity VII 1936 Milton-Freewater event was associated with this structure.
2.5.2.2 Safe Shutdown Earthquake (SSE)
The SSE for the WPPSS site is based on the following:
- 1) The maximum random earthquake in the Columbia Basin Tectonic Province will be no greater than intensity VII and can result in that intensity at the site;
- 2) The Rattlesnake - Wa'11ula lineament represents the most significant seismically active structure. We view it as having the potential of generating earthquakes of intensity VIII at a distance of little more than 10 miles from the site.
Based on the above, we have concluded that an intensity of VII-VIII is a conservative site intensity for representing the SSE. Thus we consider a horizontal acceleration of 0.25g used as the zero period limit of appropriate response spectra to be a conservative SSE. This acceleration is to be applied at the foundati,ons of Category I structures.
Under Appendix A to 10 CFR Part 100, we consider a value of 0.13 g equal, to one half of the SSE to be an conservative Operating Basis Earthquake.
. 2.5.3 Surface Faultina As stated earlier, there are no geological structures in the site vicinity that could represent a surface or near surface displacement at the site. The applicant has committed to geologically mapping all Category 1 excavations. A staff geologist will examine the open excavations at the appropriate time.
2.5.4 Stability of Subsurface Materials The upper 60 feet of sand is medium dense to very dense, and although competent for static loads, it would possess an inadequate factor of safety against liquefaction from an SSE if it should become saturated due to a rise in the groundwater table caused by the impoundment of a reservoir in the vicinity of the plant site.
Because of this possibility, the applicant plans to excavate to a depth of about 60 feet and recompact the material to an 85% average relative density in zones that support or 2
(
influence Category 1 foundations. The applicant has demonstrated that the proposed fill material will have an adequate resistance to liquefaction, due to the postulated ' earthquake, when compacted to a relative density of.75 percent. The applicant's propesed specification for the Category I fill, 85 percent average relative density, no more than 10 percent of the fill below 85 percent relative density, and a minimum of 75 percent relative density, will assure the stability of supported Category I structrues subjected to the postulated earthquake. Because of the presence of carbonates in these soils, the proposed method of compaction control l
must be modified to provide t' hat no soils showing a reaction to hcl l
shall be dried at temperatures other than as specified in ASTM Standard D2049-69.
l l
The sandy gravel, silt, and clay below a depth of 60 feet are dense and well consolidated, and will provide competent support for Category I This is confir' ed by high penetration blow counts, high structures.
m seismic compression and shear wave velocities, and stiffness results from Menard pressuremeter tests.
Settlement analyses were performed by the applicant. To eonfirm settlement calculations, the applicant will monitor rebound during and following excavation, and will monitor se'ttlement during and following construction until such time as settlement becomes insignificant.
Earthquake induced settlements of safety-related structures have been estimated at less than one-half inch.
We conclude that investigations have been adequate to define the properties of foundation soils, and that the methods and paramotors used in the design of foundations are appropriate and sufficiently conservative.
4
.