ML20127A443
| ML20127A443 | |
| Person / Time | |
|---|---|
| Site: | 05000000, Vogtle |
| Issue date: | 01/26/1983 |
| From: | Knight J Office of Nuclear Reactor Regulation |
| To: | Novak T Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19292B772 | List:
|
| References | |
| FOIA-84-624 NUDOCS 8302020179 | |
| Download: ML20127A443 (6) | |
Text
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d WASHINGTON. D. C. 20S55 mum MEl'ORANDUM FOR: Thomas M. !!ovak, Assistant Director for for Licensing, NRR FROM:
James P. Knight, Assistant Director for Components & Structures Engineering, DE
SUBJECT:
TRANSMITTAL OF GSB/HGEB STAFF REVIEW OF V0GTLE FAULT INVESTIGATION REPORT, " STUDIES OF POSTULATED MILLETT FAULT" Attached is the staff review of Georgia Power Company's report " Studies of Postulated Millett Fault." The fault investigation was prompted by the U. S. Geological Survey Open-File Report 82-156 which postulated the existence of two faults of unknown age and capability; the Millett Fault inferred to be seven miles south of the Vogtle Electric Generating Plant, and.the Statesboro Fault, 32 mi south of the plant.
The report concludes that there is no evidence for the existence of a capable fault at the locations inferred in the open file report. The staff reviewers have determined that the conclusions in the report are consistent with the information as reported, and conclude therefore that no capable fault, within the meaning of Appendix A to 10 CFR Part 100, is present in the vicinity of the Vogtle plant.
Because of the variety of techniques utilized by the applicant in the investigation, several staff reviewers contributed to the evaluation of the report: from GSB, Dr. Ina B. Alterman, Geologist, reviewed all aspects of the geologic part of the investigation; Dr. A. Ibrahim, Geophysicist, evaluated the seismic reflection study; Dr. Phyllis Sobel, Geophysicist, reviewed the seismology part of the report; and Dr. D.
Chery, Hydrologist from HGEB reported on all aspects of the hydrologic part of the study.
They may be contacted if there are any further questions.
M{
Jamqs P. Kn* ht, As istant Director for Cbmponents Structures Engineering DiyisionofEngineering
Attachment:
As stated FP-cc: See next page 30 7_6 E o Q
Review of Vogtle Report " Studies of Postulated Millett Feult" I.
Introdu: tion In October,1982, Georgia Pcwer Company submitted to the NRC a report of a fault specific investigation entitled, " Studies of Postulated Millett Fault." The report is the result of a six-month investigation in response to Oper. File Report 82-156 (OFR) by Robert E. Faye and David C.
Prowell of the U. S. Geological Survey which postulated the existence of a fault of unknown age or espability seven miles south of the Vogtle Electric Generating Plant now under construction. The open file report further inferred a second fault, parallel with the first, about 32 miles south of the plant. These postulated faults, the Millett and Statesboro Faults, were the subjects of the utility's fault investigation, with the primary focus on the former which was closer to the plant.
II. The Hillett Fault: Description and evidence As interpreted by Faye and.Prowell, the Millett Fault trends northeastward across the Savannah River, is approximately 40 miles long, and has vertically offset the buried Triassic / Cretaceous contact +600 ft on the southeast side of the fault.
The main evidence for the inferred fault came from a comparison of well cuttings taken several years before the 0FR study from two water wells, P5R and AL66.
Interpretation of the lithic fragments suggested that Triassic rocks were present below -1100 ft in PSR, but above -600 ft in AL 66 four miles to the south. Further, an examination of surface and groundwater flow records over a period of forty years indicated some anomalous characteristics which Faye and Prowell interpreted as resulting from a subsurface barrier. By extrapolation from the Belair Fault 35 miles to the north, the 0FR inferred that an impermeable gouge zone above the postulated Millett Fault forced the so'uth flowing groundwater from a lower aquifer to a higher one on the south side of the fault. As the trace of the postulated fault traverses a segment of the Savannah River where a straight stretch of the river changes to a more characteristic meandering flow pattern, the 0FR considered this observation further support for the inferred fault.
Evidence for the trend and length of the postulated faults was by extrapolation from other post-Cretaceous coastal plain faults in the southeastern United States.
While no age of faulting was suogested, the 0FR indicated that rocks at leastthroughtheEoceneepoch(55-38 mybp (millionyearsbeforethe present)) were involved.
III. Fault Investigation Inesmuch as the age and therefore capability of the inferred faults were undetermined, Georgia Power, through its licensing consultant, Southern
^'
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, Compan,k Services (SCS), undertook a vigorous investigetive progran to resolve the issue, and engaged a team of eminent earth scientists to guide and evaluate the direction and results'of the investigation.
A. Techniques SCS utilized a wide range of techniques to explore the surface and subsurface for both geologic and hydrologic information in order to
- locate and date the fault.
Included in the' study was (1) field geoloaic mapping, (2) aerial and Landsat imagery for remote sensing analysis, (3) core drilling on both sides of the Savannah River and straddlino the interval of the two wells described in the open file report (4) petrographic, x-ray and heavy mineral analyses of core samples, (5) downhole geophysical studies' including gama, neutron and electric logging, (6) seismic reflection profiling, (7) regional geophysical and seismicity studies, (7) well water level monitoring, (8) ground water modelling, and (9) analysis of surface water flow.
B.
Staff Review Because of the wide range of techniques used, several NRC staff reviewers have contributed to this evalu.! tion of the utility's report; a geologist covering the varied geologic investigations, a seismologist for the historic and present day seismicity of the area, a geophysicist for the seismic reflection profiling, and a hydrologist reviewing the surface and ground water study.
In addition, the geologist and one of the geophysicists have visited the site region with the NRC project manager ara SCS staff to examine the cores drilled for this study, the stratigraphy, and various aspects of the surface features in order to have first hand experience in evaluating the fault investigation report.
C.
Conclusions The conclusion arrived at by the applicant, based upon the results of the study, is that there is no evidence for a capable fault; and that if there is a fault, which could not be detected by any of the techniques used by the applicant, it is older than 40 mybp. The staff agrees that this conclusion is consistent with the reported information and results of the various investigative techniques.
IV. Summary of Fault Investigation and Results A brief sumary of these results and the applicant's views follow.
A. Geologic Background The plant and the postulated faults are located in the Atlantic Coastal Plain physiographic province. Except for river alluvium and gravels of Quaternary age (2 mybp-Present), the youngest, most extensively exposed formation in the region is the Hawthorn (or Altamaha) Formation of Miocene age (25-23 mybp). The olc'est exposed rock, the Blue Bluff marl of the Lisbon Formation, is a calcareous, silty, grayish fossiliferous
. unit, distinctive in lithology and fauna, and of middle Eocene age (50-40 mySP). The marl is limited in exposure in the banks of the Savannah River which has begun to cut down through it.
The Eocene formations rest unconformably on Paleocene (63-55 mybp) clays and black lignitic sands which are also distinctive. These overlie the late Cretaceous (96-63 mybp) Tuscaloosa Formation unconformsbly. The Cretaceous sediments are the oldest of the late Mesozoic (240-60 MYBP)
~
raarine transgression deposits that constitute the Coastal Plain CoVertnass.
In several places in the Piedmont, west and north of the coastal plain, Triassic down-faulted basins filled with distinctive Triassic sedimentary rocks and some Triassic-Jurassic basaltic igneous rocks are exposed. Similar basins have been recognized beneath the coastal plain.
One such basin, the Dunbarton Basin, trending northeastward, has been identified on the basis of aeromagnetic anomalies and drillino for the Savannah River Plant. The Vogtle plant overlies the basin, close to the northern boundery. The southern boundary approximately coincides with
.the location of the postulated Millett Fault. As this basin is downfaulted, presumably into Piedmont rocks, it is assumed that the rocks below and surrounding the basin are Precambrian (older than 570 mybp) and early Paleozoic (570-240 mybp) metamorphics.
B.
Geologic Investigation The geologic investigation included (1) field mapping and remote sensing to identify evidence for surface faulting; (2) core drilling with petrographic, x-ray and heavy mineral analysis of the strata in the cores in order to correlate layers from core to core to determine any offset of the strata;-(3) downhole geophysical logging, which identifies individual strata by characteristic signatures that are dependent upon the physical properties of the rock units, also with a view to correlating the strata from core to core; and (4) review of other geophysical studies.
1.
Field mapping and remote sensing techniques failed to uncover any evidence of surface faulting, or linear features indicative of surface or near surface rupture. Staff review of some of the original imagery used for the study and field checks in the site area verified this conclusion.
2.
Twelve drill cores were taken along two parallel north-south lines, crossing the inferred trace of the Millett Fault, one in South Carolina close to the two wells studied by Faye and Prowell, and one in Georgia. Along both lines, one core was taken from the location closest to the trace of the fault and the others equally spaced north and south of the fault.
Eight holes were cored in Georgia, about one mile apart north-south, and four in S.C.
Visual examinations, petrographic and mineralogic analyses identified distinctive marker beds. One of these, the Blue Bluff marl,
l
- appeared consistently between 100 ft above sea level to 100 ft below, showing no change in elevation (other than that due to the gentle regional dip to the south) on either side of the postulated fault in Georgia and South Carolina. This indicates that no vertical offset and therefore no fault of the type postulated in the USGS open file report is present down to strata at least 40 my old at the inferred location of the postulated fault.
Furthermore, Core VSC-4, on strike with, and 200 ft from, well AL66 in which the USGS interpreted Triassic rocks at an elevation of
-600 ft, was the deepest hole in the study. The core at -1000' was still in distinctive Cretaceous Tuscaloosa sands. The staff examined this core and agrees that it has none of the characteristics of Triassic rocks and looks much like other Cretaceous samples. This result is in direct disagreement with the open-file report interpretation upon which the fault is postulated.
3.
Downhole geophysical logs, especially the gama log, provided distinctive signatures that verified the petrographic identification of the. strata, and in particular the Blue Bluff marl, confirming the continuity of the unit across the inferred location of the Millett Fault.
C.
Seismic Reflection Study A nineteen mile acoustical seismic reflection survey was conducted in the Savannah River in the vicinity of the postulated Millett fault. The survey used three different energy sources, Uniboom,10 cubic inch eir gun and 20 cubic inch air gun, to obtain high resolution a.nd deep penetration of the subsurface formations. The water depth in which the survey was carried out ranges between 10-25 feet.
The reflection survey identified several key horizons, A through I, at different depths ranging between +70 to -1150 feet. Some of the horizons, such as reflector E, which correlates with the top of the limestone that is the lowest unit in the Barnwell group, of Late Eocene age (40 MYBP), and reflector G, which represents the unconformable contact between the unnamed sands of the Middle Eocene Lisbon Formation and the top of the Paleocene kaolinitic clay. (60 mybp) are well correlated with adjacent core holes. Some of the reflectors are well defined while others are weakly defined. Some of the horizons showed small features which may be indicative of past channelization or buried karstic surfaces. The continuity of the reflectors above the Triassic / Cretaceous contact and the absence of noticeable displacement in the higher horizons above -500 feet elevation indicate.the absence of
' faulting within the last 60 million years in the vicinity of the postulated Millett fault. This conclusion is in agreement with that of the applicant's report, that no capable fault has been identified by the seismic reflection data obtained for this study.
In addition, seismic reflection data obtained by the applicant from the Savannah River Plant investigation of the deeper horizons in the a
. vicinity of both plants suggest the possibility of e small normal offset of the Triassic / Cretaceous contact of 50-100 ft in the vicinity of the postulated fault. No evidence, however, for offset in younger horizons can be detected.
D.
Seismology Study The available seismicity information includes (1) felt earthquakes, (2) recent instrumentally located events, and (3) data from the Savannah River Plant array, just across the Savannah River from the Vogtle site.
The applicant concludes that historic seismicity reveals no evidence of active faulting in the area. This conclusion is consistent with the data. The seismicity near the site has been scattered and low level (maximum MM intensity VI). No clustering of earthquakes is occurring near the postulated Hillett or Statesboro faults.
E.
Hydrology Study Faye and Prowell used, as part of their case, several hydrologic arguments to support the existence of the postulated fault. These arguments were thoroughly investigated in this study by the applicant.
The issues of different unit base flows in river reaches (generally above and below the postulated fault), water well levels across the postulated fault, and ground water piezometric surface contours were addressed by their study. After carefully reviewing all the contractor's hydrologic evaluations, the staff concurs in their conclusion that the hydrologic data provide "no basis to support or preclude the existence of a fault."
IV. Conclusions On the basis of (1) the continuity of strata across the inferred location of the postulated Millett Fault as determined by (a) drill cores, (b) downhole geophysical logging and (c) seismic reflection profiles, (2) the absence of Triassic rocks at levels above -1000 ft, as shown by drill core VSC-4 on the south side of the postulated fault, (3) the scattered and icw level seismicity and (4) the hydrologic information which neither indicates nor disproves the presence of a fault, the applicant's report concludes that there is no evidence for the existence of a capable fault in the vicinity of the Vogtle plant.
The staff has carefully reviewed the report, has visited the site and examined the cores, the logs, and remote sensing imagery, and field checked the surface features. The reviewers consider the applicant's conclusion to be consistent with the data as reported, and conclude, therefore, that no capable fault as defined in Appendix A to 10 CFR Part 100 is present in the vicinity of the Vogtle plant, based on all presently available data. Should new information become available, it will be evaluated during the review for the Operating License (OL) for the plant.
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