ML20094B564
| ML20094B564 | |
| Person / Time | |
|---|---|
| Issue date: | 11/24/1975 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| References | |
| NUREG-75-087, NUREG-75-087-02.5.3, NUREG-75-87, NUREG-75-87-2.5.3, SRP-02.05.03-01, SRP-2.05.03-1, NUDOCS 9511010133 | |
| Download: ML20094B564 (6) | |
Text
NUREG 75/087 pur o,
3, U.S. NUCLEAR RESULATCRY COMMirlCN
=
o4 STANDARD REVIEW PLAN OFFICE OF NUCLEAR REACTOR REGULATION SECTION 2.5.3 SURFACE FAULTING
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REVIEW RESPONSIBILITIES Primary - Site Analysis Branch (SAB)
Secondary - None j
I.
AREAS OF REVIEW SAB reviews information in the applicant's safety analysis report (SAR) related to the exis-tence of a potential for surface faulting affecting the site. The information presented in this section results largely from detailed surface and subsurface geological and geophysical investigations performed in the site and vicinity. The following specific subjects are addressed: the structural and stratigraphic conditions of the site and vicinity (Subsection 2.5.3.1), any evidence of fault offset or evidence demonstrating the absence of faulting (Subsection 2.5.2.2), earthquakes associated with faults (Subsection 2.5.3.3), determination of age of most recent movement on faults (Subsection 2.5.3.4), determination of structural relationships of site area faults to regional faults (Subsection 2.5.3.5), identification and description of capable faults (Subsection 2.5.3.6), and zones requiring detailed fault
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investigations (Subsection 2.5.3.7).
II.
ACCEPTANCE CRITERIA The data and analyses presented in the SAR are judged acceptable if, as a minimum, they des-cribe and document the information required by References 1 and 2, and other data that are necessary, depending on the complexity of the site. The GEO-Reference File (Ref. 3) is used by the staff as the principal reference guide to judge whether or not all of the pertinent references have been consulted. References 4 through 9 are also used by the staff.
Subsection 2.5.5.? is considered acceptable if the discussions of the stratigraphy, methods of fault dating, structural geology, and geologic history of the site are complete, compare well with studies Cuducted by others in the same area, and are supported by detailed inves-tigations performed by the applicant. Site and regional geologic maps and profiles constructed at scales adequate to illustrate clearly the surficial and bedrock geology, structural geology topography, and the relationship of the safety-related foundations of the nuclear power plant to these features should be included in the SAR.
Subsection 2.5.3.2 is acceptable if sufficient surface and subsurface information is provided and supported by detailed investigations, either to confirm the absence of faulting or, if faulting is present, to demonstrate its age. If faulting is present in the site vicinity, it USNRC STANDARD REVIEW PLAN
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i must be defined as to fault geometry, amount and sense of movement, and ag2 of latest move-ment. In additirn to g;ologic evidtnce which may indicate faulting, linears interpreted from topographic maps, low-altitude aerial photographs and Environmental Resource Technology Satellite imagery should be documented and investigated. Evidence for absence of faulting is obtained by conducting site surface and subsurface investigations in such detail and areal extent to ensure that undetected offsets are not likely to exist. These investigations will vary in detail according to the geological complexity of the specific site.
Subsection 2.5.3.3 is acceptable if all historically reported earthquakes within five miles of the site or near faults which trend within five miles of the site, as discussed in Section 2.5.2, are evaluated with respect to hypocenter accuracy and source origin. In conjunction with these discussions, a plot of the earthquake epicenters superimposed on a
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map showing the local tectonic structures as defined in Section 2.5.1 should be provided.
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Estimated error regions of the earthquake epicenters should be shown.
Subsection 2.5.3.4 is acceptable when every fault, any part of which is within five miles of the site, is investigated in sufficient detail using geological and geophysical techniques of sufficient sensitivity to demonstrate the age of most recent movement. An evaluation of the sensitivity and resolution of the exploratory techniques used should be given.
Subsection 2.5.3.5 is acceptable when a discussion is given of the structural and genetic relationship between site area faulting and the regional tectonic framework. In regions of active tectonism it may be necessary to conduct detailed geological and geophysical investi-gations to demonstrate the structural relationships.of site arca faults to regional faults known to be seismically active. Both a theoretical and an observational basis for the con-clusions reached should be given.
Subsection 2.5.3.6 is acceptable when it has been demonstrated that the investigative tech-niques used have sufficient sensitivity to identify all faults greater than 1000 feet in length within five miles of the site and when the geometry, sense of movement, and amount of offset is given for each.
Subsection 2.5.3.7 is judged acceptable if the zone designated by the applicant as requiring detailed faulting investigation is consistent with the description of such a zone in Ref-erence 1.
Subsection 2.5.3.8 must be presented by the applicant if the aforementioned investigations reveal that surface displacement must be taken into account. No nuclear plant has ever been constructed on a capable fault and it is an open question as to whether it is possible to design for surface or near-surface displacement with confidence that the integrity of the safety-related features of the plant would remain intact should displacement occur. It is, therefore, staff policy to recommend relocation of plant sites found to be located on capable faults as determined by the detailed faulting investigation. If in the future it becomes possible to design for surface faulting, it will be necessary to present the design basis for surface faulting and supporting data in considerable detail.
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III.
REVIEW PROCEDURES The staff review procidure involves an evaluation to determine that the applicant has followed the investigations outlined in Reference 1.
The U.S. Geological Survey (USGS) acts as staff advisor in reviewing this section of the SAR, on a case-by-case basis. On request, the USGS provides expertise in numerous earth science disciplines and often is able to provide first-hand knowledge of the site. A literature search is conducted concerning the regional and local geology. The staff also contacts state geological surveys and universities to obtain additional data.
Generally, the steps that applicants must follow in determining the presence and extent of faulting, and whether near-surface faulting (if present) represents a hazard or not, is out-lined in the seismic and geologic siting criteria (Ref.1). Specific investigative techniques are not given in the criteria, however. The site area must be investigated by a combination of exploratory methods which may include borings, trenching, seismic profiling, geologic mapping, and geophysical investigations. The results of these explorations are cross-compared and evaluated by the staff.
It has been the policy of the staff to encourage applicants to avoid areas where there is a possibility for surface faulting. As the question of whether or not a surface faulting condition exists is so critical in determining whether a particular site is suitable, this consideration is usually addressed very early in the review. Exceptions are those cases in which a fault, the existence of which was previously unknown, is revealed in excavations during construction or is discovered during the course of other inve'stigations in the area.
When faults are identified in the site vicinity, it must be demonstrated that the faults are not capable. This is accomplished by determining the ages of the faults by absolute age dating (radiometric), associating the faulting with regional tectonic activity of known age, stratigraphic or geomorphic evidence, etc. In such cases the staff will carry out limited site observations and investigations of its own such as examinations of excavations, and selecting and dating samples taken from shear zones. Applicants are usually required to trench in the areas where major facilities are to be located.
Subsection 2.5.3.1 is evaluated by conducting an independent literature search and cross-comparing the results with the information submitted in the SAR. The comparison should show that the conclusions presented by the applicant are based on sound data, are consistent with the published reports of experts who have worked in the area, and are consistent with the conclusions of the staff and its advisors. If the applicant's conclusions and assumptions conflict with the literature, substantive investigative results to support those conclusions must be submitted to the staff for review.
Subsection 2.5.3.2 is evaluated by first determining through a literature search that all known evidences of fault offset have been considered in the investigation. The results of j
the applicant's site investigations are studied and cross-compared in detail to see if there l
is evidence of existing or potential displacements. If such evidence is found, additional investigations such as field mapping, geophysichl investigations, borings, trenching, etc.,
must be carried out to demonstrate that there is no offset or to define the characteristics of the fault if it does exist.
2.5.3-3 I
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Subsection 2.5.3.3 is reviewed in conjunction with the considsration of Section 2.5.2.
His-trric earthquaka data dirivId from thz review of Section 2.5.2 are compared with known local tectonic features and a determination is made as to whether any of these earthquakes can reasonably be associated with the local structures. This determination includes an evaluation of the error regions of the earthquake locations. When available, the earthquake source mechanisms should be evaluated with respect to fault geometry.
-v Subsection 2.5.3.4 is evaluated to determine if the age dating methodology used by the appli-cant is based on accepted geological procedures. In some cases unusual age dating techniques may be used. When such methods are employed, the staff will require extensive documentation of the technique and may treat it as a generic review item. The resolution of all age dating techniques should be carefully documented.
Subsection 2.5.3.5 is evaluated by determining through a literature search that the applicant's evaluation of the regional tectonic framework is consistent and recognized by experts whose reports appear in the published literature. The conclusions reached by the applicant should be based on sound geologic principles and should explain the available geological and geo-physical data. When special investigations are made to determine the structural relationship between faults which pass within five miles of the site and regional faults, the resolution of the investigative techniques should be given.
Subsection 2.5.3.6 is evaluated to determine if a sufficiently detailed investigation has been made by the applicant to define the specific characteristics of all capable faults located within 5 miles of the site. The fault characteristics requiring definition include:
length, orientation, relationship of the fault to regional structures; the nature, amount, j
and geologic history of displacements along the fault; and the outer limits of the fault j
zone established by mapping fault traces 50 miles along trends in both directions from the point of nearest approach to the site. The staff must be satisfied that the investigation j
covers a large eNugh area in sufficient detail to demonstrate.that there is little likeli-hood of near-surface displacement hazards associated with capable faults existing undetected near the site.
Subsection 2.5.3.7 Criteria for detennining the zone requiring detailed faulting investiga-tion are clearly outlined in Reference 1.
The staff reviews the results of the applicant's faulting investigation together with the published literature. The investigative techniques employed by the applicant are evaluated to ascertain t b t they are consistent with the state of the art. As part of this phase, experts in specific disciplines are asked to review certain aspects of the investigative program. The results of the investigation are analyzed to determine whether the outer limits of the zone requiring faulting investigation are appro-priately conservative. If there are insufficient data to substantiate the outer boundaries, more conservative assumptions are required.
Subsection 2.5.3.8 If the detailed faulting investigations reveal that there is a potential for surface displacement at the site, the staff recommends that the site be moved to an alter-nate location. In the future, when it may be possible to design a nuclear power plant for displacements, substantial information will be required to support the design basis for surface faulting.
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IV.
EVALUATION FINDINGS After completing the revier, the staff sununarizes its conclusions regarding surface faulting in the SER. If after the staff completes a detailed review of the applicant's investigations and conclusions it has been effectively demonstrated that near-surface displacement cannot occur at the site, the entire section of the SER can be sununarized by a statement such as:
l "The staff concludes that there are no surface or near-surface displacement potentialities l
existing at the site."' If it is determined that surface displacement cannot be precluded, v
l the staff notifies the applicant of its conclusions well in advance of publication of the SER.
V.
REFERENCES 1.
10 CFR Part 100, Appendix A, " Seismic and Geologic Siting Criteria for Nuclear Power Plants."
d 2.
Regulatory Guide 1.70, " Standard Format and Content of Safety Analysis Reports for Nuclear Power Plants " Revision 2.
3.
"GE0-
Reference:
Computerized File of Earth Science Titles," American Geological Institute Washington, 4
M. R. Grey, R. McAfee, Jr., and C. L. Wolf, eds., " Glossary of Geology," American Geological Institute, Washington (1972).
5.
G. V. Cohee (chairman) et. al., " Tectonic Map of the United States," U. S. Geological SurveyandAmericanAssociationofPetroleumGeologists(1962).
l 6.
State geological maps and accompanying texts.
j 7.
U. S. Geological Survey 7.5-and 15-minute topographic and geologic quadrangle maps.
4 1
8.
V. S. Department of Agriculture and U. S. Geological Survey aerial photographs.
9.
Environmental Resources Technology Satellite photographs.
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