ML020430357
| ML020430357 | |
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| Issue date: | 02/12/2002 |
| From: | Shah M NRC/NMSS/SFPO/TRD |
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This regulatory guide is being issued in draft form to involve the public in the early stages of the development of a regulatory position in this area. It hasnot received complete staff review or approval and does not represent an official NRC staff position.Public comments are being solicited on this draft guide (including any implementation schedule) and its associated regulatory analysis or value/impactstatement. Comments should be accompanied by appropriate supporting data. Written comments may be submitted to the Rules and DirectivesBranch, Office of Administration, U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001. Comments may be submitted electronically ordownloaded through the NRC's interactive web site at <WWW.NRC.GOV> through Rulemaking. Copies of comments received may be examined at theNRC Public Document Room, 11555 Rockville Pike, Rockville, MD. Comments will be most helpful if received by Requests for single copies of draft or active regulatory guides (which may be reproduced) or for placement on an automatic distribution list for singlecopies of future draft guides in specific divisions should be made to the U.S. Nuclear Regulatory Commission, Washington, DC 20555, Attention: Reproduction and Distribution Services Section, or by fax to (301)415-2289; or by email to DISTRIBUTION@NRC.GOV. Electronic copies of this draftguide are available through NRC's interactive web site (see above), or the NRC's web site <
WWW.NRC.GOV> through the Electronic Reading Roomunder Accession Number U.S. NUCLEAR REGULATORY COMMISSIONMarch 2002 OFFICE OF NUCLEAR REGULATORY RESEARCHDivision 3DG-3021 DRAFT REGULATORY GUIDEContact: M. Shah (301)415-8537DRAFT REGULATORY GUIDE DG-3021SITE EVALUATIONS AND DETERMINATION OF DESIGN EARTHQUAKE GROUND MOTION FOR SEISMIC DESIGN OF INDEPENDENT SPENT FUEL STORAGE INSTALLATIONS AND MONITORED RETRIEVABLE STORAGE INSTALLATIONS A. INTRODUCTIONThe NRC has recently published proposed amendments to 10 CFR Part 72, "Licensing 1Requirements for the Independent Storage of Spent Nuclear Fuel and High-Level Radioactive Waste, 2and Reactor-Related Greater Than Class C Waste.
" The Proposed Section 72.103, "Geological and 3Seismological Characteristics for Applications for Dry Modes of Storage on or after [insert effective date 4of Final Rule]," in paragraph (f)(1), would require that the geological, seismological, and engineering 5characteristics of a site and its environs be investigated in sufficient scope and detail to permit an 6adequate evaluation of the proposed site. The investigation must provide sufficient information to 7support evaluations performed to arrive at estimates of the design earthquake ground motion (DE) and 8to permit adequate engineering solutions to actual or potential geologic and seismic effects at the 9proposed site. In the Proposed Section 72.103, paragraph (f)(2) would require that the geologic and 10seismic siting factors considered for design include a determination of the DE for the site, the potential 11for surface tectonic and nontectonic deformations, the design bases for seismically induced floods and 12water waves, and other design conditions. In the Proposed Section 72.103, Paragraph (f)(2)(i) would 13require that uncertainties inherent in estimates of the DE be addressed through an appropriate analysis, 14such as a probabilistic seismic hazard analysis (PSHA) or suitable sensitivity analyses.
15PREPUBLICATION 2This guide is being developed to provide general guidance on procedures acceptable to 16the NRC staff for (1) conducting a detailed evaluation of site area geology and foundation 17stability, (2) conducting investigations to identify and characterize uncertainty in seismic sources 18in the site region important for the PSHA, (3) evaluating and characterizing uncertainty in the 19parameters of seismic sources, (4) conducting PSHA for the site, and (5) determining the DE to 20satisfy the requirements of 10 CFR Part 72.
21This guide contains several appendices that address the objectives stated above.
22Appendix A contains definitions of pertinent terms. Appendix B describes the rationale used to 23determine the reference probability for the DE exceedance level that is acceptable to the staff.
24Appendix C discusses determination of the probabilistic ground motion level and controlling 25earthquakes and the development of a seismic hazard information base, Appendix D discusses 26site-specific geological, seismological, and geophysical investigations. Appendix E describes a 27method to confirm the adequacy of existing seismic sources and source parameters as the basis 28for determining the DE for a site. Appendix F describes procedures for determination of the DE.
29This guide applies to the design basis of both dry cask storage Independent Spent Fuel 30Storage Installations (ISFSIs) and U.S. Department of Energy monitored retrievable storage 31installations (MRS), because these facilities are similar in design. The reference probability in 32Regulatory Position 3.4 and Appendix B does not apply to wet storage because of the greater 33consequences associated with the potential accident scenarios for these facilities. This is 34because wet storage requires active systems, such as systems to remove heat and maintain 35adequate water levels. These active systems have a higher probability of failure than the passive 36systems used in dry modes of storage, thus resulting in a greater seismic risk for wet modes of 37storage.38This guide is consistent with Regulatory Guide 1.165 (Ref. 1), but it has been modified to 39reflect ISFSI and MRS applications, experience in the use of the dry cask storage methodology, 40and advancements in the state of knowledge in ground motion modeling (for example, see 41NUREG/CR-6728 (Ref. 2)).
42Regulatory guides are issued to describe and make available to the public such 43information as methods acceptable to the NRC staff for implementing specific parts of the NRC
's 44regulations, techniques used by the staff in evaluating specific problems or postulated accidents, 45and guidance to applicants. Regulatory guides are not substitutes for regulations, and 46compliance with regulatory guides is not required. Regulatory guides are issued in draft form for 47public comment to involve the public in the early stages of developing the regulatory positions.
48Draft regulatory guides have not received complete staff review and do not represent official 49NRC staff positions.
50The information collections contained in this draft regulatory guide are covered by the 51requirements of 10 CFR Part 72, which were approved by the Office of Management and Budget 52(OMB), approval number 3150-0132. If a means used to impose an information collection does 53not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a 54person is not required to respond to, the information collection.
55B. DISCUSSION 56BACKGROUND 57 3A PSHA has been identified in the proposed Section 72.103 as a means to determine the 58DE for seismic design of an ISFSI or MRS facility. The proposed rule further recognizes that the 59nature of uncertainty and the appropriate approach to account for it depends on the tectonic 60environment of the site and on properly characterizing parameters input to the PSHA, such as 61seismic sources, the recurrence of earthquakes within a seismic source, the maximum 62magnitude of earthquakes within a seismic source, engineering estimation of earthquake ground 63motion, and the level of understanding of the tectonics. Therefore, methods other than 64probabilistic methods such as sensitivity analyses may be adequate to account for uncertainties.
65Every site and storage facility is unique, and therefore requirements for analysis and 66investigations vary. It is not possible to provide procedures for addressing all situations. In 67cases that are not specifically addressed in this guide, prudent and sound engineering judgment 68should be exercised.
69PSHA methodology and procedures were developed during the past 20 to 25 years 70specifically for evaluation of seismic safety of nuclear facilities. Significant experience has been 71gained by applying this methodology at nuclear facility sites, both reactor and non-reactor sites, 72throughout the United States. The Western United States (WUS) (west of approximately 104 o 73west longitude) and the Central and Eastern United States (CEUS) (Refs. 3, 4) have 74fundamentally different tectonic environments and histories of tectonic deformation. Results of 75the PSHA methodology applications identified the need to vary the fundamental PSHA 76methodology application depending on the tectonic environment of a site. The experience with 77these applications also served as the basis for the Senior Seismic Hazard Analysis Committee 78guidelines for conducting a PSHA for nuclear facilities (Ref. 5).
79APPROACH 80The general process to determine the DE at a new ISFSI or MRS site includes:
811.Site- and region-specific geological, seismological, geophysical, and geotechnical 82investigations, and 832.A PSHA.
84For ISFSI sites that are co-located with existing nuclear power generating stations, the 85level of effort will depend on the availability and quality of existing evaluations. In performing this 86evaluation, the applicant should evaluate whether new data require re-evaluation of previously 87accepted seismic sources and potential adverse impact on the existing seismic design bases of 88the nuclear power plant.
89CENTRAL AND EASTERN UNITED STATES 90The CEUS is considered to be that part of the United States east of the Rocky Mountain 91front, or east of longitude 104 o west (Refs. 6, 7). To determine the DE in the CEUS, an accepted 92PSHA methodology with a range of credible alternative input interpretations should be used. For 93sites in the CEUS, the seismic hazard methods, the data developed, and seismic sources 94identified by Lawrence Livermore National Laboratory (LLNL) (Refs. 3, 4, 6) and the Electric 95Power Research Institute (EPRI) (Ref. 7) have been reviewed and are acceptable to the staff.
96The LLNL and EPRI studies developed data bases and scientific interpretations of available 97information and determined seismic sources and source characterizations for the CEUS (e.g., 98earthquake occurrence rates, estimates of maximum magnitude).
99 4In the CEUS, characterization of seismic sources is more problematic than in the active 100plate-margin region because there is generally no clear association between seismicity and 101known tectonic structures or near-surface geology. In general, the observed geologic structures 102were generated in response to tectonic forces that no longer exist and have little or no correlation 103with current tectonic forces. Therefore, it is important to account for this uncertainty by the use of 104multiple alternative models.
105The identification of seismic sources and reasonable alternatives in the CEUS considers 106hypotheses presently advocated for the occurrence of earthquakes in the CEUS (e.g., the 107reactivation of favorably oriented zones of weakness or the local amplification and release of 108stresses concentrated around a geologic structure). In tectonically active areas of the CEUS, 109such as the New Madrid Seismic Zone, where geological, seismological, and geophysical 110evidence suggest the nature of the sources that generate the earthquakes, it may be more 111appropriate to evaluate those seismic sources by using procedures similar to those normally 112applied in the WUS.
113WESTERN UNITED STATES 114The WUS is considered to be that part of the United States that lies west of the Rocky 115Mountain front, or west of approximately 104 o west longitude. For the WUS, an information base 116of earth science data and scientific interpretations of seismic sources and source 117characterizations (e.g., geometry, seismicity parameters) comparable to the CEUS as 118documented in the LLNL and EPRI studies (Refs. 3, 4, 6-8) does not exist. For this region, 119specific interpretations on a site-by-site basis should be applied (Ref. 9, 10).
120The active plate-margin regions include, for example, coastal California, Oregon, 121Washington, and Alaska. For the active plate-margin regions, where earthquakes can often be 122correlated with known tectonic structures, structures should be assessed for their earthquake 123and surface deformation potential. In these regions, at least three types of sources may exist:
124(1) faults that are known to be at or near the surface, (2) buried (blind) sources that may often be 125manifested as folds at the earth
's surface, and (3) subduction zone sources, such as those in the 126Pacific Northwest. The nature of surface faults can be evaluated by conventional surface and 127near-surface investigation techniques to assess orientation, geometry, sense of displacements, 128length of rupture, quaternary history, etc.
129Buried (blind) faults are often associated with surficial deformation such as folding, uplift, 130or subsidence. The surface expression of blind faulting can be detected by mapping the uplifted 131or down-dropped geomorphological features or stratigraphy, survey leveling, and geodetic 132methods. The nature of the structure at depth can often be evaluated by deep core borings and 133geophysical techniques.
134Continental U.S. subduction zones are located in the Pacific Northwest and Alaska.
135Seismic sources associated with subduction zones are sources within the overriding plate, on the 136interface between the subducting and overriding lithospheric plates, and in the interior of the 137downgoing oceanic slab. The characterization of subduction zone seismic sources includes 138consideration of the three-dimensional geometry of the subducting plate, rupture segmentation of 139subduction zones, geometry of historical ruptures, constraints on the up-dip and down-dip extent 140of rupture, and comparisons with other subduction zones worldwide.
141The Basin and Range region of the WUS, and to a lesser extent the Pacific Northwest 142and the Central United States, exhibit temporal clustering of earthquakes. Temporal clustering is 143 5best exemplified by the rupture histories within the Wasatch fault zone in Utah and the Meers 144fault in central Oklahoma, where several large late Holocene coseismic faulting events occurred 145at relatively close intervals (hundreds to thousands of years) that were preceded by long periods 146of quiescence that lasted thousands to tens of thousands of years. Temporal clustering should 147be considered in these regions or wherever paleoseismic evidence indicates that it has occurred.
148C. REGULATORY POSITION 1491. GEOLOGICAL, GEOPHYSICAL, SEISMOLOGICAL, AND GEOTECHNICAL 150INVESTIGATIONS 1511.1 Comprehensive geological, seismological, geophysical, and geotechnical investigations of 152the site area and region should be performed. For ISFSIs co-located with existing nuclear power 153plants, the existing technical information should be used along with all other available information 154to plan and determine the scope of additional investigations. The investigations described in this 155regulatory guide are performed primarily to gather data pertinent to the safe design and 156construction of the ISFSI or MRS. Appropriate geological, seismological, and geophysical 157investigations are described in Appendix D to this guide. Geotechnical investigations are 158described in Regulatory Guide 1.132, "Site Investigations for Foundations of Nuclear Power 159Plants" (Ref. 11), and NUREG/CR-5738 (Ref. 12). Another important purpose for the site-160specific investigations is to determine whether there are any new data or interpretations that are 161not adequately incorporated into the existing PSHA data bases. Appendix E describes a method 162for evaluating new information derived from the site-specific investigations in the context of the 163 PSHA.164Investigations should be performed at four levels, with the degree of detail based on 165distance from the site, the nature of the Quaternary tectonic regime, the geological complexity of 166the site and region, the existence of potential seismic sources, the potential for surface 167deformation, etc. A more detailed discussion of the areas and levels of investigations and the 168bases for them are presented in Appendix D to this regulatory guide. General guidelines for the 169levels of investigation are as follows.
1701.1.1 Regional geological and seismological investigations are not expected to be extensive nor 171in great detail, but should include literature reviews, the study of maps and remote 172sensing data, and, if necessary, ground truth reconnaissances conducted within a radius 173of 320 km (200 miles) of the site to identify seismic sources (seismogenic and capable 174 tectonic sources).
1751.1.2 Geological, seismological, and geophysical investigations should be carried out within a 176radius of 40 km (25 miles) in greater detail than the regional investigations to identify and 177characterize the seismic and surface deformation potential of any capable tectonic 178sources and the seismic potential of seismogenic sources, or to demonstrate that such 179structures are not present. Sites with capable tectonic or seismogenic sources within a 180radius of 40 km (25 miles) may require more extensive geological and seismological 181investigations and analyses (similar in detail to investigations and analysis usually 182preferred within an 8-km (5-mile) radius).
1831.1.3 Detailed geologic, seismological, geophysical, and geotechnical investigations should be 184conducted within a radius of 8 km (5 miles) of the site, as appropriate, to evaluate the 185potential for tectonic deformation at or near the ground surface and to assess the 186 6transmission characteristics of soils and rocks in the site vicinity. Sites in the CEUS 187where geologically young or recent tectonic activity is not present may be investigated in 188less detail. Methods for evaluating the seismogenic potential of tectonic structures and 189geological features developed in Reference 13 should be followed.
1901.1.4 Very detailed geological, geophysical, and geotechnical engineering investigations should 191be conducted within the site [radius of approximately 1 km (0.5 miles)] to assess specific 192soil and rock characteristics as described in Reference 11, updated with NUREG/CR-1935738 (Ref. 12).
1941.2 The areas of investigation may be expanded beyond those specified above in regions that 195include capable tectonic sources, relatively high seismicity, or complex geology, or in regions that 196have experienced a large, geologically recent earthquake.
1971.3 Data sufficient to clearly justify all assumptions and conclusions should be presented.
198Because engineering solutions cannot always be satisfactorily demonstrated for the effects of 199permanent ground displacement, it is prudent to avoid a site that has a potential for surface or 200near-surface deformation. Such sites normally will require extensive additional investigations.
2011.4 For the site and for the area surrounding the site, lithologic, stratigraphic, hydrologic, and 202structural geologic conditions should be characterized. The investigations should include the 203measurement of the static and dynamic engineering properties of the materials underlying the 204site and an evaluation of the physical evidence concerning the behavior during prior earthquakes 205of the surficial materials and the substrata underlying the site. The properties needed to assess 206the behavior of the underlying material during earthquakes, including the potential for 207liquefaction, and the characteristics of the underlying material in transmitting earthquake ground 208motions to the foundations of the facility (such as seismic wave velocities, density, water content, 209porosity, elastic moduli, and strength) should be measured.
2102. SEISMIC SOURCES SIGNIFICANT TO THE SITE SEISMIC HAZARD 2112.1 For sites in the CEUS, when the EPRI or LLNL probabilistic seismic hazard analysis 212methodologies and data bases are used to determine the design earthquake, it still may be 213necessary to investigate and characterize potential seismic sources that were unknown or 214uncharacterized and to perform sensitivity analyses to assess their significance to the seismic 215hazard estimate. The results of the investigation discussed in Regulatory Position 1 should be 216used, in accordance with Appendix E, to determine whether the LLNL or EPRI seismic sources 217and their characterization should be updated. The guidance in Regulatory Positions 2.2 and 2.3 218below and in Appendix D of this guide may be used if additional seismic sources are to be 219developed as a result of investigations.
2202.2 When the LLNL or EPRI methods are not used or are not applicable, the guidance in 221Regulatory Position 2.3 should be used for identification and characterization of seismic sources.
222The uncertainties in the characterization of seismic sources should be addressed as appropriate.
223Seismic sources is a general term referring to both seismogenic sources and capable tectonic 224sources. The main distinction between these two types of seismic sources is that a seismogenic 225source would not cause surface displacement, but a capable tectonic source causes surface or 226near-surface displacement.
227Identification and characterization of seismic sources should be based on regional and 228site geological and geophysical data, historical and instrumental seismicity data, the regional 229 7stress field, and geological evidence of prehistoric earthquakes. Investigations to identify seismic 230sources are described in Appendix D. The bases for the identification of seismic sources should 231be identified. A general list of characteristics to be evaluated for seismic sources is presented in 232Appendix D.
2332.3 As part of the seismic source characterization, the seismic potential for each source 234should be evaluated. Typically, characterization of the seismic potential consists of four equally 235important elements:
2361. Selection of a model for the spatial distribution of earthquakes in a source.
2372. Selection of a model for the temporal distribution of earthquakes in a source.
2383. Selection of a model for the relative frequency of earthquakes of various 239magnitudes, including an estimate for the largest earthquake that could occur in 240the source under the current tectonic regime.
2414. A complete description of the uncertainty.
242 243For example, in the LLNL study a truncated exponential model was used for the 244distribution of magnitudes given that an earthquake has occurred in a source. A stationary 245Poisson process is used to model the spatial and temporal occurrences of earthquakes in a 246 source.247For a general discussion of evaluating the earthquake potential and characterizing the 248uncertainty, refer to Reference 5.
2492.3.1 For sites in the CEUS, when the LLNL or EPRI method is not used or not 250applicable (such as in the New Madrid, MO; Charleston, SC; Attica, NY, Seismic Zones), it is 251necessary to evaluate the seismic potential for each source. The seismic sources and data that 252have been accepted by the NRC in past licensing decisions may be used, along with the data 253gathered from the investigations carried out as described in Regulatory Position 1.
254Generally, the seismic sources for the CEUS are area sources because there is 255uncertainty about the underlying causes of earthquakes. This uncertainty is due to a lack of 256active surface faulting, a low rate of seismic activity, or a short historical record. The assessment 257of earthquake recurrence for CEUS area sources commonly relies heavily on catalogs of 258observed seismicity. Because these catalogs are incomplete and cover a relatively short period 259of time, it is difficult to obtain reliable estimates of the rate of activity. Considerable care must be 260taken to correct for incompleteness and to model the uncertainty in the rate of earthquake 261recurrence. To completely characterize the seismic potential for a source, it is also necessary to 262estimate the largest earthquake magnitude that a seismic source is capable of generating under 263the current tectonic regime. This estimated magnitude defines the upper bound of the 264earthquake recurrence relationship.
265The assessment of earthquake potential for area sources is particularly difficult because 266one of the physical constraints most important to the assessment, the dimensions of the fault 267rupture, is not known. As a result, the primary methods for assessing maximum earthquakes for 268area sources usually include a consideration of the historical seismicity record, the pattern and 269rate of seismic activity, the Quaternary (2 million years and younger) characteristics of the 270source, the current stress regime (and how it aligns with known tectonic structures), paleoseismic 271 8data, and analogs to sources in other regions considered tectonically similar to the CEUS.
272Because of the shortness of the historical catalog and low rate of seismic activity, considerable 273judgment is needed. It is important to characterize the large uncertainties in the assessment of 274the earthquake potential.
2752.3.2 For sites located within the WUS, earthquakes can often be associated with 276known tectonic structures. For faults, the earthquake potential is related to the characteristics of 277the estimated future rupture, such as the total rupture area, the length, or the amount of fault 278displacement. The following empirical relations can be used to estimate the earthquake potential 279from fault behavior data and also to estimate the amount of displacement that might be expected 280for a given magnitude. It is prudent to use several of the following different relations to obtain an 281estimate of the earthquake magnitude.
282Surface rupture length versus magnitude (Refs. 14-17), 283Subsurface rupture length versus magnitude (Ref. 18), 284Rupture area versus magnitude (Ref. 19), 285Maximum and average displacement versus magnitude (Ref. 18), and 286Slip rate versus magnitude (Ref. 20).
287When such correlations as in References 14-20 are used, the earthquake potential is 288often evaluated as the mean of the distribution. The difficult issue is the evaluation of the 289appropriate rupture dimension to be used. This is a judgmental process based on geological 290data for the fault in question and the behavior of other regional fault systems of the same type.
291In addition to maximum magnitude, the other elements of the recurrence model are 292generally obtained using catalogs of seismicity, fault slip rate, and other data. In some cases, it 293may be appropriate to use recurrence models with memory. All the sources of uncertainty must 294be appropriately modeled. Additionally, the phenomenon of temporal clustering should be 295considered when there is geological evidence of its past occurrence.
2962.3.3 For sites near subduction zones, such as in the Pacific Northwest and Alaska, the 297maximum magnitude must be assessed for subduction zone seismic sources. Worldwide 298observations indicate that the largest known earthquakes are associated with the plate interface, 299although intraslab earthquakes may also have large magnitudes. The assessment of plate 300interface earthquakes can be based on estimates of the expected dimensions of rupture or 301analogies to other subduction zones worldwide.
3023. PROBABILISTIC SEISMIC HAZARD ANALYSIS PROCEDURES 303A PSHA should be performed for the site as it allows the use of multiple models to 304estimate the likelihood of earthquake ground motions occurring at a site and systematically takes 305into account uncertainties that exist in various parameters (such as seismic sources, maximum 306earthquakes, and ground motion attenuation). Alternative hypotheses are considered in a 307quantitative fashion in a PSHA. Alternative hypotheses can also be used to evaluate the 308sensitivity of the hazard to the uncertainties in the significant parameters and to identify the 309relative contribution of each seismic source to the hazard.
310The following steps describe a procedure that is acceptable to the NRC staff for 311performing a PSHA.
312 93.1 Perform regional and site geological, seismological, and geophysical investigations in 313accordance with Regulatory Position 1 and Appendix D.
3143.2 For CEUS sites, perform an evaluation of LLNL or EPRI seismic sources in accordance 315with Appendix E to determine whether they are consistent with the site-specific data gathered in 316Regulatory Position 1 or require updating. The PSHA should only be updated if the new 317information indicates that the current version significantly underestimates the hazard and there is 318a strong technical basis that supports such a revision. It may be possible to justify a lower 319hazard estimate with an exceptionally strong technical basis. However, it is expected that large 320uncertainties in estimating seismic hazard in the CEUS will continue to exist in the future, and 321substantial delays in the licensing process will result in trying to justify a lower value with respect 322to a specific site. For these reasons the NRC staff discourages efforts to justify a lower hazard 323estimate. In most cases, limited-scope sensitivity studies should be sufficient to demonstrate 324that the existing data base in the PSHA envelops the findings from site-specific investigations. In 325general, significant revisions to the LLNL and EPRI data base are to be undertaken only 326periodically (every 10 years), or when there is an important new finding or occurrence. An overall 327revision of the data base would also require a reexamination of the acceptability of the reference 328probability discussed in Appendix B and used in Regulatory Position 4 below. Any significant 329update should follow the guidance of Reference 5.
3303.3 For CEUS sites only, perform the LLNL or EPRI PSHA using original or updated sources 331as determined in Regulatory Position 2. For sites in WUS, perform a site-specific PSHA (Ref. 5).
332The ground motion estimates should be made for rock conditions in the free-field or by assuming 333hypothetical rock conditions for a non-rock site to develop the seismic hazard information base 334discussed in Appendix C.
3353.4 Using the mean reference probability (5E-4/yr) described in Appendix B, determine the 5 336percent of critically damped mean spectral ground motion levels for 1 Hz (Sa,1) and 10 Hz (Sa,10)337(Ref. 2). The use of an alternative reference probability will be reviewed and accepted on a 338case-by-case basis.
3393.5 Deaggregate the mean probabilistic hazard characterization in accordance with Appendix 340C to determine the controlling earthquakes (i.e., magnitudes and distances), and document the 341hazard information base, as described in Appendix C.
3423.6 As an alternative method, instead of the controlling earthquakes approach described in 343Appendix C and Regulatory Position 4 below, determine the ground motions at a sufficient 344number of frequencies significant to the ISFSI or MRS design, and then envelope the ground 345motions to determine the DE.
3464. PROCEDURES FOR DETERMINING THE DESIGN EARTHQUAKE GROUND MOTION 347After completing the PSHA (see Regulatory Position 3) and determining the controlling 348earthquakes, the following procedures should be used to determine the DE. Appendix F 349contains an additional discussion of some of the characteristics of the DE.
3504.1 With the controlling earthquakes determined as described in Regulatory Position 3 and by 351using the procedures in Revision 3 of Reference 21 (which may include the use of ground motion 352models not included in the PSHA but that are more appropriate for the source, region, and site 353under consideration or that represent the latest scientific development), develop 5 percent of 354 10critical damping response spectral shapes for the actual or assumed rock conditions. The same 355controlling earthquakes are also used to derive vertical response spectral shapes.
3564.2 Use Sa,10 to scale the response spectrum shape corresponding to the controlling 357earthquake. If there is a controlling earthquake for Sa,1, determine that the Sa,10 scaled response 358spectrum also envelopes the ground motion spectrum for the controlling earthquake for Sa,1. 359Otherwise, modify the shape to envelope the low-frequency spectrum or use two spectra in the 360following steps. For a rock site, go to Regulatory Position 4.4.
3614.3 For non-rock sites, perform a site-specific soil amplification analysis considering 362uncertainties in site-specific geotechnical properties and parameters to determine response 363spectra at the free ground surface in the free-field for the actual site conditions. Procedures 364described in Appendix D of this guide and Reference 21 can be used to perform soil-amplification 365analyses.3664.4 Compare the smooth DE spectrum or spectra used in design at the free-field with the 367spectrum or spectra determined in Regulatory Position 2 for rock sites or determined in 368Regulatory Position 3 for the non-rock sites to assess the adequacy of the DE spectrum or 369spectra. 3704.5 To obtain an adequate DE based on the site-specific response spectrum or spectra, 371develop a smooth spectrum or spectra or use a standard broad band shape that envelopes the 372spectra of Regulatory Position 2 or 3.
373D. IMPLEMENTATION 374The purpose of this section is to provide information to applicants and licensees regarding 375the NRC staff
's plans for using this draft regulatory guide.
376This draft guide has been released to encourage public participation in its development.
377Except in those cases in which an applicant or licensee proposes an acceptable alternative 378method for complying with the specified portions of the NRC
's regulations, the methods to be 379described in the active guide reflecting public comments will be used in the evaluation of 380applications for new dry cask ISFSI and MRS facilities.
381 1 Copies are available at current rates from the U.S. Government Printing Office, P.O. Box 37082, Washington, DC20402-9328 (telephone (202)512-1800); or from the National Technical Information Service by writing NTIS at 5285 Port Royal Road, Springfield, VA 22161; (telephone (703)487-4650; <http://www.ntis.gov/ordernow>. Copies areavailable for inspection or copying for a fee from the NRC Public Document Room at 11555 Rockville Pike, Rockville, MD; the PDR
's mailing address is USNRC PDR, Washington, DC 20555; telephone (301)415-4737 or(800)397-4209; fax (301)415-3548; email is PDR@NRC.GOV.
2 Copies are available for inspection or copying for a fee from the NRC Public Document Room at 11555Rockville Pike (first floor), Rockville, MD; the PDR
's mailing address is USNRC PDR, Washington, DC 20555;telephone (301)415-4737 or 1-(800)397-4209; fax (301)415-3548; e-mail <PDR@NRC.GOV>.
11 REFERENCES 3821. USNRC, "Identification and Characterization of Seismic Sources and Determination of 383Safe Shutdown Earthquake Ground Motion," Regulatory Guide 1.165, March 1997.
3 3842. R.K. McGuire, W.J. Silva, and C.J. Constantino, "Technical Basis for Revision of 385Regulatory Guidance on Design Ground Motions: Hazard- and Risk-Consistent Ground 386Motion Spectra Guidelines," NUREG/CR-6728, October 2001.
3873. D.L. Bernreuter et al., "Seismic Hazard Characterization of 69 Nuclear Plant Sites East of 388the Rocky Mountains," NUREG/CR-5250, Volumes 1-8, 1989.
1 3894. P. Sobel, "Revised Livermore Seismic Hazard Estimates for Sixty-Nine Nuclear Power 390Plant Sites East of the Rocky Mountains," NUREG-1488, USNRC, April 1994.
1 3915. R.J. Budnitz et al., "Recommendations for Probabilistic Seismic Hazard Analysis:
392Guidance on Uncertainty and Use of Experts," NUREG/CR- 6372, Volumes 1 and 2, 393USNRC, April 1997.
1 3946. J.B. Savy et al., "Eastern Seismic Hazard Characterization Update," UCRL-ID-115111, 395Lawrence Livermore National Laboratory, June 1993.
2 (Accession number 9310190318 396in NRC's Public Document Room) 3977. Electric Power Research Institute (EPRI), "Probabilistic Seismic Hazard Evaluations at 398Nuclear Power Plant Sites in the Central and Eastern United States," NP-4726, All 399Volumes, 1989-1991.
4008. Electric Power Research Institute (EPRI), "The Earthquakes of Stable Continental 401Regions," Volume 1: Assessment of Large Earthquake Potential, EPRI TR-102261-V1, 402 1994.4039. Pacific Gas and Electric Company, "Final Report of the Diablo Canyon Long Term 404Seismic Program; Diablo Canyon Power Plant," Docket Nos. 50-275 and 50-323, 1988.
2 40510. H. Rood et al., "Safety Evaluation Report Related to the Operation of Diablo Canyon 406Nuclear Power Plant, Units 1 and 2," NUREG-0675, Supplement No. 34, USNRC, June 407 1991.1 408 3 Requests for single copies of draft or active regulatory guides (which may be reproduced) or for placement onan automatic distribution list for single copies of future draft guides in specific divisions should be made in writing to the U.S. Nuclear Regulatory Commission, Washington, DC 20555, Attention: Reproduction and Distribution Services Section, or by fax to (301)415-2289; email <DISTRIBUTION@NRC.GOV>. Copies are available for inspection or copying for a fee from the NRC Public Document Room at 11555 Rockville Pike (first floor),
's mailing address is USNRC PDR, Washington, DC 20555; telephone (301)415-4737 or1-(800)397-4209; fax (301)415-3548; e-mail <PDR@NRC.GOV>.
1211. USNRC, "Site Investigations for Foundations of Nuclear Power Plants," Regulatory Guide 4091.132, March 1979. (See also DG-1101, the proposed Revision 2 of Regulatory Guide 4101.132, February 2001.)
3 41112. N. Torres et al., "Field Investigations for Foundations of Nuclear Power Facilities,"412NUREG/CR-5738, USNRC, 1999.
1 41313. K.L. Hanson et al., "Techniques for Identifying Faults and Determining Their Origins,"414NUREG/CR-5503, USNRC, July 1999.
1 41514. D.B. Slemmons, "Faults and Earthquake Magnitude," U.S. Army Corps of Engineers, 416Waterways Experiment Station, Misc. Papers S-7-1, Report 6, 1997.
41715. D.B. Slemmons, "Determination of Design Earthquake Magnitudes for Microzonation,"418Proceedings of the Third International Microzonation Conference, University of 419Washington, Seattle, Volume 1, pp. 119-130, 1982.
42016. M.G. Bonilla, H.A. Villalobos, and R.E. Wallace, "Exploratory Trench Across the Pleasant 421Valley Fault, Nevada," Professional Paper 1274-B, U.S. Geological Survey, pp. B1-B14, 422 1984.2 42317. S.G. Wesnousky, "Relationship Between Total Affect, Degree of Fault Trace 424Complexibility, and Earthquake Size on Major Strike-Slip Faults in California," (Abs), 425Seismological Research Letters, Volume 59, No. 1, p.3, 1988.
42618. D.L. Wells and K.J. Coppersmith, "New Empirical Relationships Among Magnitude, 427Rupture Length, Rupture Width, Rupture Area, and Surface Displacement," Bulletin of the 428Seisomological Society of America, Volume 84, 1994.
42919. M. Wyss, "Estimating Maximum Expectable Magnitude of Earthquakes from Fault 430Dimensions," Geology, Volume 7 (7), pp. 336-340, 1979.
43120. D.P. Schwartz and K.J. Coppersmith, "Seismic Hazards: New Trends in Analysis Using 432Geologic Data," Active Tectonics, National Academy Press, Washington, DC, pp. 215-433230, 1986.
43421. USNRC, "Standard Review Plan for the Review of Safety Analysis Reports for Nuclear 435Power Plants," NUREG-0800, Section 2.5.2, Revision 3, 1997.
3 436APPENDIX A 437DEFINITIONS 438 Capable Tectonic Source - A capable tectonic source is a tectonic structure that can generate 439both vibratory ground motion and tectonic surface deformation such as faulting or folding at or 440near the earth
's surface in the present seismotectonic regime. It is described by at least one of 441the following characteristics:
442a. Presence of surface or near-surface deformation of landforms or geologic 443deposits of a recurring nature within the last approximately 500,000 years or at 444least once in the last approximately 50,000 years.
445b. A reasonable association with one or more moderate to large earthquakes or 446sustained earthquake activity, usually accompanied by significant surface 447deformation.
448c. A structural association with a capable tectonic source that has characteristics of 449either a or b above such that movement on one could be reasonably expected to 450be accompanied by movement on the other.
451In some cases, the geological evidence of past activity at or near the ground surface along a 452potential capable tectonic source may be obscured at a particular site. This might occur, for 453example, at a site having a deep overburden. For these cases, evidence may exist elsewhere 454along the structure from which an evaluation of its characteristics in the vicinity of the site can be 455reasonably based. Such evidence is to be used in determining whether the structure is a 456capable tectonic source within this definition.
457Notwithstanding the foregoing paragraphs, the association of a structure with geological 458structures that are at least pre-Quaternary, such as many of those found in the Central and 459Eastern regions of the United States, in the absence of conflicting evidence, will demonstrate that 460the structure is not a capable tectonic source within this definition.
461Controlling Earthquakes - Controlling earthquakes are the earthquakes used to determine 462spectral shapes or to estimate ground motions at the site. There may be several controlling 463earthquakes for a site. As a result of the probabilistic seismic hazard analysis (PSHA), 464controlling earthquakes are characterized as mean magnitudes and distances derived from a 465deaggregation analysis of the mean estimate of the PSHA.
466Design Earthquake Ground Motion (DE) - The DE is the vibratory ground motion for which 467certain structures, systems, and components, classified as important to safety, are designed, 468pursuant to Part 72. The DE for the site is characterized by both horizontal and vertical free-field 469ground motion response spectra at the free ground surface.
470Earthquake Recurrence - Earthquake recurrence is the frequency of occurrence of 471earthquakes having various magnitudes. Recurrence relationships or curves are developed for 472each seismic source, and they reflect the frequency of occurrence (usually expressed on an 473annual basis) of magnitudes up to the maximum, including measures of uncertainty.
474Intensity - The intensity of an earthquake is a qualitative description of the effects of the 475earthquake at a particular location, as evidenced by observed effects on humans, on human-built 476structures, and on the earth
's surface at a particular location. Commonly used scales to specify 477intensity are the Rossi-Forel, Mercalli, and Modified Mercalli. The Modified Mercalli Intensity 478(MMI) scale describes intensities with values ranging from I to XII in the order of severity. MMI of 479I indicates an event that was not felt except by a very few, while MMI of XII indicates total 480damage of all works of construction, either partially or completely.
481 14Magnitude
- An earthquake
's magnitude is a measure of the strength of an earthquake as 482determined from seismographic observations and is an objective, quantitative measure of the 483size of an earthquake. The magnitude is expressed in various ways based on the seismograph 484record, e.g., Richter Local Magnitude, Surface Wave Magnitude, Body Wave Magnitude, and 485Moment Magnitude. The most commonly used magnitude measurement is the Moment 486Magnitude, Mw , which is based on the seismic moment computed as the rupture force along the 487fault multiplied by the average amount of slip, and thus is a direct measure of the energy 488released during an earthquake event. The Moment Magnitude of an earthquake event (M w or M)489varies from 2.0 and higher values, and since magnitude scales are logarithmic, a unit change in 490magnitude corresponds to a 32-fold change in the energy released during an earthquake event.
491Maximum Magnitude
- The maximum magnitude is the upper bound to recurrence curves.
492Mean Annual Probability of Exceedance
- Mean annual probability of exceedance of an 493earthquake event of a given magnitude or an acceleration level is the probability that the given 494magnitude or acceleration level may exceed in a year. The mean annual probability of 495exceedance of an earthquake event is a reciprocal of the return period of the event.
496Nontectonic Deformation
- Nontectonic deformation is distortion of surface or near-surface 497soils or rocks that is not directly attributable to tectonic activity. Such deformation includes 498features associated with subsidence, karst terrain, glaciation or deglaciation, and growth faulting.
499Reference Probability
- The reference probability of occurrence of an earthquake event is the 500mean annual probability of exceeding the design earthquake.
501Response Spectrum
- A plot of the maximum values of responses (acceleration, velocity, or 502displacement) of a family of idealized single-degree-of-freedom damped oscillators as a function 503of its natural frequencies (or periods) to a specified vibratory motion input at their supports.
504Return Period
- The return period of an earthquake event is an inverse of the mean annual 505probability of exceedance of the earthquake event.
506Safe Shutdown Earthquake (SSE)
- The SSE is the vibratory ground motion for which certain 507structures, systems, and components in a nuclear power plant are designed, pursuant to 508Appendix S to 10 CFR Part 50, to remain functional. The SSE for the site is characterized by 509both horizontal and vertical free-field ground motion response spectra at the free ground surface.
510Seismic Potential
- A model giving a complete description of the future earthquake activity in a 511seismic source zone. The model includes a relation giving the frequency (rate) of earthquakes of 512any magnitude, an estimate of the largest earthquake that could occur under the current tectonic 513regime, and a complete description of the uncertainty. A typical model used for PSHA is the use 514of a truncated exponential model for the magnitude distribution and a stationary Poisson process 515for the temporal and spatial occurrence of earthquakes.
516Seismic Source
- Seismic source is a general term referring to both seismogenic sources and 517capable tectonic sources.
518Seismogenic Source
- A seismogenic source is a portion of the earth that is assumed to have 519a uniform earthquake potential (same expected maximum earthquake and recurrence 520frequency), distinct from the seismicity of the surrounding regions. A seismogenic source will 521generate vibratory ground motion but is assumed not to cause surface displacement.
522 15Seismogenic sources cover a wide range of possibilities, from a well-defined tectonic structure to 523simply a large region of diffuse seismicity (seismotectonic province) thought to be characterized 524by the same earthquake recurrence model. A seismogenic source is also characterized by its 525involvement in the current tectonic regime (the Quaternary, or approximately the last 2 million 526years).527Stable Continental Region (SCR)
- A stable continental region is composed of continental 528crust, including continental shelves, slopes, and attenuated continental crust, and excludes active 529plate boundaries and zones of currently active tectonics directly influenced by plate margin 530processes. It exhibits no significant deformation associated with the major Mesozoic-to-Cenozoic 531(last 240 million years) orogenic belts. It excludes major zones of Neogene (last 25 million years) 532rifting, volcanism, or suturing.
533Stationary Poisson Process
- A probabilistic model of the occurrence of an event over time 534(or space) that has the following characteristics: (1) the occurrence of the event in small intervals 535is constant over time (or space), (2) the occurrence of two (or more) events in a small interval is 536negligible, and (3) the occurrence of the event in non-overlapping intervals is independent.
537Tectonic Structure
- A tectonic structure is a large-scale dislocation or distortion, usually within 538the earth's crust. Its extent may be on the order of tens of meters (yards) to hundreds of 539kilometers (miles).
540 16APPENDIX B 541REFERENCE PROBABILITY FOR THE EXCEEDANCE LEVEL OF THE 542DESIGN EARTHQUAKE GROUND MOTION 543B.1INTRODUCTION 544This appendix provides a rationale for a reference probability that is acceptable to the 545NRC staff. The reference probability is used in conjunction with the probabilistic seismic hazard 546analysis (PSHA) for determining the Design Earthquake Ground Motion (DE) for ISFSI or MRS 547designs.548B.2QUESTION ON REFERENCE PROBABILITY FOR DESIGN EARTHQUAKE 549The reference probability is the mean annual probability of exceeding the DE. It is the 550reciprocal of the return period for the design earthquake.
551The NRC staff welcomes comments on all aspects of this draft regulatory guide, but is 552especially interested in receiving comments on the appropriate mean annual probability of 553exceedance value to be used for the seismic design of an ISFSI or MRS. Please note the 554following considerations and include a justification for the appropriate mean annual probability of 555exceedance value.
556The present mean annual probability of exceedance value for determining the DE for an 557ISFSI or MRS is approximately 1.0E-04 (i.e., in any one year, the probability is 1 in 10,000, which 558is the reciprocal of 1.0E-04, that the DE established for the site will be exceeded). This value is 559based on requirements for nuclear plants. The NRC is considering allowing for the use of a 560mean annual probability of exceedance value in the range of 5.0E-04 (i.e., in any one year, the 561probability is 1 in 2,000 that the DE established for the site will be exceeded) to 1.0E-04 for ISFSI 562or MRS applications. This Draft Regulatory Guide DG-3021, "Site Evaluations and Determination 563of Design Earthquake Ground Motion for Seismic Design of Independent Spent Fuel Storage 564Installations and Monitored Retrievable Storage Installations," is being developed to provide 565guidelines that are acceptable to the NRC staff for determining the DE for an ISFSI or MRS. DG-5663021 proposes to recommend a mean annual probability of exceedance value of 5.0E-04 as an 567appropriate risk-informed value for the design of a dry storage ISFSI or MRS. However, the NRC 568staff is undertaking further analysis to support a specific value. An ISFSI or MRS license 569applicant would have to demonstrate that the use of a higher probability of exceedance value 570would not impose any undue radiological risk to public health and safety. In view of this 571discussion, the NRC staff is requesting comments on the appropriate mean annual probability of 572exceedance value to be used for the seismic design of an ISFSI or MRS and a justification for 573this probability.
574B.3RATIONALE FOR THE REFERENCE PROBABILITY 575The following describes the rationale for determining the reference probability for use in 576the PSHA for a dry cask storage system (DCSS) during a seismic event. The mean reference 577probability of exceedance of 5.0E-4/yr for a seismic event is considered appropriate for the 578design of a DCSS. The use of a higher reference probability will be reviewed and accepted on a 579case-by-case basis.
580B.3.1 Part 72 Approach 581 17Part 72 regulations classify the structures, systems, and components (SSC) in an ISFSI 582or MRS facility based on their importance to safety. SSCs are classified as important to safety if 583they have the function of protecting public health and safety from undue risk and preventing 584damage to the spent fuel during handling and storage. These SSCs are evaluated for a single 585level of DE as an accident condition event only (section 72.106). For normal operations and 586anticipated occurrences (section 72.104), earthquake events are not included.
587The DCSSs for ISFSIs or MRSs are typically self-contained massive concrete or steel 588structures, weighing approximately 40 to 100 tons when fully loaded. There are very few, if any, 589moving parts. They are set on a concrete support pad. Several limitations have been set on the 590maximum height to which the casks can be lifted, based on the drop accident analysis. There is 591a minimum center-to-center spacing requirement for casks stored in an array on a common 592support pad. The most conservative estimates of structural thresholds of seismic inertia 593deceleration from a drop accident event, before the confinement is breached so as to exceed the 594permissible radiation levels, is in the range of 30 g to 40 g.
595B.3.2 Reference Probability 596The present DE is based on the requirements contained in 10 CFR Part 100 for nuclear 597power plants. In the Statement of Considerations accompanying the initial Part 72 rulemaking, 598the NRC recognized that the design peak horizontal acceleration for structures, systems, and 599components (SSCs) need not be as high as for a nuclear power reactor and should be 600determined on a "case-by-case
" basis until "more experience is gained with licensing of these 601types of units
" (45 FR 74697; November 12, 1980). With over 10 years of experience in licensing 602dry cask storage and with analyses that demonstrate robust behavior of dry cask storage 603systems (DCSSs) in accident scenarios (10 specific licenses have been issued and 9 locations 604use the general license provisions), the NRC now has a reasonable basis to consider lower and 605more appropriate DE parameters for a dry cask ISFSI or MRS. Therefore, the NRC proposes to 606reduce the DE for new ISFSI or MRS license applicants to be commensurate with the lower risk 607associated with these facilities. Factors that result in lower radiological risk at an ISFSI or MRS 608compared to a nuclear power plant include the following:
609 610 In comparison with a nuclear power plant, an operating ISFSI or MRS is a relatively 611simple facility in which the primary activities are waste receipt, handling, and storage. An 612ISFSI or MRS does not have the variety and complexity of active systems necessary to 613support an operating nuclear power plant. After the spent fuel is in place, an ISFSI or 614MRS is essentially a static operation.
615 During normal operations, the conditions required for the release and dispersal of 616significant quantities of radioactive materials are not present. There are no high 617temperatures or pressures present during normal operations or under design basis 618accident conditions to cause the release and dispersal of radioactive materials. This is 619primarily due to the low heat-generation rate of spent fuel that has undergone more than 6201 year of decay before storage in an ISFSI or MRS, and to the low inventory of volatile 621radioactive materials readily available for release to the environment.
622 The long-lived nuclides present in spent fuel are tightly bound in the fuel materials and 623are not readily dispersible. Short-lived volatile nuclides, such as I-131, are no longer 624present in aged spent fuel. Furthermore, even if the short-lived nuclides were present 625during a fuel assembly rupture, the canister surrounding the fuel assemblies would 626confine these nuclides. Therefore, the Commission believes that the seismically induced 627 18radiological risk associated with an ISFSI or MRS is significantly less than the risk 628associated with a nuclear power plant. Also, it is NRC policy to use risk-informed 629regulation as appropriate.
630 The critical element for protection against radiation release is the sealed cask containing 631the spent fuel assemblies. The standards in Part 72 in Subparts E, "Siting Evaluation 632 Factors," and F, "General Design Criteria," ensure that the dry cask storage designs are 633very rugged and robust. The casks must maintain structural integrity during a variety of 634postulated non-seismic events, including cask drops, tip-overs, and wind-driven missile 635impacts. These non-seismic events challenge cask integrity significantly more than 636seismic events. Therefore, the casks are expected to have substantial design margins to 637withstand forces from a seismic event greater than the design earthquake.
638 During a seismic event at an ISFSI or MRS, a cask may slide if lateral seismic forces are 639greater than the frictional resistance between the cask and the concrete pad. The sliding 640and resulting displacements are computed by the applicant to demonstrate that the 641casks, which are spaced to satisfy the thermal criteria in Subpart F of Part 72, are 642precluded from impacting other adjacent casks. Furthermore, the NRC staff guidance in 643reviewing cask designs is to show that public health and safety is maintained during a 644postulated DE. This can be demonstrated by showing that either casks are designed to 645prevent sliding or tip over during a seismic event, or the consequences of the calculated 646cask movements are acceptable. Even if the casks slide or tip over and then impact 647other casks or the pad during a seismic event significantly greater than the proposed DE, 648there are adequate design margins to ensure that the casks maintain their structural 649integrity.
650 The combined probability of the occurrence of a seismic event and operational failure that 651leads to a radiological release is much smaller than the individual probabilities of either of 652these events. This is because the handling building and crane are used for only a fraction 653of the licensed period of an ISFSI or MRS and for only a few casks at a time.
654Additionally, dry cask ISFSIs are expected to handle only sealed casks and not individual 655fuel assemblies. Therefore, the potential risk of a release of radioactivity caused by 656failure of the cask handling or crane during a seismic event is small.
657Additional factors for reducing the DE for new ISFSI or MRS license applicants include:
658 Because the DE is a smooth broad-band spectrum that envelops the controlling 659earthquake responses, the vibratory ground motion specified is conservative.
6601.The crane used for lifting the casks in the building is designed using the same industry 661codes as for a nuclear power plant, and has a safety factor of 5 or greater for lifted loads 662using the ultimate strength of the materials. Therefore, the crane would perform 663satisfactorily during an earthquake much larger than the design earthquake.
664 1 U.S. Department of Energy, "Natural Phenomena Hazards Design Evaluation Criteria for Department of EnergyFacilities, DOE-STD-1020-2002, January 2002. Copies are available at current rates from the U.S. Government Printing Office, P.O. Box 37082, Washington, DC 20402-9328 (telephone (202)512-1800); or from the National Technical Information Service by writing NTIS at 5285 Port Royal Road, Springfield, VA 22161; (telephone (703)487-
4650; <http://www.ntis.gov/ordernow>. Copies are available for inspection or copying for a fee from the NRC PublicDocument Room at 11555 Rockville Pike, Rockville, MD; the PDR
's mailing address is USNRC PDR, Washington,DC 20555; telephone (301)415-4737 or (800)397-4209; fax (301)415-3548; email is PDR@NRC.GOV.
192.The determination of a DE for an ISFSI or MRS is consistent with the design approach 665used in DOE Standard DOE-STD-1020, "Natural Phenomena Hazards Design Evaluation 666Criteria for Department of Energy Facilities,"1 for similar type facilities.
667Based on the preceding analysis, the NRC staff concludes that there is a reasonable 668basis to design ISFSI or MRS SSCs for a single design earthquake, using a mean annual 669probability of exceedance 5.0E-04, and adequately protect public health and safety.
670 20APPENDIX C 671DETERMINATION OF CONTROLLING EARTHQUAKES AND DEVELOPMENT 672OF SEISMIC HAZARD INFORMATION BASE 673C.1 INTRODUCTION 674This appendix elaborates on the steps described in Regulatory Position 3 of this 675regulatory guide to determine the controlling earthquakes used to define the Design Earthquake 676Ground Motion (DE) at the site and to develop a seismic hazard information base. The 677information base summarizes the contribution of individual magnitude and distance ranges to the 678seismic hazard and the magnitude and distance values of the controlling earthquakes at 1 and 10 679Hz. The controlling earthquakes are developed for the ground motion level corresponding to the 680reference probability as defined in Appendix B to this regulatory guide.
681The spectral ground motion levels, as determined from a probabilistic seismic hazard 682analysis (PSHA), are used to scale a response spectrum shape. A site-specific response 683spectrum shape is determined for the controlling earthquakes and local site conditions.
684Regulatory Position 4 and Appendix F to this regulatory guide describe a procedure to determine 685the DE using the controlling earthquakes and results from the PSHA.
686C.2 PROCEDURE TO DETERMINE CONTROLLING EARTHQUAKES 687The following approach is acceptable to the NRC staff for determining the controlling 688earthquakes and developing a seismic hazard information base. This procedure is based on a 689de-aggregation of the probabilistic seismic hazard in terms of earthquake magnitudes and 690distances. When the controlling earthquakes have been obtained, the DE response spectrum 691can be determined according to the procedure described in Appendix F to this regulatory guide.
692Step 2-1 693Perform a site-specific PSHA using the Lawrence Livermore National Laboratory (LLNL) 694or Electric Power Research Institute (EPRI) methodologies (Refs. 1-3) for CEUS sites or perform 695a site-specific PSHA for sites not in the CEUS or for sites for which LLNL or EPRI methods and 696data are not applicable, for actual or assumed rock conditions. The hazard assessment (mean, 697median, 85th percentile, and 15th percentile) should be performed for spectral accelerations at 1, 698Hz, 10 Hz, and the peak ground acceleration. A lower-bound earthquake moment magnitude, M, 699of 5.0 is recommended.
700Step 2-2 701Using the reference probability (5E-4/yr) as defined in Appendix B to this regulatory guide, 702determine the ground motion levels for the spectral accelerations at 1 and 10 Hz from the total 703mean hazard obtained in Step 2-1.
704Step 2-3 705Perform a complete PSHA for each of the magnitude-distance bins illustrated in Table 706C.1. (These magnitude-distance bins are to be used in conjunction with the LLNL or EPRI 707methods. For other situations, other binning schemes may be necessary.)
708 21Table C.1 Recommended Magnitude and Distance Bins 709Moment Magnitude Range of Bins 710Distance 711Range of Bin 712(km)7135 - 5.55.5 6.56.5 - 7>70 - 15 71415 - 25 71525 - 50 71650 - 100 717100 - 200 718200 - 300 719>300 720Step 2-4 721From the de-aggregated results of Step 2-3, the mean annual probability of exceeding the 722ground motion levels of Step 2-2 (spectral accelerations at 1 and 10 Hz) are determined for each 723magnitude-distance bin. These values are denoted by Hmdf1 for 1 Hz, and Hmdf10 for 10 Hz.
724Using Hmdf values, the fractional contribution of each magnitude and distance bin to the 725total hazard for the 1 Hz, P(m,d) 1, is computed according to:
726 P(m,d) 1 = Hmdf1/( Hmdf1)(Equation 1) 727 m d 728The fractional contribution of each magnitude and distance bin to the total hazard for the 10 Hz, 729P(m,d)10, is computed according to:
730 P(m,d) 10 = Hmdf10/( Hmdf10) (Equation 2) 731 m d 732Step 2-5 733Review the magnitude-distance distribution for the 1 Hz frequency to determine whether 734the contribution to the hazard for distances of 100 km (63 mi) or greater is substantial (on the 735order of 5 percent or greater).
736If the contribution to the hazard for distances of 100 km (63 mi) or greater exceeds 5 737percent, additional calculations are needed to determine the controlling earthquakes using the 738magnitude-distance distribution for distances greater than 100 km (63 mi). This distribution, 739P>100(m,d) 1, is defined by:
740 P>100(m,d) 1 = P(m,d) 1 / P(m,d)1 (Equation 3) 741 m d>100 742 22The purpose of this calculation is to identify a distant, larger event that may control low-743frequency content of a response spectrum.
744The distance of 100 km (63 mi) is chosen for CEUS sites. However, for all sites the 745results of full magnitude-distance distribution should be carefully examined to ensure that proper 746controlling earthquakes are clearly identified.
747Step 2-6 748Calculate the mean magnitude and distance of the controlling earthquake associated with 749the ground motions determined in Step 2 for the 10 Hz frequency. The following relation is used 750to calculate the mean magnitude using results of the entire magnitude-distance bins matrix:
751 M c = m P(m, d)10 (Equation 4) 752 d m
753where m is the central magnitude value for each magnitude bin.
754The mean distance of the controlling earthquake is determined using results of the entire 755magnitude-distance bins matrix:
756 757 Ln { Dc (10 Hz)} = Ln (d) P(m, d)10 (Equation 5) 758 d m 759where d is the centroid distance value for each distance bin.
760Step 2-7 761If the contribution to the hazard calculated in Step 2-5 for distances of 100 km (63 mi) or 762greater exceeds 5 percent for the 1 Hz frequency, calculate the mean magnitude and distance of 763the controlling earthquakes associated with the ground motions determined in Step 2-2 for the 764average of 1 Hz. The following relation is used to calculate the mean magnitude using 765calculations based on magnitude-distance bins greater than distances of 100 km (63 mi) as 766discussed in Step 2-5:
767 Mc (1Hz) = m P > 100 (m, d) 1 (Equation 6) 768 m d>100 769where m is the central magnitude value for each magnitude bin.
770The mean distance of the controlling earthquake is based on magnitude-distance bins 771greater than distances of 100 km as discussed in Step 2-5 and determined according to:
772 Ln { Dc (1 Hz)} = Ln (d) P(m, d)10 (Equation 7) 773 d>100 m 774where d is the centroid distance value for each distance bin.
775Step 2-8 776Determine the DE response spectrum using the procedure described in Appendix F of this 777regulatory guide.
778 23C.3 EXAMPLE FOR A CEUS SITE 779To illustrate the procedure in Section C.2, calculations are shown here for a CEUS site 780using the 1993 LLNL hazard results (Refs. C.1, C.2). It must be emphasized that the 781recommended magnitude and distance bins and procedure used to establish controlling 782earthquakes were developed for application in the CEUS where the nearby earthquakes 783generally control the response in the 10 Hz frequency range, and larger but distant events can 784control the lower frequency range. For other situations, alternative binning schemes as well as a 785study of contributions from various bins will be necessary to identify controlling earthquakes 786consistent with the distribution of the seismicity.
787Step 3-1 788The 1993 LLNL seismic hazard methodology (Refs. C.1, C.2) was used to determine the 789hazard at the site. A lower bound earthquake moment magnitude, M, of 5.0 was used in this 790analysis. The analysis was performed for spectral acceleration at 1 and 10 Hz. The resultant 791hazard curves are plotted in Figure C.1.
792Step 3-2 793The hazard curves at 1 and 10 Hz obtained in Step 1 are assessed at the reference 794probability value of 5E-4/yr, as defined in Appendix B to this regulatory guide. The corresponding 795ground motion level values are given in Table C.2. See Figure C.1.
796Table C.2 Ground Motion Levels 797Frequency (Hz) 798110 Spectral Acc. (cm/s/s) 79988551Step 3-3 800The mean seismic hazard is de-aggregated for the matrix of magnitude and distance bins 801as given in Table C.1.
802A complete probabilistic hazard analysis was performed for each bin to determine the 803contribution to the hazard from all earthquakes within the bin, i.e., all earthquakes with 804earthquake moment magnitudes greater than 5.0 and distance from 0 km to greater than 300 km.
805See Figure C.2 where the mean 1 Hz hazard curve is plotted for distance bin 25 - 50 km and 806magnitude bin 6 - 6.5.
807The hazard values corresponding to the ground motion levels, found in Step 2-2, and 808listed in Table C.2, are then determined from the hazard curve for each bin for spectral 809accelerations at 1 Hz and 10 Hz. This process is illustrated in Figure C.2. The vertical line 810corresponds to the value 88 cm/s/s listed in Table C.2 for the 1 Hz hazard curve and intersects 811the hazard curve for the 25 - 50 km distance bin, 6 - 6.5 magnitude bin, at a hazard value 812(probability of exceedance) of 1.07E-06 per year. Tables C.3 and C.4 list the appropriate hazard 813value for each bin for 1 Hz and 10 Hz frequencies respectively. It should be noted that if the 814mean hazard in each of the 35 bins is added up it equals the reference probability of 5.0E-04.
815 816 24Table C.3 Mean Exceeding Probability Values for Spectral Accelerations 817at 1 Hz (88 cm/s/s) 818Moment Magnitude Range of BinsDistance Range of Bin (km) 8195 - 5.55.5 6.56.5 - 7>70 - 15 8209.68E-064.61E-050.00.00.015 - 25 8210.01.26E-050.00.00.025 - 50 8220.01.49E-051.05E-050.00.050 - 100 8230.07.48E-063.65E-051.24E-050.0100 - 200 8240.01.15E-064.17E-052.98E-040.0200 - 300 8250.00.00.08.99E-060.0
> 300 8260.00.00.00.00.0Table C.4 Mean Exceeding Probability Values for Spectral Accelerations 827 at 10 Hz (551 cm/s/s) 828Moment Magnitude Range of BinsDistance Range of Bin (km) 8295 - 5.55.5 6.56.5 - 7>70 - 15 8301.68E-041.44E-042.39E-050.00.015 - 25 8312.68E-054.87E-054.02E-060.00.025 - 50 8325.30E-063.04E-052.65E-050.00.050 - 100 8330.02.96E-068.84E-063.50E-060.0100 - 200 8340.00.00.07.08E-060.0200 - 300 8350.00.00.00.00.0
> 300 8360.00.00.00.00.0Note: The values of probabilities 1.0E-07 are shown as 0.0 in Tables C.3 and C.4.
837Step 3-4 838Using de-aggregated mean hazard results, the fractional contribution of each magnitude-839distance pair to the total hazard is determined. Tables C.5 and C.6 show P(m,d) 1 and P(m,d) 10 840for the 1 Hz and 10 Hz, respectively.
841Step 3-5 842Because the contribution of the distance bins greater than 100 km in Table C.5 contains 843more than 5 percent of the total hazard for 1 Hz, the controlling earthquake for the 1 Hz 844frequency will be calculated using magnitude-distance bins for distance greater than 100 km.
845Table C.7 shows P>100 (m,d) 1 for the 1 Hz frequency.
846 847 25Table C.5 P(m,d) 1 for Spectral Accelerations at 1 Hz 848Corresponding to the Reference Probability 849Moment Magnitude Range of BinsDistance Range of Bin (km) 8505 - 5.55.5 6.56.5 - 7>70 - 15 8510.0190.0920.00.00.015 - 25 8520.00.0250.00.00.025 - 50 8530.00.0300.0210.00.050 - 100 8540.00.0150.0730.0250.0100 - 200 8550.00.0020.0830.5960.0200 - 300 8560.00.00.00.0180.0
> 300 8570.00.00.00.00.0Figures C.3 to C.5 show the above information in terms of the relative percentage 858contribution.
859Table C.6 P(m,d) 10 for Spectral Accelerations at 10 Hz 860 Corresponding to the Reference Probability 861Moment Magnitude Range of Bins Distance Range of Bin (km) 8625 - 5.55.5 6.56.5 - 7>70 - 15 8630.3360.2880.0480.00.015 - 25 8640.0540.0970.0080.00.025 - 50 8650.0110.0610.0530.00.050 - 100 8660.00.0590.0180.0070.0100 - 200 8670.00.00.00.0140.0200 - 300 8680.00.00.00.00.0
> 300 8690.00.00.00.00.0Table C.7 P>100 (m,d) 1 for Spectral Acceleration at 1 Hz 870 Corresponding to the Reference Probability 871Moment Magnitude Range of BinsDistance Range of Bin (km) 8725 - 5.55.5 6.56.5 - 7>7100 - 200 8730.00.0030.1190.8520.0200 - 300 8740.00.00.00.0260.0
>300 8750.00.00.00.00.0Note: The values of probabilities 1.0E-07 are shown as 0.0 in Tables C.5, C.6, and C.7.
876Steps 3-6 and 3-7 877To compute the controlling magnitudes and distances at 1 Hz and 10 Hz for the example 878site, the values of P>100 (m,d) 1 and P(m,d) 10 are used with m and d values corresponding to the 879mid-point of the magnitude of the bin (5.25, 5.75, 6.25, 6.75, 7.3) and centroid of the ring area 880(10, 20.4, 38.9, 77.8, 155.6, 253.3, and somewhat arbitrarily 350 km). Note that the mid-point of 881 26the last magnitude bin may change because this value is dependent on the maximum magnitudes 882used in the hazard analysis. For this example site, the controlling earthquake characteristics 883(magnitudes and distances) are given in Table C.8.
884Step 3-8 885The DE response spectrum is determined by the procedures described in Appendix F.
886Figure C.1 887Total Median HazardCurves 888C.4 SITES 889NOT IN THE CEUSThe 890determination of thecontrolling earthquakes and the seismic hazard information base for sites not in the CEUS is also 891carried out using the procedure described in Section C.2 of this appendix. However, because of 892differences in seismicity rates and ground motion attenuation at these sites, alternative 893magnitude-distance bins may have to be used. An alternative reference probability may also 894have to be developed, particularly for sites in the active plate margin region and for sites at which 895a known tectonic structure dominates the hazard.
896Table C.8 Magnitudes and Distances of Controlling Earthquakes 897 from the LLNL Probabilistic Analysis 898 1 Hz 899 10 HzMc and Dc > 100 km 900Mc and Dc 6.7 and 157 km 9015.9 and 18 km 27 902Figure C.2 1 Hz Mean Hazard 903Curve for
904 Distance Bin 25-50 km 905and MagnitudeBin 6-6.5 906 907 28 908 909 910 911 912Figure C.3 Full Distribution of Hazard for 10 Hz 9135-5.55.5-66-6.56.5-7>7Magnitude Bins 29 914 915 916 917 918 919Figure C.4 Full Distribution of Hazard for 1 Hz 9205-5.55.5-66-6.56.5-7>7Magnitude Bins 30Figure C.5 Renormalized Hazard Distribution for 921 Distances Greater than 100 km for 1 Hz 9225-5.55.5-66-6.56.5-7>7Magnitude Bins 1 Copies are available at current rates from the U.S. Government Printing Office, P.O. Box 37082, Washington, DC20402-9328 (telephone (202)512-1800); or from the National Technical Information Service by writing NTIS at 5285 Port Royal Road, Springfield, VA 22161; <http://www.ntis.gov/ordernow>; telephone (703)487-4650. Copies areavailable for inspection or copying for a fee from the NRC Public Document Room at 11555 Rockville Pike, Rockville, MD; the PDR
's mailing address is USNRC PDR, Washington, DC 20555; telephone (301)415-4737 or(800)397-4209; fax (301)415-3548; email is PDR@NRC.GOV.
2 Copies are available for inspection or copying for a fee from the NRC Public Document Room at 11555 RockvillePike (first floor), Rockville, MD; the PDR
's mailing address is USNRC PDR, Washington, DC 20555; telephone(301)415-4737 or 1-(800)397-4209; fax (301)415-3548; e-mail <PDR@NRC.GOV>.
31 REFERENCES 923C.1 P. Sobel, "Revised Livermore Seismic Hazard Estimates for Sixty-Nine Nuclear Power 924Plant Sites East of the Rocky Mountains," NUREG-1488, USNRC, April 1994.
1 925C.2 J.B. Savy et al., "Eastern Seismic Hazard Characterization Update," UCRL-ID-115111, 926Lawrence Livermore National Laboratory, June 1993. (Accession number 9310190318 in 927NRC's Public Document Room) 2 928C.3 Electric Power Research Institute (EPRI), "Probabilistic Seismic Hazard Evaluations at 929Nuclear Power Plant Sites in the Central and Eastern United States," NP-4726, All 930Volumes, 1989-1991.
931 32APPENDIX D 932GEOLOGICAL, SEISMOLOGICAL, AND GEOPHYSICAL INVESTIGATIONS TO 933CHARACTERIZE SEISMIC SOURCES 934D.1 INTRODUCTION 935As characterized for use in probabilistic seismic hazard analyses (PSHA), seismic sources 936are zones within which future earthquakes are likely to occur at the same recurrence rates.
937Geological, seismological, and geophysical investigations provide the information needed to 938identify and characterize source parameters, such as size and geometry, and to estimate 939earthquake recurrence rates and maximum magnitudes. The amount of data available about 940earthquakes and their causative sources varies substantially between the WUS (west of the 941Rocky Mountain front) and the Central and Eastern United States (CEUS), or stable continental 942region (SCR) (east of the Rocky Mountain front). Furthermore, there are variations in the amount 943and quality of data within these regions.
944In active tectonic regions there are both capable tectonic sources and seismogenic 945sources, and because of their relatively high activity rate they may be more readily identified. In 946the CEUS, identifying seismic sources is less certain because of the difficulty in correlating 947earthquake activity with known tectonic structures, the lack of adequate knowledge about 948earthquake causes, and the relatively lower activity rate. However, several significant tectonic 949structures exist and some of these have been interpreted as potential seismogenic sources (e.g., 950the New Madrid fault zone, Nemaha Ridge, and Meers fault).
951In the CEUS, there is no single recommended procedure to follow to characterize 952maximum magnitudes associated with such candidate seismogenic sources; therefore, it is most 953likely that the determination of the properties of the seismogenic source, whether it is a tectonic 954structure or a seismotectonic province, will be inferred rather than demonstrated by strong 955correlations with seismicity or geologic data. Moreover, it is not generally known what 956relationships exist between observed tectonic structures in a seismic source within the CEUS and 957the current earthquake activity that may be associated with that source. Generally, the observed 958tectonic structure resulted from ancient tectonic forces that are no longer present. The historical 959seismicity record, the results of regional and site studies, and judgment play key roles. If, on the 960other hand, strong correlations and data exist suggesting a relationship between seismicity and 961seismic sources, approaches used for more active tectonic regions can be applied.
962The primary objective of geological, seismological, and geophysical investigations is to 963develop an up-to-date, site-specific earth science data base that supplements existing 964information (Ref. D.1). In the CEUS, the results of these investigations will also be used to 965assess whether new data and their interpretation are consistent with the information used as the 966basis for accepted probabilistic seismic hazard studies. If the new data are consistent with the 967existing earth science data base, modification of the hazard analysis is not required. For sites in 968the CEUS where there is significant new information (see Appendix E) provided by the site 969investigation, and for sites in the WUS, site-specific seismic sources are to be determined. It is 970anticipated that for most sites in the CEUS, new information will have been adequately bounded 971by existing seismic source interpretations.
972The following are to be evaluated for a seismic source for site-specific source 973interpretations:
974 33Seismic source location and geometry (location and extent, both surface and subsurface).
975This evaluation will normally require interpretations of available geological, geophysical, 976and seismological data in the source region by multiple experts or a team of experts. The 977evaluation should include interpretations of the seismic potential of each source and 978relationships among seismic sources in the region in order to express uncertainty in the 979evaluations. Seismic source evaluations generally develop four types of sources: (1) 980fault-specific sources, (2) area sources representing concentrated historic seismicity not 981associated with known tectonic structure, (3) area sources representing geographic 982regions with similar tectonic histories, type of crust, and structural features, and (4) 983background sources. Background sources are generally used to express uncertainty in 984the overall seismic source configuration interpreted for the site region. Acceptable 985approaches for evaluating and characterizing uncertainties for input to a seismic hazard 986calculation are contained in NUREG/CR-6372 (Ref. D.2).
987Evaluations of earthquake recurrence for each seismic source, including recurrence rate 988and recurrence model. These evaluations normally draw most heavily on historical and 989instrumental seismicity associated with each source and paleoearthquake information.
990Preferred methods and approaches for evaluating and characterizing uncertainty in 991earthquake recurrence generally will depend on the type of source. Acceptable methods 992are described in NUREG/CR-6372 (Ref. D.2).
993Evaluations of the maximum earthquake magnitude for each seismic source. These 994evaluations will draw on a broad range of source-specific tectonic characteristics, 995including tectonic history and available seismicity data. Uncertainty in this evaluation 996should normally be expressed as a maximum magnitude distribution. Preferred methods 997and information for evaluating and characterizing maximum earthquakes for seismic 998sources vary with the type of source. Acceptable methods are contained in NUREG/CR-9996372 (Ref. D.2).
1000Other evaluations, depending on the geologic setting of a site, such as local faults that 1001have a history of Quaternary (last 2 million years) displacements, sense of slip on faults, 1002fault length and width, area of faults, age of displacements, estimated displacement per 1003event, estimated earthquake magnitude per offset event, orientations of regional tectonic 1004stresses with respect to faults, and the possibility of seismogenic folds. Capable tectonic 1005sources are not always exposed at the ground surface in the WUS as demonstrated by 1006the buried reverse causative faults of the 1983 Coalinga, 1988 Whittier Narrows, l989 1007Loma Prieta, and 1994 Northridge earthquakes. These examples emphasize the need to 1008conduct thorough investigations not only at the ground surface but also in the subsurface 1009to identify structures at seismogenic depths. Whenever faults or other structures are 1010encountered at a site (including sites in the CEUS) in either outcrop or excavations, it is 1011necessary to perform adequately detailed specific investigations to determine whether or 1012not they are seismogenic or may cause surface deformation at the site. Acceptable 1013methods for performing these investigations are contained in NUREG/CR-5503 (Ref. D.3).
1014Effects of human activities such as withdrawal of fluid from or addition of fluid to the 1015subsurface associated with mining or the construction of dams and reservoirs.
1016Volcanic hazard is not addressed in this regulatory guide and will be considered on a 1017case-by-case basis in regions where a potential for this hazard exists. For sites where 1018volcanic hazard is evaluated, earthquake sources associated with volcanism should be 1019 34evaluated and included in the seismic source interpretations input to the hazard 1020calculation.
1021D.2. INVESTIGATIONS TO EVALUATE SEISMIC SOURCES 1022D.2.1General 1023 1024Investigations of the site and region around the site are necessary to identify both 1025seismogenic sources and capable tectonic sources and to determine their potential for generating 1026earthquakes and causing surface deformation. If it is determined that surface deformation need 1027not be taken into account at the site, sufficient data to clearly justify the determination should be 1028presented in the application for an early site permit, construction permit, operating license, or 1029combined license. Generally, any tectonic deformation at the earth
's surface within 40 km (25 1030miles) of the site will require detailed examination to determine its significance. Potentially active 1031tectonic deformation within the seismogenic zone beneath a site will have to be assessed using 1032geophysical and seismological methods to determine its significance.
1033Engineering solutions are generally available to mitigate the potential vibratory effects of 1034earthquakes through design. However, engineering solutions cannot always be demonstrated to 1035be adequate for mitigation of the effects of permanent ground displacement phenomena such as 1036surface faulting or folding, subsidence, or ground collapse. For this reason, it is prudent to select 1037an alternative site when the potential for permanent ground displacement exists at the proposed 1038site (Ref. D.4).
1039In most of the CEUS, instrumentally located earthquakes seldom bear any relationship to 1040geologic structures exposed at the ground surface. Possible geologically young fault 1041displacements either do not extend to the ground surface or there is insufficient geologic material 1042of the appropriate age available to date the faults. Capable tectonic sources are not always 1043exposed at the ground surface in the WUS, as demonstrated by the buried (blind) reverse 1044causative faults of the 1983 Coalinga, 1988 Whittier Narrows, 1989 Loma Prieta, and 1994 1045Northridge earthquakes. These factors emphasize the need to conduct thorough investigations 1046not only at the ground surface but also in the subsurface to identify structures at seismogenic 1047depths.1048The level of detail for investigations should be governed by knowledge of the current and 1049late Quaternary tectonic regime and the geological complexity of the site and region. The 1050investigations should be based on increasing the amount of detailed information as they proceed 1051from the regional level down to the site area [e.g., 320 km (200 mi) to 8 km (5 mi) distance from 1052the site]. Whenever faults or other structures are encountered at a site (including sites in the 1053CEUS) in either outcrop or excavations, it is necessary to perform many of the investigations 1054described below to determine whether or not they are capable tectonic sources.
1055The investigations for determining seismic sources should be carried out at three levels, 1056with areas described by radii of 320 km (200 mi), 40 km (25 mi), and 8 km (5 mi) from the site.
1057The level of detail increases closer to the site. The specific site, to a distance of at least 1 km 1058(0.6 mi), should be investigated in more detail than the other levels.
1059The regional investigations [within a radius of 320 km (200 mi) of the site] should be 1060planned to identify seismic sources and describe the Quaternary tectonic regime. The data 1061should be presented at a scale of 1:500,000 or smaller. The investigations are not expected to 1062 35be extensive or in detail, but should include a comprehensive literature review supplemented by 1063focused geological reconnaissances based on the results of the literature study (including 1064topographic, geologic, aeromagnetic, and gravity maps and airphotos). Some detailed 1065investigations at specific locations within the region may be necessary if potential capable 1066tectonic sources or seismogenic sources that may be significant for determining the safe 1067shutdown earthquake ground motion are identified.
1068The large size of the area for the regional investigations is recommended because of the 1069possibility that all significant seismic sources, or alternative configurations, may not have been 1070enveloped by the LLNL/EPRI data base. Thus, it will increase the chances of (1) identifying 1071evidence for unknown seismic sources that might extend close enough for earthquake ground 1072motions generated by that source to affect the site and (2) confirming the PSHA
's data base.
1073Furthermore, because of the relatively aseismic nature of the CEUS, the area should be large 1074enough to include as many historical and instrumentally recorded earthquakes for analysis as 1075reasonably possible. The specified area of study is expected to be large enough to incorporate 1076any previously identified sources that could be analogous to sources that may underlie or be 1077relatively close to the site. In past licensing activities for sites in the CEUS, it has often been 1078necessary, because of the absence of datable horizons overlying bedrock, to extend 1079investigations out many tens or hundreds of kilometers from the site along a structure or to an 1080outlying analogous structure in order to locate overlying datable strata or unconformities so that 1081geochronological methods could be applied. This procedure has also been used to estimate the 1082age of an undatable seismic source in the site vicinity by relating its time of last activity to that of 1083a similar, previously evaluated structure, or a known tectonic episode, the evidence of which may 1084be many tens or hundreds of miles away.
1085In the WUS it is often necessary to extend the investigations to great distances (up to 1086hundreds of kilometers) to characterize a major tectonic structure, such as the San Gregorio-1087Hosgri Fault Zone and the Juan de Fuca Subduction Zone. On the other hand, in the WUS it is 1088not usually necessary to extend the regional investigations that far in all directions. For example, 1089for a site such as Diablo Canyon, which is near the San Gregorio-Hosgri Fault, it would not be 1090necessary to extend the regional investigations farther east than the dominant San Andreas 1091Fault, which is about 75 km (45 mi) from the site; nor west beyond the Santa Lucia Banks Fault, 1092which is about 45 km (27 mi). Justification for using lesser distances should be provided.
1093Reconnaissance-level investigations, which may need to be supplemented at specific 1094locations by more detailed explorations such as geologic mapping, geophysical surveying, 1095borings, and trenching, should be conducted to a distance of 40 km (25 mi) from the site; the data 1096should be presented at a scale of 1:50,000 or smaller.
1097Detailed investigations should be carried out within a radius of 8 km (5 mi) from the site, 1098and the resulting data should be presented at a scale of 1:5,000 or smaller. The level of 1099investigations should be in sufficient detail to delineate the geology and the potential for tectonic 1100deformation at or near the ground surface. The investigations should use the methods described 1101in subsections D.2.2 and D.2.3 that are appropriate for the tectonic regime to characterize 1102 seismic sources.
1103The areas of investigations may be asymmetrical and may cover larger areas than those 1104described above in regions of late Quaternary activity, regions with high rates of historical seismic 1105activity (felt or instrumentally recorded data), or sites that are located near a capable tectonic 1106source such as a fault zone.
1107 36Data from investigations at the site (approximately 1 km
- 2) should be presented at a scale 1108of 1:500 or smaller. Important aspects of the site investigations are the excavation and logging of 1109exploratory trenches and the mapping of the excavations for the plant structures, particularly 1110plant structures that are characterized as Seismic Category I. In addition to geological, 1111geophysical, and seismological investigations, detailed geotechnical engineering investigations, 1112as described in Regulatory Guide 1.132 (Ref. D.5) and NUREG/CR-5738 (Ref. D.6), should be 1113conducted at the site.
1114The investigations needed to assess the suitability of the site with respect to effects of 1115potential ground motions and surface deformation should include determination of (1) the 1116lithologic, stratigraphic, geomorphic, hydrologic, geotechnical, and structural geologic 1117characteristics of the site and the area surrounding the site, including its seismicity and geological 1118history, (2) geological evidence of fault offset or other distortion such as folding at or near ground 1119surface within the site area (8 km radius), and (3) whether or not any faults or other tectonic 1120structures, any part of which are within a radius of 8 km (5 mi) from the site, are capable tectonic 1121sources. This information will be used to evaluate tectonic structures underlying the site area, 1122whether buried or expressed at the surface, with regard to their potential for generating 1123earthquakes and for causing surface deformation at or near the site. This part of the evaluation 1124should also consider the possible effects caused by human activities such as withdrawal of fluid 1125from or addition of fluid to the subsurface, extraction of minerals, or the loading effects of dams 1126and reservoirs.
1127D.2.2Reconnaissance Investigations, Literature Review, and Other Sources of 1128Preliminary Information 1129Regional literature and reconnaissance-level investigations should be planned based on 1130reviews of available documents and the results of previous investigations. Possible sources of 1131information, in addition to refereed papers published in technical journals, include universities, 1132consulting firms, and government agencies. The following guidance is provided but it is not 1133considered all-inclusive. Some investigations and evaluations will not be applicable to every site, 1134and situations may occur that require investigations that are not included in the following 1135discussion. In addition, it is anticipated that new technologies will be available in the future that 1136will be applicable to these investigations.
1137D.2.3Detailed Site Vicinity and Site Area Investigations 1138The following methods are suggested but they are not all-inclusive and investigations 1139should not be limited to them. Some procedures will not be applicable to every site, and 1140situations will occur that require investigations that are not included in the following discussion. It 1141is anticipated that new technologies will be available in the future that will be applicable to these 1142investigations.
1143D.2.3.1 Surface Investigations 1144Surface exploration to assess the geology and geologic structure of the site area is 1145dependent on the site location and may be carried out with the use of any appropriate 1146combination of the geological, geophysical, and seismological techniques summarized in the 1147following paragraphs. However, not all of these methods must be carried out at a given site.
1148D.2.3.1.1. Geological interpretations should be performed of aerial photographs and other 1149remote-sensing as appropriate for the particular site conditions, to assist in identifying rock 1150 37outcrops, faults and other tectonic features, fracture traces, geologic contacts, lineaments, soil 1151conditions, and evidence of landslides or soil liquefaction.
1152D.2.3.1.2. Mapping topographic, geomorphic, and hydrologic features should be 1153performed at scales and with contour intervals suitable for analysis and descriptions of 1154stratigraphy (particularly Quaternary), surface tectonic structures such as fault zones, and 1155Quaternary geomorphic features. For coastal sites or sites located near lakes or rivers, this 1156includes topography, geomorphology (particularly mapping marine and fluvial terraces), 1157bathymetry, geophysics (such as seismic reflection), and hydrographic surveys to the extent 1158needed to describe the site area features.
1159D.2.3.1.3. Vertical crustal movements should be evaluated using: (1) geodetic land 1160surveying and (2) geological analyses (such as analysis of regional dissection and degradation 1161patterns), marine and lacustrine terraces and shorelines, fluvial adjustments (such as changes in 1162stream longitudinal profiles or terraces), and other long-term changes (such as elevation changes 1163across lava flows).
1164D.2.3.1.4. Analysis should be performed to determine the tectonic significance of offset, 1165displaced, or anomalous landforms such as displaced stream channels or changes in stream 1166profiles or the upstream migration of knick-points; abrupt changes in fluvial deposits or terraces; 1167changes in paleo-channels across a fault; or uplifted, down-dropped, or laterally displaced marine 1168 terraces.1169D.2.3.1.5. Analysis should be performed to determine the tectonic significance of 1170Quaternary sedimentary deposits within or near tectonic zones such as fault zones, including (1) 1171fault-related or fault-controlled deposits such as sag ponds, graben fill deposits, and colluvial 1172wedges formed by the erosion of a fault paleo-scarp, and (2) non-fault-related, but offset, 1173deposits such as alluvial fans, debris cones, fluvial terrace, and lake shoreline deposits.
1174D.2.3.1.6. Identification and analysis should be performed of deformation features caused 1175by vibratory ground motions, including seismically induced liquefaction features (sand boils, 1176explosion craters, lateral spreads, settlement, soil flows), mud volcanoes, landslides, rockfalls, 1177deformed lake deposits or soil horizons, shear zones, cracks or fissures.
1178D.2.3.1.7. Analysis should be performed of fault displacements, including the 1179interpretation of the morphology of topographic fault scarps associated with or produced by 1180surface rupture. Fault scarp morphology is useful for estimating the age of last displacement (in 1181conjunction with the appropriate geochronological methods described NUREG/CR-5562 (Ref.
1182D.6), approximate magnitude of the associated earthquake, recurrence intervals, slip rate, and 1183the nature of the causative fault at depth.
1184D.2.3.2 Subsurface Investigations at the Site [within 1 km (0.5 mi)]
1185 Subsurface investigations at the site to identify and describe potential seismogenic 1186sources or capable tectonic sources and to obtain required geotechnical information are 1187described in Regulatory Guide 1.132 (Ref. D.5) and updated in NUREG/CR-5738 (Ref. D.7). The 1188investigations include, but may not be confined to, the following:
1189D.2.3.2.1. Geophysical investigations that have been useful in the past include magnetic 1190and gravity surveys, seismic reflection and seismic refraction surveys, bore-hole geophysics, 1191electrical surveys, and ground-penetrating radar surveys.
1192 1193 38D.2.3.2.2. Core borings to map subsurface geology and obtain samples for testing such 1194as determining the properties of the subsurface soils and rocks and geochronological analysis; 1195D.2.3.2.3. Excavation and logging of trenches across geological features to obtain 1196samples for the geochronological analysis of those features.
1197D.2.3.2.4. At some sites, deep unconsolidated material/soil, bodies of water, or other 1198material may obscure geologic evidence of past activity along a tectonic structure. In such cases, 1199the analysis of evidence elsewhere along the structure can be used to evaluate its characteristics 1200in the vicinity of the site.
1201In the CEUS it may not be possible to reasonably demonstrate the age of youngest 1202activity on a tectonic structure with adequate deterministic certainty. In such cases the 1203uncertainty should be quantified; the NRC staff will accept evaluations using the methods 1204described in NUREG/CR-5503 (Ref. D.3). A demonstrated tectonic association of such 1205structures with geologic structural features or tectonic processes that are geologically old (at least 1206pre-Quaternary) should be acceptable as an age indicator in the absence of conflicting evidence.
1207D.2.3.3 Surface-Fault Rupture and Associated Deformation at the Site 1208A site that has a potential for fault rupture at or near the ground surface and associated 1209deformation should be avoided. Where it is determined that surface deformation need not be 1210taken into account, sufficient data or detailed studies to reasonably support the determination 1211should be presented. Requirements for setback distance from active faults for hazardous waste 1212treatment, storage and disposal facilities can be found in U.S. Environmental Protection Agency 1213regulations (40 CFR Part 264).
1214The presence or absence of Quaternary faulting at the site needs to be evaluated to 1215determine whether there is a potential hazard that is due to surface faulting. The potential for 1216surface fault rupture should be characterized by evaluating (1) the location and geometry of faults 1217relative to the site, (2) nature and amount of displacement (sense of slip, cumulative slip, slip per 1218event, and nature and extent of related folding and/or secondary faulting), and (3) the likelihood 1219of displacement during some future period of concern (recurrence interval, slip rate, and elapsed 1220time since the most recent displacement). Acceptable methods and approaches for conducting 1221these evaluations are described in NUREG/CR-5503 (Ref. D.3); acceptable geochronology dating 1222methods are described in NUREG/CR-5562 (Ref. D.7).
1223For assessing the potential for fault displacement, the details of the spatial pattern of the 1224fault zone (e.g., the complexity of fault traces, branches, and en echelon patterns) may be 1225important as they may define the particular locations where fault displacement may be expected 1226in the future. The amount of slip that might be expected to occur can be evaluated directly based 1227on paleoseismic investigations or it can be estimated indirectly based on the magnitude of the 1228earthquake that the fault can generate.
1229Both non-tectonic and tectonic deformation can pose a substantial hazard to an ISFSI or 1230MRS, but there are likely to be differences in the approaches used to resolve the issues raised by 1231the two types of phenomena. Therefore, non-tectonic deformation should be distinguished from 1232tectonic deformation at a site. In past nuclear power plant licensing activities, surface 1233displacements caused by phenomena other than tectonic phenomena have been confused with 1234tectonically induced faulting. Such structures, such as found in karst terrain; and growth faulting, 1235occurring in the Gulf Coastal Plain or in other deep soil regions, cause extensive subsurface fluid 1236withdrawal.
1237 39Glacially induced faults generally do not represent a deep-seated seismic or fault 1238displacement hazard because the conditions that created them are no longer present. However, 1239residual stresses from Pleistocene glaciation may still be present in glaciated regions, although 1240they are of less concern than active tectonically induced stresses. These features should be 1241investigated with respect to their relationship to current in situ stresses.
1242The nature of faults related to collapse features can usually be defined through 1243geotechnical investigations and can either be avoided or, if feasible, adequate engineering fixes 1244can be provided.
1245Large, naturally occurring growth faults as found in the coastal plain of Texas and 1246Louisiana can pose a surface displacement hazard, even though offset most likely occurs at a 1247much less rapid rate than that of tectonic faults. They are not regarded as having the capacity to 1248generate damaging vibratory ground motion, can often be identified and avoided in siting, and 1249their displacements can be monitored. Some growth faults and antithetic faults related to growth 1250faults and fault zones should be applied in regions where growth faults are known to be present.
1251Local human-induced growth faulting can be monitored and controlled or avoided.
1252If questionable features cannot be demonstrated to be of non-tectonic origin, they should 1253be treated as tectonic deformation.
1254D.2.4 Site Geotechnical Investigations and Evaluations 1255D.2.4.1 Geotechnical Investigations 1256The geotechnical investigations should include, but not necessarily be limited to, (1) 1257defining site soil and near-surface geologic strata properties as may be required for hazard 1258evaluations, engineering analyses, and seismic design, (2) evaluating the effects of local soil and 1259site geologic strata on ground motion at the ground surface, (3) evaluating dynamic properties of 1260the near-surface soils and geologic strata, (4) conducting soil-structure interaction analyses, and 1261(5) assessing the potential for soil failure or deformation induced by ground shaking (liquefaction, 1262differential compaction, land sliding).
1263The extent of investigation to determine the geotechnical characteristics of a site depends 1264on the site geology and subsurface conditions. By working with experienced geotechnical 1265engineers and geologists, an appropriate scope of investigations can be developed for a 1266particular facility following the guidance contained in Regulatory Guide 1.132 (Ref. D.5) updated 1267with NUREG/CR-5738 (Ref. D.6). The extent of subsurface investigations is dictated by the 1268foundation requirements and by the complexity of the anticipated subsurface conditions. The 1269locations and spacing of borings, soundings, and exploratory excavations should be chosen to 1270adequately define subsurface conditions. Subsurface explorations should be chosen to 1271adequately define subsurface conditions; exploration sampling points should be located to permit 1272the construction of geological cross sections and soil profiles through foundations of safety-1273related structures and other important locations at the site.
1274Sufficient geophysical and geotechnical data should be obtained to allow for reasonable 1275assessments of representative soil profile and soil parameters and to reasonably quantify 1276variability. The guidance found in Regulatory Guide 1.132 (Ref. D.5) and NUREG/CR-5738 (Ref.
1277D.6) is acceptable. In general, this guidance should be adapted to the requirements of the site to 1278establish the scope of geotechnical investigations for the site as well as the appropriate methods 1279that will be used.
1280 40For ISFSIs co-located with existing nuclear plants, site investigations should be conducted 1281if the existing site information is not available or insufficient. Soil/rock profiles (cross-sections) at 1282the locations of the facilities should be provided based on the results of site investigations. The 1283properties required are intimately linked to the designs and evaluations to be conducted. For 1284example, for analyses of soil response effects, assessment of strain dependent-soil-dynamic 1285modulus and damping characteristics are required. An appropriate site investigation program 1286should be developed in consultation with the geotechnical engineering representative of the 1287project team.
1288Subsurface conditions should be investigated by means of borings, soundings, well logs, 1289exploratory excavations, sampling, geophysical methods (e.g., cross-hole, down-hole, and 1290geophysical logging) that adequately assess soil and ground water conditions and other methods 1291described in NUREG/CR-5738 (Ref. D.6). Appropriate investigations should be made to 1292determine the contribution of the subsurface soils and rocks to the loads imposed on the 1293 structures.
1294A laboratory testing program should be carried out to identify and classify the subsurface 1295soils and rocks and to determine their physical and engineering properties. Laboratory tests for 1296both static and dynamic properties (e.g., shear modulus, damping, liquefaction resistance, etc.)
1297are generally required. The dynamic property tests should include, as appropriate, cyclic triaxial 1298tests, cyclic simple shear tests, cyclic torsional shear tests, and resonant column tests. Both 1299static and dynamic tests should be conducted as recommended in American Society for Testing 1300and Materials (ASTM) standards or test procedures acceptable to the staff. The ASTM 1301specification numbers for static and dynamic laboratory tests can be found in the annual books of 1302ASTM Standards, Volume 04.08. Examples of soil dynamic property and strength tests are 1303shown in Table D.1. Sufficient laboratory test data should be obtained to allow for reasonable 1304assessments of mean values of soil properties and their potential variability.
1305For coarse geological materials such as coarse gravels and sand-gravel mixtures, special 1306testing equipment and testing facility should be used. Larger sample size is required for 1307laboratory tests on this type of materials (e.g., samples with 12-inch diameter were used in the 1308Rockfalls Testing Facility). It is generally difficult to obtain in situ undisturbed samples of 1309unconsolidated gravelly soils for laboratory tests. If it is not feasible to collect test samples and, 1310thus, no laboratory test results are available, the dynamic properties should be estimated from 1311the published data of similar gravelly soils.
1312Table D.1 Examples of Soil Dynamic Property and Strength Tests 1313D 3999-91 1314(Ref. D.8) 1315Standard Test Method for the Determinationof the Modulus and Damping Properties of Soils Using the Cyclic Triaxial ApparatusD 4015-92 1316(Ref. D.9) 1317Standard Test Methods for Modulus and Damping of Soils by the Resonant-Column Method D 5311-92 1318(Ref. D10) 1319Standard Test Method for Load-Controlled Cyclic Triaxial Strength of SoilD.2.4.2 Seismic Wave Transmission Characteristics of the Site 1320To be acceptable, the seismic wave transmission characteristics (spectral amplification or 1321deamplification) of the materials overlying bedrock at the site are described as a function of the 1322 41significant structural frequencies. The following material properties should be determined for 1323each stratum under the site: (1) thickness, seismic compressional and shear wave velocities, (2) 1324bulk densities, (3) soil index properties and classification, (4) shear modulus and damping 1325variations with strain level, and (5) the water table elevation and its variation throughout the site.
1326Where vertically propagating shear waves may produce the maximum ground motion, a 1327one-dimensional equivalent-linear analysis or nonlinear analysis may be appropriate. Where 1328horizontally propagating shear waves, compressional waves, or surface waves may produce the 1329maximum ground motion, other methods of analysis may be more appropriate. However, since 1330some of the variables are not well defined and investigative techniques are still in the 1331developmental stage, no specific generally agreed-upon procedures can be recommended at this 1332time. Hence, the staff must use discretion in reviewing any method of analysis. To ensure 1333appropriateness, site response characteristics determined from analytical procedures should be 1334compared with historical and instrumental earthquake data, when such data are available.
1335D.2.4.3 Site Response Analysis for Soil Sites 1336As part of quantification of earthquake ground motions at an ISFSI or MRS site, an 1337analysis of soil response effects on ground motions should be performed. A specific analysis is 1338not required at a hard rock site. Site response analyses (often referred to as site amplification 1339analyses) are relatively more important when the site surficial soil layer is a soft clay and/or when 1340there is a high stiffness contrast (wave velocity contrast) between a shallow soil layer and 1341underlying bedrock. Such conditions have shown strong local soil effects on ground motion. Site 1342response analyses are always important for sites that have predominant frequencies within the 1343range of interest for the DE ground motions. Thus, the stiffness of the soil and bedrock as well 1344as the depth of soil deposit should be carefully evaluated.
1345In performing a site response analysis, the ground motions (usually acceleration time 1346histories) defined at bedrock or outcrop are propagated through an analytical model of the site 1347soils to determine the influence of the soils on the ground motions. The required soil parameters 1348for the site response analysis include the depth, soil type, density, shear modulus and damping, 1349and their variations with strain levels for each of the soil layers. Internal friction angle, cohesive 1350strength, and over-consolidation ratio for clay are also needed for non-linear analyses. The strain 1351dependent shear modulus and damping curves should be developed based on site-specific 1352testing results and supplemented as appropriate by published data for similar soils. The effects 1353of confining pressures (that reflect the depths of the soil) on these strain-dependent soil dynamic 1354characteristics should be assessed and considered in site response analysis. The variability in 1355these properties should be accounted in the site response analysis. The results of the site 1356response analysis should show the input motion (rock response spectra), output motion (surface 1357response spectra), and spectra amplification function (site ground motion transfer function).
1358D.2.4.4 Ground Motion Evaluations 1359D.2.4.4.1. Liquefaction is a soil behavior phenomenon in which cohesionless soils (sand, 1360silt, or gravel) under saturated conditions lose a substantial part or all of their strength because of 1361high pore water pressures generated in the soils by strong ground motions induced by 1362earthquakes. Potential effects of liquefaction include reduction in foundation bearing capacity, 1363settlements, land sliding and lateral movements, flotation of lightweight structures (such as tanks) 1364embedded in the liquefied soil, and increased lateral pressures on walls retaining liquefied soil.
1365Guidance in Draft Regulatory Guide DG-1105, "Procedures and Criteria for Assessing Seismic 1366Soil Liquefaction at Nuclear Power Plant Sites
" (Ref. D.11), is being developed to be used for 1367evaluating the site for liquefaction potential.
1368 42Investigations of liquefaction potential typically involve both geological and geotechnical 1369engineering assessments. The parameters controlling liquefaction phenomena are (1) the 1370lithology of the soil at the site, (2) the ground water conditions, (3) the behavior of the soil under 1371dynamic loadings, and (4) the potential severity of the vibratory ground motion. The following 1372site-specific data should be acquired and used along with state-of-the-art evaluation procedures 1373(e.g., Ref. D.12, Ref. D.13).
1374Soil grain size distribution, density, static and dynamic strength, stress history, and 1375geologic age of the sediments; 1376Ground water conditions; 1377Penetration resistance of the soil, e.g., Standard Penetration Test (SPT), Cone 1378Penetration Test (CPT);
1379Shear wave velocity of the soil velocity of the soil; 1380Evidence of past liquefaction; and 1381Ground motion characteristics.
1382A soil behavior phenomenon similar to liquefaction is strength reduction in sensitive clays.
1383Although this behavior phenomenon is relatively rare in comparison to liquefaction, it should not 1384be overlooked as a potential cause for land sliding and lateral movements. Therefore, the 1385existence of sensitive clays at the site should be identified.
1386D.2.4.4.2. Ground settlement during and after an earthquake that is due to dynamic loads, 1387change of ground water conditions, soil expansion, soil collapse, erosion, and other causes must 1388be considered. Ground settlement that is due to the ground shaking induced by an earthquake 1389can be caused by two factors: (1) compaction of dry sands by ground shaking and (2) 1390settlement caused by dissipation of dynamically induced pore water in saturated sands.
1391Differential settlement would cause more damage to facilities than would uniform settlement.
1392Differential compaction of cohesionless soils and resulting differential ground settlement can 1393accompany liquefaction or may occur in the absence of liquefaction. The same types of geologic 1394information and soil data used in liquefaction potential assessments, such as the SPT value, can 1395also be used in assessing the potential for differential compaction. Ground subsidence has been 1396observed at the surface above relatively shallow cavities formed by mining activities (particularly 1397coal mines) and where large quantities of salt, oil, gas, or ground water have been extracted (Ref.
1398D.14). Where these conditions exist near a site, consideration and investigation must be given to 1399the possibility that surface subsidence will occur.
1400D.2.4.4.3. The stability of natural and man-made slopes must be evaluated when their 1401failures would affect the safety and operation of an ISFSI or MRS. In addition to land sliding 1402facilitated by liquefaction-induced strength reduction, instability and deformation of hillside and 1403embankment slopes can occur from the ground shaking inertia forces causing a temporary 1404exceedance of the strength of soil or rock. The slip surfaces of previous landslides, weak planes 1405or seams of subsurface materials, mapping and dating paleo-slope failure events, loss of shear 1406strength of the materials caused by the natural phenomena hazards such as liquefaction or 1407reduction of strength due to wetting, hydrological conditions including pore pressure and 1408seepage, and loading conditions imposed by the natural phenomena events must all be 1409considered in determining the potential for instability and deformations. Various possible modes 1410 43of failure should be considered. Both static and dynamic analyses must be performed for the 1411stability of the slopes.
1412The following information, at a minimum, is to be collected for the evaluation of slope 1413instability:
1414Slope cross sections covering areas that would be affected the slope stability; 1415Soil and rock profiles within the slope cross sections; 1416Static and dynamic soil and rock properties, including densities, strengths, and 1417deformability; 1418Hydrological conditions and their variations; and 1419Rock fall events.
1420D.2.5 Geochronology 1421An important part of the geologic investigations to identify and define potential seismic 1422sources is the geochronology of geologic materials. An acceptable classification of dating 1423methods is based on the rationale described in Reference D.15. The following techniques, which 1424are presented according to that classification, are useful in dating Quaternary deposits.
1425D.2.5.1 Sidereal Dating Methods 1426Dendrochronology 1427Varve chronology 1428 1429Schlerochronology 1430 1431D.2.5.2 Isotopic Dating Methods 1432Radiocarbon 1433Cosmogenic nuclides -
36Cl, 10Be, 21Pb, and 26 Al 1434Potassium argon and argon-39-argon-40 1435Uranium series -
234 U-230Th and 235U- 231 Pa 1436210 Lead 1437Uranium-lead, thorium-lead 1438D.2.5.3 Radiogenic Dating Methods 1439Fission track 1440Luminescence 1441 44 1442Electron spin resonance 1443D.2.5.4 Chemical and Biological Dating Methods 1444Amino acid racemization 1445Obsidian and tephra hydration 1446Lichenometry 1447D.2.5.6 Geomorphic Dating Methods 1448Soil profile development 1449Rock and mineral weathering 1450Scarp morphology 1451D.2.5.7 Correlation Dating Methods 1452Paleomagnetism (secular variation and reversal stratigraphy) 1453Tephrochronology 1454Paleontology (marine and terrestrial) 1455Global climatic correlations - Quaternary deposits and landforms, marine stable isotope 1456 records, etc.
1457In the CEUS, it may not be possible to reasonably demonstrate the age of last activity of a 1458tectonic structure. In such cases the NRC staff will accept association of such structures with 1459geologic structural features or tectonic processes that are geologically old (at least pre-1460Quaternary) as an age indicator in the absence of conflicting evidence.
1461These investigative procedures should also be applied, where possible, to characterize 1462offshore structures (faults or fault zones, and folds, uplift, or subsidence related to faulting at 1463depth) for coastal sites or those sites located adjacent to landlocked bodies of water.
1464Investigations of offshore structures will rely heavily on seismicity, geophysics, and bathymetry 1465rather than conventional geologic mapping methods that normally can be used effectively 1466onshore. However, it is often useful to investigate similar features onshore to learn more about 1467the significant offshore features.
1468 1 Copies are available at current rates from the U.S. Government Printing Office, P.O. Box 37082, Washington, DC20402-9328 (telephone (202)512-1800); or from the National Technical Information Service by writing NTIS at 5285 Port Royal Road, Springfield, VA 22161; (telephone (703)487-4650; <http://www.ntis.gov/ordernow>. Copies areavailable for inspection or copying for a fee from the NRC Public Document Room at 11555 Rockville Pike, Rockville, MD; the PDR
's mailing address is USNRC PDR, Washington, DC 20555; telephone (301)415-4737 or(800)397-4209; fax (301)415-3548; email is PDR@NRC.GOV.1.2 Requests for single copies of draft or active regulatory guides (which may be reproduced) or for placement onan automatic distribution list for single copies of future draft guides in specific divisions should be made in writing to the U.S. Nuclear Regulatory Commission, Washington, DC 20555, Attention: Reproduction and Distribution Services Section, or by fax to (301)415-2289; email <DISTRIBUTION@NRC.GOV>. Copies are available for inspection or copying for a fee from the NRC Public Document Room at 11555 Rockville Pike (first floor),
's mailing address is USNRC PDR, Washington, DC 20555; telephone (301)415-4737 or1-(800)397-4209; fax (301)415-3548; e-mail <PDR@NRC.GOV>.
45 REFERENCES 1469D.1 Electric Power Research Institute, "Seismic Hazard Methodology for the Central and 1470Eastern United States," EPRI NP-4726, All Volumes, 1988 through 1991.
1471D.2 Senior Seismic Hazard Analysis Committee (SSHAC), "Recommendations for 1472Probabilistic Seismic Hazard Analysis: Guidance on Uncertainty and Use of Experts," 1473NUREG/CR-6372, USNRC, 1997.
1 1474D.3 K.L. Hanson et al., Techniques for Identifying Faults and Determining Their Origins,"1475NUREG/CR-5503, USNRC, 1 1999.1476D.4 International Atomic Energy Agency, "Earthquakes and Associated Topics in Relation to 1477Nuclear Power Plant Siting," Safety Series No. 50-SG-S1, Revision 1, 1991.
1478D.5 USNRC, "Site Investigations for Foundation of Nuclear Power Plants," Regulatory Guide 14791.132, March 1979.
2 (Proposed Revision 2, DG-1101, was issued for public comment in 1480February 2001.)
1481D.6 N. Torres et al.,"Field Investigations for Foundations of Nuclear Power Facilities,"1482NUREG/CR-5738, USNRC, 1999.
1 1483D.7 J.M. Sowers et al., "Dating and Earthquakes: Review of Quaternary Geochronology and 1484Its Application to Paleoseismology," NUREG/CR-5562, USNRC, 1998..
1 1485D.8 American Society of Testing and Materials, "Standard Test Method for the Determination 1486of the Modulus and Damping Properties of Soils Using the Cyclic Triaxial Apparatus," D 14873999, 1991.
1488D.9American Society of Testing and Materials, "Standard Test Methods for Modulus and 1489Damping of Soils by the Resonant-Column Method," D 4015, 2000.
1490D.10American Society of Testing and Materials, "Standard Test Method for Load-Controlled 1491Cyclic Triaxial Strength of Soil," D 5311, 1996.
1492D.11 USNRC, "Procedures and Criteria for Assessing Seismic Soil Liquefaction at Nuclear 1493Power Plant Sites," Draft Regulatory Guide DG-1105, issued for public comment March 1494 2001.1495 1496 46D.12 H.B. Seed and I.M. Idriss, "Ground Motions and Soil Liquefaction during Earthquakes,"1497Earthquake Engineering Research Institute, Oakland, California, Monograph Series, 1498 1982.1499D.13 H.B. Seed et al., "Influence of SPT Procedures in Soil Liquefaction Resistance 1500Evaluation," Journal of the Geotechnical Engineering Division, ASCE, 111, GT12, 1225-15011273, 1985.
1502D.14 A.W. Hatheway and C.R. McClure, "Geology in the Siting of Nuclear Power Plants,"1503Reviews in Engineering Geology, Geological Society of America, Volume IV, 1979.
1504D.15S. M. Colman, K. L. Pierce, and P.W. Birkland, "Suggested Terminology for Quaternary 1505Dating Methods," Quaternary Research, Volume 288, pp. 314-319, 1987.
1506 47APPENDIX E 1507PROCEDURE FOR THE EVALUATION OF NEW GEOSCIENCES INFORMATION OBTAINED 1508FROM THE SITE-SPECIFIC INVESTIGATIONS 1509E.1 INTRODUCTION 1510This appendix provides methods acceptable to the NRC staff for assessing the impact of 1511new information obtained during site-specific investigations on the data base used for the 1512probabilistic seismic hazard analyses (PSHA).
1513Regulatory Position 4 in this guide describes acceptable PSHAs that were developed by 1514the Lawrence Livermore National Laboratory (LLNL) and the Electric Power Research Institute 1515(EPRI) to characterize the seismic hazard for nuclear power plants and to develop the Safe 1516Shutdown Earthquake (SSE). The procedure to determine the design earthquake ground motion 1517(DE) outlined in this guide relies primarily on either the LLNL or EPRI PSHA results for the 1518Central and Eastern United States (CEUS).
1519It is necessary to evaluate the geological, seismological, and geophysical data obtained 1520from the site-specific investigations to demonstrate that these data are consistent with the PSHA 1521data bases of these two methodologies. If new information identified by the site-specific 1522investigations would result in a significant increase in the hazard estimate for a site, and this new 1523information is validated by a strong technical basis, the PSHA may have to be modified to 1524incorporate the new technical information. Using sensitivity studies, it may also be possible to 1525justify a lower hazard estimate with an exceptionally strong technical basis. However, it is 1526expected that large uncertainties in estimating seismic hazard in the CEUS will continue to exist 1527in the future, and substantial delays in the licensing process will result from trying to justify a 1528lower value with respect to a specific site.
1529In general, major recomputations of the LLNL and EPRI data base are planned 1530periodically (approximately every 10 years), or when there is an important new finding or 1531occurrence. The overall revision of the data base will also require a reexamination of the 1532reference probability discussed in Appendix B.
1533E.2 POSSIBLE SOURCES OF NEW INFORMATION THAT COULD AFFECT THE SSE 1534Types of new data that could affect the PSHA results can be put in three general 1535categories: seismic sources, earthquake recurrence models or rates of deformation, and ground 1536motion models.
1537E.2.1 Seismic Sources 1538There are several possible sources of new information from the site-specific investigations 1539that could affect the seismic hazard. Continued recording of small earthquakes, including 1540microearthquakes, may indicate the presence of a localized seismic source. Paleoseismic 1541evidence, such as paleoliquefaction features or displaced Quaternary strata, may indicate the 1542presence of a previously unknown tectonic structure or a larger amount of activity on a known 1543structure than was previously considered. Geophysical studies (aeromagnetic, gravity, and 1544seismic reflection/refraction) may identify crustal structures that suggest the presence of 1545previously unknown seismic sources. In situ stress measurements and the mapping of tectonic 1546structures in the future may indicate potential seismic sources.
1547 48Detailed local site investigations often reveal faults or other tectonic structures that were 1548unknown, or reveal additional characteristics of known tectonic structures. Generally, based on 1549past licensing experience in the CEUS, the discovery of such features will not require a 1550modification of the seismic sources provided in the LLNL and EPRI studies. However, initial 1551evidence regarding a newly discovered tectonic structure in the CEUS is often equivocal with 1552respect to activity, and additional detailed investigations are required. By means of these detailed 1553investigations, and based on past licensing activities, previously unidentified tectonic structures 1554can usually be shown to be inactive or otherwise insignificant to the seismic design basis of the 1555facility, and a modification of the seismic sources provided by the LLNL and EPRI studies will not 1556be required. On the other hand, if the newly discovered features are relatively young, possibly 1557associated with earthquakes that were large and could impact the hazard for the proposed 1558facility, a modification may be required.
1559Of particular concern is the possible existence of previously unknown, potentially active 1560tectonic structures that could have moderately sized, but potentially damaging, near-field 1561earthquakes or could cause surface displacement. Also of concern is the presence of structures 1562that could generate larger earthquakes within the region than previously estimated.
1563Investigations to determine whether there is a possibility for permanent ground 1564displacement are especially important in view of the provision to allow for a combined licensing 1565procedure under 10 CFR Part 52 as an alternative to the two-step procedure of the past 1566(Construction Permit and Operating License). In the past at numerous nuclear power plant sites, 1567potentially significant faults were identified when excavations were made during the construction 1568phase prior to the issuance of an operating license, and extensive additional investigations of 1569those faults had to be carried out to properly characterize them.
1570E.2.2 Earthquake Recurrence Models 1571There are three elements of the source zone
's recurrence models that could be affected 1572by new site-specific data: (1) the rate of occurrence of earthquakes, (2) their maximum 1573magnitude, and (3) the form of the recurrence model (e.g.,a change from truncated exponential 1574to a characteristic earthquake model). Among the new site-specific information that is most likely 1575to have a significant impact on the hazard is the discovery of paleoseismic evidence such as 1576extensive soil liquefaction features, which would indicate with reasonable confidence that much 1577larger estimates of the maximum earthquake than those predicted by the previous studies would 1578ensue. The paleoseismic data could also be significant even if the maximum magnitudes of the 1579previous studies are consistent with the paleo-earthquakes if there are sufficient data to develop 1580return period estimates significantly shorter than those previously used in the probabilistic 1581analysis. The paleoseismic data could also indicate that a characteristic earthquake model would 1582be more applicable than a truncated exponential model.
1583In the future, expanded earthquake catalogs will become available that will differ from the 1584catalogs used by the previous studies. Generally, these new catalogues have been shown to 1585have only minor impacts on estimates of the parameters of the recurrence models. Cases that 1586might be significant include the discovery of records that indicate earthquakes in a region that 1587had no seismic activity in the previous catalogs, the occurrence of an earthquake larger than the 1588largest historic earthquakes, re-evaluating the largest historic earthquake to a significantly larger 1589magnitude, or the occurrence of one or more moderate to large earthquakes (magnitude 5.0 or 1590greater) in the CEUS.
1591 49Geodetic measurements, particularly satellite-based networks, may provide data and 1592interpretations of rates and styles of deformation in the CEUS that can have implications for 1593earthquake recurrence. New hypotheses regarding present-day tectonics based on new data or 1594reinterpretation of old data may be developed that were not considered or given high weight in 1595the EPRI or LLNL PSHA. Any of these cases could have an impact on the estimated maximum 1596earthquake if the result is larger than the values provided by LLNL and EPRI.
1597E.2.3 Ground Motion Attenuation Models 1598Alternative ground motion attenuation models may be used to determine the site-specific 1599spectral shape as discussed in Regulatory Position 4 and Appendix F of this regulatory guide. If 1600the ground motion models used are a major departure from the original models used in the 1601hazard analysis and are likely to have impacts on the hazard results of many sites, a re-1602evaluation of the reference probability may be needed. Otherwise, a periodic (e.g., every 10 1603years) reexamination of the PSHA and the associated data base is considered appropriate to 1604incorporate new understanding regarding ground motion attenuation models.
1605E.3 PROCEDURE AND EVALUATION 1606The EPRI and LLNL studies provide a wide range of interpretations of the possible 1607seismic sources for most regions of the CEUS, as well as a wide range of interpretations for all 1608the key parameters of the seismic hazard model. The first step in comparing the new information 1609with those interpretations is determining whether the new information is consistent with the 1610following LLNL and EPRI parameters: (1) the range of seismogenic sources as interpreted by the 1611seismicity experts or teams involved in the study, (2) the range of seismicity rates for the region 1612around the site as interpreted by the seismicity experts or teams involved in the studies, and (3) 1613the range of maximum magnitudes determined by the seismicity experts or teams. The new 1614information is considered not significant and no further evaluation is needed if it is consistent with 1615the assumptions used in the PSHA, no additional alternative seismic sources or seismic 1616parameters are needed, or it supports maintaining or decreasing the site mean seismic hazard.
1617An example is a new ISFSI co-located near an existing nuclear power plant site that was 1618recently investigated by state-of-the-art geosciences techniques and evaluated by current hazard 1619methodologies. Detailed geological, seismological, and geophysical site-specific investigations 1620would be required to update existing information regarding the new site, but it is very unlikely that 1621significant new information would be found that would invalidate the previous PSHA.
1622On the other hand, after evaluating the results of the site-specific investigations, if there is 1623still uncertainty about whether the new information will affect the estimated hazard, it will be 1624necessary to evaluate the potential impact of the new data and interpretations on the mean of the 1625range of the input parameters. Such new information may indicate the addition of a new seismic 1626source, a change in the rate of activity, a change in the spatial patterns of seismicity, an increase 1627in the rate of deformation, or the observation of a relationship between tectonic structures and 1628current seismicity. The new findings should be assessed by comparing them with the specific 1629input of each expert or team that participated in the PSHA. Regarding a new source, for 1630example, the specific seismic source characterizations for each expert or team (such as tectonic 1631feature being modeled, source geometry, probability of being active, maximum earthquake 1632magnitude, or occurrence rates) should be assessed in the context of the significant new data 1633and interpretations.
1634 50It is expected that the new information will be within the range of interpretations in the 1635existing data base, and the data will not result in an increase in overall seismicity rate or increase 1636in the range of maximum earthquakes to be used in the probabilistic analysis. It can then be 1637concluded that the current LLNL or EPRI results apply. It is possible that the new data may 1638necessitate a change in some parameter. In this case, appropriate sensitivity analyses should be 1639performed to determine whether the new site-specific data could affect the ground motion 1640estimates at the reference probability level.
1641An example is a consideration of the seismic hazard near the Wabash River Valley (Ref.
1642E.1). Geological evidence found recently within the Wabash River Valley and several of its 1643tributaries indicated that an earthquake much larger than any historic event had occurred several 1644thousand years ago in the vicinity of Vincennes, Indiana. A review of the inputs by the experts 1645and teams involved in the LLNL and EPRI PSHAs revealed that many of them had made 1646allowance for this possibility in their tectonic models by assuming the extension of the New 1647Madrid Seismic Zone northward into the Wabash Valley. Several experts had given strong 1648weight to the relatively high seismicity of the area, including the number of magnitude five historic 1649earthquakes that have occurred, and thus had assumed the larger event. This analysis of the 1650source characterizations of the experts and teams resulted in the conclusion by the analysts that 1651a new PSHA would not be necessary for this region because an event similar to the prehistoric 1652earthquake had been considered in the existing PSHAs.
1653A third step would be required if the site-specific geosciences investigations revealed 1654significant new information that would substantially affect the estimated hazard. Modification of 1655the seismic sources would more than likely be required if the results of the detailed local and 1656regional site investigations indicate that a previously unknown seismic source is identified in the 1657vicinity of the site. A hypothetical example would be the recognition of geological evidence of 1658recent activity on a fault near a site in the SCR similar to the evidence found on the Meers Fault 1659in Oklahoma (Ref. E.2). If such a source is identified, the same approach used in the active 1660tectonic regions of the WUS should be used to assess the largest earthquake expected and the 1661rate of activity. If the resulting maximum earthquake and the rate of activity are higher than those 1662provided by the LLNL or EPRI experts or teams regarding seismic sources within the region in 1663which this newly discovered tectonic source is located, it may be necessary to modify the existing 1664interpretations by introducing the new seismic source and developing modified seismic hazard 1665estimates for the site. The same would be true if the current ground motion models are a major 1666departure from the original models. These occurrences would likely require performing a new 1667PSHA using the updated data base, and may require determining the appropriate reference 1668probability.
1669 1670 1 Copies are available for inspection or copying for a fee from the NRC Public Document Room (PDR) at 11555Rockville Pike, Rockville, MD; the PDR
's mailing address is USNRC PDR, Washington, DC 20555; telephone(301)415-4737 or (800)397-4205; fax (301)415-3548; email <PDR@NRC.GOV>.
2 Copies are available at current rates from the U.S. Government Printing Office, P.O. Box 37082, Washington,DC 20402-9328 (telephone (202)512-1800); or from the National Technical Information Service by writing NTIS at5285 Port Royal Road, Springfield, VA 22161; (telephone (703)487-4650; <http://www.ntis.gov/ordernow>. Copies are available for inspection or copying for a fee from the NRC Public Document Room at 11555 Rockville Pike, Rockville, MD; the PDR
's mailing address is USNRC PDR, Washington, DC 20555; telephone (301)415-4737 or (800)397-4209; fax (301)415-3548; email is PDR@NRC.GOV.
51 REFERENCES 1671E.1 Memorandum from A. Murphy, NRC, to L. Shao, NRC,
Subject:
Summary of a Public 1672Meeting on the Revision of Appendix A, "Seismic and Geologic Siting Criteria for Nuclear 1673Power Plants," to 10 CFR Part 100; Enclosure (Viewgraphs): NUMARC, "Development 1674and Demonstration of Industry
's Integrated Seismic Siting Decision Process," February 167523, 1993.1 1676E.2 A.R. Ramelli, D.B. Slemmons, and S.J. Brocoum, "The Meers Fault: Tectonic Activity in 1677Southwestern Oklahoma," NUREG/CR-4852, USNRC, March 1987.
2 1678 52APPENDIX F 1679PROCEDURE TO DETERMINE THE DESIGN EARTHQUAKE GROUND MOTION 1680F.1 INTRODUCTION 1681This appendix elaborates on Step 4 of Regulatory Position 4 of this guide, which 1682describes an acceptable procedure to determine the design earthquake ground motion (DE). The 1683DE is defined in terms of the horizontal and vertical free-field ground motion response spectra at 1684the free ground surface. It is developed with consideration of local site effects and site seismic 1685wave transmission effects. The DE response spectrum can be determined by scaling a site-1686specific spectral shape determined for the controlling earthquakes or by scaling a standard 1687broad-band spectral shape to envelope the ground motion levels for 1 Hz (Sa,1) and 10 Hz (Sa,10), 1688as determined in Step C.2-2 of Appendix C to this guide. The standard response spectrum is 1689generally specified at 5 percent critical damping.
1690It is anticipated that a regulatory guide will be developed that provides guidance on 1691assessing site-specific effects and determining smooth design response spectra, taking into 1692account recent developments in ground motion modeling and site amplification studies (for 1693example, Ref. F.1).
1694F.2 DISCUSSION 1695For engineering purposes, it is essential that the design ground motion response 1696spectrum be a broad-band smooth response spectrum with adequate energy in the frequencies 1697of interest. In the past, it was general practice to select a standard broad-band spectrum, such 1698as the spectrum in Regulatory Guide 1.60 (Ref. F.2), and scale it by a peak ground motion 1699parameter [usually peak ground acceleration (PGA)], which is derived based on the size of the 1700controlling earthquake. Past practices to define the DE are still valid and, based on this 1701consideration, the following three possible situations are depicted in Figures F.1 to F.3.
1702Figure F.1 depicts a situation in which a site is to be used for a certified ISFSI or MRS 1703design (if available) with an established DE. In this example, the certified design DE spectrum 1704compares favorably with the site-specific response spectra determined in Step 2 or 3 of 1705Regulatory Position 4.
1706Figure F.2 depicts a situation in which a standard broad-band shape is selected and its 1707amplitude is scaled so that the design DE envelopes the site-specific spectra.
1708Figure F.3 depicts a situation in which a specific smooth shape for the design DE 1709spectrum is developed to envelope the site-specific spectra. In this case, it is particularly 1710important to be sure that the DE contains adequate energy in the frequency range of engineering 1711interest and is sufficiently broad-band.
1712 53(Note: The above figures 1713illustratesituations for a rock site.
1714For other siteconditions, the DE spectra are compared at free-field after performing site amplification studies 1715as discussed in Step 3 of Regulatory Position 4.)
1716 1 Copies are available at current rates from the U.S. Government Printing Office, P.O. Box 37082, Washington, DC20402-9328 (telephone (202)512-1800); or from the National Technical Information Service by writing NTIS at 5285 Port Royal Road, Springfield, VA 22161; (telephone (703)487-4650; <http://www.ntis.gov/ordernow>. Copies areavailable for inspection or copying for a fee from the NRC Public Document Room at 11555 Rockville Pike, Rockville, MD; the PDR
's mailing address is USNRC PDR, Washington, DC 20555; telephone (301)415-4737 or(800)397-4209; fax (301)415-3548; email is PDR@NRC.GOV.
2 Requests for single copies of draft or active regulatory guides (which may be reproduced) or for placement onan automatic distribution list for single copies of future draft guides in specific divisions should be made in writing to the U.S. Nuclear Regulatory Commission, Washington, DC 20555, Attention: Reproduction and Distribution Services Section, or by fax to (301)415-2289; email <DISTRIBUTION@NRC.GOV>. Copies are available for inspection or copying for a fee from the NRC Public Document Room at 11555 Rockville Pike (first floor),
's mailing address is USNRC PDR, Washington, DC 20555; telephone (301)415-4737 or1-(800)397-4209; fax (301)415-3548; e-mail <PDR@NRC.GOV>.
54 REFERENCES 1717F.1 R.K. McGuire, W.J. Silva, and C.J. Constantino, "Technical Basis for Revision of 1718Regulatory Guidance on Design Ground Motions: Hazard- and Risk-Consistent 1719Ground Motion Sp[ectra Guidelines," NUREG/CR-6728, 2001.
1 1720F.2 U.S. NRC, "Design Response Spectra for Seismic Design of Nuclear Power Plants,"1721Regulatory Guide 1.60, Revision 1, December 1973.
2 1722 55REGULATORY ANALYSIS 1723A separate regulatory analysis was not prepared for this draft regulatory guide. The 1724regulatory analysis "Regulatory Analysis of Geological and Seismological Characteristics for 1725and Design of Dry Cask Independent Spent Fuel Storage Installations (10 CFR Part 72)," was 1726prepared for the amendments, and it provides the regulatory basis for this guide and examines 1727the costs and benefits of the rule as implemented by the guide. A copy of the regulatory 1728analysis is available for inspection and copying for a fee at the NRC Public Document Room, 1729as Attachment __ to SECY-______. The PDR
's mailing address is USNRC PDR, 1730Washington, DC 20555; telephone (301)415-4737 or 1-(800)397-4209; fax (301)415-3548; e-1731mail <PDR@NRC.GOV>.
1732