ML021710092
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| Issue date: | 07/31/2002 |
| From: | Shah M Office of Nuclear Regulatory Research |
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U.S. NUCLEAR REGULATORY COMMISSION July 2002 OFFICE OF NUCLEAR REGULATORY RESEARCH Division 3 DG-3021 DRAFT REGULATORY GUIDE
Contact:
M. Shah (301)415-8537 DRAFT REGULATORY GUIDE DG-3021 SITE EVALUATIONS AND DETERMINATION OF DESIGN EARTHQUAKE GROUND MOTION FOR SEISMIC DESIGN OF INDEPENDENT SPENT FUEL STORAGE INSTALLATIONS AND MONITORED RETRIEVABLE STORAGE INSTALLATIONS A. INTRODUCTION 1 The NRC has recently published proposed amendments to 10 CFR Part 72, Licensing 2 Requirements for the Independent Storage of Spent Nuclear Fuel and High-Level Radioactive Waste, 3 and Reactor-Related Greater Than Class C Waste. The Proposed Section 72.103, Geological and 4 Seismological Characteristics for Applications for Dry Modes of Storage on or after [insert effective date 5 of Final Rule], in paragraph (f)(1), would require that the geological, seismological, and engineering 6 characteristics of a site and its environs be investigated in sufficient scope and detail to permit an 7 adequate evaluation of the proposed site. The investigation must provide sufficient information to 8 support evaluations performed to arrive at estimates of the design earthquake ground motion (DE) and 9 to permit adequate engineering solutions to actual or potential geologic and seismic effects at the 10 proposed site. In the Proposed Section 72.103, paragraph (f)(2) would require that the geologic and 11 seismic siting factors considered for design include a determination of the DE for the site, the potential 12 for surface tectonic and nontectonic deformations, the design bases for seismically induced floods and 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 has not 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/impact statement. Comments should be accompanied by appropriate supporting data. Written comments may be submitted to the Rules and Directives Branch, Office of Administration, U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001. Comments may be submitted electronically or downloaded through the NRCs interactive web site at <WWW.NRC.GOV> through Rulemaking. Copies of comments received may be examined at the NRC Public Document Room, 11555 Rockville Pike, Rockville, MD. Comments will be most helpful if received by October 7, 2002.
Requests for single copies of draft or active regulatory guides (which may be reproduced) or for placement on an automatic distribution list for single copies 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 draft guide are available through NRCs interactive web site (see above), or the NRCs web site <WWW.NRC.GOV> through the Electronic Reading Room under Accession Number ML021710092.
13 water waves, and other design conditions. In the Proposed Section 72.103, Paragraph (f)(2)(i) 14 would require that uncertainties inherent in estimates of the DE be addressed through an 15 appropriate analysis, such as a probabilistic seismic hazard analysis (PSHA) or suitable 16 sensitivity analyses.
17 This guide is being developed to provide general guidance on procedures acceptable to 18 the NRC staff for (1) conducting a detailed evaluation of site area geology and foundation 19 stability, (2) conducting investigations to identify and characterize uncertainty in seismic sources 20 in the site region important for the PSHA, (3) evaluating and characterizing uncertainty in the 21 parameters of seismic sources, (4) conducting PSHA for the site, and (5) determining the DE to 22 satisfy the requirements of 10 CFR Part 72.
23 This guide contains several appendices that address the objectives stated above.
24 Appendix A contains definitions of pertinent terms. Appendix B describes the rationale used to 25 determine the reference probability for the DE exceedance level that is acceptable to the staff.
26 Appendix C discusses determination of the probabilistic ground motion level and controlling 27 earthquakes and the development of a seismic hazard information base, Appendix D discusses 28 site-specific geological, seismological, and geophysical investigations. Appendix E describes a 29 method to confirm the adequacy of existing seismic sources and source parameters as the basis 30 for determining the DE for a site. Appendix F describes procedures for determination of the DE.
31 This guide applies to the design basis of both dry cask storage Independent 32 Spent Fuel Storage Installations (ISFSIs) and U.S. Department of Energy monitored 33 retrievable storage installations (MRS), because these facilities are similar in design.
34 The reference probability in Regulatory Position 3.4 and Appendix B does not apply to 35 wet storage because applications for this means of storage are not expected, and it is 36 not cost-effective to allocate resources to develop the technical bases for such an 37 expansion of the proposed revision of Part 72.
38 This guide is consistent with Regulatory Guide 1.165 (Ref. 1), but it has been modified to 39 reflect ISFSI and MRS applications, experience in the use of the dry cask storage methodology, 40 and advancements in the state of knowledge in ground motion modeling (for example, see 41 NUREG/CR-6728 (Ref. 2)).
42 Regulatory guides are issued to describe and make available to the public such 43 information as methods acceptable to the NRC staff for implementing specific parts of the NRCs 44 regulations, techniques used by the staff in evaluating specific problems or postulated accidents, 45 and guidance to applicants. Regulatory guides are not substitutes for regulations, and 46 compliance with regulatory guides is not required. Regulatory guides are issued in draft form for 47 public comment to involve the public in the early stages of developing the regulatory positions.
48 Draft regulatory guides have not received complete staff review and do not represent official 49 NRC staff positions.
50 The information collections contained in this draft regulatory guide are covered by the 51 requirements 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 53 not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a 54 person is not required to respond to, the information collection.
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55 B. DISCUSSION 56 BACKGROUND 57 A PSHA has been identified in the proposed Section 72.103 as a means to determine the 58 DE for seismic design of an ISFSI or MRS facility. The proposed rule further recognizes that the 59 nature of uncertainty and the appropriate approach to account for it depends on the tectonic 60 environment of the site and on properly characterizing parameters input to the PSHA, such as 61 seismic sources, the recurrence of earthquakes within a seismic source, the maximum 62 magnitude of earthquakes within a seismic source, engineering estimation of earthquake ground 63 motion, and the level of understanding of the tectonics. Therefore, methods other than 64 probabilistic methods such as sensitivity analyses may be adequate to account for uncertainties.
65 Every site and storage facility is unique, and therefore requirements for analysis and 66 investigations vary. It is not possible to provide procedures for addressing all situations. In 67 cases that are not specifically addressed in this guide, prudent and sound engineering judgment 68 should be exercised.
69 PSHA methodology and procedures were developed during the past 20 to 25 years 70 specifically for evaluation of seismic safety of nuclear facilities. Significant experience has been 71 gained by applying this methodology at nuclear facility sites, both reactor and non-reactor sites, 72 throughout the United States. The Western United States (WUS) (west of approximately 104o 73 west longitude) and the Central and Eastern United States (CEUS) (Refs. 3, 4) have 74 fundamentally different tectonic environments and histories of tectonic deformation. Results of 75 the PSHA methodology applications identified the need to vary the fundamental PSHA 76 methodology application depending on the tectonic environment of a site. The experience with 77 these applications also served as the basis for the Senior Seismic Hazard Analysis Committee 78 guidelines for conducting a PSHA for nuclear facilities (Ref. 5).
79 APPROACH 80 The general process to determine the DE at a new ISFSI or MRS site includes:
81 1. Site- and region-specific geological, seismological, geophysical, and geotechnical 82 investigations, and 83 2. A PSHA.
84 For ISFSI sites that are co-located with existing nuclear power generating stations, the 85 level of effort will depend on the availability and quality of existing evaluations. In performing this 86 evaluation, the applicant should evaluate whether new data require re-evaluation of previously 87 accepted seismic sources and potential adverse impact on the existing seismic design bases of 88 the nuclear power plant.
89 CENTRAL AND EASTERN UNITED STATES 90 The CEUS is considered to be that part of the United States east of the Rocky Mountain 91 front, or east of longitude 104o west (Refs. 6, 7). To determine the DE in the CEUS, an accepted 92 PSHA methodology with a range of credible alternative input interpretations should be used. For 93 sites in the CEUS, the seismic hazard methods, the data developed, and seismic sources 94 identified by Lawrence Livermore National Laboratory (LLNL) (Refs. 3, 4, 6) and the Electric 3
95 Power Research Institute (EPRI) (Ref. 7) have been reviewed and are acceptable to the staff.
96 The LLNL and EPRI studies developed data bases and scientific interpretations of available 97 information and determined seismic sources and source characterizations for the CEUS (e.g.,
98 earthquake occurrence rates, estimates of maximum magnitude).
99 In the CEUS, characterization of seismic sources is more problematic than in the active 100 plate-margin region because there is generally no clear association between seismicity and 101 known tectonic structures or near-surface geology. In general, the observed geologic structures 102 were generated in response to tectonic forces that no longer exist and have little or no correlation 103 with current tectonic forces. Therefore, it is important to account for this uncertainty by the use of 104 multiple alternative models.
105 The identification of seismic sources and reasonable alternatives in the CEUS considers 106 hypotheses presently advocated for the occurrence of earthquakes in the CEUS (e.g., the 107 reactivation of favorably oriented zones of weakness or the local amplification and release of 108 stresses concentrated around a geologic structure). In tectonically active areas of the CEUS, 109 such as the New Madrid Seismic Zone, where geological, seismological, and geophysical 110 evidence suggest the nature of the sources that generate the earthquakes, it may be more 111 appropriate to evaluate those seismic sources by using procedures similar to those normally 112 applied in the WUS.
113 WESTERN UNITED STATES 114 The WUS is considered to be that part of the United States that lies west of the Rocky 115 Mountain front, or west of approximately 104o west longitude. For the WUS, an information base 116 of earth science data and scientific interpretations of seismic sources and source 117 characterizations (e.g., geometry, seismicity parameters) comparable to the CEUS as 118 documented in the LLNL and EPRI studies (Refs. 3, 4, 6-8) does not exist. For this region, 119 specific interpretations on a site-by-site basis should be applied (Ref. 9, 10).
120 The active plate-margin regions include, for example, coastal California, Oregon, 121 Washington, and Alaska. For the active plate-margin regions, where earthquakes can often be 122 correlated with known tectonic structures, structures should be assessed for their earthquake 123 and 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 125 manifested as folds at the earths surface, and (3) subduction zone sources, such as those in the 126 Pacific Northwest. The nature of surface faults can be evaluated by conventional surface and 127 near-surface investigation techniques to assess orientation, geometry, sense of displacements, 128 length of rupture, quaternary history, etc.
129 Buried (blind) faults are often associated with surficial deformation such as folding, uplift, 130 or subsidence. The surface expression of blind faulting can be detected by mapping the uplifted 131 or down-dropped geomorphological features or stratigraphy, survey leveling, and geodetic 132 methods. The nature of the structure at depth can often be evaluated by deep core borings and 133 geophysical techniques.
134 Continental U.S. subduction zones are located in the Pacific Northwest and Alaska.
135 Seismic sources associated with subduction zones are sources within the overriding plate, on the 136 interface between the subducting and overriding lithospheric plates, and in the interior of the 137 downgoing oceanic slab. The characterization of subduction zone seismic sources includes 138 consideration of the three-dimensional geometry of the subducting plate, rupture segmentation of 4
139 subduction zones, geometry of historical ruptures, constraints on the up-dip and down-dip extent 140 of rupture, and comparisons with other subduction zones worldwide.
141 The Basin and Range region of the WUS, and to a lesser extent the Pacific Northwest 142 and the Central United States, exhibit temporal clustering of earthquakes. Temporal clustering is 143 best exemplified by the rupture histories within the Wasatch fault zone in Utah and the Meers 144 fault in central Oklahoma, where several large late Holocene coseismic faulting events occurred 145 at relatively close intervals (hundreds to thousands of years) that were preceded by long periods 146 of quiescence that lasted thousands to tens of thousands of years. Temporal clustering should 147 be considered in these regions or wherever paleoseismic evidence indicates that it has occurred.
148 C. REGULATORY POSITION 149 1. GEOLOGICAL, GEOPHYSICAL, SEISMOLOGICAL, AND GEOTECHNICAL 150 INVESTIGATIONS 151 1.1 Comprehensive geological, seismological, geophysical, and geotechnical investigations of 152 the site area and region should be performed. For ISFSIs co-located with existing nuclear power 153 plants, the existing technical information should be used along with all other available information 154 to plan and determine the scope of additional investigations. The investigations described in this 155 regulatory guide are performed primarily to gather data pertinent to the safe design and 156 construction of the ISFSI or MRS. Appropriate geological, seismological, and geophysical 157 investigations are described in Appendix D to this guide. Geotechnical investigations are 158 described in Regulatory Guide 1.132, Site Investigations for Foundations of Nuclear Power 159 Plants (Ref. 11), and NUREG/CR-5738 (Ref. 12). Another important purpose for the site-160 specific investigations is to determine whether there are any new data or interpretations that are 161 not adequately incorporated into the existing PSHA data bases. Appendix E describes a method 162 for evaluating new information derived from the site-specific investigations in the context of the 163 PSHA.
164 Investigations should be performed at four levels, with the degree of detail based on 165 distance from the site, the nature of the Quaternary tectonic regime, the geological complexity of 166 the site and region, the existence of potential seismic sources, the potential for surface 167 deformation, etc. A more detailed discussion of the areas and levels of investigations and the 168 bases for them are presented in Appendix D to this regulatory guide. General guidelines for the 169 levels of investigation are as follows.
170 1.1.1 Regional geological and seismological investigations are not expected to be extensive nor 171 in great detail, but should include literature reviews, the study of maps and remote 172 sensing data, and, if necessary, ground truth reconnaissances conducted within a radius 173 of 320 km (200 miles) of the site to identify seismic sources (seismogenic and capable 174 tectonic sources).
175 1.1.2 Geological, seismological, and geophysical investigations should be carried out within a 176 radius of 40 km (25 miles) in greater detail than the regional investigations to identify and 177 characterize the seismic and surface deformation potential of any capable tectonic 178 sources and the seismic potential of seismogenic sources, or to demonstrate that such 179 structures are not present. Sites with capable tectonic or seismogenic sources within a 180 radius of 40 km (25 miles) may require more extensive geological and seismological 5
181 investigations and analyses (similar in detail to investigations and analysis usually 182 preferred within an 8-km (5-mile) radius).
183 1.1.3 Detailed geologic, seismological, geophysical, and geotechnical investigations should be 184 conducted within a radius of 8 km (5 miles) of the site, as appropriate, to evaluate the 185 potential for tectonic deformation at or near the ground surface and to assess the 186 transmission characteristics of soils and rocks in the site vicinity. Sites in the CEUS 187 where geologically young or recent tectonic activity is not present may be investigated in 188 less detail. Methods for evaluating the seismogenic potential of tectonic structures and 189 geological features developed in Reference 13 should be followed.
190 1.1.4 Very detailed geological, geophysical, and geotechnical engineering investigations should 191 be conducted within the site [radius of approximately 1 km (0.5 miles)] to assess specific 192 soil and rock characteristics as described in Reference 11, updated with NUREG/CR-193 5738 (Ref. 12).
194 1.2 The areas of investigation may be expanded beyond those specified above in regions that 195 include capable tectonic sources, relatively high seismicity, or complex geology, or in regions that 196 have experienced a large, geologically recent earthquake.
197 1.3 Data sufficient to clearly justify all assumptions and conclusions should be presented.
198 Because engineering solutions cannot always be satisfactorily demonstrated for the effects of 199 permanent ground displacement, it is prudent to avoid a site that has a potential for surface or 200 near-surface deformation. Such sites normally will require extensive additional investigations.
201 1.4 For the site and for the area surrounding the site, lithologic, stratigraphic, hydrologic, and 202 structural geologic conditions should be characterized. The investigations should include the 203 measurement of the static and dynamic engineering properties of the materials underlying the 204 site and an evaluation of the physical evidence concerning the behavior during prior earthquakes 205 of the surficial materials and the substrata underlying the site. The properties needed to assess 206 the behavior of the underlying material during earthquakes, including the potential for 207 liquefaction, and the characteristics of the underlying material in transmitting earthquake ground 208 motions to the foundations of the facility (such as seismic wave velocities, density, water content, 209 porosity, elastic moduli, and strength) should be measured.
210 2. SEISMIC SOURCES SIGNIFICANT TO THE SITE SEISMIC HAZARD 211 2.1 For sites in the CEUS, when the EPRI or LLNL probabilistic seismic hazard analysis 212 methodologies and data bases are used to determine the design earthquake, it still may be 213 necessary to investigate and characterize potential seismic sources that were unknown or 214 uncharacterized and to perform sensitivity analyses to assess their significance to the seismic 215 hazard estimate. The results of the investigation discussed in Regulatory Position 1 should be 216 used, in accordance with Appendix E, to determine whether the LLNL or EPRI seismic sources 217 and their characterization should be updated. The guidance in Regulatory Positions 2.2 and 2.3 218 below and in Appendix D of this guide may be used if additional seismic sources are to be 219 developed as a result of investigations.
220 2.2 When the LLNL or EPRI methods are not used or are not applicable, the guidance in 221 Regulatory Position 2.3 should be used for identification and characterization of seismic sources.
222 The uncertainties in the characterization of seismic sources should be addressed as appropriate.
223 Seismic sources is a general term referring to both seismogenic sources and capable tectonic 6
224 sources. The main distinction between these two types of seismic sources is that a seismogenic 225 source would not cause surface displacement, but a capable tectonic source causes surface or 226 near-surface displacement.
227 Identification and characterization of seismic sources should be based on regional and 228 site geological and geophysical data, historical and instrumental seismicity data, the regional 229 stress field, and geological evidence of prehistoric earthquakes. Investigations to identify seismic 230 sources are described in Appendix D. The bases for the identification of seismic sources should 231 be identified. A general list of characteristics to be evaluated for seismic sources is presented in 232 Appendix D.
233 2.3 As part of the seismic source characterization, the seismic potential for each source 234 should be evaluated. Typically, characterization of the seismic potential consists of four equally 235 important elements:
236 1. Selection of a model for the spatial distribution of earthquakes in a source.
237 2. Selection of a model for the temporal distribution of earthquakes in a source.
238 3. Selection of a model for the relative frequency of earthquakes of various 239 magnitudes, including an estimate for the largest earthquake that could occur in 240 the source under the current tectonic regime.
241 4. A complete description of the uncertainty.
242 243 For example, in the LLNL study a truncated exponential model was used for the 244 distribution of magnitudes given that an earthquake has occurred in a source. A stationary 245 Poisson process is used to model the spatial and temporal occurrences of earthquakes in a 246 source.
247 For a general discussion of evaluating the earthquake potential and characterizing the 248 uncertainty, refer to Reference 5.
249 2.3.1 For sites in the CEUS, when the LLNL or EPRI method is not used or not 250 applicable (such as in the New Madrid, MO; Charleston, SC; Attica, NY, Seismic Zones), it is 251 necessary to evaluate the seismic potential for each source. The seismic sources and data that 252 have been accepted by the NRC in past licensing decisions may be used, along with the data 253 gathered from the investigations carried out as described in Regulatory Position 1.
254 Generally, the seismic sources for the CEUS are area sources because there is 255 uncertainty about the underlying causes of earthquakes. This uncertainty is due to a lack of 256 active surface faulting, a low rate of seismic activity, or a short historical record. The assessment 257 of earthquake recurrence for CEUS area sources commonly relies heavily on catalogs of 258 observed seismicity. Because these catalogs are incomplete and cover a relatively short period 259 of time, it is difficult to obtain reliable estimates of the rate of activity. Considerable care must be 260 taken to correct for incompleteness and to model the uncertainty in the rate of earthquake 261 recurrence. To completely characterize the seismic potential for a source, it is also necessary to 262 estimate the largest earthquake magnitude that a seismic source is capable of generating under 263 the current tectonic regime. This estimated magnitude defines the upper bound of the 264 earthquake recurrence relationship.
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265 The assessment of earthquake potential for area sources is particularly difficult because 266 one of the physical constraints most important to the assessment, the dimensions of the fault 267 rupture, is not known. As a result, the primary methods for assessing maximum earthquakes for 268 area sources usually include a consideration of the historical seismicity record, the pattern and 269 rate of seismic activity, the Quaternary (2 million years and younger) characteristics of the 270 source, the current stress regime (and how it aligns with known tectonic structures), paleoseismic 271 data, and analogs to sources in other regions considered tectonically similar to the CEUS.
272 Because of the shortness of the historical catalog and low rate of seismic activity, considerable 273 judgment is needed. It is important to characterize the large uncertainties in the assessment of 274 the earthquake potential.
275 2.3.2 For sites located within the WUS, earthquakes can often be associated with 276 known tectonic structures. For faults, the earthquake potential is related to the characteristics of 277 the estimated future rupture, such as the total rupture area, the length, or the amount of fault 278 displacement. The following empirical relations can be used to estimate the earthquake potential 279 from fault behavior data and also to estimate the amount of displacement that might be expected 280 for a given magnitude. It is prudent to use several of the following different relations to obtain an 281 estimate of the earthquake magnitude.
282
- Surface rupture length versus magnitude (Refs. 14-17),
283
- Subsurface rupture length versus magnitude (Ref. 18),
284
- Rupture area versus magnitude (Ref. 19),
285
- Maximum and average displacement versus magnitude (Ref. 18), and 286
- Slip rate versus magnitude (Ref. 20).
287 When such correlations as in References 14-20 are used, the earthquake potential is 288 often evaluated as the mean of the distribution. The difficult issue is the evaluation of the 289 appropriate rupture dimension to be used. This is a judgmental process based on geological 290 data for the fault in question and the behavior of other regional fault systems of the same type.
291 In addition to maximum magnitude, the other elements of the recurrence model are 292 generally obtained using catalogs of seismicity, fault slip rate, and other data. In some cases, it 293 may be appropriate to use recurrence models with memory. All the sources of uncertainty must 294 be appropriately modeled. Additionally, the phenomenon of temporal clustering should be 295 considered when there is geological evidence of its past occurrence.
296 2.3.3 For sites near subduction zones, such as in the Pacific Northwest and Alaska, the 297 maximum magnitude must be assessed for subduction zone seismic sources. Worldwide 298 observations indicate that the largest known earthquakes are associated with the plate interface, 299 although intraslab earthquakes may also have large magnitudes. The assessment of plate 300 interface earthquakes can be based on estimates of the expected dimensions of rupture or 301 analogies to other subduction zones worldwide.
302 3. PROBABILISTIC SEISMIC HAZARD ANALYSIS PROCEDURES 303 A PSHA should be performed for the site as it allows the use of multiple models to 304 estimate the likelihood of earthquake ground motions occurring at a site and systematically takes 305 into account uncertainties that exist in various parameters (such as seismic sources, maximum 306 earthquakes, and ground motion attenuation). Alternative hypotheses are considered in a 307 quantitative fashion in a PSHA. Alternative hypotheses can also be used to evaluate the 8
308 sensitivity of the hazard to the uncertainties in the significant parameters and to identify the 309 relative contribution of each seismic source to the hazard.
310 The following steps describe a procedure that is acceptable to the NRC staff for 311 performing a PSHA.
312 3.1 Perform regional and site geological, seismological, and geophysical investigations in 313 accordance with Regulatory Position 1 and Appendix D.
314 3.2 For CEUS sites, perform an evaluation of LLNL or EPRI seismic sources in accordance 315 with Appendix E to determine whether they are consistent with the site-specific data gathered in 316 Regulatory Position 1 or require updating. The PSHA should only be updated if the new 317 information indicates that the current version significantly underestimates the hazard and there is 318 a strong technical basis that supports such a revision. It may be possible to justify a lower 319 hazard estimate with an exceptionally strong technical basis. However, it is expected that large 320 uncertainties in estimating seismic hazard in the CEUS will continue to exist in the future, and 321 substantial delays in the licensing process will result in trying to justify a lower value with respect 322 to a specific site. For these reasons the NRC staff discourages efforts to justify a lower hazard 323 estimate. In most cases, limited-scope sensitivity studies should be sufficient to demonstrate 324 that the existing data base in the PSHA envelops the findings from site-specific investigations. In 325 general, significant revisions to the LLNL and EPRI data base are to be undertaken only 326 periodically (every 10 years), or when there is an important new finding or occurrence. An overall 327 revision of the data base would also require a reexamination of the acceptability of the reference 328 probability discussed in Appendix B and used in Regulatory Position 4 below. Any significant 329 update should follow the guidance of Reference 5.
330 3.3 For CEUS sites only, perform the LLNL or EPRI PSHA using original or updated sources 331 as determined in Regulatory Position 2. For sites in WUS, perform a site-specific PSHA (Ref. 5).
332 The ground motion estimates should be made for rock conditions in the free-field or by assuming 333 hypothetical rock conditions for a non-rock site to develop the seismic hazard information base 334 discussed in Appendix C.
335 3.4 Using the mean reference probability (5E-4/yr) described in Appendix B, determine the 5 336 percent 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 338 case-by-case basis.
339 3.5 Deaggregate the mean probabilistic hazard characterization in accordance with Appendix 340 C to determine the controlling earthquakes (i.e., magnitudes and distances), and document the 341 hazard information base, as described in Appendix C.
342 3.6 As an alternative method, instead of the controlling earthquakes approach described in 343 Appendix C and Regulatory Position 4 below, determine the ground motions at a sufficient 344 number of frequencies significant to the ISFSI or MRS design, and then envelope the ground 345 motions to determine the DE.
346 4. PROCEDURES FOR DETERMINING THE DESIGN EARTHQUAKE GROUND MOTION 9
347 After completing the PSHA (see Regulatory Position 3) and determining the controlling 348 earthquakes, the following procedures should be used to determine the DE. Appendix F 349 contains an additional discussion of some of the characteristics of the DE.
350 4.1 With the controlling earthquakes determined as described in Regulatory Position 3 and by 351 using the procedures in Revision 3 of Reference 21 (which may include the use of ground motion 352 models not included in the PSHA but that are more appropriate for the source, region, and site 353 under consideration or that represent the latest scientific development), develop 5 percent of 354 critical damping response spectral shapes for the actual or assumed rock conditions. The same 355 controlling earthquakes are also used to derive vertical response spectral shapes.
356 4.2 Use Sa,10 to scale the response spectrum shape corresponding to the controlling 357 earthquake. If there is a controlling earthquake for Sa,1, determine that the Sa,10 scaled response 358 spectrum also envelopes the ground motion spectrum for the controlling earthquake for Sa,1.
359 Otherwise, modify the shape to envelope the low-frequency spectrum or use two spectra in the 360 following steps. For a rock site, go to Regulatory Position 4.4.
361 4.3 For non-rock sites, perform a site-specific soil amplification analysis considering 362 uncertainties in site-specific geotechnical properties and parameters to determine response 363 spectra at the free ground surface in the free-field for the actual site conditions. Procedures 364 described in Appendix D of this guide and Reference 21 can be used to perform soil-amplification 365 analyses.
366 4.4 Compare the smooth DE spectrum or spectra used in design at the free-field with the 367 spectrum or spectra determined in Regulatory Position 2 for rock sites or determined in 368 Regulatory Position 3 for the non-rock sites to assess the adequacy of the DE spectrum or 369 spectra.
370 4.5 To obtain an adequate DE based on the site-specific response spectrum or spectra, 371 develop a smooth spectrum or spectra or use a standard broad band shape that envelopes the 372 spectra of Regulatory Position 2 or 3.
373 D. IMPLEMENTATION 374 The purpose of this section is to provide information to applicants and licensees regarding 375 the NRC staffs plans for using this draft regulatory guide.
376 This draft guide has been released to encourage public participation in its development.
377 Except in those cases in which an applicant or licensee proposes an acceptable alternative 378 method for complying with the specified portions of the NRCs regulations, the methods to be 379 described in the active guide reflecting public comments will be used in the evaluation of 380 applications for new dry cask ISFSI and MRS facilities.
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381 REFERENCES 382 1. USNRC, Identification and Characterization of Seismic Sources and Determination of 383 Safe Shutdown Earthquake Ground Motion, Regulatory Guide 1.165, March 1997.3 384 2. R.K. McGuire, W.J. Silva, and C.J. Constantino, Technical Basis for Revision of 385 Regulatory Guidance on Design Ground Motions: Hazard- and Risk-Consistent Ground 386 Motion Spectra Guidelines, NUREG/CR-6728, October 2001.
387 3. D.L. Bernreuter et al., "Seismic Hazard Characterization of 69 Nuclear Plant Sites East of 388 the Rocky Mountains," NUREG/CR-5250, Volumes 1-8, 1989.1 389 4. P. Sobel, "Revised Livermore Seismic Hazard Estimates for Sixty-Nine Nuclear Power 390 Plant Sites East of the Rocky Mountains," NUREG-1488, USNRC, April 1994.1 391 5. R.J. Budnitz et al., "Recommendations for Probabilistic Seismic Hazard Analysis:
392 Guidance on Uncertainty and Use of Experts," NUREG/CR- 6372, Volumes 1 and 2, 393 USNRC, April 1997.1 394 6. J.B. Savy et al., "Eastern Seismic Hazard Characterization Update," UCRL-ID-115111, 395 Lawrence Livermore National Laboratory, June 1993.2 (Accession number 9310190318 396 in NRC's Public Document Room) 397 7. Electric Power Research Institute (EPRI), "Probabilistic Seismic Hazard Evaluations at 398 Nuclear Power Plant Sites in the Central and Eastern United States," NP-4726, All 399 Volumes, 1989-1991.
400 8. Electric Power Research Institute (EPRI), The Earthquakes of Stable Continental 401 Regions, Volume 1: Assessment of Large Earthquake Potential, EPRI TR-102261-V1, 402 1994.
403 9. Pacific Gas and Electric Company, "Final Report of the Diablo Canyon Long Term 404 Seismic Program; Diablo Canyon Power Plant," Docket Nos. 50-275 and 50-323, 1988.2 405 10. H. Rood et al., "Safety Evaluation Report Related to the Operation of Diablo Canyon 406 Nuclear Power Plant, Units 1 and 2," NUREG-0675, Supplement No. 34, USNRC, June 407 1991.1 1
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 Public Document Room at 11555 Rockville Pike, Rockville, MD; the PDRs 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 Rockville Pike (first floor), Rockville, MD; the PDRs 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>.
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408 11. USNRC, "Site Investigations for Foundations of Nuclear Power Plants," Regulatory Guide 409 1.132, March 1979. (See also DG-1101, the proposed Revision 2 of Regulatory Guide 410 1.132, February 2001.)3 411 12. N. Torres et al., Field Investigations for Foundations of Nuclear Power Facilities, 412 NUREG/CR-5738, USNRC, 1999.1 413 13. K.L. Hanson et al., Techniques for Identifying Faults and Determining Their Origins, 414 NUREG/CR-5503, USNRC, July 1999.1 415 14. D.B. Slemmons, Faults and Earthquake Magnitude, U.S. Army Corps of Engineers, 416 Waterways Experiment Station, Misc. Papers S-7-1, Report 6, 1997.
417 15. D.B. Slemmons, Determination of Design Earthquake Magnitudes for Microzonation, 418 Proceedings of the Third International Microzonation Conference, University of 419 Washington, Seattle, Volume 1, pp. 119-130, 1982.
420 16. M.G. Bonilla, H.A. Villalobos, and R.E. Wallace, Exploratory Trench Across the Pleasant 421 Valley Fault, Nevada, Professional Paper 1274-B, U.S. Geological Survey, pp. B1-B14, 422 1984.2 423 17. S.G. Wesnousky, Relationship Between Total Affect, Degree of Fault Trace 424 Complexibility, and Earthquake Size on Major Strike-Slip Faults in California, (Abs),
425 Seismological Research Letters, Volume 59, No. 1, p.3, 1988.
426 18. D.L. Wells and K.J. Coppersmith, New Empirical Relationships Among Magnitude, 427 Rupture Length, Rupture Width, Rupture Area, and Surface Displacement, Bulletin of the 428 Seisomological Society of America, Volume 84, 1994.
429 19. M. Wyss, Estimating Maximum Expectable Magnitude of Earthquakes from Fault 430 Dimensions, Geology, Volume 7 (7), pp. 336-340, 1979.
431 20. D.P. Schwartz and K.J. Coppersmith, Seismic Hazards: New Trends in Analysis Using 432 Geologic Data, Active Tectonics, National Academy Press, Washington, DC, pp. 215-433 230, 1986.
434 21. USNRC, Standard Review Plan for the Review of Safety Analysis Reports for Nuclear 435 Power Plants, NUREG-0800, Section 2.5.2, Revision 3, 1997.3 436 APPENDIX A 437 DEFINITIONS 3
Requests for single copies of draft or active regulatory guides (which may be reproduced) or for placement on an 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),
Rockville, MD; the PDRs 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>.
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438 Capable Tectonic Source A capable tectonic source is a tectonic structure that can generate 439 both vibratory ground motion and tectonic surface deformation such as faulting or folding at or 440 near the earths surface in the present seismotectonic regime. It is described by at least one of 441 the following characteristics:
442 a. Presence of surface or near-surface deformation of landforms or geologic 443 deposits of a recurring nature within the last approximately 500,000 years or at 444 least once in the last approximately 50,000 years.
445 b. A reasonable association with one or more moderate to large earthquakes or 446 sustained earthquake activity, usually accompanied by significant surface 447 deformation.
448 c. A structural association with a capable tectonic source that has characteristics of 449 either a or b above such that movement on one could be reasonably expected to 450 be accompanied by movement on the other.
451 In some cases, the geological evidence of past activity at or near the ground surface along a 452 potential capable tectonic source may be obscured at a particular site. This might occur, for 453 example, at a site having a deep overburden. For these cases, evidence may exist elsewhere 454 along the structure from which an evaluation of its characteristics in the vicinity of the site can be 455 reasonably based. Such evidence is to be used in determining whether the structure is a 456 capable tectonic source within this definition.
457 Notwithstanding the foregoing paragraphs, the association of a structure with geological 458 structures that are at least pre-Quaternary, such as many of those found in the Central and 459 Eastern regions of the United States, in the absence of conflicting evidence, will demonstrate that 460 the structure is not a capable tectonic source within this definition.
461 Controlling Earthquakes Controlling earthquakes are the earthquakes used to determine 462 spectral shapes or to estimate ground motions at the site. There may be several controlling 463 earthquakes for a site. As a result of the probabilistic seismic hazard analysis (PSHA),
464 controlling earthquakes are characterized as mean magnitudes and distances derived from a 465 deaggregation analysis of the mean estimate of the PSHA.
466 Design Earthquake Ground Motion (DE) The DE is the vibratory ground motion for which 467 certain structures, systems, and components, classified as important to safety, are designed, 468 pursuant to Part 72. The DE for the site is characterized by both horizontal and vertical free-field 469 ground motion response spectra at the free ground surface.
470 Earthquake Recurrence Earthquake recurrence is the frequency of occurrence of 471 earthquakes having various magnitudes. Recurrence relationships or curves are developed for 472 each seismic source, and they reflect the frequency of occurrence (usually expressed on an 473 annual basis) of magnitudes up to the maximum, including measures of uncertainty.
474 Intensity The intensity of an earthquake is a qualitative description of the effects of the 475 earthquake at a particular location, as evidenced by observed effects on humans, on human-built 476 structures, and on the earths surface at a particular location. Commonly used scales to specify 477 intensity 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 13
479 I indicates an event that was not felt except by a very few, while MMI of XII indicates total 480 damage of all works of construction, either partially or completely.
481 Magnitude An earthquakes magnitude is a measure of the strength of an earthquake as 482 determined from seismographic observations and is an objective, quantitative measure of the 483 size of an earthquake. The magnitude is expressed in various ways based on the seismograph 484 record, e.g., Richter Local Magnitude, Surface Wave Magnitude, Body Wave Magnitude, and 485 Moment Magnitude. The most commonly used magnitude measurement is the Moment 486 Magnitude, Mw , which is based on the seismic moment computed as the rupture force along the 487 fault multiplied by the average amount of slip, and thus is a direct measure of the energy 488 released during an earthquake event. The Moment Magnitude of an earthquake event (Mw or M) 489 varies from 2.0 and higher values, and since magnitude scales are logarithmic, a unit change in 490 magnitude corresponds to a 32-fold change in the energy released during an earthquake event.
491 Maximum Magnitude The maximum magnitude is the upper bound to recurrence curves.
492 Mean Annual Probability of Exceedance Mean annual probability of exceedance of an 493 earthquake event of a given magnitude or an acceleration level is the probability that the given 494 magnitude or acceleration level may exceed in a year. The mean annual probability of 495 exceedance of an earthquake event is a reciprocal of the return period of the event.
496 Nontectonic Deformation Nontectonic deformation is distortion of surface or near-surface 497 soils or rocks that is not directly attributable to tectonic activity. Such deformation includes 498 features associated with subsidence, karst terrain, glaciation or deglaciation, and growth faulting.
499 Reference Probability - The reference probability of occurrence of an earthquake event is the 500 mean annual probability of exceeding the design earthquake.
501 Response Spectrum A plot of the maximum values of responses (acceleration, velocity, or 502 displacement) of a family of idealized single-degree-of-freedom damped oscillators as a function 503 of its natural frequencies (or periods) to a specified vibratory motion input at their supports.
504 Return Period The return period of an earthquake event is an inverse of the mean annual 505 probability of exceedance of the earthquake event.
506 Safe Shutdown Earthquake (SSE) The SSE is the vibratory ground motion for which certain 507 structures, systems, and components in a nuclear power plant are designed, pursuant to 508 Appendix S to 10 CFR Part 50, to remain functional. The SSE for the site is characterized by 509 both horizontal and vertical free-field ground motion response spectra at the free ground surface.
510 Seismic Potential A model giving a complete description of the future earthquake activity in a 511 seismic source zone. The model includes a relation giving the frequency (rate) of earthquakes of 512 any magnitude, an estimate of the largest earthquake that could occur under the current tectonic 513 regime, and a complete description of the uncertainty. A typical model used for PSHA is the use 514 of a truncated exponential model for the magnitude distribution and a stationary Poisson process 515 for the temporal and spatial occurrence of earthquakes.
516 Seismic Source Seismic source is a general term referring to both seismogenic sources and 517 capable tectonic sources.
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518 Seismogenic Source A seismogenic source is a portion of the earth that is assumed to have 519 a uniform earthquake potential (same expected maximum earthquake and recurrence 520 frequency), distinct from the seismicity of the surrounding regions. A seismogenic source will 521 generate vibratory ground motion but is assumed not to cause surface displacement.
522 Seismogenic sources cover a wide range of possibilities, from a well-defined tectonic structure to 523 simply a large region of diffuse seismicity (seismotectonic province) thought to be characterized 524 by the same earthquake recurrence model. A seismogenic source is also characterized by its 525 involvement in the current tectonic regime (the Quaternary, or approximately the last 2 million 526 years).
527 Stable Continental Region (SCR) A stable continental region is composed of continental 528 crust, including continental shelves, slopes, and attenuated continental crust, and excludes active 529 plate boundaries and zones of currently active tectonics directly influenced by plate margin 530 processes. 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) 532 rifting, volcanism, or suturing.
533 Stationary 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 535 is constant over time (or space), (2) the occurrence of two (or more) events in a small interval is 536 negligible, and (3) the occurrence of the event in non-overlapping intervals is independent.
537 Tectonic Structure A tectonic structure is a large-scale dislocation or distortion, usually within 538 the earths crust. Its extent may be on the order of tens of meters (yards) to hundreds of 539 kilometers (miles).
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540 APPENDIX B 541 REFERENCE PROBABILITY FOR THE EXCEEDANCE LEVEL OF THE 542 DESIGN EARTHQUAKE GROUND MOTION 543 B.1 INTRODUCTION 544 This appendix provides a rationale for a reference probability that is acceptable to the 545 NRC staff. The reference probability is used in conjunction with the probabilistic seismic hazard 546 analysis (PSHA) for determining the Design Earthquake Ground Motion (DE) for ISFSI or MRS 547 designs.
548 B.2 QUESTION ON REFERENCE PROBABILITY FOR DESIGN EARTHQUAKE 549 The reference probability is the mean annual probability of exceeding the DE. It is the 550 reciprocal of the return period for the design earthquake.
551 The NRC staff welcomes comments on all aspects of this draft regulatory guide, but is 552 especially interested in receiving comments on the appropriate mean annual probability of 553 exceedance value to be used for the seismic design of an ISFSI or MRS. Please note the 554 following considerations and include a justification for the appropriate mean annual probability of 555 exceedance value.
556 The present mean annual probability of exceedance value for determining the DE for an 557 ISFSI or MRS is approximately 1.0E-04 (i.e., in any one year, the probability is 1 in 10,000, which 558 is the reciprocal of 1.0E-04, that the DE established for the site will be exceeded). This value is 559 based on requirements for nuclear plants. The NRC is considering allowing for the use of a 560 mean annual probability of exceedance value in the range of 5.0E-04 (i.e., in any one year, the 561 probability is 1 in 2,000 that the DE established for the site will be exceeded) to 1.0E-04 for ISFSI 562 or MRS applications. This Draft Regulatory Guide DG-3021, Site Evaluations and Determination 563 of Design Earthquake Ground Motion for Seismic Design of Independent Spent Fuel Storage 564 Installations and Monitored Retrievable Storage Installations, is being developed to provide 565 guidelines that are acceptable to the NRC staff for determining the DE for an ISFSI or MRS. DG-566 3021 proposes to recommend a mean annual probability of exceedance value of 5.0E-04 as an 567 appropriate risk-informed value for the design of a dry storage ISFSI or MRS. However, the NRC 568 staff is undertaking further analysis to support a specific value. An ISFSI or MRS license 569 applicant would have to demonstrate that the use of a higher probability of exceedance value 570 would not impose any undue radiological risk to public health and safety. In view of this 571 discussion, the NRC staff is requesting comments on the appropriate mean annual probability of 572 exceedance value to be used for the seismic design of an ISFSI or MRS and a justification for 573 this probability.
574 B.3 RATIONALE FOR THE REFERENCE PROBABILITY 575 The following describes the rationale for determining the reference probability for use in 576 the PSHA for a dry cask storage system (DCSS) during a seismic event. The mean reference 577 probability of exceedance of 5.0E-4/yr for a seismic event is considered appropriate for the 578 design of a DCSS. The use of a higher reference probability will be reviewed and accepted on a 579 case-by-case basis.
580 B.3.1 Part 72 Approach 16
581 Part 72 regulations classify the structures, systems, and components (SSC) in an ISFSI 582 or MRS facility based on their importance to safety. SSCs are classified as important to safety if 583 they have the function of protecting public health and safety from undue risk and preventing 584 damage to the spent fuel during handling and storage. These SSCs are evaluated for a single 585 level of DE as an accident condition event only (section 72.106). For normal operations and 586 anticipated occurrences (section 72.104), earthquake events are not included.
587 The DCSSs for ISFSIs or MRSs are typically self-contained massive concrete or steel 588 structures, weighing approximately 40 to 100 tons when fully loaded. There are very few, if any, 589 moving parts. They are set on a concrete support pad. Several limitations have been set on the 590 maximum height to which the casks can be lifted, based on the drop accident analysis. There is 591 a minimum center-to-center spacing requirement for casks stored in an array on a common 592 support pad. The most conservative estimates of structural thresholds of seismic inertia 593 deceleration from a drop accident event, before the confinement is breached so as to exceed the 594 permissible radiation levels, is in the range of 30 g to 40 g.
595 B.3.2 Reference Probability 596 The present DE is based on the requirements contained in 10 CFR Part 100 for nuclear 597 power plants. In the Statement of Considerations accompanying the initial Part 72 rulemaking, 598 the NRC recognized that the design peak horizontal acceleration for structures, systems, and 599 components (SSCs) need not be as high as for a nuclear power reactor and should be 600 determined on a case-by-case basis until more experience is gained with licensing of these 601 types of units (45 FR 74697; November 12, 1980). With over 10 years of experience in licensing 602 dry cask storage and with analyses that demonstrate robust behavior of dry cask storage 603 systems (DCSSs) in accident scenarios (10 specific licenses have been issued and 9 locations 604 use the general license provisions), the NRC now has a reasonable basis to consider lower and 605 more appropriate DE parameters for a dry cask ISFSI or MRS. Therefore, the NRC proposes to 606 reduce the DE for new ISFSI or MRS license applicants to be commensurate with the lower risk 607 associated with these facilities. Factors that result in lower radiological risk at an ISFSI or MRS 608 compared 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 611 simple facility in which the primary activities are waste receipt, handling, and storage. An 612 ISFSI or MRS does not have the variety and complexity of active systems necessary to 613 support an operating nuclear power plant. After the spent fuel is in place, an ISFSI or 614 MRS is essentially a static operation.
615 During normal operations, the conditions required for the release and dispersal of 616 significant quantities of radioactive materials are not present. There are no high 617 temperatures or pressures present during normal operations or under design basis 618 accident conditions to cause the release and dispersal of radioactive materials. This is 619 primarily due to the low heat-generation rate of spent fuel that has undergone more than 620 1 year of decay before storage in an ISFSI or MRS, and to the low inventory of volatile 621 radioactive 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 623 are not readily dispersible. Short-lived volatile nuclides, such as I-131, are no longer 624 present in aged spent fuel. Furthermore, even if the short-lived nuclides were present 625 during a fuel assembly rupture, the canister surrounding the fuel assemblies would 626 confine these nuclides. Therefore, the Commission believes that the seismically induced 17
627 radiological risk associated with an ISFSI or MRS is significantly less than the risk 628 associated with a nuclear power plant. Also, it is NRC policy to use risk-informed 629 regulation as appropriate.
630 The critical element for protection against radiation release is the sealed cask containing 631 the 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 633 very rugged and robust. The casks must maintain structural integrity during a variety of 634 postulated non-seismic events, including cask drops, tip-overs, and wind-driven missile 635 impacts. These non-seismic events challenge cask integrity significantly more than 636 seismic events. Therefore, the casks are expected to have substantial design margins to 637 withstand 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 639 greater than the frictional resistance between the cask and the concrete pad. The sliding 640 and resulting displacements are computed by the applicant to demonstrate that the 641 casks, which are spaced to satisfy the thermal criteria in Subpart F of Part 72, are 642 precluded from impacting other adjacent casks. Furthermore, the NRC staff guidance in 643 reviewing cask designs is to show that public health and safety is maintained during a 644 postulated DE. This can be demonstrated by showing that either casks are designed to 645 prevent sliding or tip over during a seismic event, or the consequences of the calculated 646 cask movements are acceptable. Even if the casks slide or tip over and then impact 647 other casks or the pad during a seismic event significantly greater than the proposed DE, 648 there are adequate design margins to ensure that the casks maintain their structural 649 integrity.
650 The combined probability of the occurrence of a seismic event and operational failure that 651 leads to a radiological release is much smaller than the individual probabilities of either of 652 these events. This is because the handling building and crane are used for only a fraction 653 of the licensed period of an ISFSI or MRS and for only a few casks at a time.
654 Additionally, dry cask ISFSIs are expected to handle only sealed casks and not individual 655 fuel assemblies. Therefore, the potential risk of a release of radioactivity caused by 656 failure of the cask handling or crane during a seismic event is small.
657 Additional 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 659 earthquake responses, the vibratory ground motion specified is conservative.
660 The crane used for lifting the casks in the building is designed using the same industry 661 codes as for a nuclear power plant, and has a safety factor of 5 or greater for lifted loads 662 using the ultimate strength of the materials. Therefore, the crane would perform 663 satisfactorily during an earthquake much larger than the design earthquake.
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664 The determination of a DE for an ISFSI or MRS is consistent with the design approach 665 used in DOE Standard DOE-STD-1020, Natural Phenomena Hazards Design Evaluation 666 Criteria for Department of Energy Facilities,1 for similar type facilities.
667 Based on the preceding analysis, the NRC staff concludes that there is a reasonable 668 basis to design ISFSI or MRS SSCs for a single design earthquake, using a mean annual 669 probability of exceedance 5.0E-04, and adequately protect public health and safety.
1 U.S. Department of Energy, Natural Phenomena Hazards Design Evaluation Criteria for Department of Energy Facilities, 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 Public Document Room at 11555 Rockville Pike, Rockville, MD; the PDRs 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.
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670 APPENDIX C 671 DETERMINATION OF CONTROLLING EARTHQUAKES AND DEVELOPMENT 672 OF SEISMIC HAZARD INFORMATION BASE 673 C.1 INTRODUCTION 674 This appendix elaborates on the steps described in Regulatory Position 3 of this 675 regulatory guide to determine the controlling earthquakes used to define the Design Earthquake 676 Ground Motion (DE) at the site and to develop a seismic hazard information base. The 677 information base summarizes the contribution of individual magnitude and distance ranges to the 678 seismic hazard and the magnitude and distance values of the controlling earthquakes at 1 and 10 679 Hz. The controlling earthquakes are developed for the ground motion level corresponding to the 680 reference probability as defined in Appendix B to this regulatory guide.
681 The spectral ground motion levels, as determined from a probabilistic seismic hazard 682 analysis (PSHA), are used to scale a response spectrum shape. A site-specific response 683 spectrum shape is determined for the controlling earthquakes and local site conditions.
684 Regulatory Position 4 and Appendix F to this regulatory guide describe a procedure to determine 685 the DE using the controlling earthquakes and results from the PSHA.
686 C.2 PROCEDURE TO DETERMINE CONTROLLING EARTHQUAKES 687 The following approach is acceptable to the NRC staff for determining the controlling 688 earthquakes and developing a seismic hazard information base. This procedure is based on a 689 de-aggregation of the probabilistic seismic hazard in terms of earthquake magnitudes and 690 distances. When the controlling earthquakes have been obtained, the DE response spectrum 691 can be determined according to the procedure described in Appendix F to this regulatory guide.
692 Step 2-1 693 Perform a site-specific PSHA using the Lawrence Livermore National Laboratory (LLNL) 694 or Electric Power Research Institute (EPRI) methodologies (Refs. 1-3) for CEUS sites or perform 695 a site-specific PSHA for sites not in the CEUS or for sites for which LLNL or EPRI methods and 696 data are not applicable, for actual or assumed rock conditions. The hazard assessment (mean, 697 median, 85th percentile, and 15th percentile) should be performed for spectral accelerations at 1, 698 Hz, 10 Hz, and the peak ground acceleration. A lower-bound earthquake moment magnitude, M, 699 of 5.0 is recommended.
700 Step 2-2 701 Using the reference probability (5E-4/yr) as defined in Appendix B to this regulatory guide, 702 determine the ground motion levels for the spectral accelerations at 1 and 10 Hz from the total 703 mean hazard obtained in Step 2-1.
704 Step 2-3 705 Perform a complete PSHA for each of the magnitude-distance bins illustrated in Table 706 C.1. (These magnitude-distance bins are to be used in conjunction with the LLNL or EPRI 707 methods. For other situations, other binning schemes may be necessary.)
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708 Table C.1 Recommended Magnitude and Distance Bins 709 Moment Magnitude Range of Bins 710 Distance 711 Range of Bin 5 - 5.5 5.5 - 6 6 - 6.5 6.5 - 7 >7 712 (km) 713 0 - 15 714 15 - 25 715 25 - 50 716 50 - 100 717 100 - 200 718 200 - 300 719 >300 720 Step 2-4 721 From the de-aggregated results of Step 2-3, the mean annual probability of exceeding the 722 ground motion levels of Step 2-2 (spectral accelerations at 1 and 10 Hz) are determined for each 723 magnitude-distance bin. These values are denoted by Hmdf1 for 1 Hz, and Hmdf10 for 10 Hz.
724 Using Hmdf values, the fractional contribution of each magnitude and distance bin to the 725 total hazard for the 1 Hz, P(m,d)1, is computed according to:
726 P(m,d)1 = Hmdf1/(' ' Hmdf1) (Equation 1) m d 727 728 The fractional contribution of each magnitude and distance bin to the total hazard for the 10 Hz, 729 P(m,d)10, is computed according to:
730 P(m,d)10 = Hmdf10/(' ' Hmdf10) (Equation 2) m d 731 732 Step 2-5 733 Review the magnitude-distance distribution for the 1 Hz frequency to determine whether 734 the contribution to the hazard for distances of 100 km (63 mi) or greater is substantial (on the 735 order of 5 percent or greater).
736 If the contribution to the hazard for distances of 100 km (63 mi) or greater exceeds 5 737 percent, additional calculations are needed to determine the controlling earthquakes using the 738 magnitude-distance distribution for distances greater than 100 km (63 mi). This distribution, 739 P>100(m,d)1, is defined by:
740 P>100(m,d)1 = P(m,d)1 / ' ' P(m,d)1 (Equation 3) m d>100 741 21
742 The purpose of this calculation is to identify a distant, larger event that may control low-743 frequency content of a response spectrum.
744 The distance of 100 km (63 mi) is chosen for CEUS sites. However, for all sites the 745 results of full magnitude-distance distribution should be carefully examined to ensure that proper 746 controlling earthquakes are clearly identified.
747 Step 2-6 748 Calculate the mean magnitude and distance of the controlling earthquake associated with 749 the ground motions determined in Step 2 for the 10 Hz frequency. The following relation is used 750 to calculate the mean magnitude using results of the entire magnitude-distance bins matrix:
751 Mc = 3m 3P(m, d)10 (Equation 4) d m 752 753 where m is the central magnitude value for each magnitude bin.
754 The mean distance of the controlling earthquake is determined using results of the entire 755 magnitude-distance bins matrix:
756 757 Ln { Dc (10 Hz)} = 3 Ln (d) 3 P(m, d)10 (Equation 5) d m 758 759 where d is the centroid distance value for each distance bin.
760 Step 2-7 761 If the contribution to the hazard calculated in Step 2-5 for distances of 100 km (63 mi) or 762 greater exceeds 5 percent for the 1 Hz frequency, calculate the mean magnitude and distance of 763 the controlling earthquakes associated with the ground motions determined in Step 2-2 for the 764 average of 1 Hz. The following relation is used to calculate the mean magnitude using 765 calculations based on magnitude-distance bins greater than distances of 100 km (63 mi) as 766 discussed in Step 2-5:
767 Mc (1Hz) = 3 m 3 P > 100 (m, d)1 m d>100 (Equation 6) 768 769 where m is the central magnitude value for each magnitude bin.
770 The mean distance of the controlling earthquake is based on magnitude-distance bins 771 greater than distances of 100 km as discussed in Step 2-5 and determined according to:
772 Ln { Dc (1 Hz)} = 3 Ln (d) 3 P(m, d)10 (Equation 7) d>100 m 773 774 where d is the centroid distance value for each distance bin.
775 Step 2-8 776 Determine the DE response spectrum using the procedure described in Appendix F of this 777 regulatory guide.
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778 C.3 EXAMPLE FOR A CEUS SITE 779 To illustrate the procedure in Section C.2, calculations are shown here for a CEUS site 780 using the 1993 LLNL hazard results (Refs. C.1, C.2). It must be emphasized that the 781 recommended magnitude and distance bins and procedure used to establish controlling 782 earthquakes were developed for application in the CEUS where the nearby earthquakes 783 generally control the response in the 10 Hz frequency range, and larger but distant events can 784 control the lower frequency range. For other situations, alternative binning schemes as well as a 785 study of contributions from various bins will be necessary to identify controlling earthquakes 786 consistent with the distribution of the seismicity.
787 Step 3-1 788 The 1993 LLNL seismic hazard methodology (Refs. C.1, C.2) was used to determine the 789 hazard at the site. A lower bound earthquake moment magnitude, M, of 5.0 was used in this 790 analysis. The analysis was performed for spectral acceleration at 1 and 10 Hz. The resultant 791 hazard curves are plotted in Figure C.1.
792 Step 3-2 793 The hazard curves at 1 and 10 Hz obtained in Step 1 are assessed at the reference 794 probability value of 5E-4/yr, as defined in Appendix B to this regulatory guide. The corresponding 795 ground motion level values are given in Table C.2. See Figure C.1.
796 Table C.2 Ground Motion Levels 797 Frequency (Hz) 1 10 798 Spectral Acc. (cm/s/s) 88 551 799 Step 3-3 800 The mean seismic hazard is de-aggregated for the matrix of magnitude and distance bins 801 as given in Table C.1.
802 A complete probabilistic hazard analysis was performed for each bin to determine the 803 contribution to the hazard from all earthquakes within the bin, i.e., all earthquakes with 804 earthquake moment magnitudes greater than 5.0 and distance from 0 km to greater than 300 km.
805 See Figure C.2 where the mean 1 Hz hazard curve is plotted for distance bin 25 - 50 km and 806 magnitude bin 6 - 6.5.
807 The hazard values corresponding to the ground motion levels, found in Step 2-2, and 808 listed in Table C.2, are then determined from the hazard curve for each bin for spectral 809 accelerations at 1 Hz and 10 Hz. This process is illustrated in Figure C.2. The vertical line 810 corresponds to the value 88 cm/s/s listed in Table C.2 for the 1 Hz hazard curve and intersects 811 the 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 813 value for each bin for 1 Hz and 10 Hz frequencies respectively. It should be noted that if the 814 mean hazard in each of the 35 bins is added up it equals the reference probability of 5.0E-04.
815 23
816 Table C.3 Mean Exceeding Probability Values for Spectral Accelerations 817 at 1 Hz (88 cm/s/s)
Moment Magnitude Range of Bins 818 Distance Range of Bin (km) 5 - 5.5 5.5 - 6 6 - 6.5 6.5 - 7 >7 819 0 - 15 9.68E-06 4.61E-05 0.0 0.0 0.0 820 15 - 25 0.0 1.26E-05 0.0 0.0 0.0 821 25 - 50 0.0 1.49E-05 1.05E-05 0.0 0.0 822 50 - 100 0.0 7.48E-06 3.65E-05 1.24E-05 0.0 823 100 - 200 0.0 1.15E-06 4.17E-05 2.98E-04 0.0 824 200 - 300 0.0 0.0 0.0 8.99E-06 0.0 825 > 300 0.0 0.0 0.0 0.0 0.0 826 Table C.4 Mean Exceeding Probability Values for Spectral Accelerations 827 at 10 Hz (551 cm/s/s)
Moment Magnitude Range of Bins 828 Distance Range of Bin (km) 5 - 5.5 5.5 - 6 6 - 6.5 6.5 - 7 >7 829 0 - 15 1.68E-04 1.44E-04 2.39E-05 0.0 0.0 830 15 - 25 2.68E-05 4.87E-05 4.02E-06 0.0 0.0 831 25 - 50 5.30E-06 3.04E-05 2.65E-05 0.0 0.0 832 50 - 100 0.0 2.96E-06 8.84E-06 3.50E-06 0.0 833 100 - 200 0.0 0.0 0.0 7.08E-06 0.0 834 200 - 300 0.0 0.0 0.0 0.0 0.0 835 > 300 0.0 0.0 0.0 0.0 0.0 836 Note: The values of probabilities #1.0E-07 are shown as 0.0 in Tables C.3 and C.4.
837 Step 3-4 838 Using de-aggregated mean hazard results, the fractional contribution of each magnitude-839 distance pair to the total hazard is determined. Tables C.5 and C.6 show P(m,d)1 and P(m,d)10 840 for the 1 Hz and 10 Hz, respectively.
841 Step 3-5 842 Because the contribution of the distance bins greater than 100 km in Table C.5 contains 843 more than 5 percent of the total hazard for 1 Hz, the controlling earthquake for the 1 Hz 844 frequency will be calculated using magnitude-distance bins for distance greater than 100 km.
845 Table C.7 shows P>100 (m,d)1 for the 1 Hz frequency.
846 24
847 Table C.5 P(m,d)1 for Spectral Accelerations at 1 Hz 848 Corresponding to the Reference Probability Moment Magnitude Range of Bins 849 Distance Range of Bin (km) 5 - 5.5 5.5 - 6 6 - 6.5 6.5 - 7 >7 850 0 - 15 0.019 0.092 0.0 0.0 0.0 851 15 - 25 0.0 0.025 0.0 0.0 0.0 852 25 - 50 0.0 0.030 0.021 0.0 0.0 853 50 - 100 0.0 0.015 0.073 0.025 0.0 854 100 - 200 0.0 0.002 0.083 0.596 0.0 855 200 - 300 0.0 0.0 0.0 0.018 0.0 856 > 300 0.0 0.0 0.0 0.0 0.0 857 Figures C.3 to C.5 show the above information in terms of the relative percentage 858 contribution.
859 Table C.6 P(m,d)10 for Spectral Accelerations at 10 Hz 860 Corresponding to the Reference Probability Moment Magnitude Range of Bins 861 Distance Range of Bin (km) 5 - 5.5 5.5 - 6 6 - 6.5 6.5 - 7 >7 862 0 - 15 0.336 0.288 0.048 0.0 0.0 863 15 - 25 0.054 0.097 0.008 0.0 0.0 864 25 - 50 0.011 0.061 0.053 0.0 0.0 865 50 - 100 0.0 0.059 0.018 0.007 0.0 866 100 - 200 0.0 0.0 0.0 0.014 0.0 867 200 - 300 0.0 0.0 0.0 0.0 0.0 868 > 300 0.0 0.0 0.0 0.0 0.0 869 Table C.7 P>100 (m,d)1 for Spectral Acceleration at 1 Hz 870 Corresponding to the Reference Probability Moment Magnitude Range of Bins 871 Distance Range of Bin (km) 5 - 5.5 5.5 - 6 6 - 6.5 6.5 - 7 >7 872 100 - 200 0.0 0.003 0.119 0.852 0.0 873 200 - 300 0.0 0.0 0.0 0.026 0.0 874 >300 0.0 0.0 0.0 0.0 0.0 875 Note: The values of probabilities #1.0E-07 are shown as 0.0 in Tables C.5, C.6, and C.7.
876 Steps 3-6 and 3-7 877 To compute the controlling magnitudes and distances at 1 Hz and 10 Hz for the example 878 site, the values of P>100 (m,d)1 and P(m,d)10 are used with m and d values corresponding to the 879 mid-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 25
881 the last magnitude bin may change because this value is dependent on the maximum magnitudes 882 used in the hazard analysis. For this example site, the controlling earthquake characteristics 883 (magnitudes and distances) are given in Table C.8.
884 Step 3-8 885 The DE response spectrum is determined by the procedures described in Appendix F.
886 Figure C.1 Total Mean Hazard 887 Curves 888 C.4 SITE S NOT IN THE CEUS 889 The determination of the 890 controlling earthquakes and the 891 seismic hazard information base 892 for sites not in the CEUS is also carried out using the procedure described in Section C.2 of this 893 appendix. However, because of differences in seismicity rates and ground motion attenuation at 894 these sites, alternative magnitude-distance bins may have to be used. An alternative reference 895 probability may also have to be developed, particularly for sites in the active plate margin region 896 and for sites at which a known tectonic structure dominates the hazard.
26
897 Table C.8 Magnitudes and Distances of Controlling Earthquakes 898 from the LLNL Probabilistic Analysis 899 1 Hz 10 Hz 900 Mc and Dc > 100 km Mc and Dc 901 6.7 and 157 km 5.9 and 18 km 902 Figure C.2 1 Hz Mean Hazard Curve for 903 Distance Bin 25-50 km and Magnitude Bin 6-6.5 904 905 27
906 907 908 909 5-5.5 5.5-6 6-6.5 Magnitude 6.5-7 Bins
>7 910 Figure C.3 911 Full 912 Distribution 913 of Hazard 914 for 10 Hz 28
915 916 917 918 919 920 5-5.5 5.5-6 6-6.5 6.5-7 Magnitude
>7 Bins 921 Figure C.4 922 Full 923 Distribution of Hazard for 1 Hz 29
5-5.5 5.5-6 6-6.5 Magnitude 6.5-7 Bins
>7 924 Figure C.5 925 Renormalized Hazard Distribution for 926 Distances Greater than 100 km for 1 Hz 30
927 REFERENCES 928 C.1 P. Sobel, "Revised Livermore Seismic Hazard Estimates for Sixty-Nine Nuclear Power 929 Plant Sites East of the Rocky Mountains, NUREG-1488, USNRC, April 1994.1 930 C.2 J.B. Savy et al., "Eastern Seismic Hazard Characterization Update," UCRL-ID-115111, 931 Lawrence Livermore National Laboratory, June 1993. (Accession number 9310190318 in 932 NRC's Public Document Room)2 933 C.3 Electric Power Research Institute (EPRI), "Probabilistic Seismic Hazard Evaluations at 934 Nuclear Power Plant Sites in the Central and Eastern United States," NP-4726, All 935 Volumes, 1989-1991.
1 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; <http://www.ntis.gov/ordernow>; telephone (703)487-4650. Copies are available for inspection or copying for a fee from the NRC Public Document Room at 11555 Rockville Pike, Rockville, MD; the PDRs 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 Rockville Pike (first floor), Rockville, MD; the PDRs 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
936 APPENDIX D 937 GEOLOGICAL, SEISMOLOGICAL, AND GEOPHYSICAL INVESTIGATIONS TO 938 CHARACTERIZE SEISMIC SOURCES 939 D.1 INTRODUCTION 940 As characterized for use in probabilistic seismic hazard analyses (PSHA), seismic sources 941 are zones within which future earthquakes are likely to occur at the same recurrence rates.
942 Geological, seismological, and geophysical investigations provide the information needed to 943 identify and characterize source parameters, such as size and geometry, and to estimate 944 earthquake recurrence rates and maximum magnitudes. The amount of data available about 945 earthquakes and their causative sources varies substantially between the WUS (west of the 946 Rocky Mountain front) and the Central and Eastern United States (CEUS), or stable continental 947 region (SCR) (east of the Rocky Mountain front). Furthermore, there are variations in the amount 948 and quality of data within these regions.
949 In active tectonic regions there are both capable tectonic sources and seismogenic 950 sources, and because of their relatively high activity rate they may be more readily identified. In 951 the CEUS, identifying seismic sources is less certain because of the difficulty in correlating 952 earthquake activity with known tectonic structures, the lack of adequate knowledge about 953 earthquake causes, and the relatively lower activity rate. However, several significant tectonic 954 structures exist and some of these have been interpreted as potential seismogenic sources (e.g.,
955 the New Madrid fault zone, Nemaha Ridge, and Meers fault).
956 In the CEUS, there is no single recommended procedure to follow to characterize 957 maximum magnitudes associated with such candidate seismogenic sources; therefore, it is most 958 likely that the determination of the properties of the seismogenic source, whether it is a tectonic 959 structure or a seismotectonic province, will be inferred rather than demonstrated by strong 960 correlations with seismicity or geologic data. Moreover, it is not generally known what 961 relationships exist between observed tectonic structures in a seismic source within the CEUS and 962 the current earthquake activity that may be associated with that source. Generally, the observed 963 tectonic structure resulted from ancient tectonic forces that are no longer present. The historical 964 seismicity record, the results of regional and site studies, and judgment play key roles. If, on the 965 other hand, strong correlations and data exist suggesting a relationship between seismicity and 966 seismic sources, approaches used for more active tectonic regions can be applied.
967 The primary objective of geological, seismological, and geophysical investigations is to 968 develop an up-to-date, site-specific earth science data base that supplements existing 969 information (Ref. D.1). In the CEUS, the results of these investigations will also be used to 970 assess whether new data and their interpretation are consistent with the information used as the 971 basis for accepted probabilistic seismic hazard studies. If the new data are consistent with the 972 existing earth science data base, modification of the hazard analysis is not required. For sites in 973 the CEUS where there is significant new information (see Appendix E) provided by the site 974 investigation, and for sites in the WUS, site-specific seismic sources are to be determined. It is 975 anticipated that for most sites in the CEUS, new information will have been adequately bounded 976 by existing seismic source interpretations.
977 The following are to be evaluated for a seismic source for site-specific source 978 interpretations:
32
979
- Seismic source location and geometry (location and extent, both surface and subsurface).
980 This evaluation will normally require interpretations of available geological, geophysical, 981 and seismological data in the source region by multiple experts or a team of experts. The 982 evaluation should include interpretations of the seismic potential of each source and 983 relationships among seismic sources in the region in order to express uncertainty in the 984 evaluations. Seismic source evaluations generally develop four types of sources: (1) 985 fault-specific sources, (2) area sources representing concentrated historic seismicity not 986 associated with known tectonic structure, (3) area sources representing geographic 987 regions with similar tectonic histories, type of crust, and structural features, and (4) 988 background sources. Background sources are generally used to express uncertainty in 989 the overall seismic source configuration interpreted for the site region. Acceptable 990 approaches for evaluating and characterizing uncertainties for input to a seismic hazard 991 calculation are contained in NUREG/CR-6372 (Ref. D.2).
992
- Evaluations of earthquake recurrence for each seismic source, including recurrence rate 993 and recurrence model. These evaluations normally draw most heavily on historical and 994 instrumental seismicity associated with each source and paleoearthquake information.
995 Preferred methods and approaches for evaluating and characterizing uncertainty in 996 earthquake recurrence generally will depend on the type of source. Acceptable methods 997 are described in NUREG/CR-6372 (Ref. D.2).
998
- Evaluations of the maximum earthquake magnitude for each seismic source. These 999 evaluations will draw on a broad range of source-specific tectonic characteristics, 1000 including tectonic history and available seismicity data. Uncertainty in this evaluation 1001 should normally be expressed as a maximum magnitude distribution. Preferred methods 1002 and information for evaluating and characterizing maximum earthquakes for seismic 1003 sources vary with the type of source. Acceptable methods are contained in NUREG/CR-1004 6372 (Ref. D.2).
1005
- Other evaluations, depending on the geologic setting of a site, such as local faults that 1006 have a history of Quaternary (last 2 million years) displacements, sense of slip on faults, 1007 fault length and width, area of faults, age of displacements, estimated displacement per 1008 event, estimated earthquake magnitude per offset event, orientations of regional tectonic 1009 stresses with respect to faults, and the possibility of seismogenic folds. Capable tectonic 1010 sources are not always exposed at the ground surface in the WUS as demonstrated by 1011 the buried reverse causative faults of the 1983 Coalinga, 1988 Whittier Narrows, l989 1012 Loma Prieta, and 1994 Northridge earthquakes. These examples emphasize the need to 1013 conduct thorough investigations not only at the ground surface but also in the subsurface 1014 to identify structures at seismogenic depths. Whenever faults or other structures are 1015 encountered at a site (including sites in the CEUS) in either outcrop or excavations, it is 1016 necessary to perform adequately detailed specific investigations to determine whether or 1017 not they are seismogenic or may cause surface deformation at the site. Acceptable 1018 methods for performing these investigations are contained in NUREG/CR-5503 (Ref. D.3).
1019
- Effects of human activities such as withdrawal of fluid from or addition of fluid to the 1020 subsurface associated with mining or the construction of dams and reservoirs.
1021
- Volcanic hazard is not addressed in this regulatory guide and will be considered on a 1022 case-by-case basis in regions where a potential for this hazard exists. For sites where 1023 volcanic hazard is evaluated, earthquake sources associated with volcanism should be 33
1024 evaluated and included in the seismic source interpretations input to the hazard 1025 calculation.
1026 D.2. INVESTIGATIONS TO EVALUATE SEISMIC SOURCES 1027 D.2.1 General 1028 1029 Investigations of the site and region around the site are necessary to identify both 1030 seismogenic sources and capable tectonic sources and to determine their potential for generating 1031 earthquakes and causing surface deformation. If it is determined that surface deformation need 1032 not be taken into account at the site, sufficient data to clearly justify the determination should be 1033 presented in the application for an early site permit, construction permit, operating license, or 1034 combined license. Generally, any tectonic deformation at the earths surface within 40 km (25 1035 miles) of the site will require detailed examination to determine its significance. Potentially active 1036 tectonic deformation within the seismogenic zone beneath a site will have to be assessed using 1037 geophysical and seismological methods to determine its significance.
1038 Engineering solutions are generally available to mitigate the potential vibratory effects of 1039 earthquakes through design. However, engineering solutions cannot always be demonstrated to 1040 be adequate for mitigation of the effects of permanent ground displacement phenomena such as 1041 surface faulting or folding, subsidence, or ground collapse. For this reason, it is prudent to select 1042 an alternative site when the potential for permanent ground displacement exists at the proposed 1043 site (Ref. D.4).
1044 In most of the CEUS, instrumentally located earthquakes seldom bear any relationship to 1045 geologic structures exposed at the ground surface. Possible geologically young fault 1046 displacements either do not extend to the ground surface or there is insufficient geologic material 1047 of the appropriate age available to date the faults. Capable tectonic sources are not always 1048 exposed at the ground surface in the WUS, as demonstrated by the buried (blind) reverse 1049 causative faults of the 1983 Coalinga, 1988 Whittier Narrows, 1989 Loma Prieta, and 1994 1050 Northridge earthquakes. These factors emphasize the need to conduct thorough investigations 1051 not only at the ground surface but also in the subsurface to identify structures at seismogenic 1052 depths.
1053 The level of detail for investigations should be governed by knowledge of the current and 1054 late Quaternary tectonic regime and the geological complexity of the site and region. The 1055 investigations should be based on increasing the amount of detailed information as they proceed 1056 from the regional level down to the site area [e.g., 320 km (200 mi) to 8 km (5 mi) distance from 1057 the site]. Whenever faults or other structures are encountered at a site (including sites in the 1058 CEUS) in either outcrop or excavations, it is necessary to perform many of the investigations 1059 described below to determine whether or not they are capable tectonic sources.
1060 The investigations for determining seismic sources should be carried out at three levels, 1061 with areas described by radii of 320 km (200 mi), 40 km (25 mi), and 8 km (5 mi) from the site.
1062 The level of detail increases closer to the site. The specific site, to a distance of at least 1 km 1063 (0.6 mi), should be investigated in more detail than the other levels.
1064 The regional investigations [within a radius of 320 km (200 mi) of the site] should be 1065 planned to identify seismic sources and describe the Quaternary tectonic regime. The data 1066 should be presented at a scale of 1:500,000 or smaller. The investigations are not expected to 34
1067 be extensive or in detail, but should include a comprehensive literature review supplemented by 1068 focused geological reconnaissances based on the results of the literature study (including 1069 topographic, geologic, aeromagnetic, and gravity maps and airphotos). Some detailed 1070 investigations at specific locations within the region may be necessary if potential capable 1071 tectonic sources or seismogenic sources that may be significant for determining the safe 1072 shutdown earthquake ground motion are identified.
1073 The large size of the area for the regional investigations is recommended because of the 1074 possibility that all significant seismic sources, or alternative configurations, may not have been 1075 enveloped by the LLNL/EPRI data base. Thus, it will increase the chances of (1) identifying 1076 evidence for unknown seismic sources that might extend close enough for earthquake ground 1077 motions generated by that source to affect the site and (2) confirming the PSHAs data base.
1078 Furthermore, because of the relatively aseismic nature of the CEUS, the area should be large 1079 enough to include as many historical and instrumentally recorded earthquakes for analysis as 1080 reasonably possible. The specified area of study is expected to be large enough to incorporate 1081 any previously identified sources that could be analogous to sources that may underlie or be 1082 relatively close to the site. In past licensing activities for sites in the CEUS, it has often been 1083 necessary, because of the absence of datable horizons overlying bedrock, to extend 1084 investigations out many tens or hundreds of kilometers from the site along a structure or to an 1085 outlying analogous structure in order to locate overlying datable strata or unconformities so that 1086 geochronological methods could be applied. This procedure has also been used to estimate the 1087 age of an undatable seismic source in the site vicinity by relating its time of last activity to that of 1088 a similar, previously evaluated structure, or a known tectonic episode, the evidence of which may 1089 be many tens or hundreds of miles away.
1090 In the WUS it is often necessary to extend the investigations to great distances (up to 1091 hundreds of kilometers) to characterize a major tectonic structure, such as the San Gregorio-1092 Hosgri Fault Zone and the Juan de Fuca Subduction Zone. On the other hand, in the WUS it is 1093 not usually necessary to extend the regional investigations that far in all directions. For example, 1094 for a site such as Diablo Canyon, which is near the San Gregorio-Hosgri Fault, it would not be 1095 necessary to extend the regional investigations farther east than the dominant San Andreas 1096 Fault, which is about 75 km (45 mi) from the site; nor west beyond the Santa Lucia Banks Fault, 1097 which is about 45 km (27 mi). Justification for using lesser distances should be provided.
1098 Reconnaissance-level investigations, which may need to be supplemented at specific 1099 locations by more detailed explorations such as geologic mapping, geophysical surveying, 1100 borings, and trenching, should be conducted to a distance of 40 km (25 mi) from the site; the data 1101 should be presented at a scale of 1:50,000 or smaller.
1102 Detailed investigations should be carried out within a radius of 8 km (5 mi) from the site, 1103 and the resulting data should be presented at a scale of 1:5,000 or smaller. The level of 1104 investigations should be in sufficient detail to delineate the geology and the potential for tectonic 1105 deformation at or near the ground surface. The investigations should use the methods described 1106 in subsections D.2.2 and D.2.3 that are appropriate for the tectonic regime to characterize 1107 seismic sources.
1108 The areas of investigations may be asymmetrical and may cover larger areas than those 1109 described above in regions of late Quaternary activity, regions with high rates of historical seismic 1110 activity (felt or instrumentally recorded data), or sites that are located near a capable tectonic 1111 source such as a fault zone.
35
1112 Data from investigations at the site (approximately 1 km2) should be presented at a scale 1113 of 1:500 or smaller. Important aspects of the site investigations are the excavation and logging of 1114 exploratory trenches and the mapping of the excavations for the plant structures, particularly 1115 plant structures that are characterized as Seismic Category I. In addition to geological, 1116 geophysical, and seismological investigations, detailed geotechnical engineering investigations, 1117 as described in Regulatory Guide 1.132 (Ref. D.5) and NUREG/CR-5738 (Ref. D.6), should be 1118 conducted at the site.
1119 The investigations needed to assess the suitability of the site with respect to effects of 1120 potential ground motions and surface deformation should include determination of (1) the 1121 lithologic, stratigraphic, geomorphic, hydrologic, geotechnical, and structural geologic 1122 characteristics of the site and the area surrounding the site, including its seismicity and geological 1123 history, (2) geological evidence of fault offset or other distortion such as folding at or near ground 1124 surface within the site area (8 km radius), and (3) whether or not any faults or other tectonic 1125 structures, any part of which are within a radius of 8 km (5 mi) from the site, are capable tectonic 1126 sources. This information will be used to evaluate tectonic structures underlying the site area, 1127 whether buried or expressed at the surface, with regard to their potential for generating 1128 earthquakes and for causing surface deformation at or near the site. This part of the evaluation 1129 should also consider the possible effects caused by human activities such as withdrawal of fluid 1130 from or addition of fluid to the subsurface, extraction of minerals, or the loading effects of dams 1131 and reservoirs.
1132 D.2.2 Reconnaissance Investigations, Literature Review, and Other Sources of 1133 Preliminary Information 1134 Regional literature and reconnaissance-level investigations should be planned based on 1135 reviews of available documents and the results of previous investigations. Possible sources of 1136 information, in addition to refereed papers published in technical journals, include universities, 1137 consulting firms, and government agencies. The following guidance is provided but it is not 1138 considered all-inclusive. Some investigations and evaluations will not be applicable to every site, 1139 and situations may occur that require investigations that are not included in the following 1140 discussion. In addition, it is anticipated that new technologies will be available in the future that 1141 will be applicable to these investigations.
1142 D.2.3 Detailed Site Vicinity and Site Area Investigations 1143 The following methods are suggested but they are not all-inclusive and investigations 1144 should not be limited to them. Some procedures will not be applicable to every site, and 1145 situations will occur that require investigations that are not included in the following discussion. It 1146 is anticipated that new technologies will be available in the future that will be applicable to these 1147 investigations.
1148 D.2.3.1 Surface Investigations 1149 Surface exploration to assess the geology and geologic structure of the site area is 1150 dependent on the site location and may be carried out with the use of any appropriate 1151 combination of the geological, geophysical, and seismological techniques summarized in the 1152 following paragraphs. However, not all of these methods must be carried out at a given site.
1153 D.2.3.1.1. Geological interpretations should be performed of aerial photographs and other 1154 remote-sensing as appropriate for the particular site conditions, to assist in identifying rock 36
1155 outcrops, faults and other tectonic features, fracture traces, geologic contacts, lineaments, soil 1156 conditions, and evidence of landslides or soil liquefaction.
1157 D.2.3.1.2. Mapping topographic, geomorphic, and hydrologic features should be 1158 performed at scales and with contour intervals suitable for analysis and descriptions of 1159 stratigraphy (particularly Quaternary), surface tectonic structures such as fault zones, and 1160 Quaternary geomorphic features. For coastal sites or sites located near lakes or rivers, this 1161 includes topography, geomorphology (particularly mapping marine and fluvial terraces),
1162 bathymetry, geophysics (such as seismic reflection), and hydrographic surveys to the extent 1163 needed to describe the site area features.
1164 D.2.3.1.3. Vertical crustal movements should be evaluated using: (1) geodetic land 1165 surveying and (2) geological analyses (such as analysis of regional dissection and degradation 1166 patterns), marine and lacustrine terraces and shorelines, fluvial adjustments (such as changes in 1167 stream longitudinal profiles or terraces), and other long-term changes (such as elevation changes 1168 across lava flows).
1169 D.2.3.1.4. Analysis should be performed to determine the tectonic significance of offset, 1170 displaced, or anomalous landforms such as displaced stream channels or changes in stream 1171 profiles or the upstream migration of knick-points; abrupt changes in fluvial deposits or terraces; 1172 changes in paleo-channels across a fault; or uplifted, down-dropped, or laterally displaced marine 1173 terraces.
1174 D.2.3.1.5. Analysis should be performed to determine the tectonic significance of 1175 Quaternary sedimentary deposits within or near tectonic zones such as fault zones, including (1) 1176 fault-related or fault-controlled deposits such as sag ponds, graben fill deposits, and colluvial 1177 wedges formed by the erosion of a fault paleo-scarp, and (2) non-fault-related, but offset, 1178 deposits such as alluvial fans, debris cones, fluvial terrace, and lake shoreline deposits.
1179 D.2.3.1.6. Identification and analysis should be performed of deformation features caused 1180 by vibratory ground motions, including seismically induced liquefaction features (sand boils, 1181 explosion craters, lateral spreads, settlement, soil flows), mud volcanoes, landslides, rockfalls, 1182 deformed lake deposits or soil horizons, shear zones, cracks or fissures.
1183 D.2.3.1.7. Analysis should be performed of fault displacements, including the 1184 interpretation of the morphology of topographic fault scarps associated with or produced by 1185 surface rupture. Fault scarp morphology is useful for estimating the age of last displacement (in 1186 conjunction with the appropriate geochronological methods described NUREG/CR-5562 (Ref.
1187 D.6), approximate magnitude of the associated earthquake, recurrence intervals, slip rate, and 1188 the nature of the causative fault at depth.
1189 D.2.3.2 Subsurface Investigations at the Site [within 1 km (0.5 mi)]
1190 Subsurface investigations at the site to identify and describe potential seismogenic 1191 sources or capable tectonic sources and to obtain required geotechnical information are 1192 described in Regulatory Guide 1.132 (Ref. D.5) and updated in NUREG/CR-5738 (Ref. D.7). The 1193 investigations include, but may not be confined to, the following:
1194 D.2.3.2.1. Geophysical investigations that have been useful in the past include magnetic 1195 and gravity surveys, seismic reflection and seismic refraction surveys, bore-hole geophysics, 1196 electrical surveys, and ground-penetrating radar surveys.
1197 37
1198 D.2.3.2.2. Core borings to map subsurface geology and obtain samples for testing such 1199 as determining the properties of the subsurface soils and rocks and geochronological analysis; 1200 D.2.3.2.3. Excavation and logging of trenches across geological features to obtain 1201 samples for the geochronological analysis of those features.
1202 D.2.3.2.4. At some sites, deep unconsolidated material/soil, bodies of water, or other 1203 material may obscure geologic evidence of past activity along a tectonic structure. In such cases, 1204 the analysis of evidence elsewhere along the structure can be used to evaluate its characteristics 1205 in the vicinity of the site.
1206 In the CEUS it may not be possible to reasonably demonstrate the age of youngest 1207 activity on a tectonic structure with adequate deterministic certainty. In such cases the 1208 uncertainty should be quantified; the NRC staff will accept evaluations using the methods 1209 described in NUREG/CR-5503 (Ref. D.3). A demonstrated tectonic association of such 1210 structures with geologic structural features or tectonic processes that are geologically old (at least 1211 pre-Quaternary) should be acceptable as an age indicator in the absence of conflicting evidence.
1212 D.2.3.3 Surface-Fault Rupture and Associated Deformation at the Site 1213 A site that has a potential for fault rupture at or near the ground surface and associated 1214 deformation should be avoided. Where it is determined that surface deformation need not be 1215 taken into account, sufficient data or detailed studies to reasonably support the determination 1216 should be presented. Requirements for setback distance from active faults for hazardous waste 1217 treatment, storage and disposal facilities can be found in U.S. Environmental Protection Agency 1218 regulations (40 CFR Part 264).
1219 The presence or absence of Quaternary faulting at the site needs to be evaluated to 1220 determine whether there is a potential hazard that is due to surface faulting. The potential for 1221 surface fault rupture should be characterized by evaluating (1) the location and geometry of faults 1222 relative to the site, (2) nature and amount of displacement (sense of slip, cumulative slip, slip per 1223 event, and nature and extent of related folding and/or secondary faulting), and (3) the likelihood 1224 of displacement during some future period of concern (recurrence interval, slip rate, and elapsed 1225 time since the most recent displacement). Acceptable methods and approaches for conducting 1226 these evaluations are described in NUREG/CR-5503 (Ref. D.3); acceptable geochronology dating 1227 methods are described in NUREG/CR-5562 (Ref. D.7).
1228 For assessing the potential for fault displacement, the details of the spatial pattern of the 1229 fault zone (e.g., the complexity of fault traces, branches, and en echelon patterns) may be 1230 important as they may define the particular locations where fault displacement may be expected 1231 in the future. The amount of slip that might be expected to occur can be evaluated directly based 1232 on paleoseismic investigations or it can be estimated indirectly based on the magnitude of the 1233 earthquake that the fault can generate.
1234 Both non-tectonic and tectonic deformation can pose a substantial hazard to an ISFSI or 1235 MRS, but there are likely to be differences in the approaches used to resolve the issues raised by 1236 the two types of phenomena. Therefore, non-tectonic deformation should be distinguished from 1237 tectonic deformation at a site. In past nuclear power plant licensing activities, surface 1238 displacements caused by phenomena other than tectonic phenomena have been confused with 1239 tectonically induced faulting. Such structures, such as found in karst terrain; and growth faulting, 1240 occurring in the Gulf Coastal Plain or in other deep soil regions, cause extensive subsurface fluid 1241 withdrawal.
38
1242 Glacially induced faults generally do not represent a deep-seated seismic or fault 1243 displacement hazard because the conditions that created them are no longer present. However, 1244 residual stresses from Pleistocene glaciation may still be present in glaciated regions, although 1245 they are of less concern than active tectonically induced stresses. These features should be 1246 investigated with respect to their relationship to current in situ stresses.
1247 The nature of faults related to collapse features can usually be defined through 1248 geotechnical investigations and can either be avoided or, if feasible, adequate engineering fixes 1249 can be provided.
1250 Large, naturally occurring growth faults as found in the coastal plain of Texas and 1251 Louisiana can pose a surface displacement hazard, even though offset most likely occurs at a 1252 much less rapid rate than that of tectonic faults. They are not regarded as having the capacity to 1253 generate damaging vibratory ground motion, can often be identified and avoided in siting, and 1254 their displacements can be monitored. Some growth faults and antithetic faults related to growth 1255 faults and fault zones should be applied in regions where growth faults are known to be present.
1256 Local human-induced growth faulting can be monitored and controlled or avoided.
1257 If questionable features cannot be demonstrated to be of non-tectonic origin, they should 1258 be treated as tectonic deformation.
1259 D.2.4 Site Geotechnical Investigations and Evaluations 1260 D.2.4.1 Geotechnical Investigations 1261 The geotechnical investigations should include, but not necessarily be limited to, (1) 1262 defining site soil and near-surface geologic strata properties as may be required for hazard 1263 evaluations, engineering analyses, and seismic design, (2) evaluating the effects of local soil and 1264 site geologic strata on ground motion at the ground surface, (3) evaluating dynamic properties of 1265 the near-surface soils and geologic strata, (4) conducting soil-structure interaction analyses, and 1266 (5) assessing the potential for soil failure or deformation induced by ground shaking (liquefaction, 1267 differential compaction, land sliding).
1268 The extent of investigation to determine the geotechnical characteristics of a site depends 1269 on the site geology and subsurface conditions. By working with experienced geotechnical 1270 engineers and geologists, an appropriate scope of investigations can be developed for a 1271 particular facility following the guidance contained in Regulatory Guide 1.132 (Ref. D.5) updated 1272 with NUREG/CR-5738 (Ref. D.6). The extent of subsurface investigations is dictated by the 1273 foundation requirements and by the complexity of the anticipated subsurface conditions. The 1274 locations and spacing of borings, soundings, and exploratory excavations should be chosen to 1275 adequately define subsurface conditions. Subsurface explorations should be chosen to 1276 adequately define subsurface conditions; exploration sampling points should be located to permit 1277 the construction of geological cross sections and soil profiles through foundations of safety-1278 related structures and other important locations at the site.
1279 Sufficient geophysical and geotechnical data should be obtained to allow for reasonable 1280 assessments of representative soil profile and soil parameters and to reasonably quantify 1281 variability. The guidance found in Regulatory Guide 1.132 (Ref. D.5) and NUREG/CR-5738 (Ref.
1282 D.6) is acceptable. In general, this guidance should be adapted to the requirements of the site to 1283 establish the scope of geotechnical investigations for the site as well as the appropriate methods 1284 that will be used.
39
1285 For ISFSIs co-located with existing nuclear plants, site investigations should be conducted 1286 if the existing site information is not available or insufficient. Soil/rock profiles (cross-sections) at 1287 the locations of the facilities should be provided based on the results of site investigations. The 1288 properties required are intimately linked to the designs and evaluations to be conducted. For 1289 example, for analyses of soil response effects, assessment of strain dependent-soil-dynamic 1290 modulus and damping characteristics are required. An appropriate site investigation program 1291 should be developed in consultation with the geotechnical engineering representative of the 1292 project team.
1293 Subsurface conditions should be investigated by means of borings, soundings, well logs, 1294 exploratory excavations, sampling, geophysical methods (e.g., cross-hole, down-hole, and 1295 geophysical logging) that adequately assess soil and ground water conditions and other methods 1296 described in NUREG/CR-5738 (Ref. D.6). Appropriate investigations should be made to 1297 determine the contribution of the subsurface soils and rocks to the loads imposed on the 1298 structures.
1299 A laboratory testing program should be carried out to identify and classify the subsurface 1300 soils and rocks and to determine their physical and engineering properties. Laboratory tests for 1301 both static and dynamic properties (e.g., shear modulus, damping, liquefaction resistance, etc.)
1302 are generally required. The dynamic property tests should include, as appropriate, cyclic triaxial 1303 tests, cyclic simple shear tests, cyclic torsional shear tests, and resonant column tests. Both 1304 static and dynamic tests should be conducted as recommended in American Society for Testing 1305 and Materials (ASTM) standards or test procedures acceptable to the staff. The ASTM 1306 specification numbers for static and dynamic laboratory tests can be found in the annual books of 1307 ASTM Standards, Volume 04.08. Examples of soil dynamic property and strength tests are 1308 shown in Table D.1. Sufficient laboratory test data should be obtained to allow for reasonable 1309 assessments of mean values of soil properties and their potential variability.
1310 For coarse geological materials such as coarse gravels and sand-gravel mixtures, special 1311 testing equipment and testing facility should be used. Larger sample size is required for 1312 laboratory tests on this type of materials (e.g., samples with 12-inch diameter were used in the 1313 Rockfalls Testing Facility). It is generally difficult to obtain in situ undisturbed samples of 1314 unconsolidated gravelly soils for laboratory tests. If it is not feasible to collect test samples and, 1315 thus, no laboratory test results are available, the dynamic properties should be estimated from 1316 the published data of similar gravelly soils.
1317 Table D.1 Examples of Soil Dynamic Property and Strength Tests 1318 D 3999-91 Standard Test Method for the Determination 1319 (Ref. D.8) of the Modulus and Damping Properties of Soils Using the Cyclic Triaxial Apparatus 1320 D 4015-92 Standard Test Methods for Modulus and 1321 (Ref. D.9) Damping of Soils by the Resonant-Column Method 1322 D 5311-92 Standard Test Method for Load-Controlled 1323 (Ref. D10) Cyclic Triaxial Strength of Soil 1324 D.2.4.2 Seismic Wave Transmission Characteristics of the Site 1325 To be acceptable, the seismic wave transmission characteristics (spectral amplification or 1326 deamplification) of the materials overlying bedrock at the site are described as a function of the 40
1327 significant structural frequencies. The following material properties should be determined for 1328 each stratum under the site: (1) thickness, seismic compressional and shear wave velocities, (2) 1329 bulk densities, (3) soil index properties and classification, (4) shear modulus and damping 1330 variations with strain level, and (5) the water table elevation and its variation throughout the site.
1331 Where vertically propagating shear waves may produce the maximum ground motion, a 1332 one-dimensional equivalent-linear analysis or nonlinear analysis may be appropriate. Where 1333 horizontally propagating shear waves, compressional waves, or surface waves may produce the 1334 maximum ground motion, other methods of analysis may be more appropriate. However, since 1335 some of the variables are not well defined and investigative techniques are still in the 1336 developmental stage, no specific generally agreed-upon procedures can be recommended at this 1337 time. Hence, the staff must use discretion in reviewing any method of analysis. To ensure 1338 appropriateness, site response characteristics determined from analytical procedures should be 1339 compared with historical and instrumental earthquake data, when such data are available.
1340 D.2.4.3 Site Response Analysis for Soil Sites 1341 As part of quantification of earthquake ground motions at an ISFSI or MRS site, an 1342 analysis of soil response effects on ground motions should be performed. A specific analysis is 1343 not required at a hard rock site. Site response analyses (often referred to as site amplification 1344 analyses) are relatively more important when the site surficial soil layer is a soft clay and/or when 1345 there is a high stiffness contrast (wave velocity contrast) between a shallow soil layer and 1346 underlying bedrock. Such conditions have shown strong local soil effects on ground motion. Site 1347 response analyses are always important for sites that have predominant frequencies within the 1348 range of interest for the DE ground motions. Thus, the stiffness of the soil and bedrock as well 1349 as the depth of soil deposit should be carefully evaluated.
1350 In performing a site response analysis, the ground motions (usually acceleration time 1351 histories) defined at bedrock or outcrop are propagated through an analytical model of the site 1352 soils to determine the influence of the soils on the ground motions. The required soil parameters 1353 for the site response analysis include the depth, soil type, density, shear modulus and damping, 1354 and their variations with strain levels for each of the soil layers. Internal friction angle, cohesive 1355 strength, and over-consolidation ratio for clay are also needed for non-linear analyses. The strain 1356 dependent shear modulus and damping curves should be developed based on site-specific 1357 testing results and supplemented as appropriate by published data for similar soils. The effects 1358 of confining pressures (that reflect the depths of the soil) on these strain-dependent soil dynamic 1359 characteristics should be assessed and considered in site response analysis. The variability in 1360 these properties should be accounted in the site response analysis. The results of the site 1361 response analysis should show the input motion (rock response spectra), output motion (surface 1362 response spectra), and spectra amplification function (site ground motion transfer function).
1363 D.2.4.4 Ground Motion Evaluations 1364 D.2.4.4.1. Liquefaction is a soil behavior phenomenon in which cohesionless soils (sand, 1365 silt, or gravel) under saturated conditions lose a substantial part or all of their strength because of 1366 high pore water pressures generated in the soils by strong ground motions induced by 1367 earthquakes. Potential effects of liquefaction include reduction in foundation bearing capacity, 1368 settlements, land sliding and lateral movements, flotation of lightweight structures (such as tanks) 1369 embedded in the liquefied soil, and increased lateral pressures on walls retaining liquefied soil.
1370 Guidance in Draft Regulatory Guide DG-1105, Procedures and Criteria for Assessing Seismic 1371 Soil Liquefaction at Nuclear Power Plant Sites (Ref. D.11), is being developed to be used for 1372 evaluating the site for liquefaction potential.
41
1373 Investigations of liquefaction potential typically involve both geological and geotechnical 1374 engineering assessments. The parameters controlling liquefaction phenomena are (1) the 1375 lithology of the soil at the site, (2) the ground water conditions, (3) the behavior of the soil under 1376 dynamic loadings, and (4) the potential severity of the vibratory ground motion. The following 1377 site-specific data should be acquired and used along with state-of-the-art evaluation procedures 1378 (e.g., Ref. D.12, Ref. D.13).
1379
- Soil grain size distribution, density, static and dynamic strength, stress history, and 1380 geologic age of the sediments; 1381
- Ground water conditions; 1382
- Penetration resistance of the soil, e.g., Standard Penetration Test (SPT), Cone 1383 Penetration Test (CPT);
1384
- Shear wave velocity of the soil velocity of the soil; 1385
- Evidence of past liquefaction; and 1386
- Ground motion characteristics.
1387 A soil behavior phenomenon similar to liquefaction is strength reduction in sensitive clays.
1388 Although this behavior phenomenon is relatively rare in comparison to liquefaction, it should not 1389 be overlooked as a potential cause for land sliding and lateral movements. Therefore, the 1390 existence of sensitive clays at the site should be identified.
1391 D.2.4.4.2. Ground settlement during and after an earthquake that is due to dynamic loads, 1392 change of ground water conditions, soil expansion, soil collapse, erosion, and other causes must 1393 be considered. Ground settlement that is due to the ground shaking induced by an earthquake 1394 can be caused by two factors: (1) compaction of dry sands by ground shaking and (2) 1395 settlement caused by dissipation of dynamically induced pore water in saturated sands.
1396 Differential settlement would cause more damage to facilities than would uniform settlement.
1397 Differential compaction of cohesionless soils and resulting differential ground settlement can 1398 accompany liquefaction or may occur in the absence of liquefaction. The same types of geologic 1399 information and soil data used in liquefaction potential assessments, such as the SPT value, can 1400 also be used in assessing the potential for differential compaction. Ground subsidence has been 1401 observed at the surface above relatively shallow cavities formed by mining activities (particularly 1402 coal mines) and where large quantities of salt, oil, gas, or ground water have been extracted (Ref.
1403 D.14). Where these conditions exist near a site, consideration and investigation must be given to 1404 the possibility that surface subsidence will occur.
1405 D.2.4.4.3. The stability of natural and man-made slopes must be evaluated when their 1406 failures would affect the safety and operation of an ISFSI or MRS. In addition to land sliding 1407 facilitated by liquefaction-induced strength reduction, instability and deformation of hillside and 1408 embankment slopes can occur from the ground shaking inertia forces causing a temporary 1409 exceedance of the strength of soil or rock. The slip surfaces of previous landslides, weak planes 1410 or seams of subsurface materials, mapping and dating paleo-slope failure events, loss of shear 1411 strength of the materials caused by the natural phenomena hazards such as liquefaction or 1412 reduction of strength due to wetting, hydrological conditions including pore pressure and 1413 seepage, and loading conditions imposed by the natural phenomena events must all be 1414 considered in determining the potential for instability and deformations. Various possible modes 42
1415 of failure should be considered. Both static and dynamic analyses must be performed for the 1416 stability of the slopes.
1417 The following information, at a minimum, is to be collected for the evaluation of slope 1418 instability:
1419
- Slope cross sections covering areas that would be affected the slope stability; 1420
- Soil and rock profiles within the slope cross sections; 1421
- Static and dynamic soil and rock properties, including densities, strengths, and 1422 deformability; 1423
- Hydrological conditions and their variations; and 1424
- Rock fall events.
1425 D.2.5 Geochronology 1426 An important part of the geologic investigations to identify and define potential seismic 1427 sources is the geochronology of geologic materials. An acceptable classification of dating 1428 methods is based on the rationale described in Reference D.15. The following techniques, which 1429 are presented according to that classification, are useful in dating Quaternary deposits.
1430 D.2.5.1 Sidereal Dating Methods 1431
- Dendrochronology 1432
- Varve chronology 1433 1434
- Schlerochronology 1435 1436 D.2.5.2 Isotopic Dating Methods 1437
- Radiocarbon 1438
- Cosmogenic nuclides - 36Cl, 10Be, 21Pb, and 26Al 1439
- Uranium series - 234U-230Th and 235U- 231Pa 210 1441
- Lead 1442
- Uranium-lead, thorium-lead 1443 D.2.5.3 Radiogenic Dating Methods 1444
- Fission track 1445
- Luminescence 43
1446 1447
- Electron spin resonance 1448 D.2.5.4 Chemical and Biological Dating Methods 1449
- Amino acid racemization 1450
- Obsidian and tephra hydration 1451
- Lichenometry 1452 D.2.5.6 Geomorphic Dating Methods 1453
- Soil profile development 1454
- Rock and mineral weathering 1455
- Scarp morphology 1456 D.2.5.7 Correlation Dating Methods 1457
- Paleomagnetism (secular variation and reversal stratigraphy) 1458
- Tephrochronology 1459
- Paleontology (marine and terrestrial) 1460
- Global climatic correlations - Quaternary deposits and landforms, marine stable isotope 1461 records, etc.
1462 In the CEUS, it may not be possible to reasonably demonstrate the age of last activity of a 1463 tectonic structure. In such cases the NRC staff will accept association of such structures with 1464 geologic structural features or tectonic processes that are geologically old (at least pre-1465 Quaternary) as an age indicator in the absence of conflicting evidence.
1466 These investigative procedures should also be applied, where possible, to characterize 1467 offshore structures (faults or fault zones, and folds, uplift, or subsidence related to faulting at 1468 depth) for coastal sites or those sites located adjacent to landlocked bodies of water.
1469 Investigations of offshore structures will rely heavily on seismicity, geophysics, and bathymetry 1470 rather than conventional geologic mapping methods that normally can be used effectively 1471 onshore. However, it is often useful to investigate similar features onshore to learn more about 1472 the significant offshore features.
44
1473 REFERENCES 1474 D.1 Electric Power Research Institute, "Seismic Hazard Methodology for the Central and 1475 Eastern United States," EPRI NP-4726, All Volumes, 1988 through 1991.
1476 D.2 Senior Seismic Hazard Analysis Committee (SSHAC), "Recommendations for 1477 Probabilistic Seismic Hazard Analysis: Guidance on Uncertainty and Use of Experts,"
1478 NUREG/CR-6372, USNRC, 1997.1 1479 D.3 K.L. Hanson et al., Techniques for Identifying Faults and Determining Their Origins, 1480 NUREG/CR-5503, USNRC,11999.
1481 D.4 International Atomic Energy Agency, "Earthquakes and Associated Topics in Relation to 1482 Nuclear Power Plant Siting," Safety Series No. 50-SG-S1, Revision 1, 1991.
1483 D.5 USNRC, Site Investigations for Foundation of Nuclear Power Plants, Regulatory Guide 1484 1.132, March 1979.2 (Proposed Revision 2, DG-1101, was issued for public comment in 1485 February 2001.)
1486 D.6 N. Torres et al.,Field Investigations for Foundations of Nuclear Power Facilities, 1487 NUREG/CR-5738, USNRC, 1999.1 1488 D.7 J.M. Sowers et al., Dating and Earthquakes: Review of Quaternary Geochronology and 1489 Its Application to Paleoseismology, NUREG/CR-5562, USNRC, 1998..1 1490 D.8 American Society of Testing and Materials, Standard Test Method for the Determination 1491 of the Modulus and Damping Properties of Soils Using the Cyclic Triaxial Apparatus, D 1492 3999, 1991.
1493 D.9 American Society of Testing and Materials, Standard Test Methods for Modulus and 1494 Damping of Soils by the Resonant-Column Method, D 4015, 2000.
1495 D.10 American Society of Testing and Materials, Standard Test Method for Load-Controlled 1496 Cyclic Triaxial Strength of Soil, D 5311, 1996.
1497 D.11 USNRC, Procedures and Criteria for Assessing Seismic Soil Liquefaction at Nuclear 1498 Power Plant Sites, Draft Regulatory Guide DG-1105, issued for public comment March 1499 2001.
1500 1
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 Public Document Room at 11555 Rockville Pike, Rockville, MD; the PDRs 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 on an 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),
Rockville, MD; the PDRs 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>.
45
1501 D.12 H.B. Seed and I.M. Idriss, Ground Motions and Soil Liquefaction during Earthquakes, 1502 Earthquake Engineering Research Institute, Oakland, California, Monograph Series, 1503 1982.
1504 D.13 H.B. Seed et al., Influence of SPT Procedures in Soil Liquefaction Resistance 1505 Evaluation, Journal of the Geotechnical Engineering Division, ASCE, 111, GT12, 1225-1506 1273, 1985.
1507 D.14 A.W. Hatheway and C.R. McClure, Geology in the Siting of Nuclear Power Plants, 1508 Reviews in Engineering Geology, Geological Society of America, Volume IV, 1979.
1509 D.15 S. M. Colman, K. L. Pierce, and P.W. Birkland, Suggested Terminology for Quaternary 1510 Dating Methods, Quaternary Research, Volume 288, pp. 314-319, 1987.
46
1511 APPENDIX E 1512 PROCEDURE FOR THE EVALUATION OF NEW GEOSCIENCES INFORMATION OBTAINED 1513 FROM THE SITE-SPECIFIC INVESTIGATIONS 1514 E.1 INTRODUCTION 1515 This appendix provides methods acceptable to the NRC staff for assessing the impact of 1516 new information obtained during site-specific investigations on the data base used for the 1517 probabilistic seismic hazard analyses (PSHA).
1518 Regulatory Position 4 in this guide describes acceptable PSHAs that were developed by 1519 the Lawrence Livermore National Laboratory (LLNL) and the Electric Power Research Institute 1520 (EPRI) to characterize the seismic hazard for nuclear power plants and to develop the Safe 1521 Shutdown Earthquake (SSE). The procedure to determine the design earthquake ground motion 1522 (DE) outlined in this guide relies primarily on either the LLNL or EPRI PSHA results for the 1523 Central and Eastern United States (CEUS).
1524 It is necessary to evaluate the geological, seismological, and geophysical data obtained 1525 from the site-specific investigations to demonstrate that these data are consistent with the PSHA 1526 data bases of these two methodologies. If new information identified by the site-specific 1527 investigations would result in a significant increase in the hazard estimate for a site, and this new 1528 information is validated by a strong technical basis, the PSHA may have to be modified to 1529 incorporate the new technical information. Using sensitivity studies, it may also be possible to 1530 justify a lower hazard estimate with an exceptionally strong technical basis. However, it is 1531 expected that large uncertainties in estimating seismic hazard in the CEUS will continue to exist 1532 in the future, and substantial delays in the licensing process will result from trying to justify a 1533 lower value with respect to a specific site.
1534 In general, major recomputations of the LLNL and EPRI data base are planned 1535 periodically (approximately every 10 years), or when there is an important new finding or 1536 occurrence. The overall revision of the data base will also require a reexamination of the 1537 reference probability discussed in Appendix B.
1538 E.2 POSSIBLE SOURCES OF NEW INFORMATION THAT COULD AFFECT THE SSE 1539 Types of new data that could affect the PSHA results can be put in three general 1540 categories: seismic sources, earthquake recurrence models or rates of deformation, and ground 1541 motion models.
1542 E.2.1 Seismic Sources 1543 There are several possible sources of new information from the site-specific investigations 1544 that could affect the seismic hazard. Continued recording of small earthquakes, including 1545 microearthquakes, may indicate the presence of a localized seismic source. Paleoseismic 1546 evidence, such as paleoliquefaction features or displaced Quaternary strata, may indicate the 1547 presence of a previously unknown tectonic structure or a larger amount of activity on a known 1548 structure than was previously considered. Geophysical studies (aeromagnetic, gravity, and 1549 seismic reflection/refraction) may identify crustal structures that suggest the presence of 1550 previously unknown seismic sources. In situ stress measurements and the mapping of tectonic 1551 structures in the future may indicate potential seismic sources.
47
1552 Detailed local site investigations often reveal faults or other tectonic structures that were 1553 unknown, or reveal additional characteristics of known tectonic structures. Generally, based on 1554 past licensing experience in the CEUS, the discovery of such features will not require a 1555 modification of the seismic sources provided in the LLNL and EPRI studies. However, initial 1556 evidence regarding a newly discovered tectonic structure in the CEUS is often equivocal with 1557 respect to activity, and additional detailed investigations are required. By means of these detailed 1558 investigations, and based on past licensing activities, previously unidentified tectonic structures 1559 can usually be shown to be inactive or otherwise insignificant to the seismic design basis of the 1560 facility, and a modification of the seismic sources provided by the LLNL and EPRI studies will not 1561 be required. On the other hand, if the newly discovered features are relatively young, possibly 1562 associated with earthquakes that were large and could impact the hazard for the proposed 1563 facility, a modification may be required.
1564 Of particular concern is the possible existence of previously unknown, potentially active 1565 tectonic structures that could have moderately sized, but potentially damaging, near-field 1566 earthquakes or could cause surface displacement. Also of concern is the presence of structures 1567 that could generate larger earthquakes within the region than previously estimated.
1568 Investigations to determine whether there is a possibility for permanent ground 1569 displacement are especially important in view of the provision to allow for a combined licensing 1570 procedure under 10 CFR Part 52 as an alternative to the two-step procedure of the past 1571 (Construction Permit and Operating License). In the past at numerous nuclear power plant sites, 1572 potentially significant faults were identified when excavations were made during the construction 1573 phase prior to the issuance of an operating license, and extensive additional investigations of 1574 those faults had to be carried out to properly characterize them.
1575 E.2.2 Earthquake Recurrence Models 1576 There are three elements of the source zones recurrence models that could be affected 1577 by new site-specific data: (1) the rate of occurrence of earthquakes, (2) their maximum 1578 magnitude, and (3) the form of the recurrence model (e.g.,a change from truncated exponential 1579 to a characteristic earthquake model). Among the new site-specific information that is most likely 1580 to have a significant impact on the hazard is the discovery of paleoseismic evidence such as 1581 extensive soil liquefaction features, which would indicate with reasonable confidence that much 1582 larger estimates of the maximum earthquake than those predicted by the previous studies would 1583 ensue. The paleoseismic data could also be significant even if the maximum magnitudes of the 1584 previous studies are consistent with the paleo-earthquakes if there are sufficient data to develop 1585 return period estimates significantly shorter than those previously used in the probabilistic 1586 analysis. The paleoseismic data could also indicate that a characteristic earthquake model would 1587 be more applicable than a truncated exponential model.
1588 In the future, expanded earthquake catalogs will become available that will differ from the 1589 catalogs used by the previous studies. Generally, these new catalogues have been shown to 1590 have only minor impacts on estimates of the parameters of the recurrence models. Cases that 1591 might be significant include the discovery of records that indicate earthquakes in a region that 1592 had no seismic activity in the previous catalogs, the occurrence of an earthquake larger than the 1593 largest historic earthquakes, re-evaluating the largest historic earthquake to a significantly larger 1594 magnitude, or the occurrence of one or more moderate to large earthquakes (magnitude 5.0 or 1595 greater) in the CEUS.
48
1596 Geodetic measurements, particularly satellite-based networks, may provide data and 1597 interpretations of rates and styles of deformation in the CEUS that can have implications for 1598 earthquake recurrence. New hypotheses regarding present-day tectonics based on new data or 1599 reinterpretation of old data may be developed that were not considered or given high weight in 1600 the EPRI or LLNL PSHA. Any of these cases could have an impact on the estimated maximum 1601 earthquake if the result is larger than the values provided by LLNL and EPRI.
1602 E.2.3 Ground Motion Attenuation Models 1603 Alternative ground motion attenuation models may be used to determine the site-specific 1604 spectral shape as discussed in Regulatory Position 4 and Appendix F of this regulatory guide. If 1605 the ground motion models used are a major departure from the original models used in the 1606 hazard analysis and are likely to have impacts on the hazard results of many sites, a re-1607 evaluation of the reference probability may be needed. Otherwise, a periodic (e.g., every 10 1608 years) reexamination of the PSHA and the associated data base is considered appropriate to 1609 incorporate new understanding regarding ground motion attenuation models.
1610 E.3 PROCEDURE AND EVALUATION 1611 The EPRI and LLNL studies provide a wide range of interpretations of the possible 1612 seismic sources for most regions of the CEUS, as well as a wide range of interpretations for all 1613 the key parameters of the seismic hazard model. The first step in comparing the new information 1614 with those interpretations is determining whether the new information is consistent with the 1615 following LLNL and EPRI parameters: (1) the range of seismogenic sources as interpreted by the 1616 seismicity experts or teams involved in the study, (2) the range of seismicity rates for the region 1617 around the site as interpreted by the seismicity experts or teams involved in the studies, and (3) 1618 the range of maximum magnitudes determined by the seismicity experts or teams. The new 1619 information is considered not significant and no further evaluation is needed if it is consistent with 1620 the assumptions used in the PSHA, no additional alternative seismic sources or seismic 1621 parameters are needed, or it supports maintaining or decreasing the site mean seismic hazard.
1622 An example is a new ISFSI co-located near an existing nuclear power plant site that was 1623 recently investigated by state-of-the-art geosciences techniques and evaluated by current hazard 1624 methodologies. Detailed geological, seismological, and geophysical site-specific investigations 1625 would be required to update existing information regarding the new site, but it is very unlikely that 1626 significant new information would be found that would invalidate the previous PSHA.
1627 On the other hand, after evaluating the results of the site-specific investigations, if there is 1628 still uncertainty about whether the new information will affect the estimated hazard, it will be 1629 necessary to evaluate the potential impact of the new data and interpretations on the mean of the 1630 range of the input parameters. Such new information may indicate the addition of a new seismic 1631 source, a change in the rate of activity, a change in the spatial patterns of seismicity, an increase 1632 in the rate of deformation, or the observation of a relationship between tectonic structures and 1633 current seismicity. The new findings should be assessed by comparing them with the specific 1634 input of each expert or team that participated in the PSHA. Regarding a new source, for 1635 example, the specific seismic source characterizations for each expert or team (such as tectonic 1636 feature being modeled, source geometry, probability of being active, maximum earthquake 1637 magnitude, or occurrence rates) should be assessed in the context of the significant new data 1638 and interpretations.
49
1639 It is expected that the new information will be within the range of interpretations in the 1640 existing data base, and the data will not result in an increase in overall seismicity rate or increase 1641 in the range of maximum earthquakes to be used in the probabilistic analysis. It can then be 1642 concluded that the current LLNL or EPRI results apply. It is possible that the new data may 1643 necessitate a change in some parameter. In this case, appropriate sensitivity analyses should be 1644 performed to determine whether the new site-specific data could affect the ground motion 1645 estimates at the reference probability level.
1646 An example is a consideration of the seismic hazard near the Wabash River Valley (Ref.
1647 E.1). Geological evidence found recently within the Wabash River Valley and several of its 1648 tributaries indicated that an earthquake much larger than any historic event had occurred several 1649 thousand years ago in the vicinity of Vincennes, Indiana. A review of the inputs by the experts 1650 and teams involved in the LLNL and EPRI PSHAs revealed that many of them had made 1651 allowance for this possibility in their tectonic models by assuming the extension of the New 1652 Madrid Seismic Zone northward into the Wabash Valley. Several experts had given strong 1653 weight to the relatively high seismicity of the area, including the number of magnitude five historic 1654 earthquakes that have occurred, and thus had assumed the larger event. This analysis of the 1655 source characterizations of the experts and teams resulted in the conclusion by the analysts that 1656 a new PSHA would not be necessary for this region because an event similar to the prehistoric 1657 earthquake had been considered in the existing PSHAs.
1658 A third step would be required if the site-specific geosciences investigations revealed 1659 significant new information that would substantially affect the estimated hazard. Modification of 1660 the seismic sources would more than likely be required if the results of the detailed local and 1661 regional site investigations indicate that a previously unknown seismic source is identified in the 1662 vicinity of the site. A hypothetical example would be the recognition of geological evidence of 1663 recent activity on a fault near a site in the SCR similar to the evidence found on the Meers Fault 1664 in Oklahoma (Ref. E.2). If such a source is identified, the same approach used in the active 1665 tectonic regions of the WUS should be used to assess the largest earthquake expected and the 1666 rate of activity. If the resulting maximum earthquake and the rate of activity are higher than those 1667 provided by the LLNL or EPRI experts or teams regarding seismic sources within the region in 1668 which this newly discovered tectonic source is located, it may be necessary to modify the existing 1669 interpretations by introducing the new seismic source and developing modified seismic hazard 1670 estimates for the site. The same would be true if the current ground motion models are a major 1671 departure from the original models. These occurrences would likely require performing a new 1672 PSHA using the updated data base, and may require determining the appropriate reference 1673 probability.
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1675 REFERENCES 1676 E.1 Memorandum from A. Murphy, NRC, to L. Shao, NRC,
Subject:
Summary of a Public 1677 Meeting on the Revision of Appendix A, "Seismic and Geologic Siting Criteria for Nuclear 1678 Power Plants," to 10 CFR Part 100; Enclosure (Viewgraphs): NUMARC, "Development 1679 and Demonstration of Industrys Integrated Seismic Siting Decision Process," February 1680 23, 1993.1 1681 E.2 A.R. Ramelli, D.B. Slemmons, and S.J. Brocoum, "The Meers Fault: Tectonic Activity in 1682 Southwestern Oklahoma," NUREG/CR-4852, USNRC, March 1987.2 1
Copies are available for inspection or copying for a fee from the NRC Public Document Room (PDR) at 11555 Rockville Pike, Rockville, MD; the PDRs 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 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 Public Document Room at 11555 Rockville Pike, Rockville, MD; the PDRs 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.
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1683 APPENDIX F 1684 PROCEDURE TO DETERMINE THE DESIGN EARTHQUAKE GROUND MOTION 1685 F.1 INTRODUCTION 1686 This appendix elaborates on Step 4 of Regulatory Position 4 of this guide, which 1687 describes an acceptable procedure to determine the design earthquake ground motion (DE). The 1688 DE is defined in terms of the horizontal and vertical free-field ground motion response spectra at 1689 the free ground surface. It is developed with consideration of local site effects and site seismic 1690 wave transmission effects. The DE response spectrum can be determined by scaling a site-1691 specific spectral shape determined for the controlling earthquakes or by scaling a standard 1692 broad-band spectral shape to envelope the ground motion levels for 1 Hz (Sa,1) and 10 Hz (Sa,10),
1693 as determined in Step C.2-2 of Appendix C to this guide. The standard response spectrum is 1694 generally specified at 5 percent critical damping.
1695 It is anticipated that a regulatory guide will be developed that provides guidance on 1696 assessing site-specific effects and determining smooth design response spectra, taking into 1697 account recent developments in ground motion modeling and site amplification studies (for 1698 example, Ref. F.1).
1699 F.2 DISCUSSION 1700 For engineering purposes, it is essential that the design ground motion response 1701 spectrum be a broad-band smooth response spectrum with adequate energy in the frequencies 1702 of interest. In the past, it was general practice to select a standard broad-band spectrum, such 1703 as the spectrum in Regulatory Guide 1.60 (Ref. F.2), and scale it by a peak ground motion 1704 parameter [usually peak ground acceleration (PGA)], which is derived based on the size of the 1705 controlling earthquake. Past practices to define the DE are still valid and, based on this 1706 consideration, the following three possible situations are depicted in Figures F.1 to F.3.
1707 Figure F.1 depicts a situation in which a site is to be used for a certified ISFSI or MRS 1708 design (if available) with an established DE. In this example, the certified design DE spectrum 1709 compares favorably with the site-specific response spectra determined in Step 2 or 3 of 1710 Regulatory Position 4.
1711 Figure F.2 depicts a situation in which a standard broad-band shape is selected and its 1712 amplitude is scaled so that the design DE envelopes the site-specific spectra.
1713 Figure F.3 depicts a situation in which a specific smooth shape for the design DE 1714 spectrum is developed to envelope the site-specific spectra. In this case, it is particularly 1715 important to be sure that the DE contains adequate energy in the frequency range of engineering 1716 interest and is sufficiently broad-band.
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1717 (Note: The above figures illustrate 1718 situations for a rock site. For other site 1719 conditions, the DE spectra are compared at free-field after performing site amplification studies 1720 as discussed in Step 3 of Regulatory Position 4.)
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1721 REFERENCES 1722 F.1 R.K. McGuire, W.J. Silva, and C.J. Constantino, Technical Basis for Revision of 1723 Regulatory Guidance on Design Ground Motions: Hazard- and Risk-Consistent 1724 Ground Motion Sp[ectra Guidelines, NUREG/CR-6728, 2001.1 1725 F.2 U.S. NRC, Design Response Spectra for Seismic Design of Nuclear Power Plants, 1726 Regulatory Guide 1.60, Revision 1, December 1973.2 1
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 Public Document Room at 11555 Rockville Pike, Rockville, MD; the PDRs 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 on an 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),
Rockville, MD; the PDRs 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>.
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1727 REGULATORY ANALYSIS 1728 A separate regulatory analysis was not prepared for this draft regulatory guide. The 1729 regulatory analysis Regulatory Analysis of Geological and Seismological Characteristics for 1730 and Design of Dry Cask Independent Spent Fuel Storage Installations (10 CFR Part 72), was 1731 prepared for the amendments, and it provides the regulatory basis for this guide and examines 1732 the costs and benefits of the rule as implemented by the guide. A copy of the regulatory 1733 analysis is available for inspection and copying for a fee at the NRC Public Document Room, 1734 as Attachment 3 to SECY-02-0043. The PDRs mailing address is USNRC PDR, Washington, 1735 DC 20555; telephone (301)415-4737 or 1-(800)397-4209; fax (301)415-3548; e-mail 1736 <PDR@NRC.GOV>.
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