NRC Staff Responses to Public Comments on 

Draft Regulatory Guide DG-1146 

“A Performance-Based Approach to Define the Site-Specific 

Earthquake Ground Motion” 
1 Introduction ........................................................................................................................................1

2 Comments on the Regulatory Process..............................................................................................2

3 General Topics....................................................................................................................................3

3.1 Overall Approach ........................................................................................................................3

3.2 Location of SSE Ground Motion.................................................................................................4

3.3 Code Required Check on Motions at Foundation Level .............................................................6

3.4 SSE versus Design Response Spectrum and Risk Consistent Spectrum...................................10

3.5 Other Comments........................................................................................................................11

4 Performance-Based Design Parameters.........................................................................................12

5 Site Investigation and Site Properties.............................................................................................14

5.1 Excavations and Construction ................................................................................................... 14

5.2 Definition of Rock.....................................................................................................................15

5.3 Development of Dynamic Soil Properties .................................................................................16

5.4 Other Comments........................................................................................................................17

6 Probabilistic Seismic Hazard Assessment (PSHA) Methods........................................................20

6.1 Choice of PSHA Techniques and Regulatory Stability.............................................................20

6.2 Seismic Source Characterization ...............................................................................................22

6.3 Attenuation Relationships..........................................................................................................25

6.4 Epsilon and Sigma Values in PSHA..........................................................................................26

6.5 Cumulative Absolute Velocity (CAV) Filtering........................................................................28

7 Site Response Analysis Methods and Use of Results.....................................................................29

7.1 Use of Site Response Transfer Functions..................................................................................29

7.2 Alternative Time History Based Site Response Techniques .....................................................31

7.3 Random Vibration Theory (RVT) .............................................................................................33

7.4 Controlling Earthquakes for Site Response Analyses ...............................................................34

7.5 Additional Comments................................................................................................................38

8 Range and Number of Frequencies Provided for Review ............................................................41

9 Earthquake Recordings (Time Histories) ......................................................................................44

10 Incoherency Transfer Function ..................................................................................................46

11 Soil-Structure Interaction (SSI)..................................................................................................48

12 Proposed Technical and Typographical Editing.......................................................................51

13 Comments on Specific Plant Applications.................................................................................54

14 Chronological Table of Public Comments.................................................................................56

 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 1 

1 Introduction

This document contains NRC staff responses to comments received during the public comment period for 

Draft Regulatory Guide DG-1146, which ended on December 15, 2006. During this period, the NRC 

received the following sets of comments (in chronological order): 

• Carl J. Constantino Letter dated December 2, 2006 (Internal Comments) 

• Nuclear Energy Institute (NEI) Letter dated December 7, 2006, sent by Adrian Heymer (ADAMS 

Accession No. ML063560072) 

• Bechtel Letter dated December 12, 2006, sent by Stephen D. Roth (ADAMS Accession No. 

ML063520109) 

• Jeffrey K Kimball Letter dated December 13 2006 (ADAMS Accession No. ML063520110) 

• Comments from the public during December 14, 2006 public meeting (ADAMS Accession No. 

ML063610506) 

• Comments on DG-1146 in Electric Power Research Institute (EPRI) Minutes of December 14, 

2006 public meeting (Available from EPRI) 

• NEI Letter Dated December 28, 2006, sent by Adrian Heymer. (ADAMS Accession Nos. 

ML070030382, Supersedes ML063620427 and ML063620430) 

Because a significant number of related comments were submitted by the various sources above, this 

document groups the comments by subject matter and often provides responses that apply to several 

comments. To assist the reader, all public comments are compiled in a table at the end of this document. 

This table lists the comments in chronological order, provides a brief description of the topic of the 

comments, and includes the page number in which the comment is addressed in this document. 

The comments were provided in a variety of formats. In some cases one comment addressed several 

different topics (generally through use of a list). Because this document groups and addresses the 

comments by topic, individual comments covering multiple topics were split into an appropriate number 

of sub-comments. Efforts were made to make each sub-comment as clear as the original. 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 2 

2 Comments on the Regulatory Process

NEI Specific Comment 10 (December 7, 2006) 

On page 8, paragraph 5, first sentence, the draft states, “Thus, the performance-based approach combines 

a conservative characterization of ground motion hazard, with equipment/structure performance (fragility 

characteristics) to establish risk-consistent SSEs, rather than only hazard-consistent ground shaking, as 

occurs using the hazard reference probability approach in Appendix B to Regulatory Guide 1.165 

(Ref.1).” This sentence provides the basis for having regulatory guide DG-1146 replace Regulatory 

Guide 1.165 as originally intended in the early meetings of the NEI Seismic Issues Task Force. However, 

existing applications using RG 1.165 should be allowed based on the date of the applications and the date 

of the final NRC approval of DG-1146. 

NRC Response: 

Although Regulatory Guide 1.208 is being developed for use in the nuclear power plant (NPP) 

application process, the NRC staff will treat Regulatory Guide 1.165, “Identification and 

Characterization of Seismic Sources and Determination of Safe Shutdown Earthquake Ground 

Motion,” issued March 1997, as an acceptable alternative to Regulatory Guide 1.208 in the future. 

Resolution: 

No changes are required as a result of this comment. 

NEI Specific Comment 22 (December 7, 2006) 

On page 22, section C.4, “conclusion,” first paragraph, sentence 3, the draft states, “Furthermore, the staff 

sees no adverse effects with retaining Regulatory Guide 1.165, an acceptable alternative to the new 

regulatory guide for satisfying the requirements of 10 CFR 100.23.” We concur with this statement as 

represented by our specific comment 10. 

NRC Response: 

The NRC staff and NEI representatives are in agreement on this topic. 

Resolution: 

No changes to DG-1146 are required. 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 3 

3 General Topics

3.1 Overall Approach 

NEI General Comment 7 (December 7, 2006) 

The appendices to the draft are more prescriptive than is appropriate for a Regulatory Guide. Appendix E 

is an example. This detail should be reserved for Standard Review plans. 

NRC Response: 

The NRC staff has carefully considered this comment and reviewed the document for consistency 

with other NRC guidance documents in this context. The staff has made changes to the 

appendices to bring this document more in line with the level of detail expected in a regulatory 

guide. 

Resolution: 

The staff has revised Appendices D and E. 

NEI Statement of Interpretation 4 (December 7, 2006) 

NEI has interpreted DG 1146 to allow the following: The use of the ASCE/SEI Standard 43-05 

Performance-Goal based approach for determining the SSE response spectrum - in Section 5.1, Page 16 

NRC Response: 

While not all elements of American Society of Civil Engineers/Structural Engineering Institute 

(ASCE/SEI) Standard 43-05, “Seismic Design Criteria for Structures, Systems, and Components 

in Nuclear Facilities,” are being incorporated into Regulatory Guide 1.208, the ASCE/SEI 

Standard 43-05 performance-based approach in chapters 1 and 2 of that document is being used 

for development of the site-specific ground motion response spectrum (GMRS). 

Resolution: No changes to DG-1146 are required. 

Bechtel Comment 27 (December 13, 2006) 

Page 19, Figure 3. 

a. This figure is not clear. Is the first box about developing a procedure or site specific ground 

motion? 

b. It appears that there should be a box between the first and second boxes that could read, 

“Develop spectra amplification factors or deconvolution studies,” or something similar. 

NRC Response: 

In light of the comment, it is clear the figure could have been improved. 

Resolution: 

As part of broader edits to Regulatory Guide 1.208 this figure has been removed. 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 4 

3.2 Location of SSE Ground Motion 

As a result of on-going discussions, it was decided that this regulatory guide will focus on the ground 

motion response spectrum (GMRS) which leads to the SSE; but will have minimal discussion of the final 

SSE. Full development of the SSE will be addressed in the Standard Review Plan SRP 3.7. In addressing 

the below comments, it is understood that the use of the term SSE relates to the GMRS. Because the 

GMRS leads to the SSE, the location of GMRS is also defined in the free field at free ground surface or at 

the hypothetical outcrop of the upper most competent soil layer. 

NEI Statement of Interpretation 2 (December 7, 2006)

NEI has interpreted DG 1146 to allow the following: Determination of the SSE response spectrum as a 

free-field spectrum at the ground surface or on the first competent material having shear wave velocity 

greater than 1000 fps for sites which have thin low shear wave velocity soil layers - in Section 5.3, Page 

18 

NRC Response: 

This is a reasonable interpretation. The regulations require that the SSE must be defined on a free 

ground surface. However, the NRC staff understands that if competent material is lacking at the 

original ground surface, it may be more appropriate to use an alternate location as long as ground 

motions are developed as free surface motions. Alternative locations for the site-specific ground 

motion response spectrum (GMRS) are discussed in Section 5.3 of Regulatory Guide 1.208. 

The choice of shear wave velocity measurements of 1000 fps as the definition of competent 

material comes from existing Design Certification Documentation (DCD). 

Resolution: 

For clarity, the wording in Section 5.3 has been edited. 

Bechtel Comment 1b (December 13, 2006) 

The single most important change between RG 1.165 and DG-1146 is the change from the reference 

probability approach to the performance-based approach. This change, principally by reference to ASCE 

43-05, is well defined and easy to follow. There are, however, a number of fundamental issues within 

NRC regulations and their CFR antecedents that neither RG 1.165 nor DG-1146 address. Principle among 

these is: 

b. Definition of a computationally useful horizon at which to define the SSE. 

NRC Response: 

The location of the SSE is narrowly defined by the Code of Federal Regulations and cannot be 

based on what is necessarily computationally simplest for design analyses. Some changes to 

Section 5.3 will be made for clarification. See the discussions (under NEI Statement of 

Interpretation 2) above and (under Bechtel Comment 12) below. 

Resolution: 

The staff has edited the wording in Section 5.3 to provide additional clarification. 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 5 

Bechtel Comment 5 (December 13, 2006) 

Although subsurface material properties may vary widely at undisturbed sites, it is inconceivable that a 

nuclear power plant would be founded on materials with inadequate competence to support the foundation 

mat. The definition of the SSE at the “free ground surface,” if by this is meant the undisturbed ground 

surface could, therefore, imply that the adequacy of earthquake design calculations would be related to 

completely irrelevant ground motions. Recognizing this, Section C.5.3 of the draft guide states that, ”For 

sites with one or more thin soil layers near the surface that will be excavated, the SSE is specified on an 

outcrop or a hypothetical outcrop of competent material (Vs ≥ 1000 fps) at a free surface.” 

a. It is recommended that the SSE be defined on an outcrop of competent material (Vs ≥ 1000 

fps) at any site (not only those with “thin soil layers... that will be excavated”) at the discretion of 

the applicant so long as the subsurface between this horizon and the Vs ≥ 9200 fps “hard rock” 

horizon is adequately characterized. 

b. It is recommended that the wording “at a free surface” after “outcrop” be deleted. It is 

redundant. 

NRC Response: 

The wording “at a free surface,” was intended to note that if a hypothetical outcrop of competent 

material is used, the SSE is calculated as if it is located at a free surface. The staff has adjusted 

the wording to clarify the requirement. The location of the SSE (and therefore the GMRS) is 

defined based on requirements of the Code of Federal Regulations (CFR) and must be consistent 

for all applicants. See discussion under Bechtel Comment 12, below. 

Resolution: 

See changes to Section 5.3 in the response to NEI Statement of Interpretation 2, below. 

Bechtel Comment 12 (December 13, 2006)

The new standard reactor designs have sizable embedment depth. Unless a shoring system is used, sites 

are likely to be subjected to a large excavation and backfill. In this context, the meaning of "free-field" 

should be carefully defined. On the other hand, poor surficial soil layers at some sites will require overexcavation and backfilling. Sampling and testing and site response analysis involving such poor soil 

layers is not productive for design and may amount to unstable solutions in site responses analysis. In 

this context also, the meaning of "free-field ground surface" should be clearly stated. 

NRC Response: 

The GMRS must be based only on site conditions and must be independent of various foundation 

depths, backfilling, and other design-based issues. In addition, the GMRS and the SSE must be 

defined such that there is only one SSE per NPP site. The Code of Federal Regulations defines 

the SSE as being located at the free-field free-ground surface. Working within this constraint, but 

recognizing that the SSE should not be determined based on soils layers that are not sufficiently 

competent to act as foundation material and must be removed; the concept of a “hypothetical 

outcrop” was developed. 

As a result of the above constraints, the GMRS (which leads to the SSE) is defined at either the 

free-field natural ground surface; or in cases in which the surficial soils are too soft to be used as 

foundation materials, the GMRS is defined at the upper most competent layer that will be 

exposed. This layer of competent material is called either an outcrop if it is the final excavation 

level, or a “hypothetical outcrop” if it is not. Backfill soils should not be included in the site 

response analyses leading to the GMRS. The term free-field is included to differentiate GMRS 

from in-structure motions. 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 6 

An acceptable definition of competent material is the definition provided in the design 

certification documentation (DCD), which currently uses a shear wave velocity (Vs) greater than 

1000 ft/s. Section 5.3 of Regulatory Guide 1.208 discusses the location of the GMRS. 

Resolution: 

The staff has edited the wording in Section 5.3 to provide additional clarification. 

Bechtel Comment 25 (December 13, 2006) 

Page 18, Section C.5.3, “Location of the Site Safe Shutdown Earthquake Ground Motion.” A definition 

of “thin soil layer” should be added. 

NRC Response: 

A thin soil layer was meant to imply one that will be completely removed during excavation. For 

clarity, NRC staff has edited the section. 

Resolution: 

The staff has edited the wording in Section 5.3 to provide additional clarification. 

3.3 Code Required Check on Motions at Foundation Level 

Public Comments at NRC Public Meeting Comment 1 (December 14, 2006) 

Industry representatives found wording on location of SSE in Section 5.3 acceptable, but would prefer to 

have 1146 end at the development of the site specific ground motion. The check of 0.1g at the foundation 

depth would instead be included as a check in the SRP, but not as a fundamental part of the SSE (or the 

site specific ground motion). They noted that they believe it is a design criterion, not a site criterion. 

NRC Response: 

See response below NEI Specific Comment 21. 

Bechtel Comment 26c (December 13, 2006) 

Page 18, Section C.5.4, “Determination of Safe Shutdown Earthquake.” It is recommended that the 

wording on the following issues in this section of the draft guide be revised for clarity. 

c. It may be best to apply the requirement of 0.10g motion as a separate deterministic type motion 

to check the design once the analysis is completed using the SSE motion without the 0.10g. In 

this case, limiting the amplification of motion in the free-field should be permitted. 

NRC Response: 

See response below NEI Specific Comment 21. 

NEI Specific Comment 21 (December 7, 2006) 

Page 18, in order to maintain the nature of the Uniform Hazard and Design Response Spectra for design 

application, it is suggested that the requirement of 0.10g motion at the foundation level to be separated 

from development of the design motion. This requirement can be stipulated as a separate seismic analysis 

to check the design. This would ensure the adequacy of the design and avoid development of multiple 

SSEs for a plant that may have structures with multiple embedments. 

NRC Response: 

The NRC staff agrees with the approach of treating the requirement at the foundation level as a 

separate check during the design phase. Treating this requirement at the foundation level as a 

design check both separates development of the GMRS from design considerations and maintains 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 7 

a uniform hazard for all spectral frequencies. The staff will retain Section 5.4 in the document as 

a summary, but will be edit it to reflect the change in approach. The foundation level check will 

be discussed in the Standard Review Plan. 

Resolution: 

The staff has edited Section 5.4 to address this change in approach. 

NEI Specific Comment 20 (December 7, 2006) 

On page 18, section C.5.4, “Determination of Safe Shutdown Earthquake,” first paragraph, “free field 

motion” at the foundation level should be an “outcrop motion.” 

NRC Response: 

See discussion under Bechtel comment 26a, below. 

Dr. Carl Constantino Comment 3 (December 2, 2006) 

Line 41 (page 2, paragraph 3, sentence 4) Is the 0.1g criterion defined as an outcrop or in-column PGA? 

NRC Response: 

See discussion under Bechtel comment 26a, below. 

Bechtel Comment 26a (December 13, 2006) 

Page 18, Section C.5.4, “Determination of Safe Shutdown Earthquake.” It is recommended that the 

wording on the following issues in this section of the draft guide be revised for clarity. 

a. Is the free-field motion at the foundation level discussed an "outcrop" or "within" motion? 

NRC Response: 

The comparison at the foundation level should be performed using outcrop motions for both the 

foundation-level site spectrum and the 0.1g check. This is particularly true if the check is made 

against the spectrum (anchored at 0.1g) of Regulatory Guide 1.60, “Design Response Spectra for 

Seismic Design of Nuclear Power Plants,” Revision 1, issued December 1973, which was 

designed as a surface spectrum. Use of outcrop motions eliminates two issues related to 

(potentially large) reductions of in-column motions at the natural frequency of the soil column. 

The sharp drop in ground motion at the natural period of the soil makes comparisons with a flat 

spectrum (like the Regulatory Guide 1.60 spectrum) problematic. Related to this issue, if motions 

must be increased to meet the spectrum chosen for comparison, the final resulting surface 

spectrum has a spike at the frequency affected. 

Resolution: 

The new text developed for Section 5.4 will provide clarification. 

Bechtel Comment 26f (December 13, 2006) 

Page 18, Section C.5.4, “Determination of Safe Shutdown Earthquake.” It is recommended that the 

wording on the following issues in this section of the draft guide be revised for clarity. 

f. (Page 18 and also Figure 3 on page 19) Once the foundation motion is determined from free 

field motion through deconvolution or amplification factors, “the motions at foundation level are 

compared against appropriate response spectrum with a peak ground acceleration of at least 

0.1g.” What is the appropriate response spectrum here? How will it be determined? 

NRC Response: 

See response below NEI comment 1. 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 8 

NEI Specific Comment 1 (December 28, 2006) 

On page 2, third paragraph, the draft Regulatory Guide indicates that site specific design spectra should 

be sufficient to assure that a 0.1g spectrum at the building foundation level in the free field is met. These 

minimum spectra should have an “appropriate” shape, which the NRC is currently planning to define as 

the Regulatory Guide 1.60 shape. An “appropriate” shape would include shapes that have adequate 

energy in the low frequency range, not only the Regulatory Guide 1.60 spectra. 

NRC Response: 

The Regulatory Guide 1.60 spectrum fixed at a peak ground acceleration (PGA) value of 0.1g is 

one spectrum that the NRC staff would consider acceptable for this purpose. However there may 

be other spectra that would be considered acceptable for this purpose by the NRC staff if 

justification for their use is provided. In its review the NRC staff will consider the amount of 

energy represented in the low frequency range, among other things. 

Resolution: 

The new text developed for Section 5.4 will provide clarification. 

NEI Specific Comment 2 (December 28, 2006) 

On page 18, Paragraph 7, first sentence, the draft Regulatory Guide states, “Once the SSE is developed, it 

is compared with the seismic design criteria in the design certification documentation.” When the sitespecific response spectrum is compared to the certified design spectrum, the importance of the spectral 

exceedances identified, if any, should be evaluated considering the spectral frequency ranges that control 

soil response to determine liquefaction potential (approximately 1/2 Hz to 2 Hz), structural response 

(approximately 2 Hz to 10 Hz) and equipment response (greater than 10 Hz). (Note: The frequency ranges 

shown are approximate.) 

NRC Response: 

As decided at the public meeting on December 14, 2006, Regulatory Guide 1.208 will not discuss 

this topic. The NRC staff position will be indicated in the Standard Review Plan. 

Resolution: 

No changes will be made to DG-1146. 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 9 

Bechtel Comment 26b (December 13, 2006) 

Page 18, Section C.5.4, “Determination of Safe Shutdown Earthquake.” It is recommended that the 

wording on the following issues in this section of the draft guide be revised for clarity. 

b. Development of composite spectrum in the free-field at the foundation level and subsequent 

computation of the SSE at the ground surface level would cause numerous anomalies, several are 

identified below: 

• For plants with structures having multiple embedment depths, this would amount to more 

than one SSE at the ground surface level. 

• There is a penalty for deeper embedment since the 0.10g motion is fixed at the foundation 

level in the free-field. 

• If soil amplification were to be performed for the composite foundation level motion as 

stated, it is not clear what soil properties from the set of randomized soil properties 

should be used. 

• Is the composite spectra at the foundation motion a UHRS or DRS? If it is a UHRS and 

it is amplified to the surface, should the same procedure be used to develop the DRS 

based on the slope of the hazard curve that did not include the 0.10g motion? 

• When composite motion is amplified, how is the vertical motion computed? 

NRC Response: 

The NRC staff considers it acceptable for the foundation level comparison to be treated as a 

design-level check. 

Resolution: 

The staff has edited Section 5.4 to remove the concept of a composite ground motion. 

Bechtel Comment 26d (December 13, 2006) 

Page 18, Section C.5.4, “Determination of Safe Shutdown Earthquake.” It is recommended that the 

wording on the following issues in this section of the draft guide be revised for clarity. 

d. There is wording in this section on where the SSE is to be defined, as distinct from the ground 

motions at the “free field foundation depth.” It is noted in this section that it is the motions at the 

foundation level -- not the SSE [free field surface spectrum]--where the comparison “against 

appropriate response spectrum with a peak ground acceleration of at least 0.1g.” This wording 

appears to be in conflict with Appendix S to 10 CFR Part 50, which states that the comparison is 

to be made against the SSE. Consideration should be given to clarifying this wording. 

NRC Response: 

While the regulations require the SSE to be defined at the free field ground surface, they also 

require a check of SSE consistent motions at foundation. To address both requirements, the 

concept of the composite spectrum was developed. Although the concept of the composite 

spectrum directly addressed the requirements, it led to confusion and unintended issues. By 

treating the 0.1g check as a separate design check, and not a fundamental part of the definition of 

the GMRS, this confusion is eliminated. The foundation level check will be discussed in the 

Standard Review Plan. 

Resolution: 

The new text developed for Section 5.4 provides clarification. 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 10 

3.4 SSE versus Design Response Spectrum and Risk Consistent Spectrum 

Dr. Carl Constantino Comment 4 (December 2, 2006) 

Line 52 (page 2, paragraph 6, sentence 1) I presume that the performance-based SSE is the UHRS scaled 

by the DF (the risk-consistent spectrum RCS). If so, should you so state? Then the DRS may or may not 

be the RCS, correct? 

NRC Response: 

The NRC’s performance-based GMRS is the UHRS scaled by the Design Factor. The DRS 

defined in ASCE 43-05 is the same as the NRC’s GMRS. 

Resolution: 

The NRC staff has edited Regulatory Guide 1.208 for clarity. 

Bechtel Comment 1a (December 13, 2006)

The single most important change between RG 1.165 and DG-1146 is the change from the reference 

probability approach to the performance-based approach. This change, principally by reference to ASCE 

43-05, is well defined and easy to follow. There are, however, a number of fundamental issues within 

NRC regulations and their CFR antecedents that neither RG 1.165 nor DG-1146 address. Principle 

among these is: 

a. Lack of distinction between the SSE and the DRS (design response spectra). 

NRC Response: 

The Design Response Spectrum (DRS) defined in ASCE 43-05 and the NRC’s GMRS are the 

same. They are performance based site-specific ground motion response spectrum and 

determined by scaling the UHRS (1 E-04) by a design factor. The ASCE DRS is not the same as 

the SSE, as defined in the Standard Review Plan. 

Resolution: 

Section 5.1 has been edited to clarify the differences between the GMRS and the SSE. 

Bechtel Comment 26e (December 13, 2006) 

Page 18, Section C.5.4, “Determination of Safe Shutdown Earthquake.” It is recommended that the 

wording on the following issues in this section of the draft guide be revised for clarity. 

e. It is stated in this section that development of SSE will be more fully described in NUREG0800. However, an acceptable approach is shown in Figure 3, although sufficient detail is not 

provided. Would it be better if options for the development of the SSE were more fully described 

and regulatory positions established in this draft guide? 

NRC Response: 

The additional development of the SSE in NUREG-0800, “Standard Review Plan for the Review 

of Safety Analysis Reports for Nuclear Power Plants,” was intended to deal with the 0.1g PGA 

check and the composite spectrum. Removal of the composite spectrum concept eliminated many 

of those issues. As a result, much of the guidance that would have been useful in this section is 

no longer appropriate. 

Resolution: 

The staff has edited Section 5.4 to clarify the concepts of GMRS and SSE. SSE determination 

will be fully discussed in SRP 3.7 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 11 

3.5 Other Comments 

Dr. Carl Constantino Comment 2 (December 2, 2006). 

Page 2, paragraph 3, sentence 3: ...spectrum be a smoothed spectrum compatible with the site 

characteristics,... 

NRC Response: 

The proposed changes improve the sentence. 

Resolution: 

The sentence now reads, “In view of limited data available on vibrator ground motions of strong 

earthquakes, it will usually be appropriate that the design response spectra be a smoothed 

spectrum compatible with the site characteristics.” 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 12 

4 Performance-Based Design Parameters

NEI Specific Comment 11 (December 7, 2006) 

On page 8, footnote 4 needs to be either deleted or corrected. As written, it imposes HCLPF seismic 

margin requirements that are more stringent than those imposed by SECY-93-087. There is no need for 

Footnote 4 so we suggest it be deleted. However, if retained, it should be revised to state that the HCLPF 

margin factor of 1.67 applies to the overall plant damage states leading to Seismic Core Damage (SCD) or 

LERF. It should not be necessary to demonstrate a HCLPF margin of 1.67 for every SSC in the plant. 

NRC Response: 

The NRC staff agrees with the comment. 

Resolution: 

The staff has deleted the HCLPF related statement from Regulatory Guide 1.208. 

Bechtel Comment 20 (December 13, 2006) 

Page 8, footnote. 

a. The footnote at the bottom of the page is more stringent than SECY-93-87 which requires the 

1.67 factor above the SSE for plant damage state, not for individual components. The draft guide 

will add more conservatism to the design of new nuclear power plants. Is this the intent? 

b. If a margin study or PRA will be required, as noted in this footnote, specific guidelines are 

needed to develop the motion and soil properties for the higher level motions. 

NRC Response: 

The NRC staff agrees with the comment. 

Resolution: 

The staff has updated wording in the document text and removed the footnote. 

Dr. Carl Constantino Comment 6 (December 2, 2006) 

Line 110 and Line 290 (page and page 8, paragraph 5, last sentence) Statement is incorrect because as it is 

always the case that yield is reached before failure. 

NRC Response: 

This comment relates to fact that in all cases, the inelastic deformation precedes failure and so 

this in itself does not provide a basis for the new methods. 

Resolution: 

The staff has modified the wording to address this comment. 

Bechtel Comment 3 (December 13, 2006) 

The draft guide does not explicitly mention that the new nuclear plants designed in accordance with this 

draft guide will provide lesser seismic risk. The wording on Page 4 which reads, “Setting the 

performance goal to be equivalent to the FOSID of SSCs is conservative, since the seismic demand 

resulting in the onset of significant inelastic deformation is less than that for failure of the SSCs,” implies 

that new nuclear power plants will be, on average, safer. The draft guide should include wording that 

explicitly recognizes this fact. 

NRC Response: 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 13 

See response to Dr. Carl Constantino Comment 6, above. 

Resolution: 

The staff has modified the wording in the document. 

Bechtel Comment 7 (December 13, 2006) 

Finally, the most fundamental problem with RG 1.165 was that it developed criteria based on a reference 

probability defined in terms of existing nuclear power plant SSE response spectra for frequencies between 

1 and 10 Hz, then required that new nuclear power plants be designed for ground motions at frequencies 

outside this range (and for higher frequencies, in particular) for which the SSE response spectra of 

existing nuclear power plants would have predicted a much higher reference probability. The SSE 

response spectra for existing nuclear power plants are not based on UHRS concepts and the 1-10 Hz 

window used as a benchmark is within a relatively conservative part of the UHRS. Migration to 

performance-based criteria within the same frequency range does not appear to directly address this issue. 

If, indeed, it may eventually be shown that high frequency (> 10 Hz) motions are less likely to damage 

SSCs for a given amplitude than lower frequency motions, this would introduce an additional way to 

modify the ASCE 43-05 approach in such a way as to reduce the high-frequency component of a 

performance-based SSE. It is recommended that this eventuality be acknowledged in the draft guide. 

NRC Response: 

The reference probability approach the NRC used in Regulatory Guide 1.165 was based on the 

data and the tools available at that time. The frequency range of the ground motions specified 

was limited by these constraints; Regulatory Guide 1.208 is based on the same set of data. Note 

that the Regulatory Guide 1.165 reference probability was based on probability exceeding SSE at 

5 and 10 Hz, not 1 and 10 Hz. This comment speculates about the consequences of future work 

and data. It is not appropriate to speculate about future findings within Regulatory Guide 1.208. 

Resolution: 

No changes are required in Regulatory Guide 1.208. 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 14 

5 Site Investigation and Site Properties

5.1 Excavations and Construction 

NEI Specific Comment 2 (December 7, 2006) 

On page 4, last paragraph, the draft states, “Under the combined license procedure, these kinds of features 

[e.g. faults] should be mapped and assessed as to their rupture and ground motion generating potential 

while the excavations’ walls and bases are exposed, and the NRC staff should be notified when 

excavations are open for inspection.” This requirement needs to be clarified relative to how the new 

information will be handled under the COL process and in a manner that maintains stability in the 

regulatory process. 

NRC Response: 

The NRC staff acknowledges the comment. Regulatory Guide 1.70 (DG-1145) is currently being 

updated and will clarify how this requirement will be implemented. 

Resolution: 

No changes are required to DG-1146 except as noted below to achieve consistency with language 

in the Standard Review Plan (SRP). 

NEI Specific Comment 13 (December 7, 2006) 

On page 11, fourth paragraph, third sentence, the draft states, “A commitment should be made, in 

documents (Safety Analysis Reports) supporting the license application, to geologically map all 

excavations and to notify the NRC staff when excavations are open for inspection.” A commitment, as 

requested for the major excavation is understandable, but “all excavations” is much too broad a term. For 

example, at what point does grading or ditching become an excavation? This requirement should be 

consistent with SRP 2.5.1, Section III, which requests a commitment to “geologically map all excavations 

for Seismic Category I structures, as a minimum....” This is a clearer statement. 

NRC Response: 

See response under Bechtel Comment 21, below 

Bechtel Comment 21 (December 13, 2006) 

Page 11, 4th paragraph. The draft guide states, “A commitment should be made, in documents (Safety 

Analysis Reports) supporting the license application, to geologically map all excavations and to notify the 

NRC staff when excavations are open for inspection.” It is recommended that this wording be revised to 

be consistent with SRP 2.5.1 to “geologically map all excavations for Seismic Category I structures, as a 

minimum....” 

NRC Response: 

The proposed changes in the above comments would improve Regulatory Guide 1.208 and lead 

to clarity and consistency with SRP Section 2.5.1. 

Resolution: 

The staff edited the line to read as: “A commitment should be made, in documents (Safety 

Analysis Reports) supporting the license application, to geologically map all excavations of 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 15 

significant size and to notify the NRC staff when these excavations are open for inspection. This 

should apply to excavations for construction of all Seismic Category I structures, as a minimum.” 

NEI Specific Comment 12 (December 7, 2006) 

On page 11, section C.1.3, the title of the section should be changed to read “Features Discovered During 

Excavation” rather than “Features Discovered During Construction.” This is suggested because 

excavation is the activity of concern. 

NRC Response: 

Although, the section specifically discusses excavations, there may be cases where features are 

identified that are not tied specifically to excavations. Any potential fault identified on the site 

must be investigated, regardless of how it is identified. 

Resolution: 

No change to DG-1146 is required. 

Dr. Carl Constantino Comment 7 (December 2, 2006) 

Page 4, paragraph, 4: “....faults, potential soft zones or other features of engineering significance”.... 

NRC Response: 

The staff will incorporate the proposed comment. 

Resolution: 

The line on page 4 now reads: “It should be demonstrated that deformation features discovered 

during construction (particularly faults, potential soft zones or other features of engineering 

significance) do not have the potential to compromise the safety of the plant.” 

Dr. Carl Constantino Comment 10 (December 2, 2006) 

Line 383 (page 11, paragraph 4, sentence 1): “....faults, potential soft zones or other features of 

engineering significance”.... 

NRC Response: 

The staff will incorporate the proposed comment. 

Resolution: 

The line on page 11 now reads: “It should be demonstrated that deformation features discovered 

during construction (particularly faults, potential soft zones, or other features of engineering 

significance) do not have the potential to compromise the safety of the plant.” 

5.2 Definition of Rock 

NEI Specific Comment 1 (December 7, 2006) 

On pages 3, 8, 15, A-2, E-1, and E-3, the draft refers to computing the PSHA for generic hard rock 

conditions, which are defined on page 14, Sec 4, as “... generic hard surficial hard rock conditions [i.e., 

rocks with a shear wave velocity (VS) about 2.8 km/sec (9200ft/sec)]” and in Appendix E as “... usually 

with a shear wave velocity (VS) about 2.8 km/sec (9200 ft/sec).” This is the case currently for the CEUS 

but is not the case for the WUS. It is suggested that the phrase “generic hard rock” be modified to be just 

“generic rock” and that the discussion on page E-1 of 2.8 km/sec be stated in terms of the current status 

for CEUS ground motions. It is possible in the future that generic rock ground motion models will be 

developed for the CEUS for some other commonly found rock condition. 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 16 

NRC Response: 

In terms of the probabilistic seismic hazard assessment (PSHA), the definition of rock conditions 

is dictated by the data used to develop the attenuation relationships used in the PSHA. The 

regulatory guidance should have terminology such that cases in both the Western US (WUS) and 

Central and Eastern US (CEUS) are addressed. 

Resolution: 

The staff has made edits to address this comment. 

Jeffrey K. Kimball Comment 8 (December 13, 2006) 

DG-1146 supports the development of rock-based PSHA results, using generic hard rock conditions. 

Appendix E states that generic hard rock conditions are associated with a shear wave velocity of about 2.8 

km/sec (9,200 ft/sec). The basis for defining generic hard rock at a shear wave velocity of 9,200 ft/sec is 

not provided and is inconsistent with other published definitions of hard rock based on shear wave 

velocity (see for example FEMA Report 450-1, 2003 Edition of National Earthquake Hazard Reduction 

Program Recommended Provisions for Seismic Regulations for New Buildings and Other Structures, 

where hard rock is defined by a shear wave velocity of > 5,000 ft/sec). Additionally it is not clear why an 

applicant in the Western United States would be required to generate a PSHA for hard rock site 

conditions when this shear wave velocity may only exist at deep depths. 

NRC Response: 

The universal use of the hard rock definition in DG-1146 is problematic, as discussed in the 

response above. In terms of the PSHA, the definition of rock is defined by the attenuation 

relationships and is dictated by the case history database used in the development of the 

attenuation relationships chosen for the PSHA. These definitions do not necessarily fit the 

National Earthquake Hazards Reduction Program (NEHRP) site classification system (as used in 

Federal Emergency Management Agency Report 450 and other documents). 

As noted in the comment, one would not generate a PSHA for hard rock conditions in the WUS 

because the attenuation relationships were developed using soft rock data. The staff will edit the 

document to be more inclusive and generic in nature. 

Resolution: 

The changes noted in the response to NEI Specific Comment 1 above will also address this 

comment. 

5.3 Development of Dynamic Soil Properties 

NEI Specific Comment 28 (December 7, 2006) 

On page E-3, first paragraph, second sentence states, “When site-specific laboratory data is used, the 

result should be compared to earthquake recordings on similar soils.” It is not clear why this restriction is 

added on the use of site-specific laboratory data. This restriction could have an important impact on the 

scope and cost of geotechnical investigations for the next generation nuclear power plants. Clarification 

is requested. 

NRC Response: 

During the development of the EPRI strain-dependent shear modulus and damping curves, efforts 

were made to validate the laboratory results with field data. If new site-specific curves are 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 17 

developed based on laboratory results, it is expected that these new results will also be checked 

against field data to ensure their reasonableness. 

Resolution: 

The NRC Staff has changed the statement to the following: “When new strain-dependent shear 

modulus and damping curves are developed, these curves should be compared to earthquake 

recordings on similar soils.” 

Bechtel Comment 34 (December 13, 2006) 

Pages E-2 and E-3, 6th and 7th paragraphs of Section E.3, “Site Response Analysis.” The 6th paragraph 

states, “The strain-dependent shear modulus and damping curves are developed based on site-specific 

testing results and supplemented as appropriate by published data for similar soils.” The second sentence 

on the 7th paragraph states “When site-specific laboratory data is used.” Is there a conflict between these 

two statements? 

NRC Response: 

This wording could be interpreted to have a potential conflict. The first statement was intended to 

indicate that shear modulus and damping curves developed from site-specific testing results can be 

supplemented as appropriate by published data for similar soils. The second statement asks for a 

comparison with seismic recording of similar soils. 

Resolution: 

The staff had updated the wording in Section E.3. 

5.4 Other Comments 

NEI Specific Comment 16 (December 7, 2006) 

On page 15, section C.4.1 “Site and Laboratory Investigations and Testing,” first sentence, second line, 

delete “materials, and their spatial distribution” and replace with “strata.” 

NRC Response: 

The spatial distribution of engineering properties both within individual geologic strata and across 

the site is an important consideration and should be analyzed. This is in addition to the mean and 

standard deviation of engineering properties. If properties change across a site, this should be 

accounted for in analyses. 

Resolution: 

The staff has clarified this issue in Regulatory Guide 1.208 through the addition of the wording, 

“Consideration should be paid to spatial distribution both within individual geologic strata and 

across the site.” 

Dr. Carl Constantino Comment 9 (December 2, 2006) 

Page 10, paragraph 3, last line: What is “ground-truth” recon? 

NRC Response: 

In this context, ground-truth reconnaissance refers to a visit to the potential source to perform 

first-hand investigation. 

Resolution: 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 18 

The sentence will be changed to “These investigations should include literature reviews, the study 

of maps and remote sensing data, and if necessary, on-site ground-truth reconnaissance.” 

Dr. Carl Constantino Comment 13 (December 2, 2006) 

Section C2.5.2 only considers ground failure evaluations associated with site liquefaction effects. 

However, a number of other “ground failure” issues need to be mentioned such as potential localized soft 

zones, karst features, etc. whose collapse or consolidation could impact the foundation design. 

NRC Response: 

The staff has added additional text to address other forms of ground failure. 

Resolution: 

The staff has added a paragraph that states, “In addition to liquefaction, a number of other forms 

of ground failure or ground settlement should be investigated. These forms of ground failure and 

ground settlement include localized soft zones, karst features, seismic settlement of non-saturated 

soils, all forms of mass wasting, and any other form of ground deformation that has the capacity 

to impact foundation performance or design.” 

NEI Specific Comment 23 (December 7, 2006) 

On page C-6, section C.2.4, “Surface-Fault Rupture and Associated Deformation at the Site,” third 

paragraph last sentence states, “These structures, such as those found in karst terrain, and growth faulting, 

which occurs in the Gulf Coastal Plain or in other deep soil regions, cause extensive subsurface fluid 

withdrawal.” This appears to be garbled. It does not appear to flow logically from the preceding 

sentences. It is assumed that the idea is to provide some examples of non-tectonic faulting and to indicate 

the origin and/or related surface deformation. The link between extensive subsurface fluid withdrawal 

and surface displacements should be clarified. 

NRC Response: 

The NRC staff agrees with the comment. 

Resolution: 

The NRC staff has edited the document for clarity. 

Dr. Carl Constantino Comment 8 (December 2, 2006) 

Line 139 (page 5, paragraph 1, sentence 2) I don’t understand why the approach used to account for 

uncertainties depends on the tectonic setting. 

NRC Response: 

One example of the need to consider tectonic setting in defining epistemic uncertainty relates to 

the type of faulting anticipated on a fault for which limited data are available. Because some 

attenuation relationships account for style of faulting, the tectonic setting may help to characterize 

unknown fault parameters. Uncertainty can also arise in areas where tectonic setting tends to hide 

evidence of faulting, such as in Southern California, where blind thrust faulting is common. 

Resolution: 

No change to DG-1146 is required. 

Public Comments at NRC Public Meeting: Comment 6 (December 14, 2006) 

DG 1146 details specific map scales to be used in reporting. However in the digital age, these scales 

seem out of date. Please consider revising the text. 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 19 

NRC Response: 

The NRC staff is most interested in the resolution of the underlying map data. While the use of 

digital data allows for maps that are optimally sized for visualization, it is important that maps 

provided do not imply or assume a level of resolution higher than the resolution of the underlying 

mapping. GIS can enlarge a map digitally but do not change the underlying data’s resolution. 

For example, if 1:500,000 geologic maps are imported to a GIS system, the resolution of the 

product based on these underlying maps is still consistent with a 1:500,000 map, regardless of the 

ultimate scale of the final product provided. 

Resolution: TBD 

That staff has edited DG-1146 to clarify the intent of the mapping scales noted. 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 20 

6 Probabilistic Seismic Hazard Assessment (PSHA) Methods

6.1 Choice of PSHA Techniques and Regulatory Stability 

Jeffrey K. Kimball Comment 1 (December 13, 2006) 

In October 2006 the United States Nuclear Regulatory Commission (NRC) published Draft 

Regulatory Guide DG-1146, A Performance Based Approach to Define the Site-Specific Earthquake 

Ground Motion, for public comment. Section 4 of DG-1146 states “that the proposed action will reduce 

unnecessary burden on the part of both the NRC and its licensees, while improving the process for siting 

of nuclear power plants.” Because of vague terminology and lack of appropriate guidance on what 

constitutes an appropriate probabilistic seismic hazard analysis (PSHA), implementation of DG-1146 

could well result in an unstable regulatory process, with protracted debate on PSHA related issues. 

DG-1146 outlines new methods for defining a site-specific performance based Safe Shutdown 

Earthquake (SSE), using the approach described in Chapters 1 and 2 of American Society of Civil 

Engineers (ASCE) Standard 43-05, “A Seismic Design Criteria for Structures, Systems, and Components 

in Nuclear Facilities.” 

One of the most important criterion for evaluating the acceptability of a performance-based 

approach is the suitability of the seismic hazard assessment to support the determination of an appropriate 

probabilistic seismic hazard used as part of the ASCE 43-05 process to meet the selected target 

performance goal (expressed as a target mean performance criterion of < 1x10-5 per year for the 

frequency of onset of significant inelastic deformation). It is important that any regulatory guidance 

provide regulatory stability, particularly with respect to potential changes or updates of the input 

parameters for probabilistic seismic hazard analysis (PSHA). 

Use of a site-specific mean 10-4 annual probability level to define the uniform hazard response 

spectrum (UHRS) as the starting point, based on the precedent set in ASCE 43-05, depends on the 

stability of PSHA results for a given site. While two divergent mean PSHA curves can be used to meet 

an intended target performance goal, each may result in widely different design ground motion levels or 

SSE. Divergent PSHA curves with different slopes could also result in different values for the ASCE 43-

05 “design factor”. 

NRC response: 

See response below Jeffrey K. Kimball Comment 11. 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 21 

Jeffrey K. Kimball Comment 3 (December 13, 2006) 

When NRC developed Regulatory Guide 1.165, “Identification and Characterization of Seismic 

Sources and Determination of Safe Shutdown Earthquake Ground Motion,” one of the objectives was to 

achieve regulatory stability. At that time a decision was made to use the concept of “reference 

probability,” established in part where the EPRI and LLNL PSHA results were found to provide 

consistent ground motion values. The reference probability was selected as a median 10-5 annual 

probability. It is important to note that selection of a mean annual probability (for example that needed to 

support a performance-based approach) for the “reference probability” was not possible, in part, due to 

wide differences between PSHA results based on EPRI and LLNL. 

Completion of a PSHA for a given location should be based on the latest seismic hazard 

information which depends on the geological and seismological setting of that location. One of the 

original motivations that NRC had for developing the LLNL results was to provide for an independent 

check on PSHA results derived by applicants, to ensure that the probabilistically derived ground motion 

levels were appropriate for seismic design purposes. Such a check and balance should be an explicit part 

of regulatory oversight to ensure that PSHA results provide an appropriate assessment of seismic hazard. 

Because of the divergent EPRI and LLNL PSHA results, NRC, along with the Department of 

Energy and EPRI, sponsored development of “Recommendations for Probabilistic Seismic Hazard 

Analysis: Guidance on Uncertainty and Use of Experts,” published as NUREG/CR-6372 (commonly 

referred to as the Senior Seismic Hazard Analysis Committee or SSHAC report). The sponsors of this 

work saw a need for more stability in the PSHA process. While both the EPRI and LLNL PSHAs were 

landmark efforts, neither of these studies was completed following the SSHAC guidelines, and thus could 

be legitimately challenged in terms of providing the necessary regulatory stability for application 

following the approach found in ASCE 43-05. 

Efforts to update either study (such as what has been completed to support Early Site Permit 

{ESP} applications) needs to be reviewed carefully to ensure that all PSHA input represents the current 

state of seismologic and geologic practice. It appears as if the trend is to update EPRI PSHA results and 

ignore past LLNL results. While the technical basis for this trend is not clear (other than the implication 

that applicants like the lower EPRI PSHA results), it appears to be supported by DG-1146, based on the 

precedence from Regulatory Guide 1.165 even though that reference was not linked to a performance 

based approach which requires an accurate absolute estimate of probabilistic seismic hazard. 

NRC response: 

See response below Jeffrey K. Kimball Comment 11. 

Jeffrey K. Kimball Comment 5 (December 13, 2006) 

The implication from the above discussion suggests that NRC should be capable of performing 

confirmatory PSHA assessments as part of their regulatory oversight. It is not clear whether NRC has 

maintained the capability to execute a “LLNL PSHA” for a given site location as part of their regulatory 

review and oversight. NRC needs to recognize that different organizations could execute the EPRI, 

LLNL or USGS PSHA methods for a given location, which could result in widely divergent design 

ground motions following the approach found in ASCE 43-05. Without addressing these issues it is not 

clear how regulatory guidance will result in regulatory stability. 

NRC response: 

See response below Jeffrey K. Kimball Comment 11. 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 22 

Jeffrey K. Kimball Comment 11 (December 13, 2006) 

Any updated regulatory guidance that adopts the ASCE 43-05 approach must address those steps that will 

result in PSHA stability to ensure overall regulatory stability. Use of pre-existing PSHA results (adjusted 

or not) and/or recent USGS PSHA results requires more study before such regulatory stability can be 

defined. Adjusting either the EPRI or LLNL PSHA input may not be feasible given that much of the 

original work for both of these studies is now about 20 years old. This implies that a comprehensive 

PSHA update for the CEUS may be needed. The USGS should play a prominent role if this step is taken 

to ensure appropriate integration of PSHA input parameters with the national seismic hazard map. 

Finally, NRC should be encouraged to retain the capability to perform independent PSHA confirmatory 

calculations (as they had with the LLNL PSHA code) as part of their regulatory review. 

NRC Response: 

In order to serve its mission of protecting public safety, the NRC must work towards a regulatory 

process that ensures regulatory stability, while maintaining a flexibility that allows adoption of 

the most recent technical knowledge and tools. It is important that tools and information used for 

probabilistic seismic hazard assessment (PSHA) in particular are carefully reviewed and applied. 

The development of this guide, as well as other work such as development of the SSHAC 

guidelines in NUREG/CR-6372, has been undertaken to increase stability of PSHA process. The 

NRC staff acknowledges the above observations about the characteristics of PSHA. The NRC 

staff also recognizes that PSHA is an evolving technology and is working to incorporate the most 

recent refinements in techniques and information into regulatory guidance, as appropriate. 

As noted, it is essential that the NRC retains the capability to perform independent PSHA 

calculations. Independent reviews are being performed both in-house and with the assistance of 

contractors and other federal agencies, including the U.S. Geological Survey (USGS). 

Resolution: 

The section on PSHA techniques notes the changes that have been made to DG-1146. 

Dr. Carl Constantino Comment 14 (December 2, 2006). Line C293 The DG mentions only the 

LLNL/EPRI studies. USGS hazard evaluations are currently in use for many other critical facility designs 

aside from NPP's. 

NRC Response: 

The USGS hazard evaluations are currently used in many industries and should be noted as a 

resource. In addition the USGS hazard database was is used extensively by the NRC staff in the 

review of every application. 

Resolution: 

The staff has added a discussion of the USGS as a resource. 

6.2 Seismic Source Characterization 

NEI General Comment 5 (December 7, 2006) 

The draft states that applicants may use accepted seismic source characterizations as the starting basis for 

developing inputs for a site-specific PSHA. References to such sources and existing databases are at 

various places throughout the text. But the draft provides inadequate guidance. The Regulatory Guide 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 23 

should clearly state that seismic source characterizations that have been reviewed either generically (i.e., 

LLNL, EPRI 1986) or as part of an ESP or COL application and accepted by the NRC are accepted as 

starting basis for developing inputs for a site-specific PSHA. 

NRC Response: 

See the response to the below comment. 

Public Comments at NRC Public Meeting Comment 9 (December 14, 2006) 

Industry representatives noted that in their opinion DG-1146 should clearly state that seismic source 

characterizations that have been accepted by the NRC generally or as part of an ESP or COL application 

are acceptable starting bases for subsequent site-specific PSHAs. 

NRC Response: 

The NRC staff is in general agreement with this approach as long as it is clear that the source 

characterization is only a starting point and recent work on the sources should be reviewed. 

Resolution: 

The staff has added the above concept to Section B of Regulatory Guide 1.208. 

NEI Specific Comment 4 (December 7, 2006) 

On page 5, last paragraph, the last sentence states, “However, if more up to date information is available, 

it should be incorporated if significant.” This position does not define significant or what is expected of 

the owner/operator if the more up to date information is identified following design and construction. 

NRC Response: 

Significant information would be that which can have an impact to the site hazard estimate. 

Sensitivity tests can be used to determine if the new source information is significant or not. 

Resolution: 

The staff will add wording to provide more clarity. 

NEI General Comment 1 (December 28, 2006) 

The terms, “Existing Probabilistic Seismic Hazard Assessment (PSHA) database,” and “accepted 

probabilistic seismic hazard studies,” appear at various places throughout the text of the draft Regulatory 

Guide DG – 1146. The draft does not adequately define what is meant by these terms. We recommend 

that these terms be replaced with the term, Acceptable PSHA model and be defined in the glossary as 

follows: 

Acceptable PSHA model is a method of conducting a Probabilistic Seismic Hazard Analysis 

(including the seismic sources and ground motion equations) that has been developed using 

Senior Seismic Hazard Analysis Committee (SSHAC) guidelines and that has been reviewed and 

accepted by the NRC either for generic application (e.g. the 1989 studies by LLNL and EPRI, 

with the inherent seismic source description for the CEUS) or as part of an ESP or COL 

application. Acceptable PSHA models are starting points for developing probabilistic seismic 

hazard calculations for new ESP or COL applications, yet must be updated with new information 

on seismicity, geology, geophysics, and ground motion equations, as appropriate for a site that is 

being reviewed. 

NRC Response: 

The proposed definition above is in line with NRC staff views. 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 24 

Resolution: 

The staff will add the proposed definition with some modifications to the glossary (Appendix A). 

Jeffrey K. Kimball Comment 2 (December 13, 2006) 

In three places DG-1146 uses the phrase “accepted probabilistic seismic hazard studies” (see Section B 

pages 3 and 4, Appendix C page C-1), without defining what these studies are. On page 5 DG-1146 

refers to two PSHA studies (Electric Power Research Institute {EPRI} and Lawrence Livermore National 

Laboratory {LLNL}), and states that “these databases may still represent the latest information available 

for some seismic sources” (emphasis added). In section C 1.1, page 10, the text discusses situations 

where new data or interpretations are not adequately incorporated into the existing PSHA database

(emphasis added), without defining what these databases are. It is not clear how such language will 

improve the process for siting of nuclear power plants. 

NRC Response: 

The term “accepted probabilistic seismic hazard studies” refers to site-specific studies previously 

accepted by NRC staff. It is expected that over the lifespan of Regulatory Guide 1.208 some of 

the information used in specific PSHA calculations (e.g. specific source characterizations) will 

need to be updated. Because seismic hazard analysis and fault studies are areas of active 

research, it is expected that at any future point in time previously accepted information may still 

represent the latest information available for some seismic sources and information; but not for 

others. For this reason, the NRC staff does not explicitly state in Regulatory Guide 1.208 that it 

will accept source information from any seismic source database (e.g. EPRI, LLNL or the USGS) 

because some sources detailed in these resources will inevitably become outdated. However, for 

stability it is noted that the most recent information submitted in support of applications and 

accepted by the NRC can be used as a starting point. 

Resolution: 

The staff has edited the language in this section to more directly address the above discussed 

issues. The phrase, “accepted probabilistic seismic hazard studies” has been adjusted for clarity 

and has been added to Appendix A. 

Jeffrey K. Kimball Comment 4 (December 13, 2006) 

Comprehensive PSHA studies have been completed by the United States Geological Survey (USGS) as 

part of the national seismic hazard mapping project, with results published in 1997 and 2002. The USGS 

work is being updated for release in 2007. The information and data from the USGS work provides 

important insight into how the informed scientific community views the assessment of many seismic 

hazard issues. While some issues are obvious, such as paleoliquefaction findings near Charleston, South 

Carolina, New Madrid, Missouri, and Wabash Valley, Illinois, other issues are more subtle, such as the 

preference for smoothed seismicity versus detailed definition of area seismic sources in low seismic 

hazard environments. The USGS PSHA work is not discussed in DG-1146. The USGS PSHA work can 

not be ignored given that it represents the most recent comprehensive PSHA work for the United States. 

NRC comments: 

USGS hazard maps are constantly updated. However, these maps are not targeting critical 

facility siting studies with long return periods, but civilian structures with shorter return periods. 

USGS is playing an important role in assisting NRC staff to review each application. 

Resolution: 

The staff has added a reference to the USGS source database. 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 25 

6.3 Attenuation Relationships 

NEI General Comment 4 (December 7, 2006) 

The draft should provide guidance for ground motion modeling for sites located in the WUS, referencing 

the PEER Next Generation of Attenuation (NGA) models. As the NGA models apply primarily to 

California, additional guidance is required for modeling ground motion in the plate boundary subduction 

region of the Pacific Northwest and in the Basin and Range and Rocky Mountain regions. It would be 

most appropriate to place general guidance in the Regulatory Guide with reference to detailed guidance 

on modeling ground motion to be provided in the SRP. 

NRC Response: 

The NRC staff recognizes that the NGA relationships represent a significant advancement in the 

area of WUS seismic hazard assessment and warrants a mention in the document. The NRC staff 

view is that any methods that find consensus within the scientific community should be 

considered and reviewed. The updated SRP Section 2.5.2 will also discuss the topic. 

Resolution: 

The staff has added a brief discussion of the NGA relationships in Section B of Regulatory Guide 

1.208. 

Public Comments at NRC Public Meeting Comment 8 (December 14, 2006) 

Industry representatives noted that DG-1146 should provide more guidance for ground motion in WUS 

sites. Some specific topics include the narrow definition of hard rock, which is more appropriate for 

CEUS that WUS, and the discussion of attenuation relationships that are CEUS based. 

NRC Response: 

Regulatory Guide 1.208 will address both issues raised during the public meeting. Where rock 

conditions have been mentioned, the terminology has been broadened and generally the term 

“generic rock” has been use to replace “generic hard rock.” This is discussed further in the 

“Definition of Rock” Section of this document. As noted above, Regulatory Guide 1.208 will 

include a discussion of the NGA relationships. 

Resolution: 

The staff will update the document as noted. 

NEI General Comment 2 (December 28, 2006) 

The industry comment in the referenced letter relating to the need for guidance for Western U.S. sites 

should not delay issuance of the Regulatory Guide. This topic could be developed and included as a 

revision later. 

NRC Response: 

The NRC staff accepts the recent NGA relationships for seismic sources for which they are 

explicitly designed (shallow crustal faulting in active regions of the WUS) and will note this is in 

Regulatory Guide 1.208. In addition, the NRC staff will continue to review the acceptability of 

the NGA relationships for other cases. However, as with all seismic information, these tools may 

be used as a starting point and any new information available must be reviewed. 

Resolution: 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 26 

The staff has added a brief discussion of the NGA relationships to Section B of Regulatory Guide 

1.208. 

EPRI Minutes NRC Public Meeting Comment 4 (December 14, 2006) 

The industry comment on DG-1146 relating to the need for guidance for Western US sites should not 

delay issuance of the regulatory guide. This topic could be developed and included as a revision later. 

NRC Response: 

See response to NEI General Comment 2, above. 

6.4 Epsilon and Sigma Values in PSHA 

NEI General Comment 3a (December 7, 2006) 

The draft does not clearly state the acceptability of using post-EPRI (2004) attenuation relation variability 

estimates developed in EPRI Task G.3, (“Topical Report 1009684, CEUS Ground Motion Project Final 

Report”) nor does the draft provide clarity in regards to acceptable approaches for performing dynamic 

site response analysis to develop site response functions and obtain the uniform hazard response spectra at 

the surface or appropriate control location of non-hard rock sites. The industry needs generic resolution 

of these two issues. It is our judgment that the EPRI Task G.3 sigma estimate has strong technical 

support and is the appropriate current practice. 

NRC Response: 

This comment discusses two topics. For a discussion of the EPRI Task G.3 sigma value, see 

comments below. For a discussion of dynamic site response, please see the “Site Response 

Analysis Methods and Use of Results” section on page 29 of this document. 

NEI Specific Comment 7 (December 7, 2006) 

On Page 7, topic “Choice of Epsilon in Probabilistic Seismic Hazard Analysis,” the aleatory uncertainty, 

sigma, results from the second part of Task G1.3 have been omitted. This paragraph should be expanded 

to document the reduced values of sigma documented in the Pacific Earthquake Engineering Research 

Center (PEER) Next Generation Attenuation study and reported in the results for Task G1.3. 

NRC Response: 

See response below Bechtel Comment 6c. 

Public Comments at NRC Public Meeting Comment 4 (December 14, 2006) 

Industry representatives noted that the NRC should clearly accept post-EPRI (2004) sigma estimates as 

developed in Task G1.3. It was noted that while DG 1146 specifically discussed epsilon that need to be 

used in the PSHA, it does not discuss the update to sigma proposed in the same document. Industry 

representatives questioned if this meant that the change in sigma was still in question. 

NRC Response: 

See response below Bechtel Comment 6c. 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 27 

EPRI Minutes NRC Public Meeting Comment 2 (December 14, 2006) 

DG-1146 specifically accepts the conclusion of Task G1.3 that attenuation variability cannot be 

bounded/truncated based on currently available data; however, it is silent on the recommended values of 

Sigma to be used in the analyses. 

NRC Response: 

See response below Bechtel Comment 6c. 

Bechtel Comment 6c (December 13, 2006) 

RG 1.165 gave few details concerning computing of site-specific amplification factors. DG-1146, 

benefiting from experience beginning to be gained from work on recent ESP and COL applications, 

attempts to do more to help applicants in this regard. However, further changes and clarifications to the 

wording are needed. A few specific examples of topics needing clarification or correction are: 

c. Silence on the matter of adoption of revised “sigma” estimates for EPRI (2004) attenuation 

relations developed as part of the New Plant Seismic Issues Resolution Program. 

NRC Response: 

While a discussion of epsilon is warranted in a general discussion of PSHA and applies equally 

for any attenuation relationship, the sigma value being discussed addresses a specific relationship. 

As such, it is not appropriate for Regulatory Guide 1.208 to discuss this topic. However, in the 

public meeting of December 14, 2006 it was noted that the NRC staff has accepted the new sigma 

values in previous public meetings and continues to do so. 

Resolution: 

No changes to DG-1146 are required. 

NEI Specific Comment 14 (December 7, 2006) 

On page 14, section C.3.3, “Conduct a Probabilistic Seismic Hazard Analysis,” next to the last sentence, 

the word “epsilon” is not the appropriate term and should be replaced with “standard deviation of natural 

log of ground motion.” Note that on page 7, section titled “Choice of Epsilon in Probabilistic Seismic 

Hazard Analyses” epsilon is used correctly and is consistent with Reference 15 of DG-1146, i.e., (Electric 

Power Research Institute (EPRI) and U.S. Department of Energy (DOE), “Program on Technology 

Innovation: Truncation of the Lognormal Distribution and Value of the Standard Deviation for Ground 

Motion Models in the Central and Eastern United States,” Report 1013105, February 2006). 

NRC Response: 

The NRC staff agrees with the comment. 

Resolution: 

The staff will replace the word “epsilon” with “standard deviation of natural log of ground 

motion”. 

Bechtel Comment 15 (December 13, 2006) 

Page 7, “Choice of Epsilon in Probabilistic Seismic Hazard Analyses.” It is stated that large epsilon 

values should be used to capture low probability events. It is recommended that the discussion be 

expanded to include consideration of the limitations of the source and transmissibility of the motion to the 

site. 

NRC Response: 

This is an area of ongoing research. A full discussion of this topic is outside the scope of this 

document and will likely become out of date over the life of the document. As a result, the reader 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 28 

is instead referred directly to the recent study. As research progresses, the NRC may revisit this 

issue and provide stronger guidance. 

Resolution: 

No changes to DG-1146 are required. 

6.5 Cumulative Absolute Velocity (CAV) Filtering 

NEI Statement of Interpretation 1 (December 7, 2006) 

NEI has interpreted DG 1146 to allow the following: The use of a CAV-based lower bound magnitude 

cutoff when developing the PSHA - on Page 7 

NRC Response: 

This is correct. 

Resolution: 

No changes to DG-1146 are required. 

Public Comments at NRC Public Meeting Comment 5 (December 14, 2006) 

Industry representatives noted general agreement with the guidance related to the use of the CAV-based 

lower magnitude cut off, the location of SSE as described, using the site response parameters and results 

to determine the motions at the foundation level, and using the ASCE 43-05 performance goal-based 

approach. 

NRC Response: 

See response to NEI Statement of Interpretation, above.

Bechtel Comment 17 (December 13, 2006) 

Page 7, “Lower Bound Magnitude Cutoff.” This section states that, “An empirical model for estimating 

CAV in terms of magnitude, peak ground acceleration (PGA), and duration is needed because the PSHA 

calculation does not use time histories directly.” This statement leaves the impression that the industry 

needs to develop a new model before the CAV method can be used. Is this the intent? 

NRC Response: 

The purpose of CAV filtering is to remove from the PSHA earthquake scenarios that contribute to 

hazard (as characterized by the response spectrum) but that do not have the potential to damage. 

In this case a CAV filter on the foundation motion is replaced by a minimum magnitude 

truncation threshold. This minimum magnitude is an appropriate engineering parameter derived 

from the correlation between damage and. NRC has reviewed and accepted the CAV model 

addressed in task G1.2, “Use of CAV in determining effects of small magnitude earthquakes on 

seismic hazard analysis.” Because of the requirements of NPP design, the approximation made is 

acceptably accurate. However, because there is some uncertainly associated with a lower bound 

magnitude cutoff that does not directly account for factors such as site effects, the NRC plans to 

continue to research CAV filtering and continue the existing dialogue with stakeholders on this 

topic. 

NRC Response: 

No changes to DG-1146 are required. 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 29 

7 Site Response Analysis Methods and Use of Results

7.1 Use of Site Response Transfer Functions 

NEI Statement of Interpretation 3 (December 7, 2006) 

NEI has interpreted DG 1146 to allow the following: Transferring the SSE response spectrum from the 

control location to foundation levels using the appropriate site response functions obtained from the 

dynamic site response analysis - in Section 5.4, Page 18 

NRC Response: 

SSE in this comment is recognized as what the NRC is now defining as the GMRS. There should 

be consistency between the models and the results of the site response analyses used for 

development of the SSE and other directly related analyses. As was discussed in the public 

meeting of December 14, 2006, the site-specific, SSE-consistent response spectrum developed at 

the foundation level (for purposes of providing a comparison to an appropriate spectrum with a 

PGA of 0.1g) may be calculated as a free-field surface motion based on the properties used in the 

site response analyses. 

Resolution: 

No changes to DG-1146 are required. 

NEI General Comment 1 (December 7, 2006) 

On the development of site-specific spectra (Section 4.3), the recommendation for enveloping spectra will 

give invalid spectra and should be modified. The reason is that the low-frequency earthquake will not 

have much energy content at high frequencies, so the soil will remain more linear at high frequencies and 

the amplification factors (soil/rock) will be higher than for the high-frequency earthquake. This means 

that the low-frequency site amplification applied to the UHRS will control the high-frequency envelope. 

This is not the intended result. Additionally, it is important to anchor any recommended site spectrum to 

amplitudes at the frequencies calculated by the PSHA. In recent ESP submittals this has been 7 

frequencies (100, 25, 10, 5, 2.5, 1, and 0.5 Hz). A better statement would be: 

To determine the UHRS at the free ground surface, examine the mean surface spectra calculated 

for the high-frequency and low-frequency input motions, and determine over what frequency 

range each controls the surface motion. At high frequencies, this will be the high-frequency 

motion, and at low-frequencies, the low-frequency motion. Apply the appropriate (high- or lowfrequency) amplification factors for each frequency range to the mean UHRS to calculate the 

UHRS at the free ground surface. This should be done at the frequencies where the rock PSHA 

was calculated, using the rock UHRS values, and at intermediate frequencies using appropriate 

spectral shapes for the high- and low-frequency ranges. 

NRC Response: 

See response below NRC Public Meeting Comment 10. 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 30 

Public Comments at NRC Public Meeting Comment 10 (December 14, 2006)

Industry representatives noted that the methods used in development the SSE spectrum needs to ensure 

that the exceedance frequencies of the UHRS are maintained at the surface over all structural frequencies 

of interest. They further explained their position through examples provided by Dr. McGuire. Through 

discussion it was clarified that the proposed NEI approach (i.e. multiplying the site amplification factors 

by the UHRS -- not the individual characteristic earthquakes) was what the NRC had intended to convey. 

The NRC will review the language in DG 1146 to make this point clearer. 

NRC Response: 

The comments above express, correctly, that the wording in DG-1146 is not sufficiently general 

and could lead to cases in which using the method described results in surface spectra that do not 

represent uniform hazard for all spectral periods. 

Resolution: 

A revision to Regulatory Guide 1.208 has been made to address the issue. 

Bechtel Comment 35 (December 13, 2006) 

Page E-3, last paragraph on the page. This paragraph includes the following wording: 

“Once the soil amplification functions are developed, they are applied to the free field rock 

UHRS to develop two free-field soil spectra. To determine the soil UHRS at the free-field 

ground surface, for each of the annual exceedance frequencies (1 E-04, 1 E-05, and 1 E-06), 

multiply the rock-based UHRS at all 25 points and the natural frequency of the site soil column 

by the site amplification functions, and envelop the results. These two curves are enveloped to 

determine the final free-field soil UHRS. If the two controlling earthquake response spectral 

shapes cover a broad range of frequencies such that when scaled and enveloped they approximate 

the UHRS, then it is also acceptable to multiply the high- and low-frequency controlling 

earthquake spectra by the appropriate site amplification function and envelope the results.” 

Two potential problems are identified with this wording. First, the wording states “25 points” when it 

appears it should state “30 points,” despite the problem with having 30- point rock UHRS, discussed 

previously. More importantly, two approaches are discussed. The first describes that the high- and lowfrequency developed amplification factors are applied to the entire rock UHRS spectrum, and the results 

enveloped to get the corresponding soil UHRS. This approach does not appear to be correct. Even as 

shown in the example in the draft guide, the high-frequency rock spectrum used as input for site response 

analysis has higher spectral values at high frequencies than the low frequency rock spectrum at those high 

frequencies. Due to nonlinear site response, it may be expected that the low-frequency amplification 

factors at those high frequencies will be higher than the corresponding high-frequency amplification 

factors at those high frequencies; however, this real possibility is reversed in Figure E.2. Given nonlinear 

response as expected, the low-frequency amplification factors will give higher soil UHRS values at high 

frequencies than the application of the high-frequency amp factors at those high frequencies. This 

conclusion appears counter-intuitive however. The application of the second “acceptable” method 

appears more reasonable and what the industry has usually followed. Note that this same methodology is 

again repeated in Section E.4. 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 31 

NRC Response: 

As noted in the response to the comments at the public meeting on December 14, 2006, above, 

this wording has been changed. The comment notes that the second method discussed is 

consistent with what applicants have followed in the past. This is true because the method 

follows from the guidance in Regulatory Guide 1.165. However, it has been removed from 

Regulatory Guide 1.208 to promote overall consistency with the basis that is the focus of this 

document. Regulatory Guide 1.165 will continue to be accepted as an alternate to Regulatory 

Guide 1.208. 

 

Resolution: 

The staff has edited this language in this section has been edited for clarity and consistency. 

7.2 Alternative Time History Based Site Response Techniques 

NEI General Comment 3b (December 7, 2006) 

Approaches 2A, 2B, 3, and 4 described in NUREG/CR-6728 and -6769 all are reasonable methods for 

performing the dynamic site response evaluations that represent the site material variability estimates and 

should be permitted for use in regulatory practice. 

NRC Response: 

See the response at the end of this section. 

NEI Specific Comment 17 (December 7, 2006) 

On page 16, section C.4.3, “Site Amplification Function,” second sentence states “To determine the 

UHRS..., multiply the rock based UHRS by the high frequency and low-frequency site amplification 

functions separately, and envelop the two results.” This appears to be a recommendation for method 2A. 

Please note that the industry comment in the cover letter provides a recommended rewording of this 

sentence. 

NRC Response: 

See the response at the end of this section. 

Public Comments at NRC Public Meeting Comment 7 (December 14, 2006) 

Industry representatives noted that DG-11146 should address dynamic site response analysis approaches 

to (1) develop site response function and (2) to obtain UH response spectra at surface/control locations. 

In particular it should accept approaches 2A, 2B, 3, and 4 from NUREG/CR-6728 and 6729 explicitly. 

Industry representatives asked the NRC if there is anything that they [industry] could do to make the NRC 

more comfortable with these approaches. 

NRC Response: 

See the response at the end of this section. 

EPRI Minutes NRC Public Meeting Comment 3 (December 14, 2006) 

The descriptions in DG-1146 of dynamic site response analysis appear to relate only to method 2A of 

NUREG/CR 6728. Methods 2B, 3 and 4 are more accurate and should also be acceptable. 

NRC Response: 

See the response at the end of this section. 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 32 

Bechtel Comment 1c (December 13, 2006) 

The single most important change between RG 1.165 and DG-1146 is the change from the reference 

probability approach to the performance-based approach. This change, principally by reference to ASCE 

43-05, is well defined and easy to follow. There are, however, a number of fundamental issues within 

NRC regulations and their CFR antecedents that neither RG 1.165 nor DG-1146 address. Principle 

among these is: 

b. Clear definition of an acceptable method to analyze site-specific amplification. 

NRC Response: 

See the response at the end of this section. 

Dr. Carl Constantino Comment 1 (December 2, 2006) 

The current draft implies the use of Method 2A only in the description. 

NRC Response: 

See the response at the end of this section. 

Bechtel Comment 32c (December 13, 2006) 

Page E-2, 4th paragraph of Section E.3, “Site Response Analysis.” 

c. The methodology presented in this Appendix follows Approach 2 given in NUREG/CR-6728. 

There is no discussion of other approaches (e.g., Approach 3 or 4). Consideration should be 

given to including Approaches 3 and 4. 

NRC Response: 

See the response at the end of this section. 

Jeffrey K. Kimball Comment 9 (December 13, 2006) 

Appendix E provides guidance related to seismic wave transmission analysis including section E.3, Site 

Response Analysis. The NRC sponsored a comprehensive study of ground motion related issues, 

published as NUREG/CR-6728, Technical Basis for Revision of Regulatory Guidance on Design Ground 

Motions: Hazard and Risk Consistent Ground Motion Spectra Guidelines. Chapter 6 of NUREG/CR6728 describes procedures for developing hazard consistent spectra on soil, and provides 4 approaches for 

developing soil ground motions. While Appendix E of DG-1146 provides useful guidance on site 

response related issues, the approach for developing soil ground motions represents only 1 of the 4 

approaches from NUREG/CR-6728 (approach 2). This would suggest that NRC does not encourage any 

of the other 3 approaches described in NUREG/CR-6728. Section E.3 of Appendix E should be 

expanded to provide guidance for completing soil ground motions following approaches 3 and 4 from 

NUREG/CR-6728. 

NRC Response: 

See the response at the end of this section. 

Similar comments are also included in NEI General Comment 3a (December 7, 2006). 

NRC Response: 

The NRC staff recognizes that this is an important issue. The NRC staff is in agreement that 

while one acceptable site response method has been discussed in detail in DG-1146, other 

approaches can also be accepted, including the alternate methods described in NUREG/CR-6728. 

The NRC staff also recognizes that the prescriptive nature of the appendices in DG-1146 may 

have lead to confusion. 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 33 

Resolution: 

Appendices D and E of regulatory guide 1.208 will be edited to make them less prescriptive. A 

comment on the acceptability of other methods, particularly those in NUREG/CR-6728, will be 

added. 

7.3 Random Vibration Theory (RVT) 

NEI Specific Comment 8 (December 7, 2006) 

On page 8, topic “Site Response Analysis,” second line, the words “may be” should be inserted prior to 

“used.” A frequency-domain procedure (RVT) can be used for site response, which is just as valid as a 

time-domain procedure. 

NRC Response: 

The existing language can be expanded to better address random vibration theory (RVT). 

Resolution: 

The staff will incorporate some discussion in DG-1146. 

NEI Specific Comment 9 (December 7, 2006) 

Also, the time-domain procedure is assumed on pages 57-58 (Pages E-2 and E-3) in the discussion of 

time histories and required sets of randomized parameters. This discussion should be changed to at least 

say, “If a time-domain procedure is used to calculate site response....” 

NRC Response: 

The existing language can be expanded to better address random vibration theory (RVT). 

Resolution: 

The staff will incorporate some discussion in DG-1146. 

NEI Specific Comment 26 (December 7, 2006) 

On page E-1, section E.1 item (2), the words, “If a time-domain procedure is used to calculate site 

responses,” should precede “Performing a suite of site...” This is consistent with our comment 8. 

NRC Response: 

The existing language can be expanded to better address random vibration theory (RVT). 

Resolution: 

The staff will incorporate some discussion in DG-1146. 

Bechtel Comment 6d (December 13, 2006) 

RG 1.165 gave few details concerning computing of site-specific amplification factors. DG-1146, 

benefiting from experience beginning to be gained from work on recent ESP and COL applications, 

attempts to do more to help applicants in this regard. However, further changes and clarifications to the 

wording are needed. A few specific examples of topics needing clarification or correction are: 

d. Silence on (or implied exclusion of) RVT rather than SHAKE, and Approach 4 rather than 

Approach 2 (NUREG/CR-6728), analysis of site-specific amplification factors. 

NRC Response: 

In general, either time history and RVT-based procedures can be used if the appropriate issues are 

addressed. 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 34 

Resolution: 

The staff will add general wording on RVT to Regulatory Guide 1.208. 

Bechtel Comment 14 (December 13, 2006) 

At times, the draft guide is very specific [explicit formulas for Mbar and Dbar; 60 convolution analyses 

for site response analyses] while, at other times, the wording in the draft guide is somewhat vague about 

certain issues [site response methods, e.g. Method 2A/3; number of time histories to be used in site 

response analysis]. As a result, a number of issues are not resolved in the draft guide: 

• NRC-acceptable approaches on site response: 2A, 2B, 2A/3 

• Use of RVT 

• Sigma: not just truncation of epsilon, but what of limiting sigma itself. It is recommended that 

these issues be addressed in the draft guide. 

NRC Response: 

For a discussion of sigma, please see the section entitled “Epsilon and Sigma Values in PSHA” 

on page 26 of this document. For a discussion of RVT, see comments above. For a discussion of 

alternate time-domain based site response methods, see Section 7.2 of this document. 

Bechtel Comment 10 (December 13, 2006).

In a number of locations, the draft guide assumes the soil column analysis is limited only to time history 

analysis. Currently, soil column analyses are also performed using the random vibration theory (RVT) 

along with randomized soil profiles and strain-dependent soil properties. For RVT analysis, guidance is 

needed on the input motion in terms of the acceleration response spectrum and its associated damping and 

duration. 

NRC Response: 

In general, the NRC staff currently prefers time history based procedures to RVT based 

procedures, although both are acceptable. Research on RVT is ongoing and any guidance 

developed by the NRC staff will be provided in revisions of Regulatory Guide 1.208. 

Resolution: 

General wording on RVT has been included in Regulatory Guide 1.208. 

7.4 Controlling Earthquakes for Site Response Analyses 

NEI Specific Comment 6 (December 7, 2006) 

Also on page 7, topic “Deaggregation of Mean Hazard,” first sentence lists 1E-06 as a mean annual 

probability. This probability is not needed if the ASCE/SEI Standard 43-05 Performance-Goal based 

approach is used. 

NRC Response: 

See response below Bechtel Comment 16. 

Bechtel Comment 6b (December 13, 2006) 

RG 1.165 gave few details concerning computing of site-specific amplification factors. DG-1146, 

benefiting from experience beginning to be gained from work on recent ESP and COL applications, 

attempts to do more to help applicants in this regard. However, further changes and clarifications to the 

wording are needed. A few specific examples of topics needing clarification or correction are: 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 35 

c. Confusion over the need for involving 1E-06 motions in guidelines for the SSE that, under 

ASCE 43-05, requires only 1E-04 and 1E-05 UHRS. 

NRC Response: 

See response below Bechtel Comment 16. 

Bechtel Comment 24 (December 13, 2006) 

Page 16, Section C.4.3, “Site Amplification Function.” 

This section of the draft guide states that “1E-04 and 1E-05 UHRS are used to determine the 

performance-based SSE.” On Page 15, Section C.3.5, consideration of 1E-06 annual frequency is also 

required. If the first two are adequate to define the performance-based seismic design criteria, why is the 

higher level of ground motion considered? See also the comment for Page 14, Section C.3.4. 

NRC Response: 

See response below Bechtel Comment 16. 

Bechtel Comment 16 (December 13, 2006) 

Page 7, “Deaggregation of Mean Hazard,” and Appendix E. It is not clear why motion at 1E-06 is needed 

if the ASCE performance based approach is used. See also the comment for Page 14, Section C.3.4. 

NRC Response: 

Although the 1 E-06 annual probability is not used as a basis for design, it is requested by the 

NRC staff for several reasons. This information is used as a check for reasonableness against 

historic seismicity and against the seismic source database. This information is also used with 

fragility curves to calculate core damage frequency. The NRC staff also needs the full range of 

hazard curves for ongoing work to confirm that existing methods ensure adequate performance. 

Lastly, an important application for the 1 E-06 curves is to verify the performance based results 

when hazard slope behaves non-linearly on a log-log plot after applying CAV filters. 

Resolution: 

This staff has added information to Regulatory Guide 1.208. 

Bechtel Comment 18 (December 13, 2006) 

Page 7, “Deaggregation of Mean Hazard.” This section defines the high frequency range as between 5 to 

10 Hz. This definition appears to be inconsistent with many studies which define the high frequency 

motion as greater than 10 Hz. This discrepancy should be addressed. 

NRC Response: 

This comment applies to a section that discusses site response analyses. The deaggregation of the 

mean hazard is performed for the purpose of choosing meaningful controlling earthquakes, which 

are themselves used as a basis for development of time histories necessary for time-domain based 

site response analyses. The term high frequency in this context relates to the high frequency end 

of the frequency band that impacts soil response. In the discussions of other topics, particularly 

incoherency, the term high frequency relates to the range of frequencies that are of particular 

interest for hard rock sites. Because the frequency range of interest is different for soil and hard 

rock, the description of what constitutes high frequency also differs. 

Resolution: 

No changes to DG-1146 are required. 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 36 

Dr. Carl Constantino Comment 17 (December 2, 2006) 

FigE.1: The figure shows the low frequency controlling earthquake spectrum matching the mean UHRS 

at about 3 Hz rather than at 1.75 Hz and the high frequency controlling earthquake matching at 6.5 Hz 

rather than 7.5 Hz. The word spectra should be changed to spectrum on the figure. 

NRC Response: 

The plot has been removed in an effort to bring better cohesion to the overall document. 

Resolution: 

The plot has been removed in an effort to bring better cohesion to the overall document. 

Bechtel Comment 31a (December 13, 2006) 

Page D-5, Step 9. 

a. The draft guide states that the controlling spectra should be based on the magnitude and 

distance values taken from the deaggregation and appropriate ground motion models. Later 

in Section D.3, which gives an example for a CEUS site, the draft guide comments that an 

appropriate ground motion model would be the EPRI attenuation ground motion models. It is 

noted that, for current ESP and COL applications, controlling spectra have been/are being 

developed based on the CEUS spectral shapes given in NUREG/CR-6728 rather than the 

EPRI ground motion model. This was performed based on the ease of use and also because 

the CEUS spectral shapes are defined for additional spectral periods over the range of 100 Hz 

to 0.1 Hz. It is recommended that the draft guide identify this alternate acceptable approach. 

NRC Response: 

The NRC staff agrees with this comment. 

Resolution: 

The staff has added language that identifies the use of NUREG/CR-6728 spectral shapes as an 

acceptable approach. 

Bechtel Comment 31b (December 13, 2006) 

Page D-5, Step 9. 

b. This step describes where the high- and low-frequency spectra are scaled to match the “site 

rock accelerations at 5 and 10 Hz (high-frequency) and 1 and 2.5 Hz (low-frequency).” Does this 

mean at 7.5 and 1.75 Hz, respectively? What about the remaining 26 spectral ordinates that were 

required to be calculated in the PSHA? Also, note the following wording from Section C.4.3: 

“Based on the suite of site response analyses described in Regulatory Position 4.2, site 

amplification functions are calculated. To determine the UHRS at the free-field ground 

surface for a specific annual probability of exceedance, multiply the rock-based UHRS 

by the high-frequency and low-frequency site amplification functions separately, and 

envelop the two results. If the two controlling earthquake response spectral shapes cover 

a broad range of frequencies such that when scaled and enveloped they approximate the 

UHRS, then it is also acceptable to multiply the high- and low-frequency controlling 

earthquake spectra by the appropriate site amplification function and envelope the results. 

The surface 1 E-04 and 1 E-05 UHRS are used to determine the performance-based 

SSE.” 

The typical scaling to the 7.5 and 1.75 Hz often causes the high frequency spectral shape to 

sometimes notably exceed the available high frequency PSHA values -- e.g., 25 Hz and PGA 

PSHA value. Similarly, the low-frequency spectral shape scaled typically to 1.75 Hz underrepresents the available low frequency PSHA values -- e.g., 0.5 Hz. It is recommended that 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 37 

Appendix D provide a discussion about the spectral scaling and the actual PSHA values, as does 

ASCE 43-05. Also, it is recommended that Appendix D continue with the example to 

completion, performing the spectral scaling and enveloping. 

NRC Response: 

The purpose of the controlling earthquakes concept as provided in the appendices is to provide a 

technical basis for the development of input ground motions to be used in one simplified method 

of approaching site response analyses. Because soil response is non-linear, it is important that the 

loads applied are similar to those that contribute most to the hazard at the return period (and 

frequency range) of interest. Two controlling earthquakes are used in the example. If the 

frequency ranges represented by these two spectra have a significant gap (such that the 

amplification factors for that range would not be accurate), then additional controlling 

earthquakes should be added to address this gap. 

If the analyst believes that the controlling earthquakes will not ultimately lead to an accurate 

estimation of the impact of site response, then a more complex and robust method should be used. 

This is just one method that is acceptable for many cases; but there are other methods that address 

time history development in different ways. The important factor is that any method used, be it 

simplified or complex, must accurately determine the final site specific ground motion. 

Resolution: 

The staff has added a comment on instances in which there are gaps over significant frequency 

ranges and included a reference to NUREG/CR-6827 in Regulatory Guide 1.208. 

Bechtel Comment 28 (December 13, 2006) 

Appendix D, General. Appendix D is specific about the method of determining controlling earthquakes. 

In a couple of locations, however, the wording could be more explicit in description: 

• Step 2(b) says to “calculate the average of the ground motion level . . . .” So as not to cause 

confusion, this wording could explicitly say “linear average . . .” or even “simple linear 

average....” 

• Appendix D mentions that there may be situations where “alternative binning schemes as well as 

a study of contributions from various bins will be necessary to identify controlling earthquakes 

consistent with the distribution of the seismicity.” One of the different binning schemes could be 

a re-defining of the distance bins, the center value being the “centroid of the ring area.” It would 

be most helpful to explicitly define this or give a reference for its calculation. Also, a definition 

of the “centroid of the ring area” should be included. 

NRC Response: 

The first change proposed in the comments would add clarity to Regulatory Guide 1.208. The 

second comment discusses alternative binning schemes. The comment in Regulatory Guide 

1.208 was not meant to imply different methods of defining distance. Rather, it was meant to 

allow for alternative bin allocations based on the locations and seismic potential of sources used 

in the PSHA. 

Resolution: 

The staff has edited Regulatory Guide 1.208 to address the first comment. No changes are 

required based on the second comment. 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 38 

Bechtel Comment 36 (December 13, 2006) 

Page E-3. De-aggregated scaled rock spectra may exceed the rock UHRS as shown in Figure E.1. The 

soil amplifications are computed using the de-aggregated motion. This may “overdrive” the soil column 

when compared to the rock UHRS motion and, depending on the site and its degree of soil nonlinearity, 

may reduce the soil amplification. It may best to “conform” the scaled de-aggregated to the rock UHRS 

before it is used for soil column analysis. The resultant soil amplifications can be applied to the rock 

UHRS to obtain soil UHRS. 

NRC Response: 

The example provided is only one option for performing site response analyses. This method 

represents one of the more simplified approaches discussed in NUREG/CR-6728. In some cases, 

issues can occur that lead the analyst to use a different method. It is expected that simplified 

methods, and indeed all methods, are chosen to best address the issues at hand. If this simplified 

method is used, it may be expected that the scaled rock spectra will exceed the UHRS at some 

points. 

Resolution: 

The staff has edited DG-1146 to discuss alternate site response methods, particularly those in 

NUREG/CR-6728. 

7.5 Additional Comments 

Dr. Carl Constantino Comment 15 (December 2, 2006). 

Line D377 “..a deaggregation of the mean PSHA.” 

NRC Response: 

The clarification is required. 

Resolution: 

The staff has incorporated the proposed changes. 

NEI Specific Comment 27 (December 7, 2006) 

On page E-2, section E.3, “Site Response Analysis,” fourth paragraph, fifth line, the word “within” 

should be replaced with the word “outcrop.” 

NRC Response: 

See response below.

Bechtel Comment 33 (December 13, 2006) 

Page E-2, 5th paragraph of Section E.3, “Site Response Analysis.” It is suggested that the word “within” 

be revised to “outcrop.” 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 39 

NRC Response: 

The within motion is correct in the context in which it was intended, though the wording in DG1146 is confusing. Thus, some additional wording is in order. This line was added because, in 

the experience of NRC staff, some analysts do not realize that many site response programs must 

first convert the original outcrop motion to a within motion. 

Resolution: 

The staff will revise the wording. 

Dr. Carl Constantino Comment 11 (December 2, 2006) 

 The issue of the number of convolution analyses needed for the Monte Carlo procedure depends upon the 

parameters of the soil column and the requirements for output. Typically, we have found that 30 are 

adequate to achieve the mean iterated profile and the mean estimate of the surface spectrum. Increasing 

this to 60 is fine and is in fact what we typically do to get a better estimate of the UB and LB site profile. 

However, to achieve a “reliable” estimate of the standard deviation may require more than 60 realizations. 

NRC Response 

The NRC staff agrees with the comment. 

Resolution 

The staff will add appropriate wording to Regulatory Guide 1.208. 

Bechtel Comment 32a (December 13, 2006) 

Page E-2, 4th paragraph of Section E.3, “Site Response Analysis.” 

a. The draft guide states that the spectra from the controlling earthquakes (i.e., high and low 

frequency cases) must be checked against the uniform hazard spectrum at the natural period 

of the soil column. The controlling earthquake must envelop the UHS at this spectral period. 

It is noted that, to our knowledge, this additional check has not been/is not being performed 

for the current ESP and COL applications, although it is not expected to be violated. 

NRC Response: 

Because the technique detailed in DG-1146 is a simplified method, some checks to ensure that the 

assumptions inherent in the method are met are warranted. One assumption is that the scenarios 

used appropriately capture likely soil behavior. Because the soil response is highest at the natural 

period of the soil, applying a suite of cases that are deficient in this range violates the assumptions 

of the simplified procedures. The NRC staff has begun to perform this check. 

Resolution: 

The staff has added text to Regulatory Guide 1.208 explaining the purpose of this check. 

Bechtel Comment 32b (December 13, 2006) 

Page E-2, 4th paragraph of Section E.3, “Site Response Analysis.” 

b. The guide states that it is common practice to provide plots of PGA as a function of depth. It 

is noted that this may not have been done for the past ESP applications. 

NRC Response: 

In general practice, it is a common check to review the PGA profile with depth because issues 

with G/Go curves, damping curves, and other soil properties in the model are often evident in this 

plot. 

Resolution: 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 40 

No changes will be made to DG-1146

Bechtel Comment 37 (December 13, 2006) 

Pages E-4 through E-6. It would be preferable if Figures E.1, E.2, and E.3 were based on the same 

example to provide a sense of the effects of various variables. 

NRC Response: 

Some of the figures have been removed to streamline Regulatory Guide 1.208. 

Resolution: 

Because only one of the figures remains in Regulatory Guide 1.208, no actions are required by 

the staff. 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 41 

8 Range and Number of Frequencies Provided for Review

NEI Specific Comment 15 (December 7, 2006) 

On page 14, section C.3.4 “Hazard Assessment,” a proposed re-write of this section is follows. It reflects 

the fact that hazard analyses can only be performed at structural frequencies for which equations have 

been developed for the probabilistic seismic hazard program; and the fact that fractile levels of 0.16, 0.5, 

0.84, as well as mean are the most meaningful and adequately represent the seismic hazard for a site. 

Report fractile hazard curves at the following fractile levels (p) for each ground motion 

parameter: 0.16, 0.50, 0.85, as well as mean. Report the fractile hazard curves in tabular as well 

as graphical format. Also, determine the mean UHRS for annual exceedance frequencies of 1 E04, 1 E-05, and 1E-06 at a minimum of 30 structural frequencies approximately equally spaced 

on a logarithmic frequency axis between 100 and 0.1 Hz. 

NRC Response: 

The proposed change in text provides a clear indication of the information desired. 

Resolution: 

The proposed change will be included in DG-1146 with the exception that the request for the 0.05 

and 0.95 fractile will remain. 

NEI Specific Comment 5 (December 7, 2006) 

On page 7, topic “Spectral Frequency Range Considered in the Probabilistic Seismic Hazard Analysis,” 

last sentence should be revised as follows with the underlined portion being an addition to the sentence: 

“...the hazard assessment should be conducted at a sufficient number of frequencies so that the final 

grouped motion spectrum can be reliably represented at a minimum of 30 frequencies...” This 

clarification is needed because ground motion equations do not exist for the CEUS at 30 frequencies. 

Similarly, on page D-1, section D.2 “Procedure To Determine Controlling Earthquakes,” Step 1, third 

bullet, add between “assessment” and “at” the following words, “at a sufficient number of frequencies so 

that the final ground motion spectrum can be reliably represented.” Also, on page E-3, last paragraph, 

fourth line, the draft states, “...all 25 points...” The basis for 25 is not provided; however, we assume 

that it is a misstatement of “a minimum of 30 frequencies.” If this is the case, then inserting “sufficient 

number of frequencies so that the final grouped motion spectrum can be reliably represented” is also 

appropriate. 

NRC Response: 

See response below Bechtel Comment 22. 

Jeffrey K. Kimball Comment 7 (December 13, 2006) 

Appendix D provides a procedure to determine controlling earthquakes. Step 1 of this procedure states 

that the site-specific PSHA should be conducted at a minimum of 30 frequencies, approximately equally 

spaced on a logarithmic frequency axis between 100 and 0.1 Hz. DG-1146 provides no basis that a 

minimum of 30 frequencies are needed to accurately assess the uniform hazard spectra. This implies that 

a PSHA will require ground motion attenuation models at each of these frequencies, which is not within 

the current state of practice. While there may be a need to assess closely spaced frequencies in certain 

situations, such as higher frequencies (> 10 Hz) for hard rock sites, it will not be necessary for many 

situations in terms of accurately assessing the uniform hazard spectra. 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 42 

NRC Response: 

See response below Bechtel Comment 22. 

Bechtel Comment 6a (December 13, 2006) 

RG 1.165 gave few details concerning computing of site-specific amplification factors. DG-1146, 

benefiting from experience beginning to be gained from work on recent ESP and COL applications, 

attempts to do more to help applicants in this regard. However, further changes and clarifications to the 

wording are needed. A few specific examples of topics needing clarification or correction are: 

a. Confusion over the number of frequencies for which UHRS can be computed directly (the 7 

for which EPRI attenuation relations are defined) and the number for which UHRS are to be 

specified (variously 25 or 30 between 0.1 and 100 Hz). The seven-point UHRS can be 

interpolated/extrapolated for additional points but additional assumptions/choices must be 

made to allow this. The draft guide would be improved by giving clear detailed examples of 

acceptable methods by which this could be done. 

NRC Response: 

See response below Bechtel Comment 22. 

 

Bechtel Comment 19 (December 13, 2006) 

Page 8. The ground motion models for CEUS currently are limited to less than 10 frequency points. The 

required minimum values of 30 frequencies can only be met by interpolation of the motion in between the 

frequency points. Is this the intent? 

NRC Response: 

See response below Bechtel Comment 22. 

Bechtel Comment 1d (December 13, 2006) 

There are, however, a number of fundamental issues within NRC regulations and their CFR antecedents 

that neither RG 1.165 nor DG-1146 address. Principle among these is: 

d. Definition of spectra for frequencies both much higher and lower than the 1-10 Hz frequency 

range used for the development of the SSE. 

NRC Response: 

See response below Bechtel Comment 22. 

Bechtel Comment 22 (December 13, 2006) 

Page 14, Section C.3.4, “Hazard Assessment.” The draft guide describes that the PSHA is to be 

computed at a minimum of 30 frequencies equal spaced in log-space between 100 Hz and 0.1 Hz. In 

addition, fractile hazard curves should be computed for fractile levels of: 0.05, 0.16, 0.50, 0.84 and 0.95 

as well as the mean. Uniform hazard spectra should be developed for annual probability levels of: 1E-04, 

1E-05, and 1E-06. The requirement for computing hazard curves at 30 frequencies between 100 Hz and 

0.1 Hz is not possible due to the limitation of the number of spectral periods contained in the current 

attenuation ground motion models. In addition, even ground motion attenuation models for the WUS do 

not typically go out to 10.0 second spectral period (i.e., 0.1Hz). The computation of the additional fractile 

levels and three AEP levels is not technically difficult or laborious, however, it is noted that this 

computation is not being performed for the current ESP and COL applications. No later discussion was 

found in the draft guide where the 1E-06 level ground motions are used. In fact, at the end of Section 

C.4.3 on Page 16, the draft guide states, “The surface 1E-04 and 1E-05 UHRS are used to determine the 

performance-based SSE.” 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 43 

NRC Response: 

In DG-1146, ground motion values at 30 frequencies ranging from 100 and 0.1 Hz are requested. 

While attenuation relationships do not directly calculate values at 30 frequencies within this 

range, it is common to interpolate between points to create a more robust (and smoother) hazard 

curve. This interpolation is also required for actions such as performing spectral matching on 

time histories to be used in time-history based site response and SSI analyses. Typically, 

interpolation is performed for points equally spaced on a logarithmic frequency axis, though the 

results sometimes differ between analysts. The NRC staff has requested data at 30 points to 

ensure that the more robust and smoothed response spectrum being considered in reviews is the 

same for both the applicant and the NRC reviewers. 

The staff also requests that a wide range of frequencies be reported. It is noted that attenuation 

relationships do not provide values for the full range of frequencies requested and CEUS and 

WUS relationships provide different ranges of frequencies. In the case of low frequency (long 

period) motions, one method that can be used to extrapolate the hazard curve is the 1/T to 1/T2

method. FEMA Report 450 provides a map of the long-period transition period for the United 

States and a description of the technique. 

High frequency ranges beyond those provided by attenuation relationships are in a range where 

accelerations are assumed to become constant (approaching an infinitely stiff medium and the 

true PGA). As a result, the hazard levels calculated at the highest frequency provided by the 

attenuation relationship can be used for higher frequencies. 

For the concerns regarding the 1 E-06 hazard curves, please see the response to Bechtel Comment 

16. 

Resolution: 

No changes will be made to DG-1146.
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 44 

9 Earthquake Recordings (Time Histories)

NEI Specific Comment 31 (December 7, 2006) 

We recommend that Appendix F be modified to state that if a suite of time histories are being developed 

for use in site response analysis, that the criteria for spectral matching should be applied to the average 

response spectra for the suite of time histories. 

NRC Response: 

The NRC staff agrees with the comment though Appendix F already notes that the criteria apply 

to “the average of all accelerograms.” However additional wording will be included to improve 

clarity. 

Resolution: 

The staff has edited DG-1146. 

Bechtel Comment 23 (December 13, 2006) 

Page 15, Section C.4.2, “Dynamic Site Response.” The draft guide describes that, based on the high and 

low frequency target spectra from the deaggregation analysis, the site response is performed on a suite of 

randomized soil profiles and dynamic properties. Generally, at least 60 randomized cases should be 

performed to define the mean and standard deviation of the site response. Time histories can be selected 

from the NUREG/CR-6728 database or developed separately for the controlling earthquake and 

corresponding spectra (i.e., high and low frequency). It is noted in the draft guide that the library of time 

histories provided in NUREG/CR- 6728 is currently being updated and should be completed in the 

summer of 2007. The draft guide does not, however, present any information on the changes being made. 

It could be updating the time history libraries based on the collection of additional strong motion data 

(e.g., PEER NGA) since the original database was compiled. The discussion presented in the draft guide 

indicates that only SHAKE analysis would be acceptable for the site response analysis since the draft 

guide discusses the use of time histories which would not be needed in an RVT site response analysis. 

Although the draft guide suggests a suite of 60 randomized soil profiles, the draft guide does not discuss 

the use of multiple time histories matched to the same target spectrum. The draft guide states that 60 

cases should be used to develop the mean and standard deviation of the site response; however, the 

standard deviation is not needed for the approach presented later in the document (i.e., approach 2 not 

approach 3 or NUREG/CR-6728). It is recommended that the wording on these issues in the draft guide 

be revised for clarity. 

NRC Response: 

The project to update NUREG/CR-6728 is ongoing and includes a review of the hazard curves 

and the time history database in light of current information. At this time, a discussion of the 

results cannot be provided. The use of multiple time histories is not discussed in DG-1146, but 

should be included in Regulatory Guide 1.208. Although the standard deviation of the site 

response is not further discussed in this document, it is required for later use in SSI and other 

analyses. The comment on RVT is addressed in Section 6.3 of this document. A discussion of 

RVT can be added to Regulatory Guide 1.208. 

Resolution: 

The staff has added information in Regulatory Guide 1.208 as noted. 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 45 

Bechtel Comment 38 (December 13, 2006) 

Pages F-1 and F-2. Appendix F provides the necessary criteria when developing spectrum compatible 

time histories. These criteria are very similar to the spectral matching criteria given in both NUREG/CR6728 and ASCE 43-05. One additional check that is contained in these criteria is that the mean ratio 

(match to target spectrum) be greater than 1.0 over the frequency range of 0.2 - 25.0 Hz. It is noted that, 

although this specific criterion may not have been explicitly checked for some of the spectral matches for 

the previous ESP applications, it is not expected to be violated based on meeting the other matching 

criteria (e.g., no more than 9 consecutive points below the target). 

NRC Response: 

The NRC staff agrees with the comment. 

Resolution: 

The staff will include this check in Regulatory Guide 1.208. 

Dr. Carl Constantino Comment 12 (December 2, 2006) 

Line 556 (Section 4.2, last paragraph), “....the response spectrum and have characteristics appropriate for 

the controlling earthquake.” 

NRC Response: 

The NRC staff agrees with the comment. 

Resolution: 

The staff will update wording in DG-1146 as recommended. 

Dr. Carl Constantino Comment 5 (December 2, 2006) 

Some of the records in the CEUS bins appear to have some issues. I presume that this is not the place to 

discuss the problems, but the DG should indicate that care needs to be employed when using these records 

for site response calculations. 

NRC Response: 

The NRC staff has looked into this question with the document authors, who noted that the 

records provided in the CEUS bins are expected to be used as seed motions that can be adjusted 

using a spectral matching program such as RASCAL or RSPmatch, if necessary. 

Resolution: 

The staff has addressed this issue in Regulatory Guide 1.208. 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 46 

10 Incoherency Transfer Function

Note that NRC staff review of the Incoherency Transfer Function is ongoing. This subject will be more 

fully addressed in SRP 3.7. 

NEI General Comment 2 (December 7, 2006) 

Acceptance of the use of the incoherency function as presented in the Task S2.1 reports is very important 

for utilities to file their COLs. The timeline for making plant siting decisions is critically short, and a 

common and satisfactory understanding must be reached shortly in order to support already established 

COL schedules. 

NRC Response: 

See discussion below EPRI Minutes of NRC Public Meeting Comment 1. 

Public Comments at NRC Public Meeting Comment 3 (December 14, 2006) 

Industry representatives noted that they would like incoherency explicitly mentioned in the appropriate 

NRC document(s). It was noted that they believe that incoherence effects should be incorporated into the 

SSI analyses. The function would be those proposed by EPRI and could be implemented in CLASSI and 

SASSI (perhaps in addition to other codes). It was also noted that the timeline for applicants to 

incorporate incoherency into their analyses is critically short. 

NRC Response: 

See discussion below EPRI Minutes of NRC Public Meeting Comment 1. 

EPRI Minutes NRC Public Meeting Comment 1 (December 14, 2006) 

It is critical to reach a common understanding with the NRC staff on the following topics: 1) that 

incoherency corrections to the site-specific ground response spectrum can be made, and 2) on the specific 

coherency function and methodology to be applied. 

NRC Response: 

The NRC staff understands the importance of timely review of an incoherency function in light of 

high spectral accelerations in the high-frequency range predicted by the PSHA for some CEUS 

locations. Ongoing discussions between the NRC staff and industry representatives on the topic 

of the incoherency function have been fruitful and a possible way forward was identified and 

detailed in the public meeting held on December 20-21, 2006. 

Because the method currently being proposed by industry representatives would be implemented 

as part of the SSI analyses, discussion of the incoherency function is outside the scope of 

Regulatory Guide 1.208. If an incoherency function is accepted, it would be more appropriate in 

the Standard Review Plan (NUREG-0800). 

Resolution: 

No action is required for DG-1146. However, ongoing work on the incoherency function will 

continue. 

Bechtel Comment 2 (December 13, 2006) 

The draft guide does not identify the issue that current ground motion estimates at rock sites in the CEUS 

result in high spectral accelerations in the high frequency range. This is an important issue for the 

analysis of new nuclear power plants in the CEUS region, although it is recognized that high frequency 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 47 

content is not generally damaging to typical plant structures, systems and components except for certain 

high frequency sensitive devices. It is recommended that the draft guide and/or NUREG-0800 explicitly 

address this issue, provide some discussion, and describe acceptable methods of resolution. 

NRC Response: 

It is not appropriate to discuss the issue of high ground motions in the high-frequency range in 

Regulatory Guide 1.208. However, the NRC staff is aware of the problems related to this issue 

and there in an ongoing dialogue between the NRC staff and stakeholders in relation to this topic. 

One key issue under discussion is the use of an incoherency function in SSI analyses (see 

comments above). The SSI itself will also reduce high-frequency ground motions due to the 

behavior of the NPP overall system behavior. The details of SSI are outside the scope of the 

regulatory guide, but will be addressed in Section 3.7.2 of the Standard Review Plan (NUREG0800). 

NRC staff is reviewing how an exceedance of the predicted motion above the standard plant 

design spectra will be addressed in the Standard Review Plan. Of particular interest are how 

different frequency ranges affect the individual structures, systems, and components (SSCs) and 

how exceedance in these frequency ranges should be evaluated. There is an ongoing discussion 

between the NRC staff and stakeholders that was advanced at the public meeting on December 

14, 2006. 

Resolution: 

No action is required for DG-1146. However, ongoing work on the incoherency function and 

Standard Review Plan, Section 3.7.2 will continue. 

Bechtel Comment 11 (December 13, 2006) 

The report just completed by EPRI on Task S2.1 has shown that incoherency of ground motion 

significantly affects the responses of structures on large foundations, reducing the structural response to 

the high frequency ground motions. It is also known that ground motion estimates for the CEUS at rock 

sites contain significant high frequency content as mentioned earlier. It is recommended that the draft 

guide include a discussion on the incoherency of ground motion and how it might affect the seismic 

design basis for the site. In fact, one option would be to apply the incoherency reduction during the 

process of determining the SSE. Options that are acceptable to the NRC in determining the incoherency 

effects should be discussed in the draft guide to help the industry focus on approaches that may be 

instrumental in resolving the high frequency content issues. 

NRC Response: 

As noted above, incoherency transfer functions as currently proposed by EPRI are applied in SSI 

analyses. Recent SSI analyses performed by ARES Corporation indicated that applying the 

incoherency function to reduce the SSE-based input ground motions does not produce the same 

results as when the incoherency function is applied as part of the SSI analyses directly. As a 

result, the NRC staff will not accept a reduction in the SSE ground motion based on incoherency. 

The EPRI report referenced in the comment has been superseded by more recent work. 

Resolution: 

No action is required for DG-1146. 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 48 

11 Soil-Structure Interaction (SSI)

SSI related issues will be fully addressed in relevant SRP sections. 

NEI General Comment 6 (December 7, 2006) 

Additional guidance is needed for Soil Structure Interaction (SSI) analyses using the SSE established in 

accordance with DG-1146. Industry technical committees are developing guidance for inclusion in a 

future revision of the ASCE Standards. We recognize NRC plan to include guidance in the update of the 

Standard Review Plan. The timeline for making these analyses is critically short, and a common and 

satisfactory understanding must be reached shortly in order to support already established COL schedules. 

NEI would like to have the opportunity to discuss the recommendations to be included in the Standard 

Review Plan before the Standard Review Plan is finalized. This subject could be included in the ongoing 

discussions on incorporation of incoherence in the SSI analyses. 

NRC Response: 

The NRC recognizes the importance of SSI analyses and the need for guidance development in 

this area. However, it was decided that Regulatory Guide 1.208 would not include this topic. 

Discussions related to SSI will be developed for the SRP. Changes to the SRP related to SSI will 

be developed in consultation with stakeholders and public comments will be incorporated. 

Resolution: 

No changes to DG-1146 are required. 

Public Comments at NRC Public Meeting Comment 2 (December 14, 2006) 

Industry representatives noted that they prefer to use the foundation excitation motion as that developed at 

the foundation level from the site response analyses. They further noted that they believe that the soil 

properties used for the SSI analyses should be the same as those used for the site response analyses. 

NRC Response: 

The NRC agrees that the soil properties should be consistent between the site response analyses 

and the SSI analyses, provided that changes in properties related to the change in confining stress 

are not required. 

Resolution: 

No changes to DG-1146 are required. 

Bechtel Comment 8 (December 13, 2006)

For consistency of analysis and meeting the ASCE target performance goal, the draft guide should 

provide a discussion of the application of the SSE motion and its associated strain-compatible soil 

properties for soil-structure interaction (SSI) analysis. Specifically, when randomized soil profiles are 

used, guidance for selection of limited soil columns and associated input motion for SSI analysis should 

be provided. 

NRC Response: 

As noted in the response to NEI General Comment 6 above, a discussion of SSI will not be 

included in Regulatory Guide 1.208 and is more appropriate for NUREG-0800. 

Resolution: 

No changes to DG-1146 are required. 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 49 

Bechtel Comment 4 (December 13, 2006) 

Paragraph IV(a)(1)(i), of Appendix S to 10 CFR Part 50, requires that “the SSE must be characterized by 

free-field ground motion response spectra at the free ground surface.” And that “...it will usually be 

appropriate that the design response spectra be smoothed spectra.” This language seems to imply that the 

motion is to be defined in the absence of any modification by the presence of the nuclear island (“freefield ground motion”), is unclear as to whether the “free ground surface” is in-situ at the undisturbed site 

or should include consideration of as-constructed modification of shallow soils between some at-depth 

competent material horizon and finished grade, and obscures the possibly important distinction between a 

point estimate of ground motion and an estimate of ground motion integrated over the area or the depth of 

a mat foundation, which motion will act on the structures, systems, and components (SSCs) of the nuclear 

island. 

a. It is recommended that the draft guide, NUREG-0800, and DG-1145 address these issues by 

more carefully defining the SSE and the DRS as potentially separate motions to be defined, 

respectively, in FSAR/SSAR Sections 2.5.2 and 3.7.1. Issues of modification of point ground 

motions by the foundation mat, such as may be addressed in soil-structure interaction or 

incoherency analyses, are better left to the engineering design sections of the FSAR. FSAR 

Section 2.5.2 may introduce these topics in general terms, then refer to FSAR Section 3.7.1... as 

appropriate. 

b. It is recommended that “free-field” and “free-ground surface” be defined to remove the abovenoted ambiguities. 

NRC Response: 

The SSE is defined in the free field, without the presence of the nuclear island as required by the 

regulations. The single SSE defined for a site is necessarily defined based on site conditions and 

is independent of foundation depth, backfilling, and other design-based issues that impact the 

design response spectra. As noted, these issues, as well of those related to the motions integrated 

over the mat are more relevant to SSI analyses as discussed in NUREG-0800. The staff has 

added some discussion of the difference between SSE and DRS to Section 5.1. A discussion of 

the meaning of free-ground surface has been added to Section 5.3. The suggestion that the terms 

“free field” and “free ground surface” be removed from regulations to remove ambiguities is not 

within the scope of Regulatory Guide 1.208. 

Resolution: 

As noted, the staff has added some addition language to Sections 5.1 and 5.3 

Bechtel Comment 13 (December 13, 2006) 

The SSE is required to be developed at the ground surface level. This implies a deconvolution analysis of 

the motion for embedded structures. Since the SSE is the result of a soil amplification for a wide range of 

soil columns developed by a randomization process, deconvolution in limited soil columns, particularly 

with the lower bound properties, would result in unrealistically high ground motions at the foundation 

level in the free-field. A similar problem exists if the SSE motion is defined in the free field as “outcrop” 

at any specific depth, e.g., foundation depth. The soil column analysis using limited soil columns, e.g., 

upper, mean, and lower bounds, is likely to develop motions at the ground surface level that would exceed 

the SSE if the SSE were to be developed at the ground surface using the mean results of all randomized 

profiles. This observation suggests that for application of the SSE to SSI, a consistent pair of high 

frequency and low frequency motions with their soil columns should be identified. It is recommended 

that the draft guide address this issue. 

NRC Response: 

The SSE must be defined as a free surface motion according to regulation and cannot be relocated 

based on design issues. However, a way to provide for materials that are sufficiently competent 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 50 

to be left in place has been included in Regulatory Guide 1.208. Section 5.3 provides a 

discussion of the location of the site-specific ground motion response spectrum GMRS, which 

leads to the SSE. The specific issues raised in this comment are related to design response 

spectra and to analyses used in the design phase. Regulatory Guide 1.208 will not address these 

topics in detail, but they are addressed in NUREG-0800. 

Resolution: 

No changes to Regulatory Guide 1.208 are required for this comment beyond the edits to Sections 

5.1 and 5.3 discussed elsewhere. 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 51 

12 Proposed Technical and Typographical Editing

NEI Specific Comment 3 (December 7, 2006) 

On page 5, last paragraph, second line, a period is missing between “(Refs. 9, 10)” and “A PSHA.” 

NRC Response: 

The NRC staff agrees with this comment. 

Resolution: 

The staff will incorporate the proposed changes. 

NEI Specific Comment 18 (December 7, 2006) 

On page 16, section C.5.1 “Horizontal Spectrum,” paragraph 3, sentence 1, the draft states, “The 

performance-based site-specific earthquake ground motion is developed using a method analogous the 

development of the design response spectrum (DRS)...” Add the word, “to,” after the word, “analogous.” 

NRC Response: 

The NRC staff agrees with this comment. 

Resolution: 

The staff will incorporate the proposed changes. 

NEI Specific Comment 19 (December 7, 2006) 

On page 16, section C.5.1 “Horizontal Spectrum” in the explanation of equation 1, there is a reference to 

Regulatory Position 4.4. It is assumed that this reference should be to Regulatory Position 4.3 since there 

is no Regulatory Position 4.4. 

NRC Response: 

Regulatory Position 4.3 was intended. 

Resolution: 

The staff will incorporate the necessary changes. 

NEI Specific Comment 30 (December 7, 2006) 

On page E-6, section E.4, “Free-Field Ground Surface Uniform Hazard Response Spectra,” our comment 

19 applies to this paragraph. 

NRC Response: 

See NEI Specific Comment 19. 

Resolution: 

The staff will incorporate the necessary changes. 

NEI Specific Comment 24 (December 7, 2006) 

On page C-8, second paragraph, first sentence, second line, add a space between the word “with” and the 

word “previous,” and add a space between the word “the” and “following.” 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 52 

NRC Response: 

The NRC staff agrees with this comment. 

Resolution: 

The staff will incorporate the proposed changes. 

Bechtel Comment 29 (December 13, 2006) 

Page D-3, Table D.1. The entries to the cells of the table should be stated. 

NRC Response: 

See response to NEI Comment 25, below. 

Resolution: 

No changes to DG-1146 are required. 

NEI Specific Comment 25 (December 7, 2006) 

On page D-3, Table D.1, the entries to the cells of the table need to be provided. 

NRC Response: 

The table was provided as an example for the reader’s convenience 

Resolution: 

No changes to DG-1146 are required. 

NEI Specific Comment 29 (December 7, 2006) 

On page E-5, Figure E.2, the ordinate label should be “Response Spectral Ratio” instead of “Response 

Spectral Rati.” 

NRC Response: 

The NRC staff agrees with this comment. 

Resolution: 

The staff will incorporate the proposed changes. 

Dr. Carl Constantino Comment 16 (December 2, 2006). Line E750 These strain-dependent models 

are typically referred to as the EPRI-93 curves. Should also include the reference for these. 

NRC Response: 

While the EPRI-93 curves are not the only ones available, the staff will include a reference to 

them. 

Resolution: 

The staff has added the reference to the text and to the list of references in Appendix E. 

Bechtel Comment 30 (December 13, 2006) 

Pages D-4 and D-5, Step 7. 

a. There is explanation of the calculation required if the contribution to the hazard calculated in 

Step 5 [1 - 2.5 Hz] for distances of 100 km or greater is less than 5%. (sb. greater than) 

b. Revise the last subscript in Equation 7 from “1” to “2.” 

NRC Response: 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 53 

The wording as shown is not in DG-1146. 

Resolution: 

No changes to DG-1146 are required. 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 54 

13 Comments on Specific Plant Applications

Jeffrey K. Kimball Comment 6 (December 13, 2006) 

To compound these issues, the recent submission of the Vogtle ESP application, Site Safety Analysis 

Report, further demonstrates that PSHA stability does not exist. Consistent with other ESP applications 

(North Anna, Grand Gulf, Clinton), the Vogtle applicant has chosen to use an update to the EPRI PSHA 

to assess seismic hazard and establish appropriate ground motion for seismic design. The update to the 

EPRI PSHA for Vogtle, however, is significantly different than the EPRI PSHA work used by the 

preceding three ESP applicants, and inconsistent with material provided by EPRI as part of the ongoing 

dialog regarding resolution of seismic hazard issues (Program on Technology Innovation: Assessment of 

a Performance-Based Approach for Determining Seismic Ground Motions for New Plant Sites, V1 

Performance-Based Seismic Design Spectra, V2 Seismic Hazard Result at 28 Sites; EPRI Technical 

Reports (1012044 and 1012045). Specific issues related to the EPRI PSHA update used for Vogtle are 

provided following the remaining comments. 

Jeffrey K. Kimball Comment 10 (December 13, 2006) 

Specific issues related to the EPRI PSHA update used for Vogtle ESP application, Site Safety Analysis 

Report 

• The Charleston seismic source is modeled using four possible source delineations applied to each 

of the EPRI seismic source teams. Modification of the EPRI team(s) Charleston sources, by 

necessity, requires modification of other sources (given that the revised Charleston source areas 

no longer match the aerial extent from the EPRI expert teams). This implies that the seismic 

sources beyond Charleston also need revision, not just to fill the aerial gap, but because 

Charleston is more restricted, with more frequent large earthquakes, judgments regarding nearby 

seismic sources would likely also change. The aerial gap was addressed by allowing portions of 

“old” EPRI source zones that lie outside the new replacement Charleston source zone to default 

to the existing EPRI background zones for each team. Why such an approach is assumed to 

represent the informed technical community, based on seismic source definitions that are about 

20 years old, is subject to debate. To maintain the PSHA process the expert teams should be the 

ones to agree to these adjustments. This change by itself implies that the updated EPRI PSHA 

results are inconsistent with the SSHAC process and objective of representing the informed 

scientific community (versus the views of the applicant’s contractor). 

• A key argument for not revising much of the EPRI team seismic sources relates to lack of 

paleoseismic evidence and stability of seismic activity rates outside of Charleston. Such a 

conclusion strongly suggests that there would be little technical basis for modifying the LLNL 

expert seismic sources in those locations. The basis for ignoring the LLNL seismic sources in 

terms of representing views of the informed scientific community has not been provided. 

• Review of the USGS PSHA input suggests that there is much less scientific community support 

for aerial seismic sources beyond those locations which have paleoseismic evidence for large 

prehistoric earthquakes in the central and eastern United States (CEUS). It is not clear why 

applicants would not be required to incorporate this information into their PSHA work, especially 

given that this seismic source input is much more recent compared to those portions of the EPRI 

or LLNL PSHA based on seismic source input from the 1980’s. Additionally, differences 

between EPRI and USGS for the Charleston seismic source should be evaluated. 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 55 

• Review of EPRI PSHA input for the southeast US indicates that at least one team has areas where 

there is no host seismic source zone for a large percentage of the time (Dames and Moore team, 

seismic source 53, Southern Appalachian Mobile Belt). When this zone does not exist 

(probability of activity = 0.26) there does not appear to be a replacement seismic source zone. It 

is not clear that such a view represents the informed scientific community today, especially given 

the information contained in the USGS national seismic hazard map. Review of the USGS PSHA 

input to the national map indicates that no location in the CEUS should be judged as having no 

local seismic hazard. The recent moment magnitude 6.0 earthquake in the intraplate region of the 

Gulf of Mexico provides additional evidence that moderate sized earthquake can occur anywhere. 

A complete technical review of the EPRI PSHA input is needed before it should be supported as 

providing adequate input for a mean PSHA assessment. 

• Application of the USGS PSHA code for hard rock site conditions for the Vogtle site location 

would likely show different mean PSHA results for all annual probability levels. Any differences 

between EPRI and USGS should be evaluated in detail, to determine if both results can be 

supported and should be used to represent mean PSHA derived ground motions. The figure 

provided below compares uniform hazard spectra for a return period of 10,000 years between the 

Savannah River Site (USGS results) and the Vogtle site (modified EPRI results) both for hard 

rock site conditions, suggesting the PSHA stability does not exist. 

Vogtle vs USGS Hard Rock PSHA 10,000 Year UHS

0.01

0.1

1

0.1 1 10 100

Frequency (Hz)

Spectral Acceleration (g)

EPRI Vogtle

SRS USGS

NRC Response: 

Regulatory Guide 1.208 will not discuss individual facilities. The NRC staff is currently 

reviewing the Vogtle application and will document its findings in the final SER. USGS 

is actively assisting staff in this review process. 

Resolution: 

No changes to Regulatory Guide 1.208 are required.
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 56 

14 Chronological Table of Public Comments

Comment Identifier Topic Page 

1 Dr. Carl Constantino Comment 1 (December 2, 2006) Alternative Time History Based 

Site Response Techniques 

32 

2 Dr. Carl Constantino Comment 2 (December 2, 2006) General 11 

3 Dr. Carl Constantino Comment 3 (December 2, 2006) Definition of SSE 6 

4 Dr. Carl Constantino Comment 4 (December 2, 2006) SSE versus Design Response 

Spectrum and Risk Consistent 

Spectrum 

10 

5 Dr. Carl Constantino Comment 5 (December 2, 2006) Earthquake Recordings 45 

6 Dr. Carl Constantino Comment 6 (December 2, 2006) Performance-Based Design 

Parameters 

12 

7 Dr. Carl Constantino Comment 7 (December 2, 2006) Excavations and Construction 15 

8 Dr. Carl Constantino Comment 8 (December 2, 2006) Site Investigation and Properties 

Other Comments 

18 

9 Dr. Carl Constantino Comment 9 (December 2, 2006) Site Investigation and Properties 

Other Comments 

17 

10 Dr. Carl Constantino Comment 10 (December 2, 2006) Excavations and Construction 15 

11 Dr. Carl Constantino Comment 11 (December 2, 2006) Site Response Additional 

Comments 

39 

12 Dr. Carl Constantino Comment 12 (December 2, 2006) Earthquake Recordings 45 

13 Dr. Carl Constantino Comment 13 (December 2, 2006) Site Investigation and Properties 18 

14 Dr. Carl Constantino Comment 14 (December 2, 2006) Choice of PSHA Techniques and 

Regulatory Stability 

22 

15 Dr. Carl Constantino Comment 15 (December 2, 2006) Site Response Additional 

Comments 

38 

16 Dr. Carl Constantino Comment 16 (December 2, 2006) Technical Editing 

Recommendation 

52 

17 Dr. Carl Constantino Comment 17 (December 2, 2006) Controlling Earthquakes for Site 

Response Analyses 

36 

18 NEI Interpretation 1 (December 7, 2006) CAV Filtering 28 

19 NEI Interpretation 2 (December 7, 2006) Definition of SSE 4 

20 NEI Interpretation 3 (December 7, 2006) Site Response 29 

21 NEI Interpretation 4 (December 7, 2006) Performance-Based Approach 3 

22 NEI General Comment 1 (December 7, 2006) Site Response 29 

23 NEI General Comment 2 (December 7, 2006) Incoherency Function 46 

24 NEI General Comment 3a (December 7, 2006) Attenuation Relationships 26 

25 NEI General Comment 3b (December 7, 2006) Site Response 31 

26 NEI General Comment 4 (December 7, 2006) Attenuation Relationships 25 

27 NEI General Comment 5 (December 7, 2006) Seismic Source Models 22 

28 NEI General Comment 6 (December 7, 2006) Soil-Structure Interaction 48 

29 NEI General Comment 7 (December 7, 2006) General (Appendices) 3 

30 NEI Specific Comment 1 (December 7, 2006) Definition of Hard Rock 15 

31 NEI Specific Comment 2 (December 7, 2006) Site Investigation and Properties 14 

32 NEI Specific Comment 3 (December 7, 2006) Technical Editing 

Recommendation 

51 

33 NEI Specific Comment 4 (December 7, 2006) Seismic Source Models 23 

34 NEI Specific Comment 5 (December 7, 2006) Frequencies Used in Analyses 41 

35 NEI Specific Comment 6 (December 7, 2006) Performance-Based Approach 34 

36 NEI Specific Comment 7 (December 7, 2006) Epsilon and Sigma 26 

37 NEI Specific Comment 8 (December 7, 2006) Site Response 33 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 57 

Comment Identifier Topic Page 

38 NEI Specific Comment 9 (December 7, 2006) Site Response 33 

39 NEI Specific Comment 10 (December 7, 2006) General (Regulatory Guidance) 2 

40 NEI Specific Comment 11 (December 7, 2006) HCLPF 12 

41 NEI Specific Comment 12 (December 7, 2006) Site Investigation and Properties 15 

42 NEI Specific Comment 13 (December 7, 2006) Site Investigation and Properties 14 

43 NEI Specific Comment 14 (December 7, 2006) Epsilon and Sigma 27 

44 NEI Specific Comment 15 (December 7, 2006) Frequencies Used in Analyses 41 

45 NEI Specific Comment 16 (December 7, 2006) Site Investigation and Properties 17 

46 NEI Specific Comment 17 (December 7, 2006) Site Response 31 

47 NEI Specific Comment 18 (December 7, 2006) Technical Editing 

Recommendation 

51 

48 NEI Specific Comment 19 (December 7, 2006) Technical Editing 

Recommendation 

51 

49 NEI Specific Comment 20 (December 7, 2006) Definition of SSE 6 

50 NEI Specific Comment 21 (December 7, 2006) Definition of SSE 6 

51 NEI Specific Comment 22 (December 7, 2006) General (Regulatory Guidance) 2 

52 NEI Specific Comment 23 (December 7, 2006) Technical Editing 

Recommendation 

18 

53 NEI Specific Comment 24 (December 7, 2006) Technical Editing 

Recommendation 

51 

54 NEI Specific Comment 25 (December 7, 2006) Technical Editing 

Recommendation 

52 

55 NEI Specific Comment 26 (December 7, 2006) Site Response 33 

56 NEI Specific Comment 27 (December 7, 2006) Site Response 38 

57 NEI Specific Comment 28 (December 7, 2006) Site Investigation 16 

58 NEI Specific Comment 29 (December 7, 2006) Technical Editing 

Recommendation 

52 

59 NEI Specific Comment 30 (December 7, 2006) Technical Editing 

Recommendation 

51 

60 NEI Specific Comment 31 (December 7, 2006) Earthquake Recordings 44 

61 Bechtel Comment 1a (December 13, 2006) SSE versus Design Response 

Spectrum and Risk Consistent 

Spectrum 

10 

62 Bechtel Comment 1b (December 13, 2006) Location of SSE Ground Motion 4 

63 Bechtel Comment 1c (December 13, 2006) Alternative Time History Based 

Site Response Techniques 

32 

64 Bechtel Comment 1d (December 13, 2006) Range and Number of Frequencies 

Provided for Review 

42 

65 Bechtel Comment 2 (December 13, 2006) Incoherency Transfer Function 46 

66 Bechtel Comment 3 (December 13, 2006) Performance-Based Design 

Parameters 

12 

67 Bechtel Comment 4 (December 13, 2006) Soil-Structure Interaction 49 

68 Bechtel Comment 5 (December 13, 2006) Location of SSE Ground Motion 5 

69 Bechtel Comment 6a (December 13, 2006) Range and Number of Frequencies 

Provided for Review 

41 

70 Bechtel Comment 6b (December 13, 2006) Controlling Earthquakes for Site 

Response Analyses 

34 

71 Bechtel Comment 6c (December 13, 2006) Attenuation Relationships 27 

72 Bechtel Comment 6d (December 13, 2006) Random Vibration Theory 33 

73 Bechtel Comment 7 (December 13, 2006) Performance-Based Design 

Parameters 

13 

74 Bechtel Comment 8 (December 13, 2006) Soil-Structure Interaction 48 

75 Bechtel Comment 9 (December 13, 2006) Comment 9 was missing 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 58 

Comment Identifier Topic Page 

76 Bechtel Comment 10 (December 13, 2006) General 34 

77 Bechtel Comment 11 (December 13, 2006) Incoherency Transfer Function 47 

78 Bechtel Comment 12 (December 13, 2006) Location of SSE Ground Motion 5 

79 Bechtel Comment 13 (December 13, 2006) Soil-Structure Interaction 49 

80 Bechtel Comment 14 (December 13, 2006) Random Vibration Theory 34 

81 Bechtel Comment 15 (December 13, 2006) Attenuation Relationships 27 

82 Bechtel Comment 16 (December 13, 2006) Controlling Earthquakes for Site 

Response Analysis 

35 

83 Bechtel Comment 17 (December 13, 2006) CAV Filtering 28 

84 Bechtel Comment 18 (December 13, 2006) Controlling Earthquakes for Site 

Response Analyses 

35 

85 Bechtel Comment 19 (December 13, 2006) Range and Number of Frequencies 

Provided for Review 

42 

86 Bechtel Comment 20 (December 13, 2006) Performance-Based Design 

Parameters 

12 

87 Bechtel Comment 21 (December 13, 2006) Excavations and Construction 14 

88 Bechtel Comment 22 (December 13, 2006) Range and Number of Frequencies 

Provided for Review 

42 

89 Bechtel Comment 23 (December 13, 2006) Earthquake Recordings 44 

90 Bechtel Comment 24 (December 13, 2006) Controlling Earthquakes for Site 

Response Analyses 

35 

91 Bechtel Comment 25 (December 13, 2006) Location of SSE Ground Motion 6 

92 Bechtel Comment 26a (December 13, 2006) Code Required Check on Motions 

at Foundation Level 

7 

93 Bechtel Comment 26b (December 13, 2006) Code Required Check on Motions 

at Foundation Level 

9 

94 Bechtel Comment 26c (December 13, 2006) Code Required Check on Motions 

at Foundation Level 

6 

95 Bechtel Comment 26d (December 13, 2006) Code Required Check on Motions 

at Foundation Level 

10 

96 Bechtel Comment 26e (December 13, 2006) SSE versus Design Response 

Spectrum and Risk Consistent 

Spectrum 

10 

97 Bechtel Comment 26f (December 13, 2006) Code Required Check on Motions 

at Foundation Level 

7 

98 Bechtel Comment 27 (December 13, 2006) General 3 

99 Bechtel Comment 28 (December 13, 2006) Controlling Earthquakes for Site 

Response Analyses 

37 

100 Bechtel Comment 29 (December 13, 2006) Proposed Technical and 

Typographical Editing 

52 

101 Bechtel Comment 30 (December 13, 2006) Proposed Technical and 

Typographical Editing 

52 

102 Bechtel Comment 31a (December 13, 2006) Controlling Earthquakes for Site 

Response Analyses 

36 

103 Bechtel Comment 31b (December 13, 2006) Controlling Earthquakes for Site 

Response Analyses 

36 

104 Bechtel Comment 32a (December 13, 2006) Site Response Additional 

Comments 

39 

105 Bechtel Comment 32b (December 13, 2006) Site Response Additional 

Comments 

39 

106 Bechtel Comment 32c (December 13, 2006) Alternative Time History Based 

Site Response Techniques 

32 

107 Bechtel Comment 33 (December 13, 2006) Site Response Additional 38 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 59 

Comment Identifier Topic Page 

Comments 

108 Bechtel Comment 34 (December 13, 2006) Development of Dynamic Soil 

Properties 

17 

109 Bechtel Comment 35 (December 13, 2006) Use of Site Response Transfer 

Functions 

30 

110 Bechtel Comment 36 (December 13, 2006) Controlling Earthquakes for Site 

Response Analyses 

38 

111 Bechtel Comment 37 (December 13, 2006) Site Response Additional 

Comments 

40 

112 Bechtel Comment 38 (December 13, 2006) Earthquake Recordings 45 

113 Jeffrey K. Kimball Comment 1 (December 13, 2006) Choice of PSHA Techniques and 

Regulatory Stability 

20 

114 Jeffrey K. Kimball Comment 2 (December 13, 2006) Seismic Source Characterization 24 

115 Jeffrey K. Kimball Comment 3 (December 13, 2006) Choice of PSHA Techniques and 

Regulatory Stability 

21 

116 Jeffrey K. Kimball Comment 4 (December 13, 2006) Seismic Source Characterization 32 

117 Jeffrey K. Kimball Comment 5 (December 13, 2006) Choice of PSHA Techniques and 

Regulatory Stability 

21 

118 Jeffrey K. Kimball Comment 6 (December 13, 2006) Comments on Specific Plant 

Applications 

54 

119 Jeffrey K. Kimball Comment 7 (December 13, 2006) Range and Number of Frequencies 

Provided for Review 

41 

120 Jeffrey K. Kimball Comment 8 (December 13, 2006) Definition of Rock 16 

121 Jeffrey K. Kimball Comment 9 (December 13, 2006) Alternative Time History Based 

Site Response Techniques 

32 

121 Jeffrey K. Kimball Comment 10 (December 13, 2006) Comments on Specific Plant 

Applications 

54 

122 Jeffrey K. Kimball Comment 11 (December 13, 2006) Choice of PSHA Techniques and 

Regulatory Stability 

22 

123 Public Comments at NRC Public Meeting: Comment 1 

(December 14, 2006) 

Definition of SSE 6 

124 Public Comments at NRC Public Meeting: Comment 2 

(December 14, 2006) 

Site Response/ 

Soil-Structure Interaction 

48 

125 Public Comments at NRC Public Meeting: Comment 3 

(December 14, 2006) 

Incoherency Function 46 

126 Public Comments at NRC Public Meeting: Comment 4 

(December 14, 2006) 

Epsilon and Sigma 26 

127 Public Comments at NRC Public Meeting: Comment 5 

(December 14, 2006) 

CAV Filtering 28 

128 Public Comments at NRC Public Meeting: Comment 6 

(December 14, 2006) 

Map Scaling 

129 Public Comments at NRC Public Meeting: Comment 7 

(December 14, 2006) 

Site Response 31 

130 Public Comments at NRC Public Meeting: Comment 8 

(December 14, 2006) 

Attenuation Relationships 25 

131 Public Comments at NRC Public Meeting: Comment 9 

(December 14, 2006) 

Seismic Source Characterizations 23 

132 Public Comments at NRC Public Meeting: Comment 10 

(December 14, 2006) 

Site Response 30 

133 EPRI Minutes NRC Public Meeting Comment 1 (December 

14, 2006) 

Incoherency Transfer Function 46 

134 EPRI Minutes NRC Public Meeting Comment 2 (December 

14, 2006) 

Epsilon and Sigma 27 
NRC Staff Responses to Public Comments on Draft Regulatory Guide DG-1146 60 

Comment Identifier Topic Page 

135 EPRI Minutes NRC Public Meeting Comment 3 (December 

14, 2006) 

Site Response 31 

136 EPRI Minutes NRC Public Meeting Comment 4 (December 

14, 2006) 

Attenuation Relationships 26 

137 NEI General Comment 1 (December 28, 2006) Seismic Source Characterization 23 

138 NEI General Comment 2 (December 28, 2006) Attenuation Relationships 25 

139 NEI Specific Comment 1 (December 28, 2006) Range and Number of Frequencies 

Provided for Review 

7 

140 NEI Specific Comment 2 (December 28, 2006) Proposed Technical and 

Typographical Editing 

8