ML21089A033

DG-1304 Response to Public Comments

ML21089A033
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Issue date:	08/13/2021
From:	O'Donnell E NRC/RES/DE/RGDB
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O'Donnell E
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ML21088A335	List: ML21089A033 ML21089A034 Regulatory Guide 1.243
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DG-1304 RG-1.243, Rev 0
Download: ML21089A033 (17)

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Response to Public Comments on Draft Regulatory Guide (DG)-1304 Safety-Related Steel Structures and Steel-Plate Composite Walls for other than Reactor Vessels and Containments.

Proposed Regulatory Guide (RG) 1.243 On February 10, 2021 the NRC published a notice in the Federal Register (86 FR 8928) that Draft Regulatory Guide, DG-1304, a proposed new Regulatory Guide was available for public comment. The Public Comment period ended on March 29, 2021. The NRC received comments from the individuals or organizations listed below. The NRC has combined the comments and NRC staff responses in the following table.

Comments were received from the following:

Lawrence F. Kruth for American Institute of Steel Construction ADAMS Accession No. ML21084A005 130 E. Randolph Street, Suite 2000 Chicago, Illinois 60601S ADAMS Accession No. ML21084A005 Carrie Fossaen NuScale LLC ADAMS Accession No. ML21092A005 1100 NE Circle Blvd. Suite 200 Corvallis, Oregon 97330 ADAMS Accession No. ML21092A005 Commenter Section of Specific Comments NRC Resolution DG-1304 AISC A AISC_1. 10 CFR Part 50 and 10 CFR Part 52 are referenced, but no The NRC staff does not agree with the comment. The intended reference is made to 10 CFR Part 72, Licensing Requirements for the scope of this RG is to provide guidance for applicants and Independent Storage of Spent Nuclear Fuel, High-Level Radioactive Waste, licensees under Title 10 of the Code of Federal Regulations (10 Reactor-Related Greater than Class C Waste. The draft Regulatory Guide CFR), Part 50, Domestic Licensing of Production and Utilization should include this reference since ANSI/AISC N690-18, including Steel- Facilities, and 10 CFR Part 52, Licenses, Certifications, and Plate Composite (SC) construction, may be used in these applications. Approvals for Nuclear Power Plants. However, the regulatory guide is available for case-specific use for a Part 72 facility should an applicant wish to use this RG for, as an example, steel-plate composite walls.

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Commenter Section of Specific Comments NRC Resolution DG-1304 AISC - AISC_2. The draft Regulatory Guide should also apply to Research and The NRC staff does not agree with the comment. The intended Test Reactors, and Fuels and Materials Facilities. scope of this RG is to provide guidance for applicants and licensees under Title 10 of the Code of Federal Regulations (10 CFR), Part 50, Domestic Licensing of Production and Utilization Facilities, and 10 CFR Part 52, Licenses, Certifications, and Approvals for Nuclear Power Plants. Because the current research and test reactor fleet is licensed under 10 CFR part 50, the regulatory guide is already applicable to these reactors.

However, this regulatory guide is available for case-specific use for fuels and materials facilities should an applicant wish to use this RG for, as an example, steel-plate composite walls.

AISC C.4.2, AISC_3. There appears to be an inconsistent use of AISC 360-16 versus The NRC staff agrees with the comment. References to AISC C.4.3.1, ANSI/AISC 360-16. The appropriate designation is the latter, i.e. ANSI/AISC 360-16 will be replaced with ANSI/AISC 360-16.

C.5, C.7, 360-16.

C.7.2, C.7.3, C.7.4, C.7.5, C.8, and C.11.4 AISC A AISC_4. Section A of the draft Regulatory Guide lists RG 1.29. The text The NRC staff does not agree with the comment. The words must uses the phrase must be. Since this document is listed under Related be refer to features of light-water-reactor nuclear power plants that Guidance, the phrase should be changed to should be. must be designed to withstand the effects of a safe-shutdown earthquake per NRC regulations.

AISC A, AISC_5. ASCE 43-19 should be included in the section of Related The NRC staff does not agree with the comment. This standard is References Guidance, as well as the References. not NRC guidance and has not been endorsed via an NRC guidance document.

AISC C.1.2 AISC_6. Editorial: In Section C.1.2 of the draft Regulatory Guide, revise The NRC staff agrees with the comment. References to N690 s1-N690 s1-15 to ANSI/AISC N690s1-15. 15 will be replaced with ANSI/AISC N690 s1-15.

AISC C.1.2 AISC_7. Section C.1.2 of the draft Regulatory Guide adds the requirement The NRC staff agrees with the comment. The regulatory guidance for UT testing of welded connections (in ANSI/AISC N690-18 Sections position 1.2 for the plan developed to mitigate the conditions NA3.1c and NA3.1d) that are susceptible to lamellar tearing. UT testing is creating the potential for lamellar tearing should not prescribe the not required since these provisions are focused on the need for the 2

Commenter Section of Specific Comments NRC Resolution DG-1304 responsible party to develop a plan to mitigate lamellar tearing so that no UT specific testing to be performed. Using the guidelines provided in testing is needed. UT testing will identify a delamination/discontinuity if there the User Notes of Section NA3.1c and NA3.1d of ANSI/AISC is enough loss of back reflection to identify the discontinuity. Lamellar tearing N690-18, the plan developed by the engineer of record should be can occur on a plate that passes a through thickness UT exam. The concern extensive and detailed enough to not only identify welded is that if the UT exam is mandated and the plate passes, then the possibility connections that are susceptible to lamellar tearing but also of lamellar tearing created because of a highly constrained joint design will include steps to mitigate the conditions that might create the not be addressed and can occur. Also, as an editorial comment, in the last potential for lamellar tearing. Therefore the staff will remove this sentence, change NA31.c to NA3.1c.

Regulatory Guidance Position from the guide.

C.2 AISC_8. AISC has asked Professor Bruce Ellingwood to perform an Professor Ellingwoods review comments are part of the AISC AISC independent review of Table 1, Load Combinations for the LRFD Method. comments. They specifically address Table 1. They are designated AISC has reviewed his report and agrees with his recommendations and as AISC8.1 through AISC8.4 in the column to the left. The comments. His report is included as an attachment to this letter. responses to them are found below.

AISC/ Bruce AISC8.1. Normal Load Combinations: In response to Professor Ellingwoods comments on Table 1, the Ellingwood Combination NB2-1: This combination deals with permanent staff agrees with the comment pertaining to the normal load operating loads. The load factor on Ro is 1.4 in AISC N690 and combinations. For NB2-1, the comment addresses the normal 1.0 in DG-1304. In my opinion, a load factor of 1.0 is not operating load, Ro, and the importance to factor Ro in the normal adequate to account for uncertainties in pipe reactions under load combination when the permanent loads, D and F, are also the normal operating conditions, including start-up and shut-down primary loads in the load combination, especially when the live based on various transient conditions. load, L, and the loads H, are small. The staff also agrees with the comments pertaining to the load factor for Ro in load combinations Combination NB2-2: This combination addresses maximum NB2-2, for which the primary loads are the live loads L and H, as operating live loads. Since the load combinations are based on well as for NB2-3 for which the primary load are the roof loads. The a principal action/companion action approach to probabilistic staff will revise the regulatory guidance position accordingly.

load combinations, 1.2Ro is sufficient in this combination, especially if 1.4Ro appears in NB2-1. The load 1.6Ro is conservative and no evidence has been presented that it is needed for plant safety.

Combination NB2-3: This combination addresses maximum roof loads. There is absolutely no rationale for reducing 1.6Ro to 0.8Ro in this combination; they should be the same in both combinations NB2-2 and NB2-3 (i.e., 1.2Ro), as they are in 3

Commenter Section of Specific Comments NRC Resolution DG-1304 AISC N690.

AISC/ Bruce AISC8.2. Severe environmental load combinations: The staff partly agrees with ProfessorEllingwoods comments on Ellingwood Combination NB2-4: This combination addresses maximum Table 1 for load combinations NB2-4 and NB2-5. The primary non-tornadic winds (with a return period of 3,000 years for Risk loads in those load combinations are the wind load, W, and the Category IV structures in ASCE Standard 7-16). 1.6L + 1.6Ro OBE seismic load, Eo. The staff agrees that the load factor for Ro appear as companion actions in this equation. The implication should be 1.2 for load combinations NB2-4 and NB2-5. The staff is that the maximum live load and maximum pipe reaction occur does not agree to the use of a load factor of 0.8 for the live load L.

at the same time as the 3,000-yr return period wind, which is Given that the annual frequencies of exceedance for W and Eo are nonsense. In AISC N690, these loads are 0.8L + 1.2Ro, which significantly greater than those for Es and Wt in load combinations are consistent with the reliability analyses performed three NB2-6 and NB2-7, which use a load factor of 0.8 for L, a load decades ago at BNL. factor greater than 0.8 for L should be justified for loads Combination NB2-5: This combination addresses the OBE combination NB2-4 and NB2-5. In addition, these are operational earthquake, and its companion actions have exactly the same loads up to which the plant is expected not to have to be deficiency as those on combination NB2-4. shutdown, for example the load Eo, which also justifies a higher load factor for L. ASCE 7-16 (Minimum Design Loads and Associated Criteria for Buildings and Other Structures) also uses load factors greater than 0.8 for the combination of live loads with earthquake and wind loads with annual frequencies of exceedance of the order of those for W and Eo. The staff will retain the load factor for L at 1.6 in NB2-4 and NB2-5 and will revise the regulatory guidance position for the load combinations NB2-4 and NB2-5 to change the Ro load factor to 1.2.

AISC/ Bruce AISC8.3. Extreme environmental and abnormal load combinations: The staff does not agree with Professor Ellingwoods comment.

Ellingwood Combination NB2-8: The load factor on accidental pressure has The staff has been accepting a load factor of 1.4 for the accident been increased from 1.2 to 1.4. I see no rationale for this pressure in load combination NB2-8 to reflect uncertainties in the increase; 1.2 also appears in ACI 349-13 and in several ASME calculation of the accident pressures. The codes and standards standards as well. However, there may be some more recent have not provided a justification for the generic reduction of the information that I am not aware of to support this increase. load factor from 1.4 to 1.2. However, uncertainty analysis on the calculation of the design accident pressure can justify the use of a load factor less than 1.4. The staff will add a regulatory guidance position after Table 1 to clarify this possibility.

AISC/ Bruce AISC8.4. I have reviewed statements 2.1.1 - 2.1.5 which appear below The staff does not agree with Professor Ellingwoods comment that Ellingwood Table 1 in Draft RG 1304 and agree with them. I have three additional changes to the DG are necessary to address this comment.

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Commenter Section of Specific Comments NRC Resolution DG-1304 comments, which are tangentially related to the proposed load

• 5d(2) - The version of N690 in the scope of the DG is combination requirements. I noted these previously in my May 5, 2020 ANSI/AISC N690-18. ANSI/AISC N690-18 refers to soil report, and would like to emphasize them: pressures in 5d(2) while ANSI/AISC N690s1-15 refers to 5d(2) states that if the structural effect of differential settlement dead loads as in comment AISC8.4. Section 2.3.4 in ASCE is significant, it shall be included with the dead load. I do not 7-16 says that where the structural effects of self-straining agree with this requirement. While the load factor may or may demands are expected to adversely affect structure not be the same (see, e.g., Commentary C2.3.4 of ASCE 7-16), performance, the self-straining demands shall be differential settlement is a self-straining structural action similar considered in combination with other loads. The purpose of to creep or shrinkage, whereas dead load is force-controlled. provision 5d(2) in ANSI/AISC N690-18 is to consider the Thus, their fundamental characteristics and structural effects effects of self-straining demands with a factor equal to are different, even if the load factors are the same, and those used for soil pressure loads, which is greater than the engineers should not be encouraged to think of them as factor used for dead loads. The staff agrees with that equivalent; they are not. provision. The staff guidance in the Chapter 3.8.4 of the Fluid pressure, F, is treated the same as a dead load in the Standard Review Plan (SRP), NUREG-0800, already says N690 load combinations. I suggest that you revise 5d(3) and that provisions shall be made for anticipated self-straining 5d(4) to state that if F acts to stabilize the structure against the forces and effects arising from differential settlements of destabilizing effects of lateral force or uplift, F shall be equal to foundations during construction and operation of the plant.

zero. The guidance in the SRP also says that a monitoring Load H includes loads due to weight and lateral pressure of soil, program for settlements is expected by the staff for the ground water pressure, or pressure of bulk materials. If H acts constructed facility.

to stabilize the structure, H shall be equal to zero.

• The comments pertaining to the fluid pressure, F, and to the soil pressures, H, can be case-specific and those conditions are reviewed on a case-specific basis.

Accordingly, no changes will be made to the DG.

AISC C.2.1 AISC_9. Editorial: Suggest to add (LRFD) at the end of the title for The NRC staff agrees with the comment. (LRFD) will be added at Section C.2.1 of the draft Regulatory Guide. the end of the heading for RGP 2.1 of the DG.

AISC C.2.2.6 AISC_10. In Section C.2.2.6 of the draft Regulatory Guide, revise N690- The NRC staff agrees with the comment. References to N690-18 18 to ANSI/AISC N690-18; also, in the first sentence of this section, correct will be replaced with ANSI/AISC N690-18. Also, references to NB2-7 to NB2-16. NB2-7 will be replaced with NB2-16 in RGP 2.2.6 of the DG.

AISC C.3.1 AISC_11. Sections C.3.1 and C.3.2 of the draft Regulatory Guide are The NRC staff agrees with the comment. Effective length method generally agreeable. First, please note that Appendix 7 is for the effective will be used in lieu of equivalent length method. The second part length method, and not the equivalent length method. The wording and of this sentence related to using minimum judgement will be minimum judgment is required to determine K in Section C.3.1 is vague and deleted.

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Commenter Section of Specific Comments NRC Resolution DG-1304 may be subject to interpretation. With the exception of textbook definitions of end conditions (e.g. pinned, free, or fixed), the determination of effective length factors almost always requires some significant degree of judgement.

One may argue that the use of alignment charts is pretty straight forward, but it is rare that all ten of the assumptions for using this approach are satisfied for most design conditions encountered - as a result, adjustments in the use of the alignment charts are often required and such adjustments require judgement. Does requiring minimum judgement mean that the effective length method can only be used for pinned, free, or/and fixed end conditions?

Or is minimum judgement extended to equally rare conditions satisfying all assumptions that correspond to the use of the alignment charts. In either case, such a definition of minimum judgement would severely limit the use of a design method that has been successfully used in the U.S. since the early 1960s. We do agree that it is essential that care must always be taken in computing reasonable effective length factors. With this in mind, the first part of the sentence in Section C.3.1 alone should suffice, and we suggest deleting the second part related to using minimum judgment.

AISC C.3.3 AISC_12. With respect to Section C.3.3 of the draft Regulatory Guide, AISC The NRC staff agrees with the comment. Regulatory guidance questions its validity. First, it is not clear where prediction of elastic stability position 3.3.3 will be removed from the RG.

using the direct second-order analysis method appears or used in the ANSI/AISC 360-16 Specification. The Specification does have a design method termed the direct analysis method (DM) that accounts for the five most significant effects for steel structures that are known to impact stability (see ANSI/AISC 360-16 Section C1 as referenced from ANSI/AISC N690-18 Chapter NC). This design method ensures the stability of structures and its elements. One of these effects includes consideration of second-order effects (P- and P-), which most often results in the use of a second-order elastic analysis. Further Section C.3.3 could be misleading because: i) In addition to including the effects of geometric nonlinearity and initial imperfections, DM also considers stiffness reduction due to inelasticity (another one of the five effects mentioned above) via the use of EI* and EA*, both of which are approximations accounting for potential inelasticity; ii) Realistic stress states, and the corresponding degree of yielding, are not known from the analysis; iii) An instrumental part of the DM method is to provide required strengths 6

Commenter Section of Specific Comments NRC Resolution DG-1304 (e.g. forces and moments and not stresses) for the design of members and connections by elastic analysis under factored loads, with such demands often in excess of first-yield conditions per AISCs limit states design philosophy; iv) Unless a rigorous second order analysis is performed, which is not a requirement of DM as it is defined in ANSI/AISC 360-16 Chapter C (noting that approximate methods of analysis, such as B1 and B2 analyses, are permitted), equilibrium and compatibility may not necessarily be satisfied on the deformed geometry. Thus, the stress state at the onset of instability cant be determined or assessed from the typical analysis used in the DM design method. It is further noted that limiting stresses to only be elastic within the analysis would essentially prohibit any members or components from yielding to any degree under loads factored to the strength limit-state level - a requirement that would be unreasonably conservative. It is AISCs opinion that the application of the DM method (per Chapter C) does not require engineers to verify if the stresses in structure are elastic at the onset of instability and therefore recommends that the draft Regulatory Guide Section C.3.3 be removed.

AISC C.4.2 AISC_13. ACI codes are adopting 80,000 psi as the new limit for high The NRC staff does not agree with the comment. Use of high-strength steel reinforcement. The ACI 349 Code Committee has approved strength (HS) rebar reinforcement (Grade 75 and 80) as used in 80,000 psi and it is expected to be a part of the next edition of the ACI 349 ACI 349-13 is not endorsed for general use for the scope of Code. Section C.4.2 of the draft Regulatory Guide should adopt this higher Chapter NI. Research and development that integrates limit. implications for the general use of, for example, crack control, material and component ductility, deflection limits, and strength-reduction factors, is ongoing and, therefore, its use is not generically endorsed. The staff will wait for the issuance of the new edition of ACI 349 and the justification therein for further consideration for general use.

AISC C.4.3.1 AISC_14. Section C.4.3.1 of the draft Regulatory Guide needs to provide The NRC staff does not agree with the comment. Regulatory criteria and discussion why stability sensitive structures are a concern to the guidance position 4.3.1 is provided as a guidance for the designer.

NRC staff. For additional discussion regarding regulatory guidance position 4.3.1, refer to BNL report# BNL-220652-2020-INRE, section 4.10.3 AISC 360-16 Comparison to AISC 360-10.

AISC C.4.3.2 AISC_15. Section C.4.3.2 of the draft Regulatory Guide should provide The NRC staff does not agree with the comment. The Specification has not traditionally accounted for long-term effects due to creep 7

Commenter Section of Specific Comments NRC Resolution DG-1304 guidance on how to address long-term effects since AISC standards do not and shrinkage and, as such, the stiffness prescribed is based on address this potential concern. studies examining only short-term behavior. The guidance in regulatory guidance position 4.3.2 identifies that long-term effects due to creep and shrinkage should be analyzed.

AISC C.5 AISC_16. Editorial: In the title for Section C.5 of the draft Regulatory The NRC staff agrees with the comment. References to Guide, revise to ANSI/AISC N69018, Chapter NJ - Design of ANSI/AISC N690-8 will be replaced with ANSI/AISC N690-18.

Connections. Corrections are also required in Section C.11.1, C.11.2, C.11.3, and C.11.4.

AISC C.5 AISC_17. Section C.5 of the draft Regulatory Guide indicates that an The NRC staff does not agree with the comment. The standard exception to ANSI/AISC N690-18 Chapter NJ is required because it should endorsed by the NRC staff for anchoring to concrete in nuclear refer exclusively to ACI 349 and not ACI 318. The draft Regulatory Guide also power plants is Appendix D of ACI 349-13, which the staff states that the requirements in ACI 349-13 should be used along with the endorses in RG 1.199.

regulatory provisions of RG 1.142 Revision 3, and RG 1.199 Revision 2, unless otherwise justified. AISC comments that many facilities are designed to ACI The staff will edit the regulatory guidance position for clarity as follows:

318, and to limit its use to ACI 349 would be restrictive. Additionally, AISC comments that generically referring to the requirements of ACI 349 is rather ANSI/AISC 360-16, Chapter J, section J9 refers to Chapter 17 of vague and could lead to misinterpretation. AISC proposes that no exception ACI 318-14 (Ref. 25). Appendix D of ACI 349-13 (Ref. 26) should be taken in the draft Regulatory Guide against Chapter NJ. be used instead of Chapter 17 of ACI 318-14. In addition, requirements in ACI 349-13 should be used along with the regulatory guidance positions in RG 1.199, Revision 1, unless otherwise justified.

AISC C.3.3, AISC_18. Unlike in the DM method, stability analysis per ANSI/AISC N690- The NRC staff agrees with the comment. Regulatory guidance C.7.4 18 Appendix N1 that is based on ANSI/AISC 360-16 Appendix 1, Section 1.2, position 7.4 will be removed from the RG.

requires the use of a rigorous second order analysis, which can indicate whether or not the structural system or any of its components approach instability. However, it still requires consideration of residual stresses and stiffness reduction due to potential yielding. It also requires the analysis be with loads factored to the strength limit-state level. As per our above comments of the draft Regulatory Guide Section C.3.3, design would be unreasonably conservative if stresses under factored loads at the onset of instability must be kept at or below an elastic limit. Thus, the elastic stress 8

Commenter Section of Specific Comments NRC Resolution DG-1304 requirement of draft Regulatory Guide Section C.7.4 is not appropriate and AISC suggests it be removed.

AISC C.7.5 AISC_19. Draft Regulatory Guide Section C.7.5 appears trivial and perhaps The NRC staff agrees with the comment. Regulatory Guidance unnecessary, unless there is concern that engineers need to be reminded Position 7.5 neither takes any exception to the ANSI/AISC N690-that ANSI/AISC 360-16 Appendix 1, Section 1.3, modified in accordance with 18 provisions nor adds anything to the ANSI/AISC N690-18 ANSI/AISC N690-18 Appendix N1, Section N1.3, is acceptable for use in the provisions. Therefore, it will be removed from the RG.

design of safety-related steel building structures. It is noted that the inelastic stability analysis of Section 1.3 is the most sophisticated second order analysis available, and is typically reserved by designers for assessing complex and/or overstressed structures. It is clear from the provisions appearing in Section 1.3 that the analysis shall take into account: second order effects, geometric imperfections, material nonlinearity, member and connection ductility and deformation capability.

AISC C.9 AISC_20. Section C.9 of the draft Regulatory Guide indicates that the use The NRC staff does not agree with the comment. The DG does not of ANSI/AISC N690-18 Appendix N4 will not be endorsed. However, no endorse ANSI/AISC N690-18, Appendix N4, on structural design alternative guidance is provided, nor is any basis of not accepting Appendix for fire conditions because Appendix N4 is outside the scope of the N4 is provided. This guidance should be provided in the draft Regulatory DG. The provisions in Appendix N4 are for structural design for life Guide. safety associated with the evacuation of building occupants in the event of a design-basis fire. In addition, the provisions in Appendix N4 do not address structural safety members important to safety or the loading conditions associated with a facility fire. The scope of the DG is the design of safety-related structures and structural components which are required to perform their intended safety functions under design basis conditions. Those conditions are outside the scope of Appendix N4. Regulatory Guide 1.189, Fire Protection for Nuclear Plants, provides information on fire protection performance goals.

Regulatory guidance position 9 will be edited for clarity to be:

This RG does not endorse ANSI/AISC N690-18, Appendix N4, on structural design for fire conditions because it is outside the scope of the RG.

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Commenter Section of Specific Comments NRC Resolution DG-1304 AISC C.11.1.6, AISC_21. The following discussion and comments pertain to Section The NRC staff partially agrees with the comment. The comment C.11.1.7 C.11.1.6 of the draft Regulatory Guide: address two regulatory guidance positions, 1.1.6, on the Revision 3 of RG 1.142 is based on ACI 349-13. Accordingly, this response acceptable ductility ratios for compartment pressurization, and references the relevant sections of ACI 349-13. It is acknowledged that RG 11.1.7 on the acceptable docility ratios for shear-controlled SC 1.142 takes exceptions to Section F3.5 of ACI 349-13. In particular, it permits walls.

local ductility up to 3.0, but requires that the structure should remain elastic (although it is unclear as to how this can be accomplished). Also, when shear Comment for regulatory guidance position 11.1.6 - This regulatory controls, the ductility ratio is limited to 1.3 and 1.0 when shear reinforcement guide position addresses the special case of impulsive loads is and is not provided, respectively (note that the additional exceptions associated with compartment pressurization that could affect the related to ACI 349-13 Section F3.8 are not relevant for a compartment integrity of the whole structure which can include the pressurized pressurization situation since it does not cause horizontal compression load compartment structure and, for example, the larger structure tat in the compartment walls). The following response takes these exceptions contains the compartment. For general use, the upper limit of the into account. ductility is conservatively set at 3.0 to address overall stability effects associated with compartment pressurization, for example, The commentary for ACI 349-13 Section F3.5 indicates that the reduced progressive collapse. Flexural deformations of the compartment ductility limit of 3 (from 10) has to do with the effect of compartment pressure walls associated with ductility ratios higher than 3.0 may be loading on the compartments overall structural integrity such that there is a justified by assuring overall structural integrity, namely the stability need to minimize the level of permanent deformation. It is understood that of the structure as a whole under the impulsive loads that originate response at higher ductility ratio manifests in increased permanent inside the compartment as well as the follow-on pressurization that deformation as well as more degraded condition for RC compartment walls may remain inside the compartment depending on the (especially in the vicinity of their vertical edges where significant cracking and compartment venting, and all loads acting concurrently with the spalling can occur due to lack of ties and confinement). Aside from structural impulsive loads and the follow-on compartment pressurization.

integrity concerns, such state of permanent deformation, likely accompanied by significant cracking and spalling, can be problematic from the The regulatory guidance position will be revised to be:

compartments functionality standpoint. This limitation is necessary for RC compartments because ACI 349 does not require special detailing at a The permissible displacement ductility ratio in flexure should not compartments corners (e.g., increased rebar development length and/or lack exceed 3.0 for loads such as internal blast overpressure and of ties); the presence of direct tension and flexure leads to severe compartment pressurization, which could affect the integrity of the cracking/spalling as the rebars undergo large tensile strains associated with structure as a whole. Flexural deformations of the compartment increased ductility ratio. walls or slabs associated with ductility ratios greater than 3.0 can be justified by assuring the structural integrity of the structure. The In contrast to ACI 349, ANSI/AISC N690-18 Section NB3.14 requires the justification should consider the impulsive loads originating from connections to be designed for full expected strength of the connected within the pressurized compartment including the follow-on members (or with significant overstrength); also, ties are required in SC walls pressurization that may remain inside the compartment and act as 10

Commenter Section of Specific Comments NRC Resolution DG-1304 (typically the ties and shear connectors are more closely spaced within the sustained loads depending on the compartment venting as well as connection region). These features and the resulting confining action all other loads acting concurrently with the impulsive loads and the enhance the SC compartments structural integrity. For SC walls, aside from follow-on compartment pressurization.

absence of crack control related concerns, the prospect of spalling under large strains is also entirely prevented because of the presence of faceplates.

For these reasons, unlike RC compartment walls, the SC compartment walls Comment for regulatory guidance position 11.1.7 - The staff does need not be subjected to reduced ductility limitation (i.e., ductility limit of 10, not agree with the comment. Test data for four-point beam test which is explained below, remains appropriate for all SC applications). setups show that the ducility depends on, for example, the shear span ratio and may not be the same for all conditions. In addition,

[As an aside, it is noted that ACI 349 Section F3.3 permits the limit of 10 for the information on the cited Figure C-A-N9.3.6(a) is for strength doubly-reinforced RC beams and walls/slabs (except for compartment rather than for ductility. Test data reviewed shows that while applications, for which ACI 349 Section F3.5 limits the ductility ratio to 3). ductilities such as those in the ANSI/AISC N690-18 can be This provision is quite applicable to SC walls, and ANSI/AISC N690-18 achieved, they are likely to depend on structural configuration therefore simply (conservatively) adopted it. This is because SC sections are factors on factors such as the shear span ratio. The higher doubly reinforced with equal reinforcement on both faces (and it is on the ductilies may be justified for specific design conditions but those exterior in the form of faceplates); this arrangement essentially prevents the conditions for general use have not been defined. The regulatory prospect of flexure- induced concrete crushing due to increasing tensile strain guidance position will be revised for clarification to read:

on the tension reinforcement (i.e., this cross- sectional/curvature related ductility consideration, which is particularly relevant to singly-reinforced For shear-controlled SC walls with yielding shear reinforcement cross- sections, is less of a concern for doubly-reinforced sections, especially spaced at section thickness divided by two or smaller, the ductility ones with equal reinforcement). It is further noted that the presence of small- ratio is no greater than 1.3. For shear-controlled SC walls with to-moderate magnitude of simultaneous membrane tension force due to yielding shear reinforcement spaced in excess of the section compartment pressurization does not adversely impact the cross-sections thickness divided by two or for shear-controlled SC walls with flexural/rotational ductility because the tension force it continues to ensure nonyielding reinforcement, the ductility ratio is limited to 1.0. Higher that the behavior is controlled by steel yielding, rather than by concrete ductility factors up to the values in ANSI/AISC N690-18, Section crushing.] N9.1.6b should be justified on a case-specific basis.

The following rationale is provided regarding why ANSI/AISC N690-18 Section N9.1.6b does not adhere to the RG 1.142 exception concerning differentiation between local and global ductility. When subjected to internal pressurization, compartment walls experience significant flexure in combination with low-to- moderate membrane tension forces (as explained above, an SC walls behavior is steel-controlled and hence quite ductile against these force effects at a cross-section level). Each wall will encounter 11

Commenter Section of Specific Comments NRC Resolution DG-1304 the following sequence of plastic hinge formation before a mechanism state is formed for that wall: hinges at ends (negative moment regions), followed by a hinge along midspan (the walls will essentially behave like a collection of adjoining beam segments that span horizontally). It is noted that the mechanism state at an individual wall level is not immediately tantamount to sudden failure because the rotational ductility of the midspan hinge is not necessarily exhausted (this is especially true for dynamic/short-lasting load).

A global mechanism state will be reached only after all four walls of the compartment have formed the three hinges in each wall segment (furthermore, all walls can simultaneously reach their individual mechanism state only if the compartment is doubly symmetric). Compared to this backdrop, the ductility provisions of Section N9.1.6b are written in terms of displacement ductility, which will have to be evaluated for each wall segment.

Accordingly, the real question is whether a displacement ductility ratio of 10 can lead to (or exceed) the response state associated with the mechanism formation for an SC wall segment (and even if it does, will that lead to the mechanism state for the compartment as whole). This concern is in turn related to the limitation imposed in Section F3.5 of ACI 349-13 because of a concern about the extent of permanent deformations and the degraded wall condition that can occur for RC walls. In contrast, because they are equally reinforced in tension and compression, SC walls can support very large curvature and rotational ductility that would equal or exceed a comparable RC beam. Being that the ductility limit of 10 is acceptable for a doubly-reinforced beam, it follows that the same should be conservatively acceptable for SC wall in a compartment application. It is expected that each constituent wall segment of the compartment will be below its mechanism state this response ductility level (and thus the compartment on the whole will be at a response state that is below its global mechanism state).

Regarding ductility limits for shear-controlled walls, the following comments are provided:

It is important to note that there is no such thing as SC wall without cross-ties (i.e., the ties are required as part of the standards General Requirements).

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Commenter Section of Specific Comments NRC Resolution DG-1304 As such, the accompanying ductility limits are predicated on whether the ties are ductile and spaced at less than or equal to half the wall thickness. A ductility limit of 1.6 is imposed for the condition when the associated shear failure is steel controlled and hence reasonably ductile (as evidenced from numerous SC specimens tested as beams in four-point test setups). The ductility ratio is limited to 1.3 for situations with non-ductile ties and/or when the tie spacing is in excess of half the wall thickness. This is considered reasonable because of the expected overstrength since the corresponding out-of-plane shear capacity provision is conservative (this is due to the expected overstrength since a shear-controlled section signifies that the shear span-to-depth ratio must be quite small, whereby as seen from Figure C-A-N9.3.6(a), the concrete resistance to out-of-plane shear increases due to the strut-and-tie action).

Finally, there is no basis provided in the draft Regulatory Guide for reducing the ductility ratios to 1.3 and 1.0 in Section C.11.1.7.

AISC AISC_22. The following discussion and comments refer to Section C.11.2 The NRC staff agrees in part with the comment.

of the draft Regulatory Guide:

The User Note to ANSI/AISC N690-18 Section N9.2.1(a) refers the designer Regulatory guidance position 11.2 will be revised to read:

to the accompanying commentary for analysis guidelines (as well as the refined modeling requirements around openings provided in Section N9.1.7). Section N9.2.5 specifies that the required strength for each The commentary recommends that at least four to six elements should be member load type may be determined by averaging the demand used along the short direction of a wall panel, and six to eight elements along over areal extents of the wall (referred to as panel sections) that its long direction (this guidance is further illustrated in Fig. C-A-N9.2.9, which are less than or equal to twice the wall thickness in length and also clarifies that the element size for elements in the connection region is to width, except at connections and openings, where the panel be less than or equal to the SC wall thickness). Because of these section dimensions are limited to the wall thickness. These provisions/guidelines, it is unlikely that an analyst will use only a few panel averaging guidelines are acceptable in conjunction with sections for modeling a wall panel, and therefore no further caution is recommendations in the commentary to N9.2.1.2. Other deemed necessary in the draft Regulatory Guide. Hence, ANSI/AISC N690- conditions will be reviewed on a case-specific basis.

18 stipulated an upper limit of demand averaging equals to 2xtsc in the interior regions and 1xtsc in connecting regions and around openings. See Figure C-A-N9.2.9. The ANSI/AISC N690-18 code committee provided these rules in order to minimize evaluation on a case-specific basis which potentially would result in a high number of requests from NRC to 13

Commenter Section of Specific Comments NRC Resolution DG-1304 applicants/licensees for additional information (RAI), a situation that the new Regulatory Guide wants to avoid.

AISC C.11.4 AISC_23. Section C.11.4 of the draft Regulatory Guide should refer back The NRC staff agrees with the comment. References to to ANSI/AISC N690-18 Chapter ND instead of ANSI/AISC 360-16 Chapter D. ANSI/AISC 360-16 Chapter D will be replaced with ANSI/AISC N690-18 Chapter ND.

NuScale Page 2, NSP_1. Citations to Part 52 requirements are incomplete. 10 CFR 52.77 is The NRC staff partially agrees with the comment. The staff agrees Power, LLC Additional not relevant. Its unclear what portion of 10 CFR 52.47 and 52.79 are that 10 CFR 52.77 is not relevant and the reference to it will be Requireme relevant. Similar requirements for SDA and manufacturing license removed from applicable regulations section of the RG. Even nts applications are not cited. Further, analogous Part 50 application though 10 CFR 52.47 and 52.79 deal with the various subsets of requirements are not cited. the technical information in the contents of applications, this RG can be part of that technical information and thus should list these Proposed Resolution: Either provide all applicable Part 50 and 52 regulations applicable additional requirements. The relevant Part 50 provisions with the specific relevant provision, or omit the incomplete Part 52 that apply to this RG are already listed under Applicable regulations. Regulations in Part A, Introduction, of the RG.

NuScale Page 3, NSP_2. ASCE/SEI 37-14 is listed as related guidance. This standard is The NRC staff agrees with the comment. The reference to the Power, LLC Related not NRC guidance and has not been endorsed via an NRC guidance American Society of Civil Engineers (ASCE)/Structural Engineering Guidance document. Institute (SEI) 37-14, Design Loads on Structures during Construction will be removed from this section and a reference to Proposed Resolution: Delete ASCE/SEI 37-14 from related guidance. If the ASCE/SEI 37-14 will be added to regulatory gudiance position contents of that standard are relevant and appropriate, it should be directly 2.1.1.

addressed within this guidance document as an acceptable standard. .

NuScale Page 5, NSP_3. BNL-220652-2020-INRE is discussed as technical background The NRC staff disagrees with the comment. ANSI/AISC N690-18 Power, LLC Section B, for this DG. It describes the assessment of ANSI/AISC N690-18 for use in does not address the effects of corrosion on exterior SC walls.

Paragraph nuclear power plants. BNL-220652-2020-INRE (page 4-10) Design for Conditions where corrosion could impair the strength or 5 Corrosion Effects, states: Where corrosion could impair the strength or serviceability of an exterior SC wall can vary widely depending on serviceability of a structure, structural components shall be designed to the exposure and performance requirements of those walls. In the tolerate corrosion or shall be protected against corrosion. The DG does not absence of provisions in the ANSI/AISC N690-18, design of address design considerations for corrosion effects. exterior SC walls to tolerate corrosion or protect against corrosion where corrosion could impair their strength or serviceability will be Proposed Resolution: Provide in the RG additional criteria, if any, for exterior subject to case-specific review and individual project SC walls susceptible to corrosion. specifications.

NuScale Page 8, NSP_4. The DG states In load combination (NB2-9), 0.7Ess is to be The NRC staff agrees with this editorial comment and will make Power, LLC Section C, combined absolutely with the accident loads. 0.7Ess appears to be a typo. the correction.

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Commenter Section of Specific Comments NRC Resolution DG-1304 Paragraph 2.1.5 Proposed Resolution: Replace with 0.7Es.

NuScale Page 10, NSP_5. While section 4.2 is applicable to high strength reinforcement, The NRC staff agrees with the comment. The Regulatory guidance Power, LLC Section C, clarify the use of high strength structural steel with yield stress up to 75 ksi. position applies to steel reinforcing bars and it will be edited to be:

Paragraph 4.2 Proposed Resolution: Provide a statement that if not using high strength Consistent with RG 1.142, Revision 3, this RG does not endorse, reinforcement, this RG endorses the use of structural steel with yield stress in general, the use of high-strength steel reinforcing bars (yield not to exceed the 75 ksi in design using the rules of ANSI/AISC N690-2018, strength greater than 60,000 pounds per square inch in design Chapter NI. (ANSI/AISC N690-2018, Chapter NI, on the design of composite members refers to Chapter I of ANSI/AISC 360-16, which allows the use of high-strength reinforcing bars). If high-strength steel reinforcing bars are used, applicants should demonstrate its adequacy for specific use of the design by testing, analysis, or performance evaluation.

NuScale Page 13, NSP_6. It is unclear if the 25% increase in faceplate thickness as The NRC staff agrees with the comment. The last sentence of Power, LLC Section C, described in Section N9.1.6c is required. regulatory guidance position 11.1.9 will be edited for clarity to be:

Paragraph 11.1.9 Proposed Resolution: Clarify whether the 25% increase in Section N9.1.6c is The penetration depth as well as the concrete and faceplate applicable. thickness required to prevent penetration are from applicable rational methods or pertinent test data together with the conditions in N9.1.6c of ANSI/AISC N690-18 for the faceplate thickness.

NuScale Page 13, NSP_7. The DG states These averaging guidelines are generic and may The staff agrees in part with comment. Regulatory guidance Power, LLC Section C, not be suitable in all cases. The implementation of these guidelines or any provision 11.2 will be modified to be:

Paragraph alternate averaging methodology will be subject to case-specific review by 11.2 the NRC staff. Additional guidance on the suitability and implementation of Section N9.2.5 specifies that the required strength for each averaging guidelines is needed. member load type may be determined by averaging the demand over areal extents of the wall (referred to as panel sections) that Proposed Resolution: Provide criteria or examples of cases where the are less than or equal to twice the wall thickness in length and averaging guidelines are deemed not suitable. Identify considerations for width, except at connections and openings, where the panel acceptable implementation of the averaging guidelines or an alternate section dimensions are limited to the wall thickness. These averaging methodology. averaging guidelines are acceptable in conjunction with recommendations in the commentary to N9.2.1.2. Other conditions will be reviewed on a case-specific basis.

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Commenter Section of Specific Comments NRC Resolution DG-1304 NuScale Page 7, NSP_8. In response to Docket NRC-2019-0100, Safety Related Concrete The staff agrees with the comment. The comment justifies the use Power, LLC Section C, Structures for Nuclear Power Plants (Other than Reactor Vessels and of a load factor less than one based on two main considerations:

Table 1 Containments), DG-1283, the leadership of ACI 349 provided comments as The first consideration is that the use of a load factor of 1.0 as in documented in Adams Accession number ML19176A439. Comment 5 states ACI 349-13, Appendix C, was associated with higher strength as follows: reduction factors than those in ACI 349-13, Chapter 9 and ANSI/AISC N690-18.

We disagree with the NRC position to require a load factor of 1.0 for live The second consideration is that the combination of loads should load. The load factors in Chapter 9 ACI 349- 13 are associated with lower account for the expected maximum lifetime value of the dominat strength (phi) factors; ACI 349-13 Appendix C load factors are used with loads in the combination and an arbitrary point in time value of the higher strength (phi) factors. Thus, increasing load factors in ACI 349-13 other loads using established approaches in structural design. In Chapter 9 to match those of ACI-349-13 AppendixC erroneously alters the case of abnormal or extreme environmental load combinations, the global safety factor. It is also noted that ACI 318 allows live load the dominat load are either the abnormal loads or the extreme reductions that result in an equivalent load factor of 0.5L. These environmental loads while the companion loads like the live load reductions are not permitted in nuclear safety-related construction. It is should act at their expected arbitrary point in time values. This is strongly recommend that the NRC review their position in this regard.

especially relevant for dominant loads with small annual Regarding the load factor in ACI 349-13 for live load, as explained in the probabilities of exceedance as is the case of the abnormal or commentary of ASCE 7 Section C2.3, the loads used in design account extreme environmental loads. The peer-reviewed article for the maximum lifetime value as well as arbitrary point-in-time values, Probability-Based Design Criteria for Nuclear Plant Structures, by with the maximum lifetime value always controlling. When many different H. Hwang, B. Ellingwood, M. Shinozuka and M. Reich, Journal of types of loads are superimposed in a load combination, as is the case for Structural Engineering, American Society of Civil Engineers abnormal or extreme load combinations, the arbitrary point-in-time value (ASCE), 113(5), 1987, reports results from a NRC-sponsored or the mean value of the load (accounting for industry variation) should be research project. That paper refers to a survey of live loads in used. The live load mean value varies between 0.5 to 0.8 of the nuclear power plant which provides the mean live load at about maximum lifetime value. The value of 0.8L is used for load combination 9-0.36 times the nominal value, L, with a coefficient of variation of 5 to 9-9 on this basis.

0.54. This result and the low annual probability of exceedance for the abnormal and extreme environmental loads contribute to NuScale agrees and considers comment #5 on live load also applicable to justifying the use of a load factor of 0.8 for L in those load DG-1304.

combinations. The load factors in Table 1 will be revised to use a factor of 0.8 for L in oad combinations NB2-6, 7, 8 and 9 in Table Proposed Resolution: Apply a value of 0.8 for live load instead of 1.0 for load 1.

combinations as per ANSI/AISC N690-18 Section NB2.5.

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Commenter Section of Specific Comments NRC Resolution DG-1304 NuScale Page 7, NSP_9. In response to Docket NRC-2019-0100, Safety Related Concrete The staff agrees with the comment. This comment is the same as Power, LLC Section C, Structures for Nuclear Power Plants (Other than Reactor Vessels and comment AISC_8.1 and comment AISC_8.2 in what pertains the Table 1 Containments), DG-1283, the leadership of ACI 349 provided comments as load Ro. As in the response to comments AISC_8.1 and AISC 8.2, documented in Adams Accession number ML19176A439. Comment 4 states the load factor for Ro in load combination NB2-1 will be changed to as follows: 1.4 and the load factor for Ro for load combinations NB2-2, NB2-4 and NB2-5 will be changed to 1.2 In as much as Ro is computed mainly from thermally- induced elongation of piping, it is not clear why this should be associated with enhanced uncertainty as stated in the NRC position. Note also that there is already significant conservatism associated with the use of an envelope of temperatures for these cases. Please note that the nuclear industry has long struggled with the difficulty of dealing with temperature loads on nuclear structures. The self-relieving nature of the temperature load makes it less critical than other loads. Adding larger load factors sends a wrong message to the designers that the way to deal with temperature is to make the structure stronger. This again is counter-productive to a rational design. Furthermore, the codes recognize the cumulative approach contained in ASCE 7, which holds that as an increasing number of loading types are combined, the less likely it is that the peaks of these loads will occur concurrently. Ro is consistently addressed in this regard in ASCE 43, ACI 349 and AISC N690.

NuScale agrees and considers comment #4 on Ro applicable for DG-1304.

Proposed Resolution: Ro should not be treated same as live load (L) in load combinations. Apply Ro to be consistent with ANSI/AISC N690- 18 Section NB2.5.

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