ML25241A297

Lessons Learned from the Standard Design Approval Review of the NuScale Power, LLC, US460 Design

ML25241A297
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Site:	05200050
Issue date:	08/29/2025
From:	Fosaaen C NuScale
To:	Jeremy Bowen Office of Nuclear Reactor Regulation, Document Control Desk
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ML25241A296	List: ML25241A297
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LO-186537
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LO-186537 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com August 29, 2025 Docket No.52-050 Jeremy Bowen Deputy Director for New Reactors (Acting)

U.S. Nuclear Regulatory Commission Washington, DC 20555-0001

SUBJECT:

Lessons Learned from the Standard Design Approval Review of the NuScale Power, LLC US460 Design

REFERENCES:

1) NRC letter to NuScale, Standard Design Approval for the NuScale Power Company, LLC US460 Power Plant Design, dated May 29, 2025 (ML25129A004)

2) NuScale letter to NRC, Lessons-Learned from the Design Certification Review of the NuScale Power, LLC Small Modular Reactor, LO-0221-74035, dated February 19, 2021 (ML21050A431)

Dear Mr. Bowen:

This letter presents lessons learned from the U.S. Nuclear Regulatory Commission (NRC) review of the NuScale Power, LLC (NuScale) standard design approval application (SDAA) for the US460 design, completed in Reference 1.

NuScale met with the NRC on July 15 and 16, 2025 to discuss lessons learned from the SDAA review. NuScale appreciates the NRCs willingness to engage in productive discussions and the shared commitment to continuous improvement. The meeting reflected on review areas that went well, review areas that did not go well, and recommendations for improvement in future reviews. This letter is not a comprehensive summary of those meeting discussions. Rather, this letter presents NuScales most significant recommendations to the NRC for improvement that support future reviews. In some cases, the current recommendations from the US460 SDAA review overlap with recommendations previously made to the NRC by NuScale in Reference 2 after the US600 design certification application (DCA) review. NuScale believes that the following recommendations are also consistent with implementation of Executive Order 14300 for reform of the NRC issued in May 2025 and with the Nuclear Energy Institutes (NEIs) recommendations in its July 2025 report Accelerating NRC Reform: Industry Recommendations. NuScale will be internally documenting lessons learned and NuScale actions for improvement as well; the NuScale internal actions are not included in this letter.

The recommendations are for the NRC to:

1. Fully implement the use of core-teams or multi-disciplinary teams within the NRC staff for the review, particularly for identification and resolution of complicated issues by applying a risk-informed, holistic safety perspective. The consequence of not using

LO-186537 Page 2 of 3 08/29/2025 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com teams is that areas of the review can be held up by an individual NRC reviewer who may not understand the broader view of an issue.

2.

Drive to consensus on risk-insights early in the review and then use those risk-insights to focus the NRC staff review on risk-significant areas. The consequence of not reaching a consensus early in the review and using it to focus the review is that time and effort (both applicant and NRC staff) is misdirected on topics that are not risk-significant.

3.

Establish an appeal process to resolve disagreements between applicants and the NRC staff with respect to preliminary interpretations of requirements and guidance.

The consequence of the absence of such a process is that regulatory burden has steadily increased from one applicant to the next without consideration of whether new staff positions have merit from a safety perspective.

4.

Promote flexibility in reading of regulations and regulatory guidance to favor risk-informed decision making consistent with the Commissions direction in Staff Requirements Memorandum SRM-SECY-19-0036 to apply risk-informed principles when strict, prescriptive application of deterministic criteriais unnecessary to provide for reasonable assurance of adequate protection. The consequence of overly restrictive readings of regulations and regulatory guidance is that individual NRC staff may impede implementation of the SRM, resulting in increased review durations and costs even where risk-insights demonstrate reasonable assurance of adequate protection.

5.

Define credible. Numerous NRC requirements incorporate the concept of credible.

The consequence of a lack of a definition is unpredictability in the review as interpretations vary among the staff, resulting in increased review durations and costs even for events of incredibly low frequencies and often with insignificant radiological consequences. A workable definition will aso help effectuate implementation of Executive Order 14300. to this letter provides more information and justification for these recommendations. Enclosure 1 contains the proprietary slides developed by NuScale for the meetings on July 15 and 16, 2025, with some minor edits based on comments made during the meetings. NuScale requests that these proprietary slides be withheld from public disclosure in accordance with the requirements of 10 CFR § 2.390. The enclosed affidavit (Enclosure 2) supports this request.

I appreciate the NRCs consideration of these recommendations. If you have any questions, please contact me at 541-452-7126 or at cfosaaen@nuscalepower.com.

Sincerely, Carrie Fosaaen Vice President, Regulatory Affairs and Services NuScale Power, LLC

LO-186537 Page 3 of 3 08/29/2025 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com Distribution:

Michael F. King, Executive Director for Operations (Acting)

Marissa G. Bailey, Executive Director, ACRS Greg Bowman, Director, Office of Nuclear Reactor Regulation (Acting)

Michele Sampson, Director, Division of New and Renewed Licenses Mahmoud Jardaneh, Chief, New Reactor Licensing Branch, NRC Getachew Tesfaye, Senior Project Manager, NRC Lessons Learned from the Standard Design Approval of the NuScale US460 Design, Nonproprietary PM-185644, Revision 1, US460 SDAA Lessons Learned, Proprietary Affidavit of Carrie Fosaaen, AF-186631

LO-186537 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com Lessons Learned from the Standard Design Approval of the NuScale US460 Design, Nonproprietary

to LO-186537 Page 1 of 10 NuScale Nonproprietary Lessons Learned from the Standard Design Approval of the NuScale US460 Design 1.0 Purpose This report identifies and discusses significant issues and challenges NuScale observed during the NRCs review of the NuScale US460 standard design approval application (SDAA), and identifies potential improvements in the review process to ameliorate these challenges for future applications.

The NRC has begun a period of reviewing novel reactor designs at what may prove an unprecedented pace, with several advanced light water and non-light-water reactor designs in various stages of active review, pre-application consideration, or under development for future submittal.

NuScale views the issues addressed herein as major challenges for efficient and timely review of a new reactor design. This report discusses NuScales perspective as a light-water reactor applicant seeking standard design approval. The lessons learned are broadly applicable to other designs and licensing processes under NRCs Parts 50 and 52 frameworks.

2.0

Background

The NRC previously completed review of the NuScale US600 design certification application (DCA). The NRC staff completed review of the US600 DCA in approximately 41 months following docketing of the application. Although the review was successful, NuScale provided recommendations for improvement in Reference 5.1. The NuScale US460 SDAA was submitted with plans for an expedited schedule based on the experience gained in the US600 DCA review and expectation of improvements from the lessons learned. The NRC staff completed review of the US460 SDAA in approximately 22 months following docketing of the application.

While the reduction in review schedule from US600 DCA to US460 SDAA was significant, part of the reduction is because of the limited differences between the designs. Executive Order 14300 for reform of the NRC directs a review duration of 18 months, including for applications that may not have had a prior submittal to reference as a baseline like in the case for the NuScale US460 SDAA. Therefore, additional actions are likely needed to achieve further gains in review efficiency. During the course of the US460 SDAA review, NuScale identified several overarching problems with the review process and review criteria that could yield significant efficiencies in the review of future applications, without impacting the effectiveness of the NRCs review. These recommendations complement, and provide some specific actions to implement, some of those made by the Nuclear Energy Institute (NEI) in their recent report Accelerating NRC Reform: Industry Recommendations (Reference 5.3).

to LO-186537 Page 2 of 10 NuScale Nonproprietary 3.0 Discussion 3.1 Review by Core Teams or Multi-Disciplinary Teams The NRC review of NuScales US460 SDAA followed approximately two years after the successful completion of the NRC review of NuScales US600 DCA. In addition, the US460 design was largely an evolutionary iteration from the US600 design. Because of this short time elapsed between reviews and design similarities, both NuScale and the NRC believed that the review of the US460 SDAA would be most efficient by striving for continuity in the review process. Therefore, the US460 SDAA review was performed by separate NRC staff working as individuals with different areas or review responsibilities, typically by branch.

Despite the short interval between US600 DCA and US460 SDAA reviews, there was some amount of turnover that had occurred within the NRC. This turnover resulted in different individuals reviewing a topic for the US460 SDAA than had reviewed the topic for the US600 DCA. In other cases, individual reviewers may have been assigned additional roles since the US600 DCA review such that their focus on a topic was not the same as it had been previously.

These situations caused delays while reviewers came up to speed or led to re-opening of areas of review that were previously resolved in the US600 DCA. In addition, the progress in the review became subject to individual reviewers who may not have understood the broader view of an issue. Discussions between NRC staff and NuScale then became focused on answering detailed individual questions out of context from the rest of the review.

A prime example of the occurrence of this issue during the US460 SDAA review is for the topic of density wave oscillation (DWO). The assigned individual NRC reviewers asked over one hundred questions about the details of possible DWO occurrence without consideration of the broader issue. Significant effort was expended on answering these questions without a clear connection to overall issue resolution. Later in the review, combined with a shift in NuScale strategy, additional reviewers were brought in as part of a more multi-disciplinary approach. The multi-disciplinary approach focused on the broader issue of potential consequences of DWO occurrence, online monitoring, and steam generator inspections. Once the multi-disciplinary approach was adopted for review, the DWO issue was resolved quickly.

The review of the augmented direct current power system (EDAS) and loss-of-coolant accident (LOCA) break spectrum are other examples where the review experienced delays from individual NRC reviewers. Later expansion of the NRC review team to use a multi-disciplinary approach led to progress and issue closure.

The NRC's Lessons Learned report from the US600 review (Reference 5.2) advised the use of an interdisciplinary review team for new and advanced reactor reviews. That report recommended such a team be established prior to initiating the application review. The team would be used to identify any cross-cutting technical and regulatory issues, assess their risk significance, and ensure that the staff performs its review of a unique new reactor design in an integrated manner, and that the team would assure safety holistically, giving appropriate credit to programs that are implemented following the design phase. As exemplified in the preceding examples, NuScale observes that these recommendations were only partially implemented for the US460 review. The use of a single, interdisciplinary, overarching review team from the outset of the review process may have helped prevent or mitigate several of the challenges discussed in this report.

to LO-186537 Page 3 of 10 NuScale Nonproprietary For these reasons, NuScale recommends to fully implement the use of core-teams or multi-disciplinary teams within the NRC staff for the review, particularly for identification and resolution of complicated issues by applying a risk-informed, holistic safety perspective. By using this approach from the beginning of the review, a broader view of issues will be ensured and delays caused by individual reviewers will be minimized.

3.2 Drive to Consensus on Risk-Insights to Focus the Review The NRC review of NuScales US460 SDAA was intended to be risk-informed. Risk-insights from the probabilistic risk assessment (PRA) were to be used to identify areas of the design that were risk-significant. NRC resources would then be directed to focus the review on those areas.

There were reasons to be confident in the PRA for the US460 SDAA since it was developed from the PRA for the US600 DCA and had been subjected to a NuScale self-assessment prior to submittal. In general, this approach was successful for focusing the review and making it more efficient. However, the risk-insights from the PRA themselves were also subject to NRC review. Delays in the review of the risk-insights caused a cascading effect where the scope of the review expanded.

For example, risk-insights from the PRA showed that EDAS was not a risk-significant system.

However, PRA reviewers did not reach this same conclusion early in the review. Instead, PRA reviewers continued to ask questions about EDAS throughout the review. Because there was no early consensus between NuScale and the NRC regarding the EDAS risk-insights, non-PRA reviewers did not clearly understand the risk-significance of the system. Believing that EDAS might be risk-significant, the non-PRA reviewers expanded their scope of deterministic review.

In the end, consensus was reached between NuScale and the NRC that EDAS was not risk-significant. With this outcome, the level of review of EDAS by non-PRA reviewers exceeded what should have been necessary for a system that was not risk-significant.

For these reasons, NuScale recommends to drive to consensus on risk-insights early in the review so that those risk-insights can be used to focus the NRC staff review on risk-significant areas. If the preliminary NRC review of the PRA risk-insights identifies areas of possible disagreement with the applicant, additional resources should be applied to resolving those disagreements as soon as possible. By resolving the disagreements and reaching consensus early in the review, the non-PRA reviewers can be directed to focus their time and effort on the risk-significant areas of the design. This approach will avoid delays caused by excessive review of areas that are not risk-significant.

The NEI document Accelerating NRC Reform: Industry Recommendations, (Reference 5.3) also identifies the need to enhance safety focus by using risk insights and eliminating unnecessary regulatory requirements and processes. The NEI recommendation is consistent with this NuScale recommendation.

3.3 Establish an Appeal Process to Resolve Disagreements After completion of the US600 DCA review, NuScale provided the NRC with recommendations for improvement in Reference 5.1. One of the recommendations (#1 in Reference 5.1) was to establish an appeal process to resolve disagreements between applicants and the NRC staff with respect to preliminary interpretations of requirements and guidance. In Reference 5.2, Section 3, the NRC responded to the NuScale recommendation by stating, the staff has

to LO-186537 Page 4 of 10 NuScale Nonproprietary determined that establishing a new and separate appeal process is unnecessary. As a result, the appeal process recommended by NuScale was not in place during the US460 SDAA review.

Like with the US600 DCA review, the US460 SDAA review resulted in numerous disagreements concerning the design between NuScale and the NRC, ranging from minor to significant. With an application review process as extensive and thorough as the NRCs, it is expected and common for these types of disagreements to occur. However, each disagreement is a source of delay in the application review, and thus a cost borne by the applicant. In most instances, the disagreements were resolved through the ordinary course via an exchange of information in audit question responses, request for additional information (RAI) responses, and in meetings.

Too often, NuScale - like previous applicants or like during the US600 review - effectively had little choice but to concede to the NRC staffs position in order to keep the application moving forward toward completion of the Final Safety Evaluation Report (FSER).

Multiple examples were provided in Reference 5.1, Section 3.1.1, for the US600 DCA to support the recommendation at that time. An example specific to the US460 SDAA demonstrating the continued need for an appeal process is the LOCA break spectrum issues. Two separate but related issues were raised by the NRC staff regarding NuScales LOCA break spectrum. In both cases, there was a fundamental disagreement between the NRC staff and NuScale about the interpretation of 10 CFR 50.46. NuScale believed (and continues to believe) that 10 CFR 50.46 only requires explicit analysis of piping failures and that failures of other types of components can be excluded from explicit analysis if certain criteria were met, as was done in the US600 DCA. Some members of the NRC staff believed that 10 CFR 50.46 requires explicit analysis of all hypothetical breaks, regardless of the likelihood. NuScale sought to escalate the issue to NRC senior management. Although NRC senior management seemed in favor of NuScales interpretation of 10 CFR 50.46 and the applicability of US600 DCA precedent, there was no formal process to move the issue forward quickly. NuScale considered appealing to the Commission directly, but ultimately elected not to do so because of time constraints. In the interest of maintaining schedule, NuScale made changes to the US460 SDAA in line with the NRC staff interpretation (while still disagreeing with the particular interpretation).

The problem in the instance of this example, and others of lesser visibility, is that a process is not available to gain a clear understanding of the NRC staffs position and the basis for it, or to appeal that position to a separate decision maker. Therefore, an applicant is forced to concede to the NRC staffs position in order to maintain schedule and manage review costs, or to informally engage management in an effort to reach consensus. In order to promote regulatory clarity, certainty, and efficiency, a process and arbiter should be established to consider and decide significant disagreements in a timely manner. This need becomes even greater in the context of shorter overall review schedules. In the case of the US600 DCA review that lasted almost four years, there was sufficient time to appeal to the Commission. NuScale did appeal one issue successfully to the Commission. In the case of the two-year schedule planned for the US460 SDAA review, it was essentially not possible to appeal to the Commission and adhere to the schedule. For future applicants, Executive Order 14300 directs a review schedule of 18 months (i.e., shorter than the US460 SDAA review). With a further shortened schedule, future applicants will not have time to appeal to the Commission. Therefore, a separate process for appeal is needed.

The appeal process should be developed and implemented for new license applications.

Specifically, where an applicant believes that NRC staff are misconstruing regulatory

to LO-186537 Page 5 of 10 NuScale Nonproprietary requirements, changing position on meeting requirements, or erroneously concluding the design fails to meet acceptance criteria, an applicant and NRC staff should be able to present their positions to a neutral arbiter to render a decision. Important features of this process include:

That the decision maker be neutral and well informed of both perspectives, That the process is carried out and the decision rendered transparently and efficiently, and That the decision be binding to the extent feasible on the NRC staff and Advisory Committee on Reactor Safeguards (ACRS).

An additional benefit of the appeal process may be to reduce NRC staff nonconcurences that risk review schedule delays. An NRC staff member able to argue their position to an appeal boday may be satisfied that their views have been fully considered. If feasible, the appeal process could formally supplant the nonconcurrence process in some circumstances.

While the appeal process needs to have an established structure, it need not be unduly formalized because it is not tied to a regulatory imperative and not binding on the Commissions findings. Completing this process in a 60-day timeframe supports fast-moving application reviews as will be the case going forward based on Executive Order 14300. The effort and time involved dissuades an applicant from appealing trivial disagreements, bringing only consequential matters for appeal. Additional details of what this process could look like were provided in Reference 5.1, Section 3.1.2, when NuScale recommended this process previously.

3.4 Promote Flexibility for Using Risk-Informed Approaches As described in Section 3.3 above, NuScale previously provided the NRC with recommendations for improvement in Reference 5.1 following the US600 DCA. One of the recommendations (#2 in Reference 5.1) was to implement risk-informed decision making consistent with the Commissions Staff Requirements Memorandum SRM-SECY-19-0036. The Commission directed the Staff to apply risk-informed principles when strict, prescriptive application of deterministic criteriais unnecessary to provide for reasonable assurance of adequate protection. In Reference 5.1, NuScale noted that the direction in SRM-SECY-19-0036 was not applied in the US600 DCA review other than for one specific decision and recommended that the direction be applied more broadly.

In Reference 5.2, Section 3, the NRC responded that the NuScale recommendation aligns well with the staffs lessons learned that reviews need to be conducted using a holistic, risk-informed review strategy. The NRC response further identified that, as part of NRCs transformational efforts to become a modern and risk-informed regulator, the NRC staff published NUREG/KM-0016, Guidance for Integrating Risk Insights into NRC Decisions, in March 2021. This publication provides detailed guidance on using the Be riskSMART framework and contains example case studies from across a series of disciplines.

With SRM-SECY-19-0036 and NUREG/KM-0016 both being in place in advance of the US460 SDAA submittal, NuScale expected that they would be used to promote risk-informed approaches. However, NuScale observed that some NRC staff was still resistant to implementing the intent of SRM-SECY-19-0036 and continued to favor strict, prescriptive application of deterministic criteria over risk-informed principles even when there was reasonable assurance of adequate protection. When challenged by NuScale, the NRC staff

to LO-186537 Page 6 of 10 NuScale Nonproprietary indicated that SRM-SECY-19-0036 and NUREG/KM-0016 were not applicable when NRC regulations specified a strict, deterministic approach. The NRC staff believed exemptions from NRC regulations were necessary to use a risk-informed approach. NuScale disagreed with this because NuScale believed the NRC staff was reading and interpreting the NRC regulations in an overly restrictive manner and not considering other interpretations. NuScale believes that the intent of SRM-SECY-19-0036 and NUREG/KM-0016 is to encourage flexibility in the way that regulations are read and interpreted to favor risk-informed approaches whenever possible. In other words, SRM-SECY-19-0036 and NUREG/KM-0016 should form a foundational approach to avoid an overly constrained or restrictive view of existing regulations and guidance.

One example from the US460 SDAA review is the LOCA break spectrum issues. Two separate but related issues were raised by the NRC staff regarding NuScales LOCA break spectrum. In both cases, NuScale and the NRC staff reached agreement that there was reasonable assurance of adequate protection against the particular LOCA scenarios. With this reasonable assurance, NuScale expected that SRM-SECY-19-0036 provided the roadmap to resolve the issue without having to take exemption from 10 CFR 50.46. Some of the NRC staff, reading and interpreting 10 CFR 50.46 in an overly restrictive manner, insisted that an explicit exemption from 10 CFR 50.46 was required before using the more risk-informed approach to demonstrate reasonable assurance. Because exemptions from 10 CFR 50.46 are not typical, NuScale was hesitant to request such an exemption. Absent an efficient means to appeal the NRC staff interpretation (see recommendation in Section 3.3), NuScale ultimately elected to request an exemption from 10 CFR 50.46 and it was granted by the NRC. However, the disagreement over the need for the exemption resulted in significant effort and delays in resolving the issue. The effort and delays seem especially concerning from an efficiency perspective given the agreement between NRC staff and NuScale that there was reasonable assurance of adequate protection. Viewing 10 CFR 50.46 in light of SRM-SECY-19-0036 and NUREG/KM-0016 should have led to a quicker resolution of the issue without the need for unnecessary paperwork for an exemption.

Another example from the US460 SDAA review is the safety-classification of EDAS. NuScale classified EDAS as a nonsafety-related system in accordance with NuScale procedures and consistent with regulations and regulatory guidance. Some NRC staff disagreed with this classification based on a particular interpretation of the 10 CFR 50.2 definition of safety-related combined with a strict, prescriptive, deterministic approach to the treatment of EDAS in the safety analysis. NuScale believed that the direction in SRM-SECY-19-0036 once again provided a roadmap to resolve the issue by focusing on the reasonable assurance of adequate protection rather than a rigid reading of NRC regulations and regulatory guidance. Disagreements on the interpretations and applicability of SRM-SECY-19-0036, and no efficient means for NuScale to appeal the NRC staff interpretation (see recommendation in Section 3.3), led to delays in resolving the issue. After expansion of the NRC review team to use a multi-disciplinary approach (see recommendation in Section 3.1), NuScale believed that the issue had been resolved successfully with no change in EDAS classification (i.e., nonsafety-related). However, at the end of the review, some members of the NRC staff used the non-concurrence process to re-state their particular interpretation of NRC regulations and regulatory guidance based on a strict, prescriptive, deterministic approach. Discussion of the non-concurrence with the NRC staff and with the ACRS identified that the non-concurring staff did not have a safety concern (i.e., there was reasonable assurance of adequate protection). This lack of safety concern was evident in the proposed resolutions to the non-concurrence that recommended NuScale or NRC staff-initiated exemptions. This example highlights the continued resistance of some NRC staff

to LO-186537 Page 7 of 10 NuScale Nonproprietary in viewing NRC regulations and regulatory guidance in light of SRM-SECY-19-0036 and NUREG/KM-0016.

As the Commission concluded in SRM-SECY-19-0036, risk information is an important tool to help resolve such contentious issues. The value of risk information in such cases is that it provides a quantified representation of a new designs safety performance with respect to specific issues that NRC staff historically consider deterministically, where NRC staff might otherwise apply acceptance criteria and positions developed for large LWRs with different safety profiles. New designs such as NuScales substantially differ from the designs on which the existing regulatory framework was built, in ways that fundamentally alter the presumed safety profile of the plant, such that the existing framework of requirements and guidance identifies apparent gaps in the design with little safety significance when considered holistically. Until a risk-informed, technology-neutral framework is completed and proven, use of risk information in individual licensing decisions is an important tool to close such gaps. Despite the Commissions direction in SRM-SECY-19-0036, the NRC staff has continued to favor a strict, prescriptive application of deterministic criteria even when there is agreement on reasonable assurance of adequate protection.

In order to ensure a broad applicability and use of SRM-SECY-19-0036 and NUREG/KM-0016, NRC staff procedures and training are necessary to ensure that risk insights are incorporated into the NRC staffs review early and effectively. Training is also necessary to ensure the approach envisioned in SRM-SECY-19-0036 and NUREG/KM-0016 permeate the NRC staff culture. Where possible, existing NRC regulations and regulatory guidance should be viewed from the perspective of SRM-SECY-19-0036 and NUREG/KM-0016. An NRC staff philosophy or approach where each use of risk-informed principles requires a corresponding exemption from existing NRC regulations or other similar unnecessary paperwork would tend to discourage its use, even if unintentionally. At some point, the very low risk posed by the NuScale design (as exemplified by the very low core damage frequency and large release frequency) is the risk-insight that has meaning. Given a low enough risk level, public health and safety are adequately protected and the NRC mission is satisfied.

Although this recommendation is not identical to recommendation #2 in Reference 5.1 (discussed in detail in Reference 5.1, Section 3.2), it builds upon it in light of the US460 SDAA experience.

The NEI document Accelerating NRC Reform: Industry Recommendations, (Reference 5.3) also recommends to [e]xpand the use of risk-informed, performance-based regulation agency-wide. The NEI recommendation is consistent with this NuScale recommendation.

3.5 Define Credible As described in Section 3.3 above, NuScale previously provided the NRC with recommendations for improvement in Reference 5.1 following the US600 DCA. One of the recommendations (#3 in Reference 5.1) was to define credible. In Reference 5.2, Section 3, the NRC responded to the NuScale recommendation by stating that credible would not be defined because developing generic definitions of credible may not present the most technology-inclusive approach. As a result, there was no definition in place during the US460 SDAA review. The NRC response in Reference 5.2 did state that the staff is taking several actions to ensure that the expectations are clear and predicable for defining accident sequences, including

to LO-186537 Page 8 of 10 NuScale Nonproprietary appropriate controls to prevent and mitigate potential accident consequences and taking probabilistic considerations into account as appropriate. However, these staff actions, if taken, were not successful in preventing recurrence of the same issues that prompted the previous recommendation to define credible. Therefore, NuScale is repeating the recommendation in this letter.

The notion of whether an occurrence is credible is the basis for, a pervasive feature of, and an inextricable aspect of NRCs regulatory framework. Whether an event is credible or not informs the scope of numerous requirements and NRC staff positions, either explicitly or implicitly. Yet the meaning of credible in any of its various contexts continues to elude definition, impeding regulatory certainty and review predictability.

Multiple examples were provided in Reference 5.1, Section 3.3.1, for the US600 DCA to support the recommendation at that time. An example specific to the US460 SDAA demonstrating the continued need for a definition of credible is the treatment of EDAS in the safety analyses.

Because EDAS was classified as a nonsafety-related system, the typical deterministic, conservative approach would be to assume EDAS failure in the safety analysis of a design-basis event. In most scenarios, the assumed EDAS failure did not pose a challenge to acceptance criteria. However, it was possible to hypothesize a specific scenario (or set of scenarios) where EDAS failure could result in a challenge to acceptance criteria. The specific scenario involved only certain initiating events combined with multiple individual failures causing an overall EDAS failure at a very specific time and under a very specific set of plant conditions, and excluding the expected response of trained, licensed reactor operators. NuScale calculated the expected frequency of occurrence of the scenario, noted that it was orders of magnitude below NRC safety goals, and concluded the scenario could be excluded because it was not credible. Some NRC staff took the position that because the scenario could be hypothesized through a particular application of strict, deterministic assumptions, that the scenario was therefore credible, regardless of its frequency of occurrence. The disagreement between NuScale and NRC staff regarding whether the scenario was credible could not be resolved because there was no clear definition of credibility. Despite the assurances in Reference 5.2 that the staff is taking several actions to ensure that the expectations are clear and predicable for defining accident sequences, including appropriate controls to prevent and mitigate potential accident consequences and taking probabilistic considerations into account as appropriate, there was still a significant disagreement between NRC and NuScale regarding accident sequences.

The lack of a definition or clear explanation of the meaning of credible frustrates applicants and introduces significant regulatory uncertainty. Despite a history of attempts, challenges, and reluctance to define credible, a clear and consistent NRC definition should be achievable and is appropriate given the state of PRA technology and the tools available to compensate for it.

NuScale believes that disagreements, like the one regarding the treatment of EDAS in the safety analysis for the US460 SDAA, could be avoided by defining credible.

Defining credible would also be consistent with the implementation of Executive Order 14300 that identifies a need to alter the policy of minimizing even trivial risks and focus on credible, realistic risks. A clear, measurable definition of credible will facilitate the implementation of that direction. For example, a credible accident definition would directly inform the scope of events to be analyzed as postulated accidents and the magnitude of the hypothetical source term under current regulations (10 CFR 52.137(a)(2) and equivalent). Additional details of what a definition

to LO-186537 Page 9 of 10 NuScale Nonproprietary of credible could look like were provided in Reference 5.1, Section 3.3.2, when NuScale recommended this previously.

The NEI document Accelerating NRC Reform: Industry Recommendations, (Reference 5.3) also identifies the need to [e]nsure that reactor safety assessment focus on credible, realistic risks. The NEI recommendations are to [e]stablish clear probability thresholds for events and hazards to be considered in a reactors design and to [e]stablish guidance on addressing unlikely events with defense-in-depth. These NEI recommendations are consistent with this NuScale recommendation.

4.0 Conclusion NuScale views the SDAA review as a successful demonstration of the NRCs ability to review an advanced reactor design in a reasonable timeframe. However, the review process needs to and can continue to be made more efficient and predictable, reducing the substantial burden on applicants and the NRC, while enhancing focus on matters important to safety. To that end, NuScale recommends that the NRC:

1. Fully implement the use of core-teams or multi-disciplinary teams within the NRC staff for the review, particularly for identification and resolution of complicated issues by applying a risk-informed, holistic safety perspective. The consequence of not using teams is that areas of the review can be held up by an individual NRC reviewer who may not understand the broader view of an issue.

2. Drive to consensus on risk-insights early in the review and then use those risk-insights to focus the NRC staff review on risk-significant areas. The consequence of not reaching a consensus early in the review and using it to focus the review is that time and effort (both applicant and NRC staff) is misdirected on topics that are not risk-significant.

3. Establish an appeal process to resolve disagreements between applicants and the NRC staff with respect to preliminary interpretations of requirements and guidance.

The consequence of the absence of such a process is that regulatory burden has steadily increased from one applicant to the next without consideration of whether new staff positions have merit from a safety perspective.

4. Promote flexibility in reading of regulations and regulatory guidance to favor risk-informed decision making consistent with the Commissions direction in Staff Requirements Memorandum SRM-SECY-19-0036 to apply risk-informed principles when strict, prescriptive application of deterministic criteriais unnecessary to provide for reasonable assurance of adequate protection. The consequence of overly restrictive readings of regulations and regulatory guidance is that individual NRC staff may impede implementation of the SRM, resulting in increased review durations and costs even where risk-insights demonstrate reasonable assurance of adequate protection.

5. Define credible. Numerous NRC requirements incorporate the concept of credible.

The consequence of a lack of a definition is unpredictability in the review as

to LO-186537 Page 10 of 10 NuScale Nonproprietary interpretations vary among the staff, resulting in increased review durations and costs even for events of incredibly low frequencies and often with insignificant radiological consequences. A workable definition will aso help effectuate implementation of Executive Order 14300.

These recommendations can be implemented relatively quickly in order to prepare the NRC for forthcoming reviews of numerous advanced reactor designs, including any NuScale application.

NuScale looks forward to further discussions with NRC and other interested stakeholders on these topics.

5.0 References 5.1 NuScale letter to NRC, Lessons-Learned from the Design Certification Review of the NuScale Power, LLC Small Modular Reactor, LO-0221-74035, dated February 19, 2021 (ML21050A431).

5.2 NRC Staff Lessons Learned Report for the Review of NuScale SMR Design Certification Application, dated March 31, 2022 (ML22088A161).

5.3 NEI letter to NRC, Industry Recommendations on Accelerating NRC Reform, dated July 31, 2025 (ML25212A198 and ML25212A199).

LO-186537 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com PM-185644, Revision 1, US460 SDAA Lessons Learned, Proprietary

LO-186537 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvallis, Oregon 97330 Office 541.360.0500 Fax 541.207.3928 www.nuscalepower.com Affidavit of Carrie Fosaaen, AF-186631

AF-186631 Page 1 of 2 NuScale Power, LLC AFFIDAVIT of Carrie Fosaaen I, Carrie Fosaaen, state as follows:

(1)

I am the Vice President of Regulatory Affairs of NuScale Power, LLC (NuScale), and as such, I have been specifically delegated the function of reviewing the information described in this Affidavit that NuScale seeks to have withheld from public disclosure, and am authorized to apply for its withholding on behalf of NuScale.

(2)

I am knowledgeable of the criteria and procedures used by NuScale in designating information as a trade secret, privileged, or as confidential commercial or financial information. This request to withhold information from public disclosure is driven by one or more of the following:

(a)

The information requested to be withheld reveals distinguishing aspects of a process (or component, structure, tool, method, etc.) whose use by NuScale competitors, without a license from NuScale, would constitute a competitive economic disadvantage to NuScale.

(b)

The information requested to be withheld consists of supporting data, including test data, relative to a process (or component, structure, tool, method, etc.), and the application of the data secures a competitive economic advantage, as described more fully in paragraph 3 of this Affidavit.

(c)

Use by a competitor of the information requested to be withheld would reduce the competitors expenditure of resources, or improve its competitive position, in the design, manufacture, shipment, installation, assurance of quality, or licensing of a similar product.

(d)

The information requested to be withheld reveals cost or price information, production capabilities, budget levels, or commercial strategies of NuScale.

(e)

The information requested to be withheld consists of patentable ideas.

(3)

Public disclosure of the information sought to be withheld is likely to cause substantial harm to NuScales competitive position and foreclose or reduce the availability of profit-making opportunities. The accompanying presentation reveals distinguishing aspects about the NuScale licensing strategy and approach used for the US460 standard design approval application (SDAA).

NuScale has invested significant resources to develop these strategies and approaches, including the expenditure of a considerable sum of money.

The precise financial value of the information is difficult to quantify, but it is a key element of the licensing strategy and approach for a NuScale plant and, therefore, has substantial value to NuScale.

If the information were disclosed to the public, NuScales competitors would have access to the information without purchasing the right to use it or having been required to undertake a similar expenditure of resources. Such disclosure would constitute a misappropriation of NuScale's intellectual property, and would deprive NuScale of the opportunity to exercise its competitive advantage to seek an adequate return on its investment.

(4)

The information sought to be withheld is in the enclosed presentation entitled US460 SDAA Lessons Learned, PM-185644, Revision 1. The enclosure contains the designation Proprietary at the top of each page containing proprietary information.

AF-186631 Page 2 of 2 (5)

The basis for proposing that the information be withheld is that NuScale treats the information as a trade secret, privileged, or as confidential commercial or financial information. NuScale relies upon the exemption from disclosure set forth in the Freedom of Information Act (FOIA), 5 USC § 552(b)(4), as well as exemptions applicable to the NRC under 10 CFR §§ 2.390(a)(4) and 9.17(a)(4).

(6)

Pursuant to the provisions set forth in 10 CFR § 2.390(b)(4), the following is provided for consideration by the Commission in determining whether the information sought to be withheld from public disclosure should be withheld:

(a)

The information sought to be withheld is owned and has been held in confidence by NuScale.

(b)

The information is of a sort customarily held in confidence by NuScale and, to the best of my knowledge and belief, consistently has been held in confidence by NuScale. The procedure for approval of external release of such information typically requires review by the staff manager, project manager, chief technology officer or other equivalent authority, or the manager of the cognizant marketing function (or his delegate), for technical content, competitive effect, and determination of the accuracy of the proprietary designation.

Disclosures outside NuScale are limited to regulatory bodies, customers and potential customers and their agents, suppliers, licensees, and others with a legitimate need for the information, and then only in accordance with appropriate regulatory provisions or contractual agreements to maintain confidentiality.

(c)

The information is being transmitted to and received by the NRC in confidence.

(d)

No public disclosure of the information has been made, and it is not available in public sources. All disclosures to third parties, including any required transmittals to NRC, have been made, or must be made, pursuant to regulatory provisions or contractual agreements that provide for maintenance of the information in confidence.

(e)

Public disclosure of the information is likely to cause substantial harm to the competitive position of NuScale, taking into account the value of the information to NuScale, the amount of effort and money expended by NuScale in developing the information, and the difficulty others would have in acquiring or duplicating the information. The information sought to be withheld is part of NuScale's licensing strategy that provides NuScale with a competitive advantage over other firms in the industry. NuScale has invested significant human and financial capital in developing this strategy and NuScale believes it would be difficult for others to duplicate the strategy without access to the information sought to be withheld.

I declare under penalty of perjury that the foregoing is true and correct. Executed on August 29, 2025.

Carrie Fosaaen