ML24095A292

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Kairos - Hermes 2 Docs - Preliminary Chapter of Hermes 2 SE
ML24095A292
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Site: Hermes  File:Kairos Power icon.png
Issue date: 04/04/2024
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NRC
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References
Download: ML24095A292 (23)
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Text

From:

Cayetano Santos Sent:

Thursday, April 4, 2024 2:47 PM To:

Weidong Wang; Larry Burkhart Cc:

Michael Orenak; Matthew Hiser; Brian Bettes; William Jessup

Subject:

Preliminary Chapter of Hermes 2 SE Attachments:

Chapter 01 - The Facility.pdf

Weidong, Attached is another one of the preliminary chapters from the safety evaluation (SE) for the Hermes 2 construction permit application. This chapter has been reviewed by branch chiefs and received a preliminary review by OGC. However, this chapter is not final because it still needs to be reviewed by division management and receive the final OGC review. Thus, this preliminary chapter could change between now and the approved SE that will be sent to ACRS for formal review. I am sending this chapter in advance so that members can become familiar with the safety evaluation and begin preparing for the formal review.

Nine preliminary chapters were provided to you on March 14, 2024. I expect to send the remaining preliminary chapters to you piecemeal after they receive the preliminary OGC review by April 16, as the first planned subcommittee meeting is May 16. However, if the more complex chapters (e.g., chapters 5 and 13) are delayed beyond April 16, I will let you know ASAP.

Kairos Power submitted Revision 0 of the preliminary safety analysis report (PSAR) for Hermes 2 in July 2023. All preliminary SE chapters being sent to the ACRS refer to Revision 1 of the PSAR. Although Revision 1 of the PSAR has not been submitted, Kairos stated their intent to do so once all PSAR changes are known (i.e., the end of the technical review). The current list of docketed PSAR changes that will be incorporated into Revision 1 of the PSAR can be found in ADAMS and on the NRC public webpage at https://www.nrc.gov/reactors/non-power/new-facility-licensing/hermes2-kairos/documents.html.

The staff has taken a different approach toward the Hermes 2 SE considering that Hermes 1 and Hermes 2 CP applications have most of the same information. Due to these similarities, the staff leveraged the Hermes 1 SE to the extent possible for Hermes 2, using an incorporation by reference for many sections. The following description, taken from Chapter 1 of the Hermes 2 SE, discusses how the staffs review of Hermes 1 was applied to its review of the Hermes 2:

Use of Docketed Information The staffs review of the Hermes 2 CP application was informed by the Hermes 1 CP application review. The Hermes 2 facility includes many SSCs that are identical to those that would be used in the Hermes 1 facility. Accordingly, large portions of the Hermes 1 PSAR are identical to the Hermes 2 PSAR. In the July 14, 2023, CP application submittal,

Kairos highlighted the differences between the Hermes 1 and Hermes 2 PSARs in two ways. First, Kairos used blue font in the Hermes 2 PSAR to identify any modified or new text. Second, Kairos provided a summary of the information deleted from the Hermes 1 PSAR to generate the Hermes 2 PSAR (ML23195A132).

In addition, Kairos identified the docketed information and audit information from Hermes 1 that is applicable to the Hermes 2 CP application in two letters dated October 27, 2023 (ML23300A141 and ML22300A144). This information is considered docketed information for the Hermes 2 CP application and was used to inform the staffs review.

Format and Content of Hermes 2 Safety Evaluation Sections Based on the consistencies between the Hermes 1 and Hermes 2 PSARs described above, the staff leveraged the Hermes 1 SE to the greatest extent possible to support its review of the Hermes 2 CP application. Accordingly, applicable contents of the Hermes 1 SE were incorporated by reference into this SE. To determine which Hermes 1 SE content could be incorporated by reference, the staff reviewed the differences between the Hermes 1 and Hermes 2 PSARs. Where the Hermes 2 PSAR only contained minor deviations (e.g., minimal or no effect on the NRC SE or editorial changes, as compared to the Hermes 1 PSAR), the staffs SE was largely limited to incorporating by reference applicable portions of the Hermes 1 SE. Similarly, where the Hermes 2 PSAR contained a limited number of significant but discrete changes, but was otherwise identical to the Hermes 1 PSAR, the staffs SE was likewise limited to an evaluation of the variances between the two PSARs. In this case, the balance of the staffs SE also incorporated by reference applicable portions of the Hermes 1 SE. Based on this approach, many of the Hermes 2 SE sections are organized using the following structure:

Brief introduction summarizing the Hermes 2 PSAR content with a focus on any changes in comparison to the Hermes 1 PSAR.

Regulatory evaluation section that, in most cases, incorporates by reference the regulations and guidance from the corresponding section of the Hermes 1 SE due to the similarities between the Hermes 1 and Hermes 2 facility designs.

Technical evaluation that:

o Identifies the consistent and modified Hermes 2 PSAR information, as compared to the Hermes 1 PSAR.

o Incorporates by reference, as appropriate, content from the Hermes 1 SE for PSAR information that is consistent between Hermes 1 and Hermes 2.

o Evaluates the new design information and non-editorial changes (i.e.,

minor and/or few significant changes), as compared to the Hermes 1 SE.

The depth of the staff review provided for each change is dependent on the significance of that change.

A full conclusion specific to the Hermes 2 review.

For Hermes 2 PSAR sections that contain entirely new information and/or several significant changes when compared to the Hermes 1 PSAR, the staff performed its evaluation without incorporation by reference from the Hermes 1 SE. One example of a section which reflects such an evaluation by the staff is Section 5.2, Intermediate Heat Transport System, of this SE related to the intermediate salt loops. These systems are not in the design of the Hermes 1 test reactor; therefore, they were not evaluated by the

staff in its review of the Hermes 1 CP application. Accordingly, the staff evaluated this system without incorporation by reference of the Hermes 1 SE.

If you have any questions, please contact me or Mike Orenak.

-Tanny Santos

Hearing Identifier:

Kairos_Hermes2_CPDocs_Public Email Number:

10 Mail Envelope Properties (MW4PR09MB90107CBB8B9890E65D486EABE53C2)

Subject:

Preliminary Chapter of Hermes 2 SE Sent Date:

4/4/2024 2:47:00 PM Received Date:

4/4/2024 2:46:00 PM From:

Cayetano Santos Created By:

Cayetano.Santos@nrc.gov Recipients:

"Michael Orenak" <Michael.Orenak@nrc.gov>

Tracking Status: None "Matthew Hiser" <Matthew.Hiser@nrc.gov>

Tracking Status: None "Brian Bettes" <Brian.Bettes@nrc.gov>

Tracking Status: None "William Jessup" <William.Jessup@nrc.gov>

Tracking Status: None "Weidong Wang" <Weidong.Wang@nrc.gov>

Tracking Status: None "Larry Burkhart" <Lawrence.Burkhart@nrc.gov>

Tracking Status: None Post Office:

MW4PR09MB9010.namprd09.prod.outlook.com Files Size Date & Time MESSAGE 6049 4/4/2024 2:46:00 PM Chapter 01 - The Facility.pdf 246511 Options Priority:

Normal Return Notification:

No Reply Requested:

No Sensitivity:

Normal Expiration Date:

1 THE FACILITY This chapter of the safety evaluation (SE) provides a general introduction to the Hermes 2 test reactor facility and an overview of the topics covered in detail in other chapters of this SE, including areas of review, regulatory criteria and guidance, review procedures and findings, and conclusions.

1.1 Introduction This SE documents the results of the U.S Nuclear Regulatory Commission (NRC) staffs (the staffs) technical review of the construction permit (CP) application submitted by Kairos Power LLC (Kairos) under Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Domestic Licensing of Production and Utilization Facilities, for a two-unit test reactor facility. The test reactor facility is referred to as Hermes 2. An environmental review was also performed for the Hermes 2 CP application and its evaluation and conclusions are documented in a draft environmental assessment (EA) issued on [month] xx, 2024 (Agencywide Documents Access and Management System (ADAMS) Accession No. MLxxxxxxxxx), Environmental Assessment for the Construction Permit for the Kairos Hermes 2 Test Reactor Facility, and Draft Finding of No Significant Impact (FONSI), dated [month] xx, 2024 (CITE).

By letter dated July 14, 2023 (ML23195A122), Kairos submitted its application for CPs, which, if granted, would allow Kairos to construct Hermes 2 in Oak Ridge, Tennessee. The staff acknowledged receipt of Kaiross application for CPs in the Federal Register (FR)

(88 FR 51876) on August 4, 2023. Kairos submitted the following in its CP application:

x Description and safety assessment of the site required by 10 CFR 50.34(a)(1).

x Environmental report required by 10 CFR 50.30(f).

x General information required by 10 CFR 50.33, Contents of applications; general information.

x Agreement limiting access to classified information required by 10 CFR 50.37, Agreement limiting access to Classified Information.

The staff conducted a docketing acceptance review of Kaiross application and, by letter dated September 11, 2023 (ML23233A167), determined that Kaiross CP application was complete and acceptable for docketing. The application was assigned Docket Nos. 50-611 and 50-612 for Hermes 2 Unit 1 and Unit 2, respectively. A notice of docketing of Kaiross CP application was published in the FR on September 15, 2023 (88 FR 63632). A notice of a 60-day opportunity to request a hearing and petition for leave to intervene was published in the FR on November 22, 2023 (88 FR 81439). No petitions were filed in response to the notice.

The safety review of the Hermes 2 CP application is based on information in the application, as revised and supplemented. Unless otherwise stated, this SE evaluates the information contained in the original application dated July 14, 2023 (Pkg. ML23195A121); the information in Revision 1 of Kaiross Preliminary Safety Analysis Report (PSAR), dated [month] xx, 2024 (MLxxxxxxxxx), which supersedes the PSAR Revision 0 included in the original application; the information in Revision 1 of technical report KP-TR-017-NP, KP-FHR [Kairos Power fluoride

Revision 1 of the Hermes 2 PSAR, submitted [month] xx, 2024, incorporated all previously submitted changes to PSAR chapters.

THIS NRC STAFF DRAFT SE HAS BEEN PREPARED AND IS BEING RELEASED TO SUPPORT INTERACTIONS WITH THE ACRS. THIS DRAFT SE HAS NOT BEEN SUBJECT TO FULL NRC MANAGEMENT AND LEGAL REVIEWS AND APPROVALS, AND ITS CONTENTS SHOULD NOT BE INTERPRETED AS OFFICIAL AGENCY POSITIONS.

salt-cooled high temperature reactor] Core Design and Analysis Methodology, dated September 29, 2022 (ML22272A598); the information in Revision 2 of technical report KP-TR-022-NP, Hermes 2 Postulated Event Methodology, dated June 30, 2023 (ML23195A131); and the information in the following application supplements:

x Kairos Power Response to Hermes 2 General Audit Question 1.5-1, dated October 27, 2023, ML23300A143.

x Kairos Power Response to Hermes 2 General Audit Question 1.5-2, dated October 27, 2023, ML23300A144.

x Kairos Power Additional Information Related to Hermes 2 Construction Permit Application - PSAR Chapter 1, dated October 31, 2023, ML23304A312.

x Kairos Power Transmittal of Changes to Hermes 2 Construction Permit Application -

PSAR Chapter 13 and KP-TR-022, dated December 22, 2023, Pkg. ML23356A078.

x

[Placeholder for RCI regarding contamination and Flibe-water interaction]

Kairos currently has an active construction permit, number CPTR-6, for the Hermes test reactor, which was issued on December 14, 2023. Hermes 2 is proposed to be built on the same site as the Hermes test reactor, and each Hermes 2 reactor unit is proposed to be of similar size and design as the Hermes reactor. The NRC staff reviewed the design differences between the two facilities in this SE. For clarity on distinguishing between the two facilities, the Hermes test reactor will be referred to as Hermes 1 throughout this SE.

1.1.1 Areas of Review The Hermes 2 CP application review consisted of two concurrent reviews: (1) a safety review of the Hermes 2 PSAR and (2) an environmental review of the Hermes 2 Environmental Report.

The staff reviewed the Hermes 2 PSAR against applicable regulatory requirements using appropriate regulatory guidance and standards, as discussed below, to assess the sufficiency of the preliminary design of Hermes 2. As part of this review, the staff evaluated descriptions and discussions of the Hermes 2 structures, systems, and components (SSCs), with special attention to design and operating characteristics, unusual or novel design features, and principal safety considerations. The preliminary design of Hermes 2 was evaluated to ensure the sufficiency of principal design criteria (PDC), design bases, and information relative to materials of construction, general arrangement, and approximate dimensions, sufficient to provide reasonable assurance that the final design will conform to the design bases. In addition, the staff reviewed Kaiross identification and justification for the selection of those variables, conditions, or other items that are determined to be probable subjects of technical specifications for the facility, with special attention given to those items that may significantly influence the final design. The SSCs were also evaluated to ensure that they would adequately provide for the prevention of accidents and the mitigation of consequences of accidents. The staff considered the preliminary analysis and evaluation of the design and performance of the Hermes 2 SSCs with the objective of assessing the risk to public health and safety resulting from operation of the facility.

The staff completed an environmental review in accordance with the National Environmental Policy Act (42 [United States Code] USC §4321 et seq.,) (NEPA) to determine the potential impacts of the proposed action on the human environment and reasonable alternatives to Kaiross proposal. Based on a review of the environmental report submitted as part of the Hermes 2 CP application and the results of the environmental impact statement (EIS) recently issued for Hermes 1, the NRC staff concluded that it would be prudent to first prepare a draft EA

to determine whether preparation of an EIS would be necessary or whether a finding of no significant impact (FONSI) could be issued for the Hermes 2 CPs based on factors unique to the Hermes 2 CP application. These factors include, among others, the similar design of Hermes 2 and Hermes 1 and the staffs final EIS for Hermes 1 covering the same site as Hermes 2 and documenting the environmental impacts from the proposed Hermes 1 CP as all SMALL impacts.

The staff prepared a draft EA and draft FONSI for the Hermes 2 CP application in accordance with the requirements in 10 CFR 51.30, Environmental assessment, 10 CFR 51.31, Determinations based on environmental assessment, and 10 CFR 51.32, Finding of no significant impact. Consistent with 10 CFR 51.33, Draft finding of no significant impact; distribution, the staff offered a 30-day public comment period in the FR on [month] xx, 2024 (XX FR XXXXX). After consideration of the public comments, the staff [placeholder for staff determination].

1.1.2 Regulatory Basis and Acceptance Criteria In accordance with 10 CFR 50.35(a), a CP (in this situation, two CPs) authorizing Kairos to proceed with the construction of the Hermes 2 facility may be issued if the NRC makes the following findings:

1. The applicant has described the proposed design of the facility, including, but not limited to, the principal architectural and engineering criteria for the design, and has identified the major features or components incorporated therein for the protection of the health and safety of the public.
2. Such further technical or design information as may be required to complete the safety analysis, and which can reasonably be left for later consideration, will be supplied in the final safety analysis report (FSAR).
3. Safety features or components, if any, which require research and development have been described by the applicant and a research and development program will be conducted that is reasonably designed to resolve any safety questions associated with such features or components.
4. On the basis of the foregoing, there is reasonable assurance that: (i) such safety questions will be satisfactorily resolved at or before the latest date stated in the application for completion of construction of the proposed facility, and (ii) taking into consideration the site criteria contained in 10 CFR Part 100, Reactor Site Criteria, the proposed facility can be constructed and operated at the proposed location without undue risk to the health and safety of the public.

As provided in 10 CFR 100.2, Scope, the siting requirements in 10 CFR Part 100 apply to applications for site approval for the purpose of constructing and operating stationary power and testing reactors pursuant to the provisions of [10 CFR Part 50]. Kairos submitted a CP application for a testing facility. Therefore, the staff evaluated the Hermes 2 site-specific conditions using the applicable criteria in 10 CFR Part 100, in addition to those in 10 CFR Part 50. The staffs review evaluated the geography and demography of the site; nearby industrial, transportation, and military facilities; site meteorology; site hydrology; and site geology, seismology, and geotechnical engineering to ensure that issuance of CPs will not be inimical to public health and safety. The staffs review also evaluated SSCs and equipment designed to ensure safe operation, performance, and shutdown when subjected to extreme

weather, floods, seismic events, missiles (including aircraft impacts), chemical and radiological releases, and loss of offsite power. A detailed review of the Hermes 2 site can be found in Chapter 2, Site Characteristics, of this SE.

The CPs, if issued, would constitute an authorization for Kairos to proceed with construction of the Hermes 2 facility. The staffs evaluation of the preliminary design and analysis of the Hermes 2 facility does not constitute approval of the safety of any design feature or specification, nor did Kairos request such approval for any part of the Hermes 2 design. Such approval will be made following the evaluation of the final design of the facility, as described in the FSAR as part of Kaiross operating license (OL) application for Hermes 2.

In addition to the findings listed in 10 CFR 50.35, Issuance of construction permits, a CP application must also provide sufficient information to allow the Commission to make the following determinations in accordance with 10 CFR 50.40, Common standards, and 10 CFR 50.50, Issuance of licenses and construction permits:

1. There is reasonable assurance: (i) that the construction of the facility will not endanger the health and safety of the public, and (ii) that construction activities can be conducted in compliance with the Commissions regulations.
2. The applicant is technically qualified to engage in the construction of its proposed facility in accordance with the Commissions regulations.
3. The applicant is financially qualified to engage in the construction of its proposed facility in accordance with the Commissions regulations.
4. The issuance of a permit for the construction of the facility would not be inimical to the common defense and security or to the health and safety of the public.
5. After weighing the environmental, economic, technical and other benefits of the facility against environmental and other costs and considering reasonable available alternatives, the issuance of these CPs, subject to the conditions for protection of the environment set forth herein, is in accordance with Subpart A of 10 CFR Part 51 of the Commissions regulations and all applicable requirements have been satisfied.
6. The application meets the standards and requirements of the Atomic Energy Act and the Commissions regulations, and that notifications, if any, to other agencies or bodies have been duly made.

The staffs evaluation of Hermes 2s preliminary design and analysis was based primarily upon the following 10 CFR requirements:

x 10 CFR 50.2, Definitions.

x 10 CFR 50.21, Class 104 licenses; for medical therapy and research and development facilities.

x 10 CFR 50.33(f) x 10 CFR 50.34(a) x 10 CFR 50.35 x

10 CFR 50.40 x

10 CFR 50.41, Additional standards for class 104 licenses.

x 10 CFR 50.50 x

10 CFR 50.55, Conditions of construction permits, early site permits, combined licenses, and manufacturing licenses.

x 10 CFR 50.58, Hearings and report of the Advisory Committee on Reactor Safeguards.

x 10 CFR Part 50, Appendix C, A Guide for the Financial Data and Related Information Required to Establish Financial Qualifications for Construction Permits and Combined Licenses.

x 10 CFR Part 50, Appendix E, Emergency Planning and Preparedness for Production and Utilization Facilities.

x 10 CFR 100.10, Factors to be considered when evaluating sites.

x 10 CFR 100.11, Determination of exclusion area, low population zone, and population center distance.

The regulations of 10 CFR 50.40 require that:

the processes to be performed, the operating procedures, the facility and equipment, the use of the facility, and other technical specifications, or the proposals, in regard to any of the foregoing collectively provide reasonable assurance that the applicant will comply with the regulations in this chapter, including the regulations in part 20 of this chapter, and that the health and safety of the public will not be endangered.

With respect to 10 CFR Part 20, Standards for Protection Against Radiation, which is referred to in 10 CFR 50.40, the staff assessed whether Kairos had identified the relevant requirements for an operating facility and provided descriptions of the preliminary facility design to determine whether the PSAR provides an acceptable basis for the development of SSCs and whether there is reasonable assurance that Kairos will comply with the regulations in 10 CFR Part 20 during Hermes 2 operation. Because Kairos has not applied for licenses to receive, possess, use, transfer, or dispose of byproduct, source, or special nuclear material, the staff did not evaluate whether requirements in 10 CFR Part 20 would be met for the construction of the two Hermes 2 reactors.

As required by 10 CFR 50.34(a)(3)(i), Kairos must describe the PDC for its Hermes 2 facility in the PSAR. However, for the Hermes 2 test reactors, Kairos is not required to follow 10 CFR Part 50, Appendix A, General Design Criteria [GDCs] for Nuclear Power Plants, which applies only to water-cooled nuclear power reactors. Section 3.1.1, Design Criteria, of the Hermes 2 PSAR states the following regarding the PDC for Hermes 2:

Kairos Power has also developed a set of principal design criteria (PDC) applicable for the KP-FHR technology which has been reviewed and approved by the NRC in Principal Design Criteria for the Kairos Power Fluoride Salt-Cooled High Temperature Reactor. [ML20167A174] The application of these criteria to the SSCs of the test reactor are shown in Table 3.1-2 ["Principal Design Criteria]. Note that while the facility contains two reactor units, no safety-related SSCs are shared between the reactor units, which satisfies PDC 5. Therefore, PDC 5 is not further discussed within this safety analysis report. Specific details regarding how the other PDC are met by the design are described in the individual sections throughout this safety analysis report as summarized in Table 3.1-2.

The staff reviewed Kaiross description of the Hermes 2 PDC, as described in the PSAR Sections identified in Table 3.1-2 and in the NRC-approved topical report KP-TR-003-NP-A, Principal Design Criteria for the Kairos Power Fluoride Salt-Cooled High Temperature Reactor, as applicable to the test reactor facility.

The staff used established guidance and acceptance criteria that it determined to be relevant to the review of the Hermes 2 CP application, noting that much of this guidance was originally developed for completed designs of water-cooled nuclear reactors. In order to determine the acceptance criteria necessary for demonstrating compliance with regulatory requirements in 10 CFR, the staff used the following:

x NUREG-1537, Part 1, Guidelines for Preparing and Reviewing Applications for the Licensing of Non-Power Reactors, Format and Content, issued February 1996 x

NUREG-1537, Part 2, Guidelines for Preparing and Reviewing Applications for the Licensing of Non-Power Reactors, Standard Review Plan and Acceptance Criteria, issued February 1996 As appropriate, the staff used additional guidance (e.g., NRC regulatory guides, Institute of Electrical and Electronics Engineers standards, American National Standards Institute/American Nuclear Society standards, and NRC office instructions) in its review of the Hermes 2 CP application. The additional guidance was used based on the technical judgment of the reviewer, as well as references in NUREG-1537, Parts 1 and 2; and the Hermes 2 CP application.

1.1.3 Review Procedures The staffs review of the Hermes 2 application was informed by NUREG-1537, the Hermes 1 SE (Pkg. ML23158A265), as well as other relevant guidance cited therein, cited in the application, or used based on the staffs technical judgment. In particular, Kaiross Hermes 2 CP application only seeks authorization to construct the proposed Hermes 2 facility. Therefore, the level of detail needed in the application and the staffs corresponding SE is different than that needed for an OL application and corresponding SE. For the purposes of issuing a CP, the Hermes 2 facility may be adequately described at a functional or conceptual level in the PSAR. As such, Kairos has deferred providing some design and analysis details until the submission of its FSAR with its OL application.

The objective of the staffs evaluation was to assess the sufficiency of information contained in the Hermes 2 application for the issuance of CPs in accordance with the requirements of 10 CFR Part 50. An in-depth evaluation of the Hermes 2 final design will be performed following the docketing of an OL application and its accompanying FSAR.

1.1.3.1 Use of Docketed Information The staffs review of the Hermes 2 CP application was informed by the Hermes 1 CP application review. The Hermes 2 facility includes many SSCs that are identical to those that would be used in the Hermes 1 facility. Accordingly, large portions of the Hermes 1 PSAR are identical to the Hermes 2 PSAR. In the July 14, 2023, CP application submittal, Kairos highlighted the differences between the Hermes 1 and Hermes 2 PSARs in two ways. First, Kairos used blue font in the Hermes 2 PSAR to identify any modified or new text. Second, Kairos provided a summary of the information deleted from the Hermes 1 PSAR to generate the Hermes 2 PSAR (ML23195A132).

In addition, Kairos identified the docketed information and audit information from Hermes 1 that is applicable to the Hermes 2 CP application in two letters dated October 27, 2023 (ML23300A141 and ML22300A144). This information is considered docketed information for the Hermes 2 CP application and was used to inform the staffs review.

1.1.3.2 Format and Content of Hermes 2 Safety Evaluation Sections Based on the consistencies between the Hermes 1 and Hermes 2 PSARs described above, the staff leveraged the Hermes 1 SE to the greatest extent possible to support its review of the Hermes 2 CP application. Accordingly, applicable contents of the Hermes 1 SE were incorporated by reference into this SE. To determine which Hermes 1 SE content could be incorporated by reference, the staff reviewed the differences between the Hermes 1 and Hermes 2 PSARs. Where the Hermes 2 PSAR only contained minor deviations (e.g., minimal or no effect on the NRC SE or editorial changes, as compared to the Hermes 1 PSAR), the staffs SE was largely limited to incorporating by reference applicable portions of the Hermes 1 SE.

Similarly, where the Hermes 2 PSAR contained a limited number of significant but discrete changes, but was otherwise identical to the Hermes 1 PSAR, the staffs SE was likewise limited to an evaluation of the variances between the two PSARs. In this case, the balance of the staffs SE also incorporated by reference applicable portions of the Hermes 1 SE. Based on this approach, many of the Hermes 2 SE sections are organized using the following structure:

x Brief introduction summarizing the Hermes 2 PSAR content with a focus on any changes in comparison to the Hermes 1 PSAR.

x Regulatory evaluation section that, in most cases, incorporates by reference the regulations and guidance from the corresponding section of the Hermes 1 SE due to the similarities between the Hermes 1 and Hermes 2 facility designs.

x Technical evaluation that:

o Identifies the consistent and modified Hermes 2 PSAR information, as compared to the Hermes 1 PSAR.

o Incorporates by reference, as appropriate, content from the Hermes 1 SE for PSAR information that is consistent between Hermes 1 and Hermes 2.

o Evaluates the new design information and non-editorial changes (i.e., minor and/or few significant changes), as compared to the Hermes 1 SE. The depth of the staff review provided for each change is dependent on the significance of that change.

x A full conclusion specific to the Hermes 2 review.

For Hermes 2 PSAR sections that contain entirely new information and/or several significant changes when compared to the Hermes 1 PSAR, the staff performed its evaluation without incorporation by reference from the Hermes 1 SE. One example of a section which reflects such an evaluation by the staff is Section 5.2, Intermediate Heat Transport System, of this SE related to the intermediate salt loops. These systems are not in the design of the Hermes 1 test reactor; therefore, they were not evaluated by the staff in its review of the Hermes 1 CP application. Accordingly, the staff evaluated this system without incorporation by reference of the Hermes 1 SE.

1.1.4 Resolving Technical Issues For those technical areas that require additional information, the staff has several options:

1. The staff may determine that such technical issues must be resolved prior to the issuance of a CP.
2. The staff may determine that such information may be left until the submission of the OL application.
3. The staff may require that such technical issues be resolved prior to the completion of construction, but after the issuance of a CP.

Technical issues that fall within the scope of the first option require additional information to be provided in order to establish PDC and/or design bases so that the staff may have confidence that the final facility design will conform to the design basis. The staff resolves such technical issues through audits, requests for confirmation (RCIs), and requests for additional information (RAIs).

In the second and third options, the staff may also use audits or issue RCIs and RAIs to resolve identified technical issues. These types of technical issues include those that require a design maturity beyond what is required by 10 CFR 50.34(a) to issue a CP. Although determining what constitutes a preliminary versus a final design may be somewhat subjective, according to 10 CFR 50.34(a), a preliminary design must include PDC, the design bases, and general facility arrangement and approximate dimensions. This information should be sufficient to provide reasonable assurance that the final design will conform to the design bases with adequate margin for safety. The staff may use audits or issue RCIs and RAIs if it determines that doing so is necessary for the applicant to acknowledge certain technical deficiencies that could impact the final design. Appropriate responses include commitments to resolving these deficiencies either in the FSAR or before the completion of construction.

Audits are designed to maximize the efficiency of the staffs review. During an audit, the applicant can respond to questions, the staff can readily evaluate the applicants responses, and the need for formal correspondence between the staff and the applicant is reduced, resulting in improved review efficiency. As part of its review of the Hermes 2 CP application, the staff conducted a general audit of the Hermes 2 PSAR. In this audit, Kairos supplemented the PSAR and provided clarifications through its responses to the staffs questions during audit meetings and in docketed correspondence. The staff documented the results of the Hermes 2 general audit in a report issued on [month] xx, 2024 (MLxxxxxxxxx).The staff also issued requests for confirmation of information on [month] xx, 2024 (MLxxxxxxxxx) and received a response from Kairos on [month] xx, 2024 (MLxxxxxxxxx)

Additionally, Appendix A, Post Construction Permit Activities - Construction Permit Conditions and Additional Items for the Operating License Application, of this SE contains a listing of those elements of design, analysis, and administration identified as requiring additional research and development or resolution by Kairos. The staff determined that resolution of these items is not necessary for the issuance of CPs, but that Kairos should ensure that these items are fully addressed in the FSAR supporting a Hermes 2 OL application. The staff is tracking these items to ensure they are considered during the review of an OL application for Hermes 2.

1.1.5 Ongoing Research and Development The provisions of 10 CFR 50.34(a)(8) allow for ongoing research and development (R&D) to confirm the adequacy of the design of SSCs to resolve safety questions prior to the completion of construction. In accordance with 10 CFR 50.34(a)(8), and as described in Section 1.3.9, Research and Development, of the Hermes 2 PSAR, Kairos has identified the following ten ongoing research and development activities:

x Perform a laboratory testing program to confirm fuel pebble behavior (Section 4.2.1, Reactor Fuel) x Develop a high temperature material surveillance sampling program for the reactor vessel[s] and internal[s] (Section 4.3.4, Testing and Inspection)

x Perform testing of high temperature material to qualify Alloy 316H and ER16-8-2 (Section 4.3, Reactor Vessel System) x Perform analysis related to potential oxidation in certain postulated events for the qualification of the graphite used in the reflector structure[s] (Section 4.3) x Development and validation of computer codes for core design and analysis methodology (Section 4.5, Nuclear Design) x Develop and perform qualification testing for a fluidic diode device (Section 4.6, Thermal-Hydraulic Design) x Justification of thermodynamic data and associated vapor pressure correlations of representative species (Section 5.1.3, System Evaluation) x Complete compatibility evaluations of the intermediate coolant and reactor coolant chemical interaction (Section 5.1.3) x Develop process sensor technology for key reactor process variables (Section 7.5.3, System Evaluation) x Develop the reactor coolant chemical monitoring instrumentation (Section 9.1.1, Chemistry Control System)

In support of these activities, Kairos has provided descriptions of the affected SSCs and identified the additional development that is needed. By letter dated October 27, 2023 (ML23300A144), Kairos stated that these research and development activities will be completed in advance of the completion of construction of Hermes 2, Unit 1. Enclosure 1, General Information, of the CP application states that the latest date for completion of construction of Hermes 2 Unit 1 is expected to be December 31, 2027, with construction of Hermes 2, Unit 2, expected to be completed by December 31, 2028. As described in Appendix A to this SE, the staff is tracking these activities and will verify that they are resolved prior to the completion of construction.

1.1.6 Advisory Committee on Reactor Safeguards Review To support the Advisory Committee on Reactor Safeguards (ACRS) in providing an independent review and report to the Commission regarding the Hermes 2 CP application, the staff presented the findings and conclusions of this SE to the ACRS subcommittee on [month] xx and xx, 2024 and the full committee on [month] xx, 2024. After the meeting, the ACRS issued a letter to the Commission with their recommendations regarding the Hermes 2 CP application to meet the requirements of 10 CFR 50.58, Hearings and report of the Advisory Committee on Reactor Safeguards. The ACRS letter is provided in Appendix C of this SE.

1.1.7 Application Availability Publicly available documents related to the Hermes 2 CP application may be obtained online in the Agencywide Documents Access and Management System (ADAMS) Public Documents collection at https://www.nrc.gov/reading-rm/adams.html. To begin the search, select ADAMS Public Documents and then select Begin Web-based ADAMS Search. For problems with ADAMS, please contact the NRCs Public Document Room (PDR) reference staff at 1-800-397-4209 or by email to PDR.Resource@nrc.gov.

The versions of the Hermes 2 PSAR, submitted July 14, 2023, and [month] xx, 2024, are publicly available in ADAMS. Other public documents and correspondence related to this application may be found by searching Hermes 2s docket numbers, 50-611 and 50-612, in ADAMS (input 05000611 and 05000612 into ADAMS, respectively). Portions of the application

or correspondence containing sensitive information (e.g., proprietary information) are being withheld from public disclosure pursuant to 10 CFR 2.390, Public inspections, exemptions, requests for withholding.

1.1.8 NRC Staff Contact Information The project manager for this SE was Michael Orenak, Senior Project Manager, Division of Advanced Reactors and Non-power and Utilization Facilities, U.S. Nuclear Regulatory Commission. Mr. Orenak may be contacted regarding this SE by telephone at 301-415-3229 or email at Michael.Orenak@nrc.gov. Appendix B, Principal Contributors, to this SE provides a listing of principal contributors, including areas of technical expertise and chapters of authorship.

1.2 Summary and Conclusions on Principal Safety Considerations The staff evaluated the descriptions and discussions of the proposed Hermes 2 facility, as described in Kaiross CP application, as supplemented. Based on its review, the staff makes the following findings:

1. Applicable standards and requirements of the Atomic Energy Act and Commission regulations have been met.
2. The acceptance criteria in or referenced in NUREG-1537 have been satisfied for a preliminary design supporting a CP application where the criteria were found to be applicable to the design.
3. Required notifications to other agencies or bodies related to this licensing action have been duly made.
4. Based on the preliminary design of the facility, there is reasonable assurance that the final design will conform to the design basis with adequate margin for safety.
5. There is reasonable assurance that the facility can be constructed in conformity with the permit, the provisions of the Atomic Energy Act, and the Commissions regulations.
6. Kairos has considered the expected consequences of several postulated credible accidents and a maximum hypothetical accident, emphasizing those that could lead to a release of fission products. The staff has evaluated the accident analyses presented by Kairos in the PSAR and determined that the calculated potential radiation doses outside the Hermes 2 site are not likely to exceed the guidelines of 10 CFR Part 100.

Furthermore, SSCs have been designed to provide for the prevention of accidents and the mitigation of consequences of accidents.

7. Releases of radioactive materials and wastes from the facility are not expected to result in concentrations outside the limits specified by 10 CFR Part 20, Subpart D, Radiation Dose Limits for Individual Members of the Public, and are as low as is reasonably achievable (ALARA).
8. The financial information, technical analyses and programs, and organization as described in the application, as supplemented, demonstrate that Kairos is financially and technically qualified to engage in the construction of its proposed facility in accordance with the Commissions regulations.
9. The preliminary emergency plan provides reasonable assurance that Kairos will be prepared to assess and respond to emergency events.
10. The application presents information at a level of detail that is appropriate for general familiarization and understanding of the proposed facility.
11. The application describes the relationship of specific facility design features to reactor operation.
12. Issuance of the CPs will not be inimical to the common defense and security or to the health and safety of the public.

Therefore, the staff finds that, subject to certain conditions, the preliminary design and analysis of the Hermes 2 facility, as described in the PSAR, is sufficient and meets the applicable regulatory requirements and guidance for the issuance of CPs in accordance with 10 CFR 50.35.

Further technical information or design information required to complete the safety analysis in support of operation can reasonably be left for later consideration in the FSAR. Appendix A to this SE identifies certain permit conditions that the staff recommends the Commission include if the CPs are issued. Additionally, Appendix A contains a listing of those elements of design, analysis, and administration identified as requiring additional development, description, or resolution by Kairos to support an OL application. The staff has determined that while resolution of these items is not necessary for the issuance of CPs, it is the responsibility of Kairos to ensure that these items have been fully addressed in the Hermes 2 FSAR supporting an OL application. The staff is tracking these items and will verify their implementation during the staffs review of a Hermes 2 OL application.

In addition, as discussed in PSAR Section 1.3.9 and Section 1.1.5 of this SE, Kairos has identified several ongoing R&D activities to confirm the adequacy of the design of SSCs to resolve safety questions prior to the completion of construction. The staff is tracking these activities, which are also listed in Appendix A to this SE, and will verify that they are resolved prior to the completion of construction.

Based on these findings as documented in this SE, and subject to the permit conditions identified in Appendix A of this SE, the staff recommends that the Commission make the following conclusions for the issuance of CPs for Hermes 2 in accordance with 10 CFR 50.35, 10 CFR 50.40, and 10 CFR 50.50:

1. Kairos has described the proposed design of Hermes 2, including, but not limited to, the principal architectural and engineering criteria for the design, and has identified the major features or components incorporated therein for the protection of the health and safety of the public.
2. Such further technical or design information as may be required to complete the safety analysis, and which can reasonably be left for later consideration, will be supplied in the FSAR.
3. Safety features or components that require R&D have been described by Kairos and an R&D program will be conducted that is reasonably designed to resolve any safety questions associated with such features or components.
4. On the basis of the foregoing, there is reasonable assurance that: (i) such safety questions will be satisfactorily resolved at or before the latest date stated in the application for completion of construction of the proposed facility, and (ii) taking into consideration the site criteria contained in 10 CFR Part 100, the proposed facility can be constructed and operated at the proposed location without undue risk to the health and safety of the public.
5. There is reasonable assurance: (i) that the construction of the Hermes 2 facility will not endanger the health and safety of the public, and (ii) that construction activities can be conducted in compliance with the Commissions regulations.
6. Kairos is technically qualified to engage in the construction of its proposed Hermes 2 facility in accordance with the Commissions regulations.
7. Kairos is financially qualified to engage in the construction of its proposed Hermes 2 facility in accordance with the Commissions regulations.
8. The issuance of permits for the construction of the Hermes 2 facility would not be inimical to the common defense and security or to the health and safety of the public.
9. After weighing the environmental, economic, technical, and other benefits of the facility against environmental and other costs and considering reasonable available alternatives, the issuance of the CPs, subject to the conditions for protection of the environment set forth therein, is in accordance with Subpart A, National Environmental Policy ActRegulations Implementing Section 102(2), of 10 CFR Part 51 of the Commissions regulations and all applicable requirements have been satisfied.
10. The application meets the standards and requirements of the Atomic Energy Act and the Commissions regulations, and notifications to other agencies or bodies have been duly made.

1.3 General Description The staff evaluated the sufficiency of the general description of the Hermes 2 facility, as presented in Section 1.3, General Description of the Facility, of the Hermes 2 PSAR, in part using the guidance and acceptance criteria from Section 1.3, General Description, of NUREG-1537, Parts 1 and 2.

In Section 1.3.1, Geographical Location, of the Hermes 2 PSAR, Kairos states that Hermes 2 will be located within the East Tennessee Technology Park in Oak Ridge, Tennessee. The property is at the site of the former Oak Ridge Gaseous Diffusion Plant and is approximately 185 acres (74.8 hectares). From the 1950s through the mid-1980s, uranium enrichment operations occurred at the plant. Since then, the site has been restored to a brownfield by the U.S. Department of Energy (DOE).

In Section 1.3.3.2, Operating Characteristics, of the Hermes 2 PSAR, Kairos states that the Hermes 2 reactors will each operate at a power of 35 megawatts thermal (design rated thermal power) and the combined electrical power output will be 20 megawatts electric for a licensed lifetime of 11 years. The staff determined that the Hermes 2 facility will be considered a Class 104(c) test reactor because Kairos will not recover more than 50 percent of its annual cost of owning and operating the Hermes 2 facility through energy for sale or commercial distribution in accordance with the regulations in 10 CFR 50.21(c) and 10 CFR 50.22. A description of the PDC for the facility is provided in PSAR Section 3.1.1. The PDC are based on NRC-approved Kairos Power Topical Report KP-TR-003-NP-A.

In addition to the brief descriptions provided in Section 1.3 of the Hermes 2 PSAR, more detailed descriptions of the facility design features are provided for the following:

x Safety systems (PSAR Chapter 4, Reactor Description, Chapter 5, Heat Transport System, and Table 3.6-1, Structures, Systems, and Components) x Engineered safety features (PSAR Chapter 6, Engineered Safety Features) x Instrumentation, control, and electrical systems (PSAR Chapter 7, Instrument and Control Systems, and Chapter 8, Electric Power Systems) x Reactor coolant, power generation system, and other auxiliary systems (PSAR Chapter 9, Auxiliary Systems)

x Radioactive waste management provisions or system and radiation protection (PSAR Chapter 11, Radiation Protection Program and Waste Management)

As described in subsequent SE chapters, the design of Hermes 2 includes engineered safety features to mitigate design-basis events or accidents, control and protection systems, equipment and processes related to handling and storage of byproduct material and special nuclear material, a power generation system, and fire protection systems. Additional controls are also provided by the Hermes 2 radiation protection program, ALARA program, radioactive waste management program, quality assurance program, fire protection program, and other programs that are described in the PSAR.

1.4 Shared Facilities and Equipment The staff evaluated the sufficiency of the evaluation of shared facilities and equipment, as presented in Section 1.4, Shared Facilities and Equipment, of the Hermes 2 PSAR, using the guidance and acceptance criteria from Section 1.4, Shared Facilities and Equipment, of NUREG-1537, Parts 1 and 2. The acceptance criteria state that a non-power reactor (e.g., test reactor) facility should be designed to accommodate all uses or malfunctions of the shared facilities without degradation of the facility, and the reactor should be designed to avoid the spread of contamination to any shared facilities or equipment.

Due to the unique nature of the two-unit test reactor facility, the staff reviewed the shared systems (equipment) between Unit 1 and Unit 2. Consistent with the review procedures of NUREG-1537, Part 2, Section 1.4, the staff confirmed that all facilities or equipment shared by the Hermes 2 facility are discussed in the PSAR. The shared systems and equipment are all non-safety related and summarized as follows:

x Plant control system (PCS): The PCS is a non-safety related control system which controls reactor startup, changes in power levels, reactor shutdown, heat transport, and the power generation system. Because it is a non-safety related system, failure of the PCS would not affect the safety-related features of Hermes 2. A detailed review of the PCS can be found in Section 7.2, Plant Control System, of this SE.

x Main control room: The main control room contains operator and supervisor workstation terminals that provide alarms, annunciations, personnel and equipment interlocks, and process information. No operator actions performed nor safety-related SSCs located in the main control room are credited for mitigating the consequences of postulated events.

A detailed review of the main control room can be found in Section 7.4 Main Control Room and Remote Shutdown Panel, of this SE.

x Normal and backup power: The electrical system is a non-safety-related system which provides power to support internal operation of plant equipment. Following a postulated event, SSCs do not require electrical power to perform safety-related functions due to the passive plant design. A detailed review of the electrical systems can be found in Chapter 8, Electrical Power Systems of this SE.

x Power generation systems: The power generation system consists of the steam system, turbine generator system, and feedwater and condensate system. The majority of the power generation system is shared between Unit 1 and Unit 2, with the exception of unit-specific steam superheaters and associated piping and components. The power generation system does not perform any safety-related functions. A detailed review of the power generation system can be found in Section 9.9, Power Generation System, of this SE.

x Plant communication systems: The communication systems are common to both units and facilitate communications during normal and emergency conditions between essential areas of the facility and between locations remote to the facility. The communication systems are not safety-related. A detailed review of the communication systems can be found in Section 9.5, Communication, of this SE.

x Service water system: The service water system draws water from municipal sources and provides the water to other water systems and supports general facility services (e.g., potable water). The service water system is not safety-related and is not credited for the mitigation of postulated events. A detailed review of the service water system can be found in Section 9.7.1, Service Water System, of this SE.

x Treated water system: The treated water system provides chemistry control and supplies make-up water to the component cooling water system, the chilled water system, and the safety-related decay heat removal system, and the power generation system deaerator. The treated water system is not a safety-related system and is not credited for the mitigation of postulated events. A detailed review of the treated water system can be found in Section 9.7.2, Treated Water System, of this SE.

x Auxiliary site services: Auxiliary site services include non-safety related systems and equipment that support operation of the plant, such as machine shops, chemistry laboratory, sewers, lighting, warehousing, and storage. The auxiliary services are not credited for the mitigation of postulated events and will be built so that they will not interfere with the ability of safety-related SSCs to perform their safety function(s). A detailed review of the auxiliary site services can be found in Section 9.8.5, Auxiliary Site Services, of this SE.

x Facility physical security: Section 12.8, Security, of the Hermes 2 PSAR states that a description of the security plan for the facility will be provided during the Hermes 2 OL application. In Table 3.6-1, Structures, Systems, and Components, the physical security system is stated to be non-safety related. A detailed review of the physical security system will be performed by the staff during the Hermes 2 OL application review.

x Sensors: Sensors will be used to provide information about temperature, pressure, neutron count rates, level, flow of the primary coolant and area radiation levels as input to multiple control and protection subsystems. Section 7.1 Instrumentation and Controls Overview, of the Hermes 2 PSAR states that safety-related sensors are not shared between Unit 1 and Unit 2. Non-safety-related sensors that control and monitor shared systems are shared between Unit 1 and Unit 2. A detailed review of the sensors can be found in Section 7.5, Sensors, of this SE.

x Fire protection: The fire protection systems are designed to detect, control, and extinguish fires so that a continuing fire will not prevent safe shutdown or result in an uncontrolled release of radioactive material that exceeds acceptance criteria. The Hermes 2 fire protection systems consist of unit-specific systems that serve each reactor building and common systems that serve the shared turbine building and the shared main control room. The fire protection systems do not perform safety-related functions. A detailed review of the fire protection system can be found in Section 9.4, Fire Protection Systems and Programs, of this SE.

x Radiation monitoring: Section 11.1.4, Radiation Monitoring and Surveying, of the Hermes 2 PSAR states that details of radiation monitoring and surveying, including a description of the equipment, methods, and procedures will be provided during the Hermes 2 OL application. In Table 3.6-1 of the Hermes 2 PSAR, the radiation monitoring system is stated to be non-safety-related. A detailed review of radiation monitoring and surveying will be performed by the staff during the Hermes 2 OL application review.

Since the Hermes 2 preliminary design identifies all shared systems as non-safety related, a malfunction or a loss of function of these shared systems would not affect the safety-related SSCs or result in conditions in which contamination could be spread. The staff finds that the loss of the shared systems would not affect the operation of the reactors, damage the reactors or their capability to be safely shutdown, or lead to uncontrolled release of radioactive material to unrestricted areas.

On the basis of its review of PSAR Section 1.4 and other relevant PSAR chapters, the staff finds that the level of detail provided regarding the Hermes 2 shared systems demonstrates an adequate basis for preliminary design and satisfies the applicable acceptance criteria of NUREG-1537, Part 2, Section 1.4. Therefore, the staff concludes that the information in Section 1.4 of the Hermes 2 PSAR on shared facilities and equipment is sufficient and meets the applicable regulatory requirements and guidance for the issuance of CPs in accordance with 10 CFR 50.35.

1.5 Comparison with Similar Facilities The staff evaluated the sufficiency of Kaiross comparison of Hermes 2 with other similar facilities1, as presented in Section 1.5, Comparison with Similar Facilities, of the Hermes 2 PSAR, using the guidance and acceptance criteria from Section 1.5, Comparison with Similar Facilities, of NUREG-1537, Parts 1 and 2.

Section 1.5 of the Hermes 2 PSAR states that the two Hermes 2 reactors will use pebble-based tristructural isotropic (TRISO) fuel with molten fluoride salt coolant. Kairos states that there are no existing or historical reactors that have used this specific fuel and coolant technology combination. However, Kairos states that the use of molten fluoride salt coolant was demonstrated in the Molten Salt Reactor Experiment (MSRE) at Oak Ridge National Laboratory.2 In addition, the use of pebble-based fuel designs with pebbles containing graphite moderator and TRISO fuel particles has been demonstrated in high-temperature gas-cooled pebble bed reactors (PBRs), which have been designed, constructed, and operated internationally. Kairos states that Hermes 2 fuel is similar to the PBR fuel, but has slightly smaller pebbles, is cooled by a molten fluoride salt coolant instead of an inert gas, is buoyant in the coolant, and includes an annular fuel layer within the pebble. TRISO particle fuel in stationary (non-pebble) particle form, (similar to the particles that would be contained within Hermes 2 fuel pebbles) has been used in other high-temperature gas-cooled reactor (HTGR) designs, including the Peach Bottom Unit 1 and Fort St. Vrain power reactors that were constructed and operated in the United States.3 Section 1.5.2.2, Graphite, of the Hermes 2 PSAR states that the two Hermes 2 reactors will use graphite as a moderator, which is similar to several other operating designs such as the 1 As noted in Section 1.1, the Hermes 1 facility is similar to the proposed Hermes 2 facility. However, the Hermes 1 final design was not completed, nor was construction of Hermes 1 completed, before the finalization of this SE. Because the NUREG-1537, Part 2, Section 1.5, criteria are focused on comparison to existing facilities, Hermes 1 was not included for comparison in this section.

2 The MSRE, which operated from 1965 to 1969 at power levels up to approximately 8 megawatts-thermal, utilized fuel dissolved in the salt coolant.

3 Peach Bottom Unit 1, which operated from 1967 to 1974, was a 200 megawatt-thermal helium-cooled graphite moderated power reactor. Fort St. Vrain Nuclear Power Plant, which operated from 1979 until 1989, was a 842 megawatt-thermal helium-cooled graphite moderated power reactor.

Advanced Gas-Cooled Reactor (AGR) type reactors designed and operated in the United Kingdom. For comparison, the Hermes 2 reactors will use a primary coolant containing a molten salt that is a mixture of lithium fluoride (LiF) and beryllium fluoride (BeF2) (commonly referred to as Flibe) in addition to graphite reflector assemblies on the bottom, top, and sides of the active core to provide neutron moderation, while the AGRs used graphite for neutron moderation and carbon dioxide as coolant. Section 1.5.3, Comparison of Support Systems, of the Hermes 2 PSAR states that the Hermes 2 reactors auxiliary systems, such as inventory control and chemistry monitoring, while Flibe-based, are functionally similar to conventional systems used at other reactors. In addition, other Hermes 2 auxiliary systems, including ventilation, cooling water, electrical power, power generation system, and instrumentation and control systems, are also generally conventional in nature.

The staff found that Kairos identified a number of similar facilities covering key aspects of the Hermes 2 design. MSRE provides relevant experience with molten fluoride salt coolant, while PBR experience is relevant to the use of pebbles with TRISO fuel particles. In addition, TRISO particle fuel has been used in previously operating HTGRs. Finally, AGR experience is relevant to the use of graphite as a neutron moderator as is planned in the Hermes 2 reactors design.

The staff determined that this collective experience of safe operation from multiple other reactor technologies with a number of key Hermes 2 design features provides additional confidence in the inherent safety of those design features.

Consistent with the review procedures of NUREG-1537, Part 2, Section 1.5, the staff confirmed that the characteristics of any facilities compared with the proposed facility were similar and relevant. The staff also verified that the operating history of facilities cited by Kairos generally demonstrated consistently safe operation, use, and protection of the public.

Based on its review, the staff finds that the level of detail provided on comparisons with similar facilities satisfies the applicable acceptance criteria of NUREG-1537, Part 2, Section 1.5 (considering that Hermes 2 would use a novel design that, while different from that of any existing or historical reactors, includes several key design features that are similar to those of other reactors), allowing the staff to make the following findings:

1. Kairos has compared the design bases and safety considerations of Hermes 2 with similar facilities, as practicable. The history of these facilities and their design features relevant to the Hermes 2 demonstrates consistently safe operation that is acceptable to the staff.
2. Aspects of the Hermes 2 design that are similar to features in other facilities that have been found acceptable to the staff, or otherwise demonstrated successful operation, should be expected to perform in a similar manner to these comparable features in other facilities.
3. Kairos is using test data and operational experience from facilities with similar components and design features in designing Hermes 2 components, as practicable.

Therefore, the staff concludes that the comparisons with similar facilities, as described in PSAR Section 1.5, are sufficient and meet the applicable regulatory requirements and guidance for the issuance of a CP in accordance with 10 CFR 50.35.

1.6 Summary of Operations The staff evaluated the sufficiency of the summary of Hermes 2 operations, as presented in Section 1.6, Summary of Operations, of the Hermes 2 PSAR, using the guidance and acceptance criteria from Section 1.6, Summary of Operations, of NUREG-1537, Parts 1 and 2.

Consistent with the review procedures of NUREG-1537, Part 2, Section 1.6, the staff verified that Kairos summarized the proposed operations of Hermes 2.

In Section 1.6 of the Hermes 2 PSAR, Kairos states that the purpose of Hermes 2 will be to test and demonstrate the key technologies, design features, and safety functions of Kaiross KP-FHR technology, as well as to provide data and insights for the design and licensing of a KP-FHR commercial power reactor. Hermes 2 would operate over its full range of power during a 11-year lifetime and produce approximately 20 MW of electrical power. In Chapter 4, Reactor Description, of the Hermes 2 PSAR, Kairos states that the reactors will each be designed with the capability to achieve power levels up to 35 megawatts-thermal. Kairos states that further information regarding Hermes 2 operations and programs will be provided in an OL application.

Based on its review of the information in PSAR Section 1.6 and other PSAR chapters, the staff finds that Kaiross information regarding the proposed operation of Hermes 2 is consistent with relevant assumptions and analyses in later PSAR chapters in which any safety implications of the proposed operations are evaluated. Therefore, the summary of operations satisfies the applicable acceptance criteria of NUREG-1537, Part 2, Section 1.6. Accordingly, the staff concludes that the summary of operations, as described in PSAR Section 1.6, is sufficient and meets the applicable regulatory requirements and guidance for the issuance of CPs in accordance with 10 CFR 50.35. Further technical or design information required to complete the safety analysis may reasonably be left for later consideration in an OL application.

1.7 Compliance with the Nuclear Waste Policy Act of 1982 The Nuclear Waste Policy Act of 1982 (42 USC § 10101) provides that the U.S. government is responsible for the permanent disposal of high-level radioactive waste and spent nuclear fuel, but the cost of disposal should be the responsibility of the generators and owners of such waste and spent fuel. Section 1.7, Compliance with the Nuclear Waste Policy Act of 1982, of the Hermes 2 PSAR states:

Kairos Power intends to enter into a contract with the Department of Energy (DOE) for the disposition of high-level waste and spent nuclear fuel. The contract will provide that the DOE accept title to the fuel and the obligation to take the spent fuel and/or high-level waste for storage or reprocessing. This will be discussed further in the application for the Operating License, consistent with Section 302(b)(1) of the Nuclear Waste Policy Act of 1982.

The staff evaluated the sufficiency of Kaiross compliance with the Nuclear Waste Policy Act using the guidance and acceptance criteria from Section 1.7, Compliance with the Nuclear Waste Policy Act of 1982, of NUREG-1537, Parts 1 and 2. The staff determined that to be in compliance at the CP stage, Kairos needs to submit documentation showing communications in good faith between Kairos and the DOE to enter into a contract for the disposition of high-level waste and nuclear fuel. By letter dated October 31, 2023 (ML23304A312), Kairos provided documentation from the DOE that Kairos is actively and in good faith negotiating on a contract under section 302(b) of the Nuclear Waste Policy Act. Because Kairos has provided documentation of good faith negotiations with the Department of Energy, the staff finds that

Kairos is in compliance with the Nuclear Waste Policy Act at the CP stage, consistent with NUREG-1537, Part 2, Section 1.7.

1.8 Facility Modifications and History The staff evaluated the sufficiency of Kaiross descriptions of facility modifications and history, as presented in Section 1.8, Facility Modifications and History, of the Hermes 2 PSAR, using the guidance and acceptance criteria from NUREG-1537, Parts 1 and 2, Section 1.8, Facility Modifications and History.

As stated in PSAR Section 1.8, This report is an application for the new construction of a non-power reactor facility. There are no prior operating histories of existing Nuclear Regulatory Commission licensed facilities nor modifications to existing licensed facilities to report. The staff determined that there are no existing facilities, there have been no modifications, and there is no history to report on the Hermes 2 test reactor facility.

Therefore, the staff concludes that Kaiross description of facility modifications and history in the PSAR Section 1.8 is sufficient and meets the applicable regulatory requirements and guidance for the issuance of CPs for a test reactor facility in accordance with 10 CFR 50.35.

1.9 References Kairos Power LLC, KP-TR-003-NP-A, "Principal Design Criteria for the Kairos Power Fluoride Salt-Cooled, High Temperature Reactor," Revision 1, June 12, 2020, ML20167A174.

. KP-TR-017-NP, KP-FHR Core Design and Analysis Methodology, Revision 1, September 29, 2022, ML22272A598.

. KP-TR-022-NP, " Hermes 2 Postulated Event Methodology," Revision 2, June 30, 2023, ML23195A131.

. Submittal of the Construction Permit Application for the Hermes 2 Kairos Power Fluoride Salt-Cooled, High Temperature Non-Power Reactor, July 14, 2023, Pkg. ML23195A121.

. Enclosure 10: Summary of PSAR Deletions, July 14, 2023, ML23195A132

. Kairos Power LLC, Response to Hermes 2 General Audit Question 1.5-1, October 27, 2023, ML23300A143.

. Kairos Power Response to Hermes 2 General Audit Question 1.5-2, October 27, 2023, ML23300A144.

. Kairos Power LLC - Additional Information Related to Hermes 2 Construction Permit Application - PSAR Chapter 1, October 31, 2023, ML23304A312.

. Kairos Power, LLC, Transmittal of Changes to Hermes 2 Construction Permit Application

- PSAR Chapter 13 and KP-TR-022, December 22, 2023, Pkg. ML23356A078.

. Submittal of the Preliminary Safety Analysis Report for the Kairos Power Fluoride Salt-Cooled, High Temperature Non-Power Reactor (Hermes 2), Revision 1, [month] xx, 2024, Pkg.

MLxxxxxxxxx.

Nuclear Regulatory Commission (U.S.) (NRC). NUREG-1537, Part 1, Guidelines for Preparing and Reviewing Applications for the Licensing of Non-Power Reactors, Format and Content, February 1996, ML042430055.

. NUREG-1537, Part 2, Guidelines for Preparing and Reviewing Applications for the Licensing of Non-Power Reactors, Standard Review Plan and Acceptance Criteria, February 1996, ML042430048.

. Safety Evaluation for the Kairos Power LLC Construction Permit Application for the Hermes Non-Power Test Reactor, June 16, 2023, Pkg. ML23158A265.

. Acceptance for Docketing of the Hermes 2 Non-power Test Reactor Construction Permit Application Submitted by Kairos Power LLC, September 11, 2023, ML23233A167.

. Hermes 2 General Audit Plan, October 3, 2023, ML23268A446.

. [Placeholder for RCI regarding contamination]

. Summary Report for the Regulatory Audit of Kairos Power LLC Hermes 2 Construction Permit Preliminary Safety Analysis Report - General Audit, [month] xx, 2024, MLxxxxxxxxx.

. Draft Environmental Assessment for the Construction Permit for the Kairos Hermes 2 Test Reactor, Draft Report for Comment. [month] xx, 2024, MLxxxxxxxxx.

. Hermes Test Reactor Construction Permit, December 14, 2023, ML23338A258

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