ML24114A280

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Kairos - Hermes 2 Docs - Preliminary Chapter of Hermes 2 SE to ACRS
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From: Cayetano Santos Sent: Tuesday, April 23, 2024 2:41 PM To: Weidong Wang; Larry Burkhart Cc: Michael Orenak; Matthew Hiser; Brian Bettes; Josh Borromeo

Subject:

Preliminary Chapter of Hermes 2 SE to ACRS Attachments: Chapter 04 - Reactor Description.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.

Eleven preliminary chapters were provided to you on March 14, April 4, and April 22, 2024.

If possible, I will send additional preliminary chapters to you piecemeal after they receive the preliminary OGC for the first planned subcommittee meeting on May 16, 2024.

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: 13

Mail Envelope Properties (MW4PR09MB9010D64979E5277505F851B5E5112)

Subject:

Preliminary Chapter of Hermes 2 SE to ACRS Sent Date: 4/23/2024 2:41:16 PM Received Date: 4/23/2024 2:41:00 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 "Josh Borromeo" <Joshua.Borromeo@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 5948 4/23/2024 2:41:00 PM Chapter 04 - Reactor Description.pdf 231205

Options Priority: Normal Return Notification: No Reply Requested: No Sensitivity: Normal Expiration Date:

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.

4 REACTOR DESCRIPTION

The reactor description addresses the principal features, operating characteristics, and parameters of the Hermes 2 test reactor facility. The Hermes 2 reactor cores generate heat by controlled fission of the tristructural isotropic (TRISO) fuel in a molten fluoride salt (Flibe) coolant that provides heat removal.

This chapter of the Kairos Power LLC (Kairos) Hermes 2 test reactor construction permit (CP) safety evaluation (SE) describes the U.S. Nuclear Regulatory Commission (NRC) staffs (the staffs) technical review and evaluation of the preliminary information regarding the Hermes 2 reactors. This information is presented in Chapter 4, Reactor Description, of the Hermes 2 preliminary safety analysis report (PSAR), Revision 1, as supplemented. The staff reviewed PSAR Chapter 4 against applicable regulatory requirements using regulatory guidance and standards to assess the sufficiency of the preliminary information Kairos provided regarding the Hermes 2 facility for the issuance of CPs in accordance with Title 10, Code of Federal Regulations (10 CFR) Part 50, Domestic Licensing of Production and Utilization Facilities. As part of this review, the staff evaluated information regarding the Hermes 2 facility, with special attention given to design and operating characteristics, unusual or novel design features, and principal safety considerations. The staff evaluated the preliminary design of the Hermes 2 facility to ensure the design criteria and information relative to construction are sufficient to provide reasonable assurance that the final design will conform to the design basis. In addition, the staff reviewed Kaiross identification and justification for the selection of those variables, conditions, or other items which are determined to be probable subjects of technical specifications (TSs) for the facility, with special attention given to those items which may significantly influence the final design.

In its review of areas relevant to Hermes 2 PSAR Chapter 4, the staff considered the information in technical report KP-TR-017, KP-FHR [Kairos Power fluoride salt-cooled high temperature reactor] Core Design and Analysis Methodology, Revision 1, dated September 30, 2022 (Agencywide Documents Access and Management System (ADAMS)

Accession No. ML23195A130), and technical report KP-TR-022, Hermes 2 Postulated Event Analysis Methodology, Revision 2, dated June 30, 2023 (ML23195A131), which are both components of the Hermes 2 CP application (ML23195A121).

4.1 Summary Description

Section 4.1, Summary Description, of the Hermes 2 PSAR provides a high-level overview of the reactor design. The Hermes 2 reactors are a fluoride molten-salt cooled pebble bed design that can each achieve a thermal power of up to 35 megawatts (MW). The reactor design employs a high-temperature graphite matrix coated TRISO particle fuel and a chemically stable, low pressure molten fluoride salt coolant (Flibe). The TRISO fuel and Flibe coolant constitute the functional containment. PSAR Section 4.1 provides an overview of the key design parameters, such as reactor power, inlet and outlet temperature, operating pressure, and fuel materials and enrichment levels. PSAR Chapter 4 describes various key aspects of the reactor design, including the reactor core (fuel, control and shutdown system, neutron startup source),

reactor vessel and internals, biological shield, nuclear design, thermal-hydraulic design, and reactor vessel support system.

NUREG-1537, Guidelines for Preparing and Reviewing Applications for the Licensing of Non-Power Reactors, Part 1, Format and Content, and Part 2, Standard Review Plan and Acceptance Criteria, Section 4.1, Summary Description, do not stipulate any specific review findings for the summary description of the reactor design. Therefore, the staff did not make any findings relative to PSAR Section 4.1. PSAR Sections 4.2 through 4.7 provide detailed descriptions of key aspects of the reactor design. The corresponding sections of this SE document the staffs review findings on these aspects of the reactor design.

4.1.1 Common Regulatory Evaluation for Reactor Systems

Common regulatory requirements for reactor systems evaluated in Chapter 4 are identified below. Any additional requirements or guidance specific to a system are identified in the subsection for that system. The common regulatory requirements for the evaluation of the Hermes 2 reactor systems are:

x Title 10 of the Code of Federal Regulations (10 CFR) 50.34(a)(4), which requires, in part, A preliminary analysis and evaluation of the design and performance of structures, systems, and components [SSCs] of the facility x 10 CFR 50.35, Issuance of construction permits.

x 10 CFR 50.40, Common standards.

4.2 Reactor Core

The subsections within Section 4.2, Reactor Core, of the Hermes 2 PSAR provide a description of the reactor cores, including the reactor fuel, reactivity control and shutdown, and neutron sources.

4.2.1 Reactor Fuel

4.2.1.1 Introduction

Section 4.2.1, Reactor Fuel, of the Hermes 2 PSAR describes the fuel design, the qualification of the fuel, and the design bases that the fuel must meet. In addition, the section provides an overview of fuel manufacturing and a testing and inspection plan. The TRISO fuel particle, composed of a uranium oxycarbide fuel kernel encased in coating layers to limit fission product releases, is a key component of the functional containment and along with the reactor coolant, provide the credited barriers to the release of radioactivity to the environment.

4.2.1.2 Regulatory Evaluation

The requirements in the common regulatory evaluation for reactor systems in Section 4.1.1 of this SE apply to the reactor fuel. Additionally, the staff reviewed Section 4.2.1.2, Regulatory Evaluation, of the Hermes 1 SE for applicability to the Hermes 2 SE. Based on the similarities between the Hermes 1 and Hermes 2 facility designs and the consistency of the reactor fuel design between Hermes 1 and Hermes 2, the staff finds that the regulations and guidance listed in Section 4.2.1.2 of the Hermes 1 SE are applicable to Hermes 2. Therefore, this section incorporates by reference Section 4.2.1.2 of the Hermes 1 SE.

4.2.1.3 Technical Evaluation

The staff reviewed Section 4.2.1 of the Hermes 2 PSAR and compared it to the equivalent section in the Hermes 1 PSAR (Section 4.2.1, Reactor Fuel). The staff found that Section 4.2.1 of the Hermes 2 PSAR contains information consistent with that in the Hermes 1 PSAR, except for a minor and editorial change, which is evaluated below. The staff also verified that the Hermes 2 reactor fuel design and functionality remain identical to Hermes 1. Based on these consistencies, this section incorporates by reference Section 4.2.1.3, Technical Evaluation, of the Hermes 1 SE.

4.2.1.3.1 Minor Change Compared to the Hermes 1 PSAR

The minor change in Hermes 2 PSAR Section 4.2, as compared to the information in Hermes 1 PSAR Section 4.2, includes the following:

x Staff use of technical report KP-TR-022 instead of technical report KP-TR-018, Hermes Postulated Event Analysis to inform the evaluation.

For the review of Hermes 2 PSAR Section 4.2.1, the staff used the information contained in technical report KP-TR-022 that details the postulated event methodology for Hermes 2. For the review of Hermes 1 PSAR Section 4.2.1, the staff used the information contained in technical report KP-TR-018. The postulated event analysis results in KP-TR-018 used to review Hermes 1 PSAR Section 4.2.1 remain the same in KP-TR-022 for the Hermes 2 design.

Therefore, the staff finds the evaluation and findings from Section 4.2.1.3 of the Hermes 1 SE are applicable to Hermes 2.

On the basis of its review, the staff finds that the level of detail provided regarding the Hermes 2 reactor fuel demonstrates an adequate basis for a preliminary design; meets principal design criteria (PDC) 10, 16, 34, and 35; and satisfies the applicable acceptance criteria of NUREG-1537, Part 2, Section 4.2.1, Reactor Fuel, to support safety functions including functional containment.

4.2.1.4 Conclusion

Based on staff findings above, and as incorporated by reference from the Hermes 1 SE, the staff concludes the information in Hermes 2 PSAR Section 4.2.1 is sufficient and meets the applicable guidance and regulatory requirements identified in this section for the issuance of CPs in accordance with 10 CFR 50.35 and 10 CFR 50.40. Further information as may be required to complete the review of Hermes 2 reactor fuel can reasonably be left for later consideration at the operating license (OL) stage since this information is not necessary for the review of a CP application.

4.2.2 Reactivity Control and Shutdown System

4.2.2.1 Introduction

Section 4.2.2, Reactivity Control and Shutdown System, of the Hermes 2 PSAR describes the reactivity control and shutdown system (RCSS). The RCSS inserts and withdraws control and shutdown elements to control reactivity in the reactor core during normal operation and in response to abnormal conditions or postulated events to ensure safe shutdown. There are four control elements that insert into the graphite reflector and three shutdown elements that insert into the pebble bed. Control elements can be positioned throughout their range of travel and are non-safety-related. Shutdown elements are safety-related and have two positions: (1) fully withdrawn or (2) fully inserted.

4.2.2.2 Regulatory Evaluation

The requirements in the common regulatory evaluation for reactor systems in Section 4.1.1 of this SE apply to the RCSS. Additionally, the staff reviewed Section 4.2.2.2, Regulatory Evaluation, of the Hermes 1 SE for applicability to the Hermes 2 SE. Based on the similarities between the Hermes 1 and Hermes 2 facility designs and the consistency of the RCSS design between Hermes 1 and Hermes 2, the staff finds that the regulations and guidance listed in Section 4.2.2.2 of the Hermes 1 SE are applicable to Hermes 2. Therefore, this section incorporates by reference Section 4.2.2.2 of the Hermes 1 SE.

4.2.2.3 Technical Evaluation

The staff reviewed Section 4.2.2 of the Hermes 2 PSAR and compared it to the equivalent section in the Hermes 1 PSAR (Section 4.2.2, Reactivity Control and Shutdown System). The staff found that Section 4.2.2 of the Hermes 2 PSAR contains information consistent with that in the Hermes 1 PSAR, except for minor changes that are evaluated below. The staff also verified that the Hermes 2 RCSS design and functionality remain identical to Hermes 1. Based on these consistencies, this section incorporates by reference Section 4.2.2.3, Technical Evaluation, of the Hermes 1 SE.

4.2.2.3.1 Minor Changes Compared to the Hermes 1 PSAR

The minor changes in Hermes 2 PSAR Section 4.2.2 as compared to the information in Hermes 1 PSAR Section 4.2.2, include the following:

x The RCSS SSCs are not shared between Unit 1 and Unit 2.

x The portion of the plant control system (PCS) that controls the RCSS is not shared between Unit 1 and Unit 2.

In Hermes 2 PSAR Section 4.2.2, Kairos states that the RCSS SSCs and the portion of the PCS that controls the RCSS are not shared between Unit 1 and Unit 2. This design approach increases the degree of independence between the two units and reduces the potential for a postulated event in one unit affecting the safe operation of the other unit. The independence of the two units is important for demonstrating compliance with the requirements in 10 CFR 100.11(b) for determining the size of the exclusion area and low population zone boundaries. Further evaluation of how Kairos will comply with the requirements of 10 CFR 100.11(b) is provided in SE Chapter 13. Based on the above, the staff finds Kaiross approach to not sharing RCSS SSCs, nor the portion of the PCS that controls the RCSS, acceptable.

On the basis of its review, the staff finds that the level of detail provided regarding the Hermes 2 RCSS demonstrates an adequate basis for a preliminary design; is consistent with PDC 2, 4, 23, 26, 28, and 29; and satisfies the applicable acceptance criteria of NUREG-1537, Part 2, Section 4.2.2, Control Rods, to support safety functions including reactivity control and reactor shutdown.

4.2.2.4 Conclusion

Based on staff findings above, and as incorporated by reference from the Hermes 1 SE, the staff concludes the information in Hermes 2 PSAR Section 4.2.2 is sufficient and meets the applicable guidance and regulatory requirements identified in this section for the issuance of CPs in accordance with 10 CFR 50.35 and 10 CFR 50.40. Further information as may be required to complete the review of the Hermes 2 RCSS can reasonably be left for later consideration at the OL stage since this information is not necessary for the review of a CP application.

4.2.3 Neutron Startup Source

4.2.3.1 Introduction

Section 4.2.3, Neutron Startup Source, of the Hermes 2 PSAR discusses the neutron startup sources, which provide a neutron flux to the source range ex-core detectors for initial and subsequent startups. Each reactor unit has its own neutron startup source.

4.2.3.2 Regulatory Evaluation

The requirements in the common regulatory evaluation for reactor systems in Section 4.1.1 of this SE apply to the neutron startup sources. There are no additional regulatory requirements applicable to the neutron startup sources.

The applicable guidance for evaluating the Hermes 2 neutron startup sources is as follows:

x NUREG-1537, Part 1 and Part 2, Section 4.2.4, Neutron Startup Source.

4.2.3.3 Technical Evaluation

The staff reviewed Section 4.2.3 of the Hermes 2 PSAR and compared it to the equivalent section in the Hermes 1 PSAR (4.2.3, Neutron Startup Source). The staff found that Section 4.2.3 of the Hermes 2 PSAR contains information consistent with that in the Hermes 1 PSAR, except for minor changes, that are evaluated below. The staff also verified that the Hermes 2 neutron startup source design and functionality remain identical to Hermes 1. Based on these consistencies, this section incorporates by reference Section 4.2.3.3, Technical Evaluation, of the Hermes 1 SE.

4.2.3.3.1 Minor Change Compared to the Hermes 1 PSAR

The minor change in Hermes 2 PSAR Section 4.2.3, as compared to the information in Hermes 1 PSAR Section 4.2.3, includes the following:

x The neutron startup sources are not shared between Unit 1 and Unit 2.

In Hermes 2 PSAR Section 4.2.3, Kairos states that the neutron startup sources are not shared between Unit 1 and Unit 2. Due to the radioactivity of the neutron startup sources, the staff views this as being consistent with as low as reasonably achievable principles for minimizing exposure. Additionally, the neutron startup sources do not perform any safety functions. Based on the above, the staff finds that not sharing neutron startup sources is acceptable.

On the basis of its review, the staff finds that the level of detail provided regarding the Hermes 2 neutron startup sources demonstrates an adequate basis for a preliminary design and satisfies the applicable acceptance criteria of NUREG-1537, Part 2, Section 4.2.4, Neutron Startup Source.

4.2.3.4 Conclusion

Based on the staff findings above, and as incorporated by reference from the Hermes 1 SE, the staff concludes that the information in Hermes 2 PSAR Section 4.2.3 is sufficient and meets the applicable guidance and regulatory requirements identified in this SE section for the issuance of CPs in accordance with 10 CFR 50.35 and 10 CFR 50.40. Further information as may be required to complete the review of the Hermes 2 reactor neutron startup sources can reasonably be left for later consideration at the OL stage since this information is not necessary for the approval of a CP application.

4.3 Reactor Vessel System

4.3.1 Introduction

Section 4.3, Reactor Vessel System, of the Hermes 2 PSAR states that the reactor vessel system contains the reactor core and provides for circulation of reactor coolant and pebbles as well as insertion of the RCSS elements in the reactor core. The reactor vessel consists of a shell, a flat top head, and a flat bottom head, and contains the reactor internals. The reactor internals include the graphite reflector blocks, fluidic diodes, the core barrel, and reflector support structure. The reactor vessel system is secured to the reactor vessel support system (RVSS), which is evaluated in Section 4.7 of this SE. The top head of the reactor vessel system contains penetrations and is described in PSAR Section 4.3.1.1.1, Vessel Top Head. PSAR Section 1.3.3.2, Operating Characteristics, states that the planned operational lifetime of each reactor at 35 MW thermal power is 11 years.

4.3.2 Regulatory Evaluation

The requirements in the common regulatory evaluation for reactor systems in Section 4.1.1 of this SE apply to the reactor vessel system. Additionally, the staff reviewed Section 4.3.2, Regulatory Evaluation, of the Hermes 1 SE for applicability to the Hermes 2 SE. Based on the similarities between the Hermes 1 and Hermes 2 facility designs and the consistency of the reactor vessel system between Hermes 1 and Hermes 2, the staff finds that the regulations and guidance listed in Section 4.3.2 of the Hermes 1 SE are applicable to Hermes 2. Therefore, this section incorporates by reference Section 4.3.2 of the Hermes 1 SE.

4.3.3 Technical Evaluation

The staff reviewed Section 4.3 of the Hermes 2 PSAR and compared it to the equivalent section in the Hermes 1 PSAR (Section 4.3, Reactor Vessel System). The staff found that Section 4.3 of the Hermes 2 PSAR contains information consistent with that in the Hermes 1 PSAR, except for one minor change and a few significant changes, which are evaluated below in SE Sections 4.3.3.1 and 4.3.3.2, respectively. The staff found that the following portions of Section 4.3 in the Hermes 2 PSAR contain information consistent with the Hermes 1 PSAR (e.g., minor or editorial changes only):

x Sections 4.3.1, Description, 4.3.2, 4.3.4, Testing and Inspection, and 4.3.5, References x All information in Section 4.3.3, System Evaluation, except for the change in operational life from 4 to 11 years; the discussions about Table 4.3-3, Testing Requirements to Extend the ASME [American Society of Mechanical Engineers]

Qualification of ER 16-8-2, through Table 4.3-8, Qualification Requirements for Graphite Irradiation; and clarification of the reactor vessel system design for degradation.

x Tables 4.3-1, Reactor Vessel Top Head Penetrations; Table 4.3-2, Load Combinations for the Reactor Vessel System; and Figure 4.3-1, The Reactor Vessel System, through Figure 4.3-3, The Reactor Vessel System Secondary Hold-Down Structure

Since the Hermes 2 reactor vessel system design and functionality largely remain identical, apart from the differences evaluated below, Section 4.3 of the Hermes 2 PSAR contains information consistent with Section 4.3 of the Hermes 1 PSAR. Based on these consistencies, this section incorporates by reference Section 4.3.3, Technical Evaluation, of the Hermes 1 SE.

4.3.3.1.1 Minor Change Compared to the Hermes 1 PSAR

The minor change in Hermes 2 PSAR Section 4.3, as compared to the information in Hermes 1 PSAR Section 4.3, includes the following:

x In Section 4.3.1, the intermediate heat transport system (IHTS) is mentioned as also unavailable along with the primary heat transport system (PHTS) during postulated events when the reactor vessel uses natural circulation to remove heat from the reactor core after an event.

This minor change accurately reflects the design of Hermes 2 having an IHTS and properly acknowledges that the IHTS would not be available during postulated events when the PHTS is not available, and the reactor vessel provides an alternative flow path to allow natural circulation of the reactor coolant to remove decay heat from the reactor core. Based on the above, the staff finds that the discussion of the IHTS as unavailable during certain events is acceptable.

4.3.3.1.2 Significant Changes Compared to the Hermes 1 PSAR

The significant changes contained in Section 4.3 of the Hermes 2 PSAR, as compared to Section 4.3 of the Hermes 1 PSAR, include information regarding the following:

x Operational lifetime of Hermes 2 is 11 years, compared to the 4 years of Hermes 1.

x Addition of Tables 4.3-3 through 4.3-8 that describe plans for material qualification testing of an test reactor with a 11-year lifetime, which was not previously described in KP-TR-013-P-A, Revision 4, Metallic Materials Qualification for the Kairos Power Fluoride Salt-Cooled High-Temperature Reactor, and KP-TR-014-P-A, Graphite Material Qualification for the Kairos Power Fluoride Salt-Cooled High-Temperature Reactor, Revision 4

These changes are identified in:

x Section 4.3.3 x Tables 4.3-3 through 4.3-8

The staff evaluated the sufficiency of this additional preliminary information regarding the Hermes 2 reactor vessel system against NUREG-1537, Part 2, Section 4.3, Reactor Tank or Pool, and PDC 14 and 31. Tables 4.3-3 through 4.3-6, Irradiation Effects Testing of Metallic Materials, provide the qualification tests required for a test reactor with an 11-year operational lifetime for 316H stainless steel (SS) and weld materials. The staff reviewed the information in these tables to evaluate the qualification tests that will be performed to justify the ability of the reactor vessel system to withstand degradation over the 11-year lifetime. Table 4.3-7, Qualification Requirements of Unirradiated Graphite Mechanical and Thermal Properties, and Table 4.3-8 provide the qualification tests required for graphite materials to support a 11-year operational lifetime.1

PSAR Table 4.3-3 shows that qualification testing will be performed to extend qualification of the ER16-8-2 weld filler metal. Table 4.3-3 shows that the tests for creep-fatigue will increase the maximum test temperature for the 11-year lifetime when compared to the 5-year lifetime, and the creep test times will be extended up to 20,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> past the 10,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> testing planned for Hermes 1. The staff finds the preliminary information is consistent with PDC 14 and 31 and the guidance in NUREG-1537, Part 2, Section 4.3, to ensure that the vessel can withstand applied stresses because the proposed tests were extended in time and temperature to align with the proposed Hermes 2 facility lifetime and operating temperatures. As described in the staff SE to KP-TR-013-P-A, the staff will review the data to extend qualification of ER16-8-2 to ensure it meets the requirements of the ASME Boiler and Pressure Vessel Code,Section III, Division 5, High Temperature Reactors.

PSAR Table 4.3-4, Testing Requirements for Reactor Design, updates testing requirements for certain mechanical testing of metallic materials, including stress relaxation cracking. These tests are consistent with those proposed in KP-TR-013-P-A. Table 4.3-4 shows that the stress relaxation cracking tests in KP-TR-013-P-A for the commercial power reactor will be used for the design of Hermes 2. The staff determined that the modified qualification testing requirements to account for the longer plant life is conservative because it uses the previously approved qualification methodology for the longer lifetime reactor. The staff finds that the preliminary information is consistent with PDC 14 and 31 and the guidance in NUREG-1537, Part 2, Section 4.3, and provides assurance that the vessel can withstand stresses it will experience over its proposed 11-year lifetime.

PSAR Table 4.3-5, Environmental Compatibility Testing of Metallic Materials, updates the environmental compatibility testing originally listed in KP-TR-013-P-A to extend corrosion test times and add corrosion testing with postulated intermediate coolant contamination for Hermes

2. Additionally, Table 4.3-5 shows that the full test matrix described in KP-TR-013-P-A for slow strain rate testing and for corrosion fatigue and stress corrosion cracking will be performed to support Hermes 2. This provides assurance that the final design will conform to the Hermes 2 design bases because the extended corrosion test times are reasonable to develop corrosion rates and the addition of intermediate coolant contamination tests account for the possibility of intermediate to primary contamination. Performing the full test matrix (i.e., for a commercial reactor lifetime) to support Hermes 2 is conservative as these tests were previously approved to support a reactor with a longer operating lifetime. Additionally, Table 4.3-5 shows in-situ creep tests will be performed for Hermes 2 which is appropriate to determine effects of the Flibe environment on time-dependent material degradation (i.e., creep) for the proposed 11-year reactor lifetime. The staff finds the preliminary information consistent with PDC 14 and 31 because corrosion test times were increased to a duration commensurate with a longer plant

1 Tables 4.3-3 through 4.3-8 also include the qualification programs for a 5-year non-power reactor and a commercial power reactor; however, PSAR Section 4.3.3 stated they are included for information purposes only. Therefore, the staff did not review the 5-year non-power reactor or commercial power reactor programs.

lifetime and the full power reactor test matrix will be used for slow strain rate, corrosion fatigue, and stress corrosion cracking tests. This preliminary information is also consistent with guidance in NUREG-1537, Part 2, Section 4.3, to ensure the vessel material is chemically compatible with the environment.

PSAR Table 4.3-6 states that the test matrix from KP-TR-013-P-A will be used for Hermes 2 in conjunction with inspection and monitoring programs. This provides the staff with assurance that the final design will conform to the design bases as this is consistent with the prior staff approval of KP-TR-013-P-A. The staff finds that the preliminary information is consistent with PDC 14 and 31 because the irradiation qualification program will be implemented per KP-TR-013-P-A, ensuring the appropriate data is used to account for potential irradiation-induced corrosion, cracking, and embrittlement in the design of Hermes 2 reactor systems. This information is also consistent with the guidance in NUREG-1537, Part 2, Section 4.3, for ensuring that the vessel material is resistant to irradiation effects.

PSAR Tables 4.3-7 and 4.3-8 update graphite qualification requirements for an 11-year graphite component lifetime. PSAR Table 4.3-7 does not reflect any changes from the unirradiated mechanical and thermal properties testing matrices found in KP-TR-013-P-A. This is acceptable because the qualification envelope for unirradiated properties does not change as a function of plant life. The changes in Table 4.3-8 from the matrices found in KP-TR-013-P-A reflect that if basic irradiation property data exceed the qualification envelope, then new data will be collected. Table 4.3-8 also states that final design data and turnaround analysis will demonstrate that Hermes 2 graphite components will not reach turnaround, and if components exceed this point, then irradiation creep data will be obtained and used for analysis. These changes provide the staff with assurance that the final design will conform to the design bases because collecting new irradiation data if plant parameters exceed the qualification envelope is consistent with the NRC staffs approval of KP-TR-013-P-A. Additionally, ensuring graphite does not reach turnaround for a non-power reactor, or obtaining new irradiation creep data, is consistent with the NRC approval of KP-TR-013-P-A. The staff finds that the preliminary information consistent with PDC 10, 34, 35, 36, 37, and 74 because the changes in graphite properties will be accounted for to ensure a coolable core geometry, forming the natural circulation flow path, and allowing for insertion of reactivity elements. This preliminary information is also consistent with the guidance in NUREG-1537, Part 2, Section 4.3, for ensuring that the graphite material is compatible with the chemical, thermal, mechanical, and radiation environments. Additionally, as described in Appendix A to this SE, the staff will review the final design at the OL stage to ensure that graphite components will not reach turnaround as a function of temperature and fluence, or the staff will confirm that irradiation creep data that bounds the anticipated Hermes 2 conditions is collected.

In addition, as stated Appendix A to this SE and discussed as part of Kaiross response to general audit question 4.3-3 (see general audit report at MLxxxxxxxxx), the effects of thermal embrittlement of metallic materials on the mechanical performance of safety-related components in the proposed 11-year operational lifetime will be assessed by Kairos in the OL application.

Based on the evaluation above, the staff finds that the preliminary information on the reactor vessel system is consistent with PDC 14, 31, 34, 35, 36, 37, and 74. The staff also finds that the preliminary information is consistent with the NUREG-1537, Part 2, Section 4.3, guidance in that it provides reasonable assurance of the reactor vessel systems reliability and integrity for its anticipated life.

4.3.4 Conclusion

Based on the staff findings above, and as incorporated by reference from the Hermes 1 SE, the staff concludes the information in Hermes 2 PSAR Section 4.3 is sufficient and meets the applicable guidance and regulatory requirements identified in this section for the issuance of CPs in accordance with 10 CFR 50.35 and 50.40. Further information as may be required to complete the review of Hermes 2 reactor vessel system can reasonably be left for later consideration at the OL stage since this information is not necessary for the review of a CP application.

4.4 Biological Shield

4.4.1 Introduction

Section 4.4, Biological Shield, of the Hermes 2 PSAR describes the preliminary design information on the biological shield, including its design bases. The biological shield functions to protect plant workers and the public from radiological exposure as well as to reduce radiation damage to plant equipment. The biological shield also reduces the potential exposure of plant workers to beryllium, should there be a coolant leak. The biological shield is made up of a primary biological shield, which surrounds the reactor vessel, and a secondary biological shield which encloses the primary to secondary heat transfer system and the inventory management system. The primary and secondary biological shields are composed of reinforced concrete.

4.4.2 Regulatory Evaluation

The requirements in the common regulatory evaluation for reactor systems in Section 4.1.1 of this SE apply to the biological shield design. Additionally, the staff reviewed Section 4.4.2, Regulatory Evaluation, of the Hermes 1 SE for applicability to the Hermes 2 SE. Based on the similarities between the Hermes 1 and Hermes 2 facility designs and the consistency of the biological shield design between Hermes 1 and Hermes 2, the staff finds that the regulations and guidance listed in Section 4.4.2 of the Hermes 1 SE are applicable to Hermes 2. Therefore, this section incorporates by reference Section 4.4.2 of the Hermes 1 SE.

4.4.3 Technical Evaluation

The staff reviewed Section 4.4 of the Hermes 2 PSAR and compared it to the equivalent section in the Hermes 1 PSAR (Section 4.4, Biological Shield). The staff found that Section 4.4 of the Hermes 2 PSAR contains information consistent with that in the Hermes 1 PSAR, except for a few minor changes, which are evaluated below. The staff also verified that the Hermes 2 biological shield design and functionality remain similar to Hermes 1. Based on these consistencies, this section incorporates by reference Section 4.4.3,Technical Evaluation, of the Hermes 1 SE.

4.4.3.1 Minor Changes Compared to the Hermes 1 PSAR

The minor changes in Hermes 2 PSAR Section 4.4, as compared to the information in Hermes 1 PSAR Section 4.4, include the following:

x The primary to intermediate heat transfer system is also enclosed in the secondary biological shield and the corresponding discussion in Section 4.4.1 and Figure 4.4-1, Primary and Secondary Biological Shield, are updated accordingly.

x Kairos states in Section 4.4.1 of the Hermes 2 PSAR that the biological shield is not shared between Unit 1 and Unit 2.

In Hermes 2 PSAR Section 4.4, Kairos states that the secondary biological shield will encase the primary to intermediate heat transfer system as well as the reactor vessel and inventory management systems. The change in the secondary biological shield boundary does not affect the biological shield design basis, which is evaluated in Section 3.6 of this SE. Based on the above, the staff finds that enclosing the primary to intermediate heat transfer system within the secondary biological shield and having separate biological shields for Unit 1 and Unit 2 is acceptable.

On the basis of its review, the staff finds that the level of detail provided regarding the Hermes 2 biological shield demonstrates an adequate basis for a preliminary design and satisfies the applicable acceptance criteria of NUREG-1537, Part 2, Section 4.4, Biological Shield, to support safety functions of protecting the health and safety of the facility staff and public.

4.4.4 Conclusion

Based on staff findings above, and as incorporated by reference from the Hermes 1 SE, the staff concludes the information in Hermes 2 PSAR Section 4.4 is sufficient and meets the applicable guidance and regulatory requirements identified in this section for the issuance of CPs in accordance with 10 CFR 50.35 and 10 CFR 50.40. Further information, as may be required to complete the review of Hermes 2 biological shield, can reasonably be left for later consideration at the OL stage since this information is not necessary for the review of a CP application.

4.5 Nuclear Design

4.5.1 Introduction

Section 4.5, Nuclear Design, of the Hermes 2 PSAR describes the Hermes 2 nuclear design, including core design, fuel and moderator pebbles, reactor coolant, and graphite reflectors for neutron moderation and shielding. The reactor core is comprised of a packed bed of approximately a total of 36,000 spherical fuel pebbles and spherical moderator pebbles. The core is roughly 60 percent pebbles and 40 percent reactor coolant by volume. Neutron moderation is provided by a graphite reflector, which also increases neutron economy and shields the reactor structures from fast neutrons, moderator pebbles, graphite in the fueled pebbles, and the reactor coolant, Flibe. The core is slightly under-moderated during all operating conditions.

4.5.2 Regulatory Evaluation

The requirements in the common regulatory evaluation for reactor systems in Section 4.1.1 of this SE apply to the nuclear design. Additionally, the staff reviewed Section 4.5.2, Regulatory Evaluation, of the Hermes 1 SE for applicability to the Hermes 2 SE. Based on the similarities between the Hermes 1 and Hermes 2 facility designs and the consistency of the nuclear design between Hermes 1 and Hermes 2, the staff finds that the regulations and guidance listed in Section 4.5.2 of the Hermes 1 SE are applicable to Hermes 2. Therefore, this section incorporates by reference Section 4.5.2 of the Hermes 1 SE.

4.5.3 Technical Evaluation

The staff reviewed Section 4.5, Nuclear Design, of the Hermes 2 PSAR and compared it to the equivalent section in the Hermes 1 PSAR (Section 4.5, Nuclear Design). The staff found that Section 4.5 of the Hermes 2 PSAR contains information consistent with that in the Hermes 1 PSAR. The staff also verified that the Hermes 2 nuclear design and functionality remain identical to Hermes 1. Based on these consistencies, this section incorporates by reference Section 4.5.3, Technical Evaluation, of the Hermes 1 SE.

On the basis of its review, the staff finds that the level of detail provided regarding the Hermes 2 nuclear design demonstrates an adequate basis for preliminary design, is consistent with PDC 10, 11, 12, and 26, and satisfies the applicable acceptance criteria of NUREG-1537, Part 2, Section 4.5, Nuclear Design, to support safety functions including controlling reactivity, ensuring shutdown margin, preventing power oscillations, and ensuring specified acceptable system radionuclide release design limits are not exceeded in any postulated events or normal operations.

4.5.4 Conclusion

Based on staff findings above, and as incorporated by reference from the Hermes 1 SE, the staff concludes the information in Hermes 2 PSAR Section 4.5 is sufficient and meets the applicable guidance and regulatory requirements identified in this section for the issuance of CPs in accordance with 10 CFR 50.35 and 10 CFR 50.40. Further information as may be required to complete the review of the Hermes 2 nuclear design can reasonably be left for later consideration at the OL stage since this information is not necessary for the review of a CP application.

4.6 Thermal-Hydraulic Design

4.6.1 Introduction

Section 4.6, Thermal-Hydraulic Design, of the Hermes 2 PSAR, discusses the Hermes 2 thermal-hydraulic design. Hermes 2 includes a number of design features that ensure effective heat transport from the fuel pebble to the reactor coolant and ultimately to the heat rejection system.

4.6.2 Regulatory Evaluation

The requirements in the common regulatory evaluation for reactor systems apply to the thermal-hydraulic design. Additionally, the staff reviewed Section 4.6.2, Regulatory Evaluation, of the Hermes 1 SE for applicability to the Hermes 2 SE. Based on the similarities between the Hermes 1 and Hermes 2 facility designs and the consistency of the thermal-hydraulic design between Hermes 1 and Hermes 2, the staff finds that the regulations and guidance listed in Section 4.6.2 of the Hermes 1 SE are applicable to Hermes 2. Therefore, this section incorporates by reference Section 4.6.2 of the Hermes 1 SE.

4.6.3 Technical Evaluation

The staff reviewed Section 4.6 of the Hermes 2 PSAR and compared it to the equivalent section in the Hermes 1 PSAR (Section 4.6, Thermal-Hydraulic Design). The staff found that Section 4.6 of the Hermes 2 PSAR contains information consistent with that in the Hermes 1 PSAR, except for one minor and one significant change, which are reviewed below in SE Sections 4.6.3.1 and 4.6.3.2, respectively. The staff found that the following portions of Section 4.6 in the Hermes 2 PSAR contain information consistent with the Hermes 1 PSAR (e.g., minor or editorial changes only):

x Sections 4.6.1.1, Core Geometry, through 4.6.4 Testing and Inspection x Table 4.6-1, Summary of Thermal Hydraulic Parameters x Figure 4.6-1, Coolant Flow Path

Since the Hermes 2 system design and functionality largely remain identical, apart from the differences evaluated below, Section 4.6 of the Hermes 2 PSAR contains information consistent with Section 4.6 of the Hermes 1 PSAR. Based on these consistencies, this section incorporates by reference Section 4.6.3, Technical Evaluation, of the Hermes 1 SE.

4.6.3.1 Minor Change Compared to the Hermes 1 PSAR

The minor change in Hermes 2 PSAR Section 4.6, as compared to the information in Hermes 1 PSAR Section 4.6, includes the following:

x Technical report KP-TR-022, Revision 0, replaces KP-TR-018, Revision 2.

KP-TR-022 replaces KP-TR-018 in the Hermes 2 PSAR and addresses postulated events for Hermes 2, including new potential event initiators for the Hermes 2 design. The postulated events unique to Hermes 2 are further evaluated in Chapter 13 of this SE. As discussed in KP-TR-022, the thermal-hydraulic computer codes and correlations used in the Hermes 2 model are identical to those used in the Hermes 1 model. Since the same thermal-hydraulic computer codes and correlations are used in both models, the insights and analysis results derived using KP-TR-018 are the same as those derived using KP-TR-022. Based on the above, the staff finds that the use of KP-TR-022 is acceptable.

4.6.3.2 Significant Change Compared to the Hermes 1 PSAR

The significant change in Section 4.6 of the Hermes 2 PSAR, as compared to Section 4.6 of the Hermes 1 PSAR, include information regarding the following:

x The IHTS is added to the list of systems that play a key role in the thermal-hydraulic design of the reactor system in PSAR Section 4.6.1, Description.

In Hermes 2 PSAR Section 4.6.1, Kairos states that the IHTS affects the thermal-hydraulic design of the facility. Due to the design of Hermes 2, the IHTS is thermally connected to the PHTS through the intermediate heat exchanger and will correspondingly affect the thermal-hydraulic design. A more detailed description of the IHTS design and its subsystems is available in PSAR Section 5.2, Intermediate Heat Transport System.

The staff performed scoping calculations specific to the Hermes 2 design; these are discussed in Chapter 13 of this SE. Based on these calculations, the staff concluded that the TRISO fuel is expected to maintain its integrity during postulated events. In addition, as discussed in Chapter 13 of this SE, the maximum hypothetical accident (MHA) remains bounding for all postulated events applicable to the Hermes 2 design. Considering the results of the Hermes 2 scoping calculations and the bounding MHA, the staff determined that the relationship between power and flow of the Hermes 2 heat transport systems, as well as the thermal inertia of the coolant, ensures that heat transfer can be achieved at a rate that maintains the design conditions of the core. Therefore, the staff concluded that the Hermes 2 reactor system is designed with appropriate margin to ensure that specified acceptable system radionuclide release design limits are not exceeded during normal operations, transients, or accident conditions. Based on the above, the staff finds that the preliminary information on the Hermes 2 thermal-hydraulic design is consistent with PDC 10, 34, and 35. The staffs review of PDC 12 is incorporated by reference from Section 4.6.3.3 of the Hermes 1 SE because the thermal-hydraulic design characteristics that affect reactor power oscillations are consistent between Hermes 1 and Hermes 2. These characteristics include high thermal inertia and no two-phase flow in the coolant, and an atmospheric reactor pressure. Based on the above, the staff finds that the addition of the IHTS to the list of systems that play a key role in the thermal-hydraulic design is acceptable.

The staff is not approving the use of Kaiross thermal-hydraulic codes or correlations beyond their support for the staffs findings related to the issuance of CPs. While the staff reviewed uncertainties in the Hermes 2 Kairos Power Systems Analysis Module (KP-SAM) and STAR-CCM+ models, the staff did not make any findings regarding Kaiross validation and verification plan of codes or derivations of uncertainties in the KP-SAM and STAR-CCM+

models because it is not required or necessary for the issuance of CPs. Kaiross validation and verification plan of codes and derivations of uncertainties will be reviewed at the OL stage.

On the basis of its review, the staff finds that the level of detail provided regarding the thermal-hydraulic design demonstrates an adequate basis for preliminary design; is consistent with PDC 10, 12, 34, and 35; and satisfies the applicable acceptance criteria of NUREG-1537, Part 2, Section 4.6, Thermal-Hydraulic Design, to support safety functions of providing sufficient heat removal and preventing power oscillations.

4.6.4 Conclusion

Based on staff findings above, and as incorporated by reference from the Hermes 1 SE, the staff concludes the information in Hermes 2 PSAR Section 4.6 is sufficient and meets the applicable guidance and regulatory requirements identified in this section for the issuance of CPs in accordance with 10 CFR 50.35 and 10 CFR 50.40. Further information as may be required to complete the review of the thermal-hydraulic design can reasonably be left for later consideration at the OL stage since this information is not necessary for the review of a CP application.

4.7 Reactor Vessel Support System

4.7.1 Introduction

Section 4.7, Reactor Vessel Support System, of the Hermes 2 PSAR discusses the reactor vessel support system (RVSS) design. PSAR Section 4.7.1, Description, states that the RVSS provides structural support for the reactor vessel and the vessel internals. The RVSS supports the full weight of the vessel, fuel, coolant, vessel internals, and the head-mounted components.

The RVSS is designed to transmit pressure, seismic, and thermal loads to the cavity structures and address thermal expansion during initial heat-up and postulated events.

4.7.2 Regulatory Evaluation

The requirements in the common regulatory evaluation for reactor systems apply to the RVSS.

Additionally, the staff reviewed Section 4.7.2, Regulatory Evaluation, of the Hermes 1 SE for applicability to the Hermes 2 SE. Based on the similarities between the Hermes 1 and Hermes 2 facility designs and the consistency of the RVSS design between Hermes 1 and Hermes 2, the staff finds that the regulations and guidance listed in Section 4.7.2 of the Hermes 1 SE are applicable to Hermes 2. Therefore, this section incorporates by reference Section 4.7.2 of the Hermes 1 SE.

4.7.3 Technical Evaluation

The staff reviewed Section 4.7 of the Hermes 2 PSAR and compared it to the equivalent section in the Hermes 1 PSAR (Section 4.7, Reactor Vessel Support System). The staff found that Section 4.7 of the Hermes 2 PSAR contains information consistent with that in the Hermes 1 PSAR, except for a minor change, which is reviewed below. The staff also verified that the Hermes 2 RVSS design and functionality remain identical to Hermes 1. Based on these consistencies, this section incorporates by reference Section 4.7.3, Technical Evaluation, of the Hermes 1 SE.

4.7.3.1 Minor Change Compared to the Hermes 1 PSAR

The minor change in Hermes 2 PSAR Section 4.7, as compared to the information in Hermes 1 PSAR Section 4.7, includes the following:

x Section 4.7.1 states that the RVSS is not shared by Unit 1 and Unit 2.

Kairos states that the RVSS is not shared between Unit 1 and Unit 2. With the Hermes 2 facility design housing each reactor in a separate building, it is appropriate to have one RVSS for each unit. Based on the above, the staff finds that having a separate RVSS for each unit is acceptable.

On the basis of its review, the staff finds that the level of detail provided regarding the Hermes 2 RVSS demonstrates an adequate basis for a preliminary design; is consistent with PDC 2, 4, and 74; and with the acceptance criteria of NUREG-1537, Part 2, Section 4.2.5 Core Support Structure, and Section 4.3, Reactor Tank or Pool, to support safety functions to provide structural support for the reactor vessel and the vessel internals.

4.7.4 Conclusion

Based on staff findings above, and as incorporated by reference from the Hermes 1 SE, the staff concludes the information in Hermes 2 PSAR Section 4.7 is sufficient and meets the applicable guidance and regulatory requirements identified in this section for the issuance of CPs in accordance with 10 CFR 50.35 and 10 CFR 50.40. Further information as may be required to complete the review of Hermes 2 RVSS can reasonably be left for later consideration at the OL stage since this information is not necessary for the review of a CP application.

4.8 Summary and Conclusions on the Reactor Description

The staff evaluated the information regarding the Hermes 2 reactor design, as described in PSAR Chapter 4, and finds that the preliminary information on, and design criteria of, the reactors, including the PDC, design bases, and information relating to materials of construction, general arrangement, and approximate dimensions: (1) provide reasonable assurance that the final design will conform to the design bases, (2) meet all applicable regulatory requirements, and (3) meet the applicable acceptance criteria in NUREG-1537, Part 2. Based on these findings, the staff makes the following conclusions regarding issuance of CPs in accordance with 10 CFR 50.35 and 10 CFR 50.40:

x Kairos has described the proposed design of the reactors, including, but not limited to, the principal 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.

x Such further technical or design information as may be required to complete the safety analysis of the reactors, and which can reasonably be left for later consideration, will be provided in the final safety analysis report as part of the OL application.

x Safety features or components which require research and development have been described by Kairos and a research and development program (see SE Section 1.1.5, Ongoing Research and Development) will be conducted that is reasonably designed to resolve any safety questions associated with such features or components.

x There is reasonable assurance that safety questions will be satisfactorily resolved at or before the latest date stated in the application for completion of construction of the proposed Hermes 2 facility.

x 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.

x 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.

4.9 References

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19. Seismic Design Criteria for Structures, Systems, and Components in Nuclear Facilities.

ASCE, Reston, VA. 2019.

American Society of Mechanical Engineers, Boiler and Pressure Vessel Code,Section III, Division 5, High Temperature Reactors, ASME: New York, NY. 2017.

Electric Power Research Institute (EPRI). Uranium Oxycarbide (UCO) Tristructural (TRISO)-

Coated Particle Fuel Performance. Topical Report EPRI-AR-1(NP)-A. EPRI Report

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Hu, G., et al. Development of a Reference Model for Molten-Salt-Cooled Pebble-Bed Reactor Using SAM, ANL/NSE-20/31, September 2020. Accessed via:

https://www.osti.gov/biblio/1674975.

Hu, Rui, Zou, Ling, Hu, Guojun, Nunez, Daniel, Mui, Travis, & Fei, Tingzhou. SAM Theory Manual, ANL/NSE-17/4, Revision 1, February 2021. United States.

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Huddar, L. R. (2016). Heat Transfer in Pebble-Bed Nuclear Reactor Cores Cooled by Fluoride Salts. UC Berkeley. ProQuest ID: Huddar_berkeley_0028E_16718. Merritt ID:

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

. KP-FHR Fuel Performance Methodology, KP-TR-010-NP-A, Revision 3 June 2021, ML22125A278 (redacted version).

. Fuel Qualification Methodology for the Kairos Power Fluoride Salt-Cooled High Temperature Reactor (KP-FHR), KP-TR-011-NP-A, Revision 2, June 2022, ML23089A398 (redacted version).

. Metallic Materials Qualification for the Kairos Power Fluoride Salt-Cooled High-Temperature Reactor, KP-TR-013-NP-A, Revision 4, September 2022, ML23102A179 (redacted version).

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ML23055A672. (Includes KP-TR-018, Postulated Event Analysis Methodology, Revision 2 (redacted version), as Enclosure 3.)

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ML23151A743.

. Hermes 2 Postulated Event Methodology, KP-TR-022-P, June 30, 2023, ML23195A129 (redacted version)

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MLxxxxxxxxx.

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. Regulatory Guide (RG) 1.143, Revision 2, Design Guidance for Radioactive Waste Management Systems, Structures, and Components Installed in Light-Water-Cooled Nuclear Power Plants, NRC: Washington, D.C. November 2001. ML013100305.

. Regulatory Guide (RG) 1.87, Revision 2, Acceptability of ASME Code Section III, Division 5, High Temperature Reactors, NRC: Washington, D.C. January 2023. ML22101A263.

. NUREG-2245, Technical Review of the 2017 Edition of ASME Code,Section III, Division 5, High Temperature Reactors, NRC: Washington, D.C. January 2023. ADAMS Accession Nos. ML23030B636.

. Final Safety Evaluation by the Office of Nuclear Reactor Regulation Related to Topical Report KP-TR-011, Revision 2, Fuel Qualification Methodology For The Kairos Power Flouride Salt-Cooled High Temperature Reactor (KP-FHR) (EPID [L-2020-TOP-0046]), NRC:

Washington, D.C. March 2023. ADAMS Accession Nos. ML23048A326.

. Summary Report for the Regulatory Audit of Kairos Power LLC Hermes Construction Permit Preliminary Safety Analysis Report - General Audit, June 2023, ML23160A287.

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

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

Umeda, M., Sugiyama, T., Nagas, F., Fuketa, T., Ueta, S., & Sawa, K. (2010). Behavior of Coated Fuel Particle of High-Temperature Gas-Cooled Reactor under Reactivity-Initiated Accident Conditions. Journal of Nuclear Science and Technology, Vol 47:11, pp. 991-997.

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