ML26016A667
| ML26016A667 | |
| Person / Time | |
|---|---|
| Site: | 99902069 |
| Issue date: | 01/28/2026 |
| From: | Cuadrado De Jesus S Office of Nuclear Reactor Regulation |
| To: | Kairos Power |
| References | |
| Download: ML26016A667 (0) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001
SUMMARY
REPORT FOR THE REGULATORY AUDIT OF KAIROS POWER, LLC -
THERMOPHYSICAL PROPERTIES MAY 2024 - JULY 2025 Applicant:
Kairos Power, LLC Applicant Address:
707 W. Tower Ave, Suite A Alameda, CA 94501 Plant Name(s) and Unit(s): Kairos - Hermes Test Reactor Hermes 2 Test Reactor Facility Fluoride-Salt-Cooled, High-Temperature Reactor Project No.:
99902069
1.0 BACKGROUND
AND PURPOSE Kairos Power LLC (Kairos) began pre-application engagement with the U.S. Nuclear Regulatory Commission (NRC) staff on its Kairos Power Fluoride-Salt-Cooled, High-Temperature Reactor (KP-FHR) in October 2018. In December of 2020, Kairos announced that the Hermes test reactor would be used to support future development of the KP-FHR. The NRC issued a construction permit (CP) on December 14, 2023, for the Hermes test reactor to be located at a site in Oak Ridge, Tennessee (Agencywide Documents Access and Management System (ADAMS) Accession No. ML23338A260). The NRC issued two CPs on November 21, 2024, for the Hermes 2 test reactor facility located at an adjacent site (ML24324A019).
Kairos plans to submit operating license (OL) applications for Hermes and Hermes 2 in accordance with Part 50 of Title 10 of the Code of Federal Regulations (10 CFR), which will include Final Safety Analysis Reports (FSARs). Over the past several years, Kairos submitted several topical reports (TRs) and technical reports that apply to both the Hermes test reactors and the full-scale KP-FHR reactor. A key reference in the Hermes, Hermes 2, and KP-FHR FSARs will be TR KP-TR-005-P-A, Reactor Coolant for the Kairos Power Fluoride Salt-Cooled High Temperature Reactor (ML20219A591), which provides key thermophysical properties for use in safety analyses. This TR was reviewed and approved by the NRC staff subject to limitations and conditions. One such condition is for Kairos to perform confirmatory analyses to ensure referenced data from the Oak Ridge National Laboratory (ORNL) Molten Salt Reactor Experiment (MSRE) is of appropriate quality and applicable to Kairos reactor designs.
This audit is a continuation of audit activities performed August through October 2021 (ML21194A439), prior to the NRCs staff acceptance of Kaiross CP applications for Hermes and Hermes 2. A summary report of the 2021 audit was issued in February 2022 (ML21364A106).
During the 2021 audit, the NRC staff examined available thermophysical property data reports (i.e., reports on density, heat capacity, viscosity, and thermal conductivity) and evaluated corroborating sources. This included but was not limited to discussion of historical data used within the corroboration. Similarly, this audits purpose is to gain familiarization with the data and data corroboration described in updated thermophysical property reports that were not available during the 2021 audit, including those concerning vapor pressure, melting point, and latent heat.
This audit enabled the NRC staff to gain a better understanding of Kaiross process to determine
that referenced historical data is appropriate to use in the safety analyses for the Hermes, Hermes 2, and KP-FHR reactor designs.
2.0 AUDIT REGULATORY BASES The basis for the audit includes the regulatory requirements in paragraph (b)(4) of 10 CFR 50.34, Contents of applications; technical information. This provision requires that each application for an OL contain an FSAR that includes an analysis and evaluation of the design and performance of structures, systems, and components.
3.0 AUDIT OBJECTIVES The NRC staff reviewed supporting calculations and met with subject matter experts to discuss details of the Kairos data corroboration effort and Kaiross plans to satisfy limitations and conditions from TR KP-TR-005-P-A.
4.0 SCOPE OF THE AUDIT AND AUDIT ACTIVITIES The audit was conducted during the months of May 2024 through July 2025, via the Kairos electronic reading room (ERR). The NRC staff conducted the audit in accordance with the Office of Nuclear Reactor Regulation (NRR) Office Instruction NRR-LIC-111, Revision 2 Regulatory Audits (ML24309A281). The NRC staff did not acquire any documents during the audit.
Members of the audit team, listed below, were selected based on their detailed knowledge of the subject. Audit team members included:
Cathleen Ridder, NRR (Reactor Systems Engineer, Lead Technical Reviewer)
Pravin Sawant, NRR (Senior Nuclear Engineer, Technical Reviewer)
Yamir Diaz Castillo, NRR (Reactor Operations Engineer, Technical Reviewer)
Samuel Cuadrado de Jesús, NRR (Project Manager)
The NRC staff reviewed the following documents:
Review of Flibe Thermophysical Property Legacy Data: Latent Heat, Revision 2.
Review of Flibe Thermophysical Property Legacy Data: Melting Point, Revision 1.
Vapor Pressure: Flibe Property Attribute Review (FPAR) of Legacy Flibe Vapor Pressure Data, Revision 2 Vapor Pressure: Flibe Property Attribute Review (FPAR) of Legacy Flibe Vapor Pressure Data, Revision 3.
Qualification Methods for Existing (Legacy) Data, Revision 0.
Quality Assurance Plan for Flibe Thermophysical Properties Data Qualification, Revision A.
Flibe Thermophysical Properties, Revision 1.
Review of Flibe Thermophysical Property Legacy Data: Density, Revision 0.
Review of Flibe Thermophysical Property Legacy Data: Viscosity, Revision 0.
Review of Flibe Thermophysical Property Legacy Data: Heat Capacity, Revision 0.
Review of Flibe Thermophysical Property Legacy Data: Thermal Conductivity, Revision 0.
Vapor Pressure: Flibe Property Attribute Review (FPAR) of Legacy Data, Revision 1.
Thermophysical Properties of Flibe Audit Entrance Meeting, May 29, 2024.
Thermophysical Properties Audit NRC Follow-up Question Responses on Latent Heat and Melting Point (Non-Public), May 1, 2025.
5.0
SUMMARY
OF OBSERVATIONS The NRC staff examined the documents listed above. During this examination the NRC staff noted the purpose of the document, identified key inputs and their sources, and noted the key
results. A summary of the NRC staffs observations is provided below.
- 1. In general, the reports reviewed were thorough and covered the relevant topics for data corroboration of the specified properties.
- 2. Procedures and analyses were generally consistent with the data corroboration process described in Section 402 of Subpart 4.2.3, Guidance on Qualification of Existing Data, in American Society of Mechanical Engineers (ASME) Code NQA-1-2019, Quality Assurance Requirements for Nuclear Facility Applications.
- 3. Utilizing independent sources of corroborating data for the qualification of thermophysical property data is an important aspect reviewed by the NRC staff in licensing applications involving thermophysical properties.
- 4. The primary and corroborating sources pertaining to the vapor pressure property data had limited independence. However, this thermophysical property was assessed to be of low safety significance.
- 5. Kairos updated select reports with additional information on the sources and justification of the uncertainty ranges; such information would provide a well-documented basis to support review of future licensing submittals.
6.0 EXIT BRIEFING The NRC staff conducted an audit closeout meeting on July 9, 2025. At the exit briefing the NRC staff reiterated the purpose of the audit and summarized audit activities.
7.0 EXIT REQUESTS FOR ADDITIONAL INFORMATION RESULTING FROM AUDIT No additional information requests were generated as a result of this audit.
8.0 OPEN ITEMS AND PROPOSED CLOSURE PATHS Not applicable. There were no deviations from the audit plan.
Package: ML26016A664 Summary Report: ML26016A667 Transmittal email: ML26016A666
- concurred by email OFFICE NRR/DANU/UTB2/BC NRR/DANU/UAL1/PM NRR/DANU/UAL1/BC NAME Cde-Messieres*
SCuadrado JBorromeo*
DATE 12/23/2025 1/16 /2026 1/27 /2026