ML24222A276
| ML24222A276 | |
| Person / Time | |
|---|---|
| Site: | 99902069 |
| Issue date: | 08/22/2024 |
| From: | Cayetano Santos NRC/NRR/DANU/UAL1 |
| To: | Kairos Power |
| References | |
| EPID L-2024-TOP-0013 | |
| Download: ML24222A276 (1) | |
Text
KAIROS POWER, LLC - KP-FHR CORE DESIGN AND ANALYSIS MEHTODOLOGY TOPICAL REPORT AUDIT PLAN (EPID NO. L-2024-TOP-0013)
Applicant:
Kairos Power, LLC Applicant Address:
707 W. Tower Ave, Suite A Alameda, CA 94501 Project No.:
99902069
Background:
Kairos Power LLC (Kairos) began pre-application discussions with the U.S. Nuclear Regulatory Commission (NRC) staff on its proposed 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. On December 14, 2023, the NRC staff issued a construction permit to Kairos for the Hermes 1 test reactor (Agencywide Documents Access and Management System (ADAMS) Accession No. ML23338A260). Since 2018 Kairos has submitted several topical and technical reports that apply to both the Hermes 1 test reactor, as well as the KP-FHR commercial power reactor. As discussed in meetings held on November 30, 2023, February 20, 2024, and March 6, 2024, Kairos planned to submit a topical report (TR) on the KP-FHR core design and analysis methodology. This TR would support future KP-FHR test and power reactor operating license (OL) applications. By letter dated April 3, 2024, Kairos submitted KP-TR-024, KP-FHR Core Design and Analysis Methodology Topical Report. On June 20, 2024, the NRC staff determined that the TR presented sufficient information to begin a detailed technical review.
Purpose:
The purpose of this audit is for the NRC staff to gain a better understanding of KP-TR-024, KP-FHR Core Design and Analysis Methodology Topical Report, by providing an opportunity to review and discuss material used to support statements or conclusions in the TR. The audit is expected to facilitate a more effective and efficient review by allowing the NRC staff to review and discuss supporting material with the objective of improving communication and eliminating unnecessary requests for additional information. The NRC staff plans to audit documentation, calculations, and computer code information needed to verify information and conclusions in the TR. If the NRC staff identifies information that is needed to support a finding, Kairos will need to submit that information on the application docket.
Regulatory Audit Basis:
The bases for the audit are the regulations in Title 10 of the Code of Federal Regulations (10 CFR) pertinent to the NRC staffs review of a future Hermes OL application, particularly 10 CFR
2 Part 50, Domestic Licensing of Production and Utilization Facilities, sections 50.34, Contents of applications; technical information, 50.40, Common standards, and 50.57, Issuance of operating license.
Regulatory Audit Scope This audit team will review documentation and calculations that provide technical support to KP-TR-024, KP-FHR Core Design and Analysis Methodology Topical Report. The audit scope will cover all the chapters and appendices of the TR.
Information and Other Material Necessary for the Regulatory Audit At this time, the staff requests that the following documents be made available for audit.
Additional documents may be requested during the review:
The comprehensive neutronics phenomena identification and ranking table (PIRT) for the KP-FHR (referred to in TR section 3.1.1, "Neutronics Phenomena," and summarized in TR appendix C, "Neutronics PIRT Results for the KP-FHR"); see related audit question 3.1-1 below.
Documentation of the sensitivity analyses for nominal steady state conditions referred to in TR section 3.1.3, "Key Thermal Hydraulics Phenomena"; see related audit question 3.1-3 below.
Any user guide or input manual developed for the STAR-CCM+ input models; see related audit question 4.2-1 below.
Reference 8 listed in the TR: K. Wakao, S. Kaguei and T. Funazkri, "Effect of fluid dispersion coefficients on particle-to-fluid heat transfer coefficients in packed beds,"
Chemical Engineering Science, vol. 34, pp. 325-326, 1978.
Audit questions (additional questions may be asked during the review):
[Question 1.2-1] Section 1.2.2, Principal Design Criteria for the Reactor Core, of the TR discusses the principal design criteria (PDC) that apply to the KP-FHR reactor core.
Please explain how the core design tools presented in this TR are used to show compliance with PDC 12. Describe the analyses that would be performed to support the conclusions that the KP-FHR core is inherently stable and that a detection system for power-oscillations is not required are justified. Section 6.2.5, Nuclear Stability, of the TR provides limited qualitative discussion on nuclear stability under the condition of asymmetric rod operation. However, the scope of PDC 12 is broader. PDC 12 requires the reactor core; associated structures; and associated coolant, control, and protection systems to be designed to ensure that power oscillations that can result in conditions exceeding specified acceptable system radiological release limits (SARRDLs) are not possible or can be reliably and readily detected and suppressed. It is possible that the methodology presented in this TR can play some role in analyses to address PDC 12.
However, it is not clear how the proposed methodology can address all the elements of the analyses necessary to perform a PDC 12 evaluation (e.g., adequate modeling of control systems, assurance that the proposed numerical methods are applicable to evaluate the stability, etc.).
[Question 2.3-1] Please explain the two approaches to reactor startup modeling, the mixed bed and critical height approaches, in greater detail than is provided in TR
3 section 2.3, Operational Regimes. For example, describe the assumptions regarding core composition and distribution of pebble types in the core. Explain any other unique methodology features needed to support the startup modeling for the mixed bed approach vs. critical height approach.
[Question 3.1-1] Section 3.1.1 and appendix C of the TR provide discussion on neutronics PIRT results for the KP-FHR.
o The advanced high-temperature reactor (AHTR) PIRT is used as the reference PIRT. Please explain how the unique KP-FHR design features are addressed in the PIRT.
o Please explain the sentence "The outcome of benchmarking the methodology against the PIRT revealed adequacy of the fidelity in the best estimate methods to capture the physics of the FHR core" in section 3.1.1 of the TR and the process of benchmarking the methodology against a PIRT. The staff notes that a PIRT usually guides methodology development. Fidelity of a methodology to capture the physics of important phenomena identified in the PIRT is usually demonstrated by performing validations against applicable data (analytical and experimental). Initial PIRT rankings could be based on expert input and/or analysis. The PIRT rankings could be further validated using the experimental data or limited sensitivity calculations. It is essential for staff to understand the process used to develop the PIRT and how it is confirmed that all the high ranked phenomena are properly identified and characterized.
[Question 3.1-2] Section 3.1.2, Key DEM Phenomena, of the TR identifies factors important for modeling in the discrete elements method (DEM) model. The staff would expect fluid or coolant thermophysical properties (including temperature/composition effect) to play a critical role in determining the forces on the pebble. Similarly, the staff believes that coolant flow distribution could be an important input for the DEM model analysis. However, these factors are not identified in section 3.1.2 as factors influencing the DEM figures-of-merit (FOMs). Please clarify all the factors/phenomena/boundary conditions that are important for the DEM model and discuss why core pressure gradient, temperature and coolant flow distribution, thermophysical properties, etc. are not identified as factors influencing the FOMs in section 3.1.2.
[Question 3.1-3] In section 3.1.3, Key Thermal Hydraulics Phenomena, of the TR, the approach used to identify the phenomena important for core thermal-hydraulic (TH) analysis is not clear. It appears that the methodology considers phenomena identified for the steady state conditions from the Kairos Power thermal fluid PIRT. Section 3.1.3 also states that the importance ranking in the reference PIRT was "outside the scope" of core TH applications, and sensitivity analysis is used for the identification of important phenomena.
o Please explain how the generic thermal fluid PIRT for postulated events was adopted for the core steady-state TH analysis. Please explain similarities and differences between the thermal fluid PIRT and the conclusions reached in TR section 3.1.3 (e.g., FOMs, transient vs. steady state, etc.) and the process/justifications used to identify the applicable PIRT phenomena from the generic Kairos Power thermal fluid PIRT.
o Section 3.1.3 identifies the phenomena/processes that must be modeled to calculate core TH FOMs reliably. Why are the following phenomena/processes not considered as important for core-TH analysis:
4 Core power distribution boundary condition Core heat transfer mechanisms such as conduction, radiation, and conduction inside pebbles and layers of TRISO particles Fluid thermophysical properties 3-D or asymmetric temperature and flow distributions and other phenomena specific to large power reactor
[Question 3.1-4] Please explain how fast neutron fluence and temperatures are used to inform geometrical and thermophysical property correlations as stated in TR section 3.1.3.
[Question 3.2-1] It is not clear from the discussion in TR section 3.2, General Modeling Approach, if the reactor vessel wall is part of the core TH model. Please explain how the heat transfer or heat loss from the reactor vessel to the decay heat removal system (DHRS) and its impact on the reactor vessel temperature are accounted for in the model.
[Question 3.3-1] It appears there may be a typographical error in Equation 3 in TR section 3.3, DEM Modeling Paradigm. Please confirm the accuracy of Equation 3 as written in the TR and as coded in the model.
[Question 4.2-1] A multi-physics computational fluid dynamics (CFD) code, STAR-CCM+, is used for the DEM and core TH modeling. The staff notes that, as a generic purpose CFD tool, STAR-CCM+ includes numerous user options that allow a user to exercise a wide range of field equations, discretization options, closing relations, constitutive equations, nodalization, and numerical methods. It is essential to ensure that the code models, correlations, and various code options selected in the methodology application calculations remain the same as those used in the supporting validations.
Please explain how this control is achieved in the methodology (e.g., user guidelines):
o Please identify the code inputs that have an impact on selected field equations, discretization, and numerical methods. The closing/constitutive relations selected should be clearly identified in the TR.
[Question 5.2-1] Please discuss or provide further background/context/documentation on the appropriateness of the simplified KP-FHR model described in section 5.2.1.1.
Team Assignments Alex Siwy - Senior Nuclear Engineer, Audit Lead (responsible for audit summary report)
Pravin Sawant - Senior Nuclear Engineer Ben Adams - General Engineer Joshua Kaizer - Senior Nuclear Engineer Andrew Bielen - Senior Reactor Systems Engineer (Neutronics)
Cayetano Santos Jr. - Senior Project Manager (responsible for audit logistics and audit summary report)
Matthew Hiser - Senior Project Manager Brian Bettes - Project Manager Additional audit team members may be added as needed.
5 Logistics Entrance Meeting:
August 2024, estimated and subject to change Exit Meeting:
December 2024, estimated and subject to change The NRC staff requests that all the documents in the audit scope be provided by Kairos on an online reference portal. An online reference portal, established by Kairos, would allow the NRC staff access to technical information. Use of the online reference portal is acceptable provided that Kairos establishes measures to limit access to specific NRC staff (e.g., based on NRC e-mail addresses or the use of passwords which will only be assigned to the NRC staff directly involved in the audit on a need-to-know basis) and to make the documents view-only (i.e.,
prevent the NRC staff from saving, copying, downloading, or printing any documents). The conditions associated with the online reference portal must be maintained throughout the audit process. The NRC staff who should initially be granted access to the portal are listed in the Team Assignments section above. The NRC audit project managers will provide Kairos with the names of additional NRC staff who should be granted access.
The audit will follow the guidance in the Office of Nuclear Reactor Regulation (NRR), Office Instruction LIC-111, Regulatory Audits (ML19226A274). Audit meetings will take place primarily in a virtual format, using Microsoft Teams, or via other, similar platform. Audit meetings will be scheduled on an as-needed basis after the entrance meeting and once the NRC staff has had the opportunity to review any documents placed in the online reference portal. If a site visit is needed, review topics will be provided to Kairos and mutually agreeable dates will be established.
The audit duration is anticipated to be approximately 4 months with activities occurring intermittently during that period. The audit period may be reduced or extended, depending on the progress made by the NRC staff and Kairos in addressing audit questions.
Special Requests The NRC staff requests that Kairos make their technical staff and subject matter experts available to answer questions during the audit.
Deliverables At the completion of the audit, the audit team will issue an audit summary within 90 days after the exit meeting but will strive for a shorter duration. The audit summary will be declared and entered as an official agency record in ADAMS and be made available for public viewing through the publicly available records component of ADAMS.
6 References Title 10 of the Code of Federal Regulations NRR Office Instruction LIC-111, Regulatory Audits If you have any questions regarding this matter, please contact me at 301-415-7270 or via email at Cayetano.Santos@nrc.gov.
Date: August 22, 2024 Cayetano Santos Jr., Sr. Project Manager Advanced Reactor Licensing Branch 1 Division of Advanced Reactors and Non-Power Production and Utilization Facilities Office of Nuclear Reactor Regulation CAYETANO SANTOS Digitally signed by CAYETANO SANTOS Date: 2024.08.22 09:06:57 -04'00'
ML24222A276 OFFICE NRR/DANU/UAL1:PM NRR/DANU/UAL1:LA NRR/DANU/UTB1:LEAD NAME CSantos DGreene ASiwy DATE 8/9/2024 8/13/2024 8/19/2024 OFFICE NRR/DANU/UAL1:BC NRR/DANU/UAL1:PM NAME JBorromeo CSantos DATE 8/15/2024 8/22/2024