ML24197A184
| ML24197A184 | |
| Person / Time | |
|---|---|
| Site: | Kemmerer, 99902100 File:TerraPower icon.png |
| Issue date: | 07/15/2024 |
| From: | Stephanie Devlin-Gill NRC/NRR/DANU/UAL1 |
| To: | |
| References | |
| EPID L-2024-TOP-0010 | |
| Download: ML24197A184 (1) | |
Text
OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - EXPORT CONTROLLED INFORMATION Enclosure OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - EXPORT CONTROLLED INFORMATION TERRAPOWER, LLC - AUDIT PLAN FOR TOPICAL REPORT TP-LIC-RPT-0008, "PARTIAL FLOW BLOCKAGE METHODOLOGY," REVISION 1 (EPID NO. L-2024-TOP-0010)
Applicant:
TerraPower, LLC Applicant Address:
15800 Northup Way, Bellevue, WA 98008 Plant Name:
Natrium Project No.:
99902100
Background:
By letter dated March 26, 2024, TerraPower, LLC (TerraPower) submitted topical report (TR)
TP-LIC-RPT-0008, Partial Flow Blockage Methodology," Revision 1 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML24085A822) to the U.S. Nuclear Regulatory Commission (NRC) staff. The TR provides an overview and description of evaluation models (EM) developed for the Natrium reactor to evaluate partial flow blockage events within a sodium fast reactor. On April 22, 2024, the NRC staff found that the material presented in the TR provides technical information in sufficient detail to enable the NRC staff to conduct a detailed technical review (ML24107B049).
TerraPower requested the NRC staffs review and approval of the EM presented in the TR for use by future applications utilizing the Natrium design. The applicants overall licensing methodology follows the technology-inclusive, risk-informed, and performance-based approach outlined in Revision 0 of Regulatory Guide (RG) 1.233 Guidance for a Technology-Inclusive, Risk-Informed, and Performance-Based Methodology to Inform the Licensing Basis and Content of Applications for Licenses, Certifications, and Approvals for Non-Light Water Reactors, Revision 0 (ML20091L698).
Purpose:
The purpose of the audit is for the NRC staff to gain a more detailed understanding of TerraPowers EM to evaluate partial flow blockage events for the Natrium sodium fast reactor. A secondary purpose of the audit is to identify any information that will require docketing to support the NRC staffs safety evaluation.
Regulatory Audit Basis:
The basis for the audit includes:
Title 10 of the Code of Federal Regulations (10 CFR) 50.34(a)(4) and 10 CFR 50.34(b)(4), which apply to applicants for construction permits and operating licenses, respectively. These sections require analysis and evaluation of the design and performance of structures, systems, and components (SSCs) of the facility with the objective of assessing the risk to public health and safety resulting from operation of the facility and including determination of the margins of safety during normal operations and
OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - EXPORT CONTROLLED INFORMATION OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - EXPORT CONTROLLED INFORMATION transient conditions anticipated during the life of the facility, and the adequacy of SSCs provided for the prevention of accidents and the mitigation of the consequences of accidents.
Paragraph 50.43(e) of 10 CFR requires that reactor designs that differ significantly from light-water reactor designs licensed before 1997 may only be approved if there has been appropriate demonstration of their safety features. The requirements in 10 CFR 50.43(e)(1)(i) and (ii) describe that demonstration of safety feature performance and interdependent effects through analysis, appropriate test programs, experience, or a combination thereof. The requirements in 10 CFR 50.43(e)(1)(iii) states that sufficient data should exist on the safety features to assess the analytical tools for safety analysis over a sufficient range of plant conditions.
Regulatory Audit Methodology:
The regulatory audit will follow the guidance in the Office of Nuclear Reactor Regulation (NRR)
Office Instruction LIC-111 Regulatory Audits, Revision 1 (ML19226A274), and focus on information provided by TerraPower in an electronic reading room (ERR).
Information and Other Material Necessary for the Regulatory Audit:
The NRC staff requests access to TerraPower documents associated with the particle flow blockage methodology as discussed in the TR. The NRC staff also requests TerraPower make available the information or subject matter experts necessary to respond to the enclosed audit inquiries. These inquiries primarily fall into the following general categories:
Justification for various assumptions made in the TR; Additional information as to how TerraPower assessed the ((
));
Additional details regarding figures of merit; and General clarifications throughout the TR.
Team Assignments:
Reed Anzalone Senior Nuclear Engineer Stephanie Devlin-Gill Senior Project Manager, Audit Manager Walter Williams Reactor Systems Engineer, Audit Lead Logistics:
Entrance Meeting 4:00 PM ET, July 25, 2024 Exit Meeting September 30, 2024 Audit meetings will take place in a virtual format, using Microsoft Teams or another 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 ERR.
The audit will begin on July 25, 2024, and continue as necessary, with activities occurring intermittently during the audit period. The audit period may be reduced or extended, depending on the progress made by the NRC staff and TerraPower in addressing audit questions.
OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - EXPORT CONTROLLED INFORMATION OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - EXPORT CONTROLLED INFORMATION 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.
If you have questions about this audit, please contact me at 301-415-5301 or via email at Stephanie.Devlin-Gill@nrc.gov.
Sincerely,
/RA/
Stephanie Devlin-Gill, Senior Project Manager Advanced Reactors Licensing Branch 1 Division of Advanced Reactors and Non-Power Production and Utilization Facilities Office of Nuclear Reactor Regulation Project No.: 99902100
Enclosure:
As stated cc: TerraPower Natrium via GovDelivery
OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - EXPORT CONTROLLED INFORMATION Enclosure OFFICIAL USE ONLY - PROPRIETARY INFORMATION OFFICIAL USE ONLY - EXPORT CONTROLLED INFORMATION AUDIT QUESTIONS RELATED TO TP-LIC-RPT-0008 REVISION 1 "PARTIAL FLOW BLOCKAGE METHODOLOGY"
- 1) Pertaining to the entire TR:
a) ((
))
b) Provide justification for ((
))
c) Provide clarification regarding the use of Computational Fluid Dynamics.
d) Provide clarification, at a high level, how the semi-empirical model is implemented in Mongoose++.
- 2) TR section 1,
Introduction:
Provide additional detail regarding licensing basis event frequencies cited to support partial flow blockage analyses (e.g., is the accumulation of debris used to determine licensing basis event frequency specific to wire wrap degradation or does it include other blockage initiating events).
- 3) TR section 3.1, Assumptions, assumption 3.1: The partial flow blockage occurrence is assumed to be ((
))
- 4) TR section 3.1, assumption 3.3:
a) Provide additional detail and justification for assuming ((
))
b) Provide additional explanation to justify the use of ((
))
- 5) TR section 3.1, assumption 3.6: ((
)) Provide additional justification for assumption 3.6.
- 6) TR section 3.1, assumption 3.9: Provide additional information on ((
))
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- 7) TR section 3.1, assumption 3.12:
a) ((
))
b) ((
))
- 8) TR section 3.1, assumption 3.13: ((
))
- 9) TR section 3.1, assumption 3.14: ((
))
- 10) TR section 5.1.1, [Evaluation Model Development and Assessment Process (EMDAP)]
Step 1: Specify Analysis Purpose, Transient Class, and Power Plant Class: The NRC staff seeks clarification as to whether the ((
))
- 11) TR section 5.1.1: Table 5-1, Local Fault Events due to Partial Flow Blockage, contains multiple entries that state: ((
)) This does not appear to be a complete sentence; please clarify.
- 12) TR section 5.1.2, EMDAP Step 2: Specify Figures of Merit: The TR puts forward fuel temperature as a figure of merit (FOM) for the partial flow blockage analysis.
a) Fuel-cladding-chemical-interaction (FCCI) and constituent redistribution will result in local solidus temperatures in the fuel system that are significantly less than equilibrium U-Zr solidus lines. The NRC staff requests TerraPower clarify the lower solidus temperatures considered, particularly in the TATNF analysis, in addition to cladding wastage and creep. In table 5-3, "Figures of Merit, the ((
)) Additionally, the NRC staff notes that during the audit on TP-LIC-RPT-0004, "Design Basis Accident Methodology for In-Vessel Events without Radiological Release" (ML24064A195) TerraPower proposed changes clarifying that the ((
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)) Please discuss the discrepancy and provide an appropriate justification.
b) Clarify if the fuel temperature is still considered as a FOM in the methodology since it is only briefly cited in the modeling or sample analyses provided in the TR.
- 13) TR section 5.1.2, table 5-3: Fuel, cladding, and coolant temperature are listed as FOMs without discussion on how these will be quantified (e.g., peak temperatures, inner, mid-wall, outer cladding temperature, fuel centerline temperature, peak coolant, average coolant).
While these may be inferred throughout the TR, provide a concise definition of each FOM for clarity to ensure they capture appropriate phenomena.
Bundle 5B with a 14-Subchannel Edge Blockage: The ingredients found within select EM characteristics (i.e., constituents, phases, geometrical configurations, fields, and transport process) become fully coolant focused (i.e., cladding and fuel are removed from the scope).
Fuel and cladding are included again in section 5.3.2, EMDAP Step 11: Establish EM Structure. Clarify that all modeled ingredients are consistent and propagate throughout the TR, or if not, why some are excluded.
- 15) TR section 5.1.4, EMDAP Step 4: Identify and Rank Phenomena and Processes: Provide the PIRT report for audit review.
- 16) TR section 5.1.4, table 5-7, PIRT Rankings with Rationales for Partial Flow Blockage within a Fuel Assembly: ((
))
- 17) TR section 5.1.4, table 5-7: Provide additional discussion of regarding ((
))
- 18) TR section 5.2 "EMDAP Element 2: Develop Assessment Base, ((
))
- 19) TR section 5.2.2, EMDAP Step 6: Perform Scaling Analysis and Identify Similarity Criteria:
Discuss why surrogate FOMs were developed for cladding temperature but not fuel temperature.
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- 20) TR section 5.2.2: To ensure adequate independence of validation data, please clarify whether or not the ORNL or Power Reactor and Nuclear Fuel Development Corporation data were used in the past to inform or develop Mongoose++.
- 21) TR section 5.2.2.4.1, Consistent Geometry with Viscous and Conduction Terms: Provide confirmation regarding the assumption of variables being held constant in the non-dimensional Naiver-Stokes equations, such as ((
))
- 22) TR section 5.2.3.2, Phenomena Validation Matrix for Existing Data: ((
))
- 23) TR section 5.3.1, EMDAP Step 10: Establish an EM Development Plan: Provide access to the Mongoose++ theory manual and associated sensitivity studies.
- 24) TR section 5.3.1.2.2, Evaluation Matrix: Table 5-21, Evaluation of Code Ability to Model Phenomena within PIRT for Partial Flow Blockage, indicates that ((
))
- 25) TR section 5.3.1.2.4, Mongoose++ Selection: Provide reference 22, Tang, Y. S., Coffield, R. D. and Markley, R. A., Thermal Analysis of Liquid Metal Fast Breeder Reactors, 1978.
Provide additional justification for why there are minimal impacts from ((
))
- 26) TR section 5.4.1.1.1.3.2, Axial Turbulent Momentum Mixing: This section ((
))
- 27) TR section 5.4.4, EMDAP Step 16: Determine Capability of Field Equations to Represent Processes and Phenomena and the Ability of Numeric Solutions to Approximate Equation Set: Regarding the source for values in Table 5-34, Fuel Properties for Evaluation of Numerical Techniques of Mongoose++ for Partial Flow Blockage, ((
))
- 28) TR section 5.4.4: ((
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))