ML25210A204

Letter: Terrapower, Llc. - Final Safety Evaluation of Topical Report Nat-9395, Partial Flow Blockage Methodology, Revision 0

ML25210A204
Person / Time
Site:	99902100
Issue date:	08/07/2025
From:	Joshua Borromeo Office of Nuclear Reactor Regulation
To:	George Wilson TerraPower
References
EPID L-2024-TOP-0010
Download: ML25210A204 (1)

Text

August 7, 2025 George Wilson Senior Vice President, Regulatory Affairs TerraPower, LLC 15800 Northup Way Bellevue, WA 98008

SUBJECT:

TERRAPOWER, LLC - FINAL SAFETY EVALUATION OF TOPICAL REPORT NAT-9395, "PARTIAL FLOW BLOCKAGE METHODOLOGY," REVISION 0 (EPID NO. L-2024-TOP-0010)

Dear George Wilson:

On March 26, 2024, 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 staff). The TR provides an overview and description of evaluation models (EMs) developed to evaluate partial flow blockage events within the Natrium sodium fast reactor (SFR). On April 22, 2024, the staff found that the material presented in the TR provides technical information in sufficient detail to enable the staff to conduct a detailed technical review of (ML24107B049). The staff conducted a regulatory audit (ML24197A184, ML25210A318) on the TR from July 25, 2024, to April 10, 2025.

TerraPower submitted a revision of the TR (ML25129A064), which was renumbered from TP-LIC-RPT-0008 to NAT-9395, Revision 0, to clarify portions of the TR as discussed during the audit. NAT-9395, Revision 0, summarizes the partial flow EM methodology in the context of the Regulatory Guide (RG) 1.203, Transient and Accident Analysis Methods, (ML053500170) Evaluation Model Development and Assessment Process (EMDAP) process.

The enclosed final safety evaluation (SE) is being provided to TerraPower, because the NRC staff has found NAT-9395, Revision 0, acceptable for referencing the licensing actions to the extent specified and under the limitations and conditions delineated in the TR. The final SE defines the basis for the NRC staffs acceptance of the TR.

The NRC staff requests that TerraPower publish an approved version of this TR within 3 months of receipt of this letter. The approved version should incorporate this letter and the enclosed SE after the title page. The approved version should include a -A (designating approved) following the TR identification symbol.

If you have any questions, please contact Stephanie Devlin-Gill at (301) 415-5301 or via email at Stephanie.Devlin-Gill@nrc.gov.

Sincerely,

/RA/

Joshua Borromeo, Chief Advanced Reactor 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

Pkg: ML25210A192 Letter: ML25210A204 Enclosure (Public): ML25210A206 Enclosure (Non-Public): ML25210A205 OFFICE NRR/DANU/UTB2:BC NRR/DANU/UAL1:PM NRR/DANU/UAL1:LA NAME CdeMessieres SDevlin-Gill DGreene DATE 07/29/2025 06/23/2025 07/30/2025 OFFICE NRR/DANU/UAL1:BC NAME JBorromeo DATE 8/07/2025