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Uso ACRS Subcommittee Meeting Slides Oct 8 & Oct 9 - Transient Overview
	ML25281A200
Person / Time
Site:	Kemmerer File:TerraPower icon.png
Issue date:	10/08/2025
From:	; TerraPower
To:	; Office of Nuclear Reactor Regulation
References
	DE-NE0009054
	Download: ML25281A200 (1)
	v • d • e

SUBJECT TO DOE COOPERATIVE AGREEMENT NO. DE-NE0009054 Copyright © 2025 TerraPower, LLC. All Rights Reserved SUBJECT TO DOE COOPERATIVE AGREEMENT NO. DE-NE0009054 Copyright © 2025 TerraPower, LLC. All Rights Reserved a TerraPower & GE Vernova Hitachi Nuclear Energy technology Overview of Plant Transients and LBEs

SUBJECT TO DOE COOPERATIVE AGREEMENT NO. DE-NE0009054 Copyright © 2025 TerraPower, LLC. All Rights Reserved CP stage analyses are developed in an appropriately conservative manner Biasing of key inputs, modeling approaches, acceptance criteria Generally applied DBA conservatisms to all LBE categories Plant responses to transients are generally stylized and grouped based on similar characteristics. Example groupings:

Reactivity transient Rod withdrawal, seismic, overcooling Loss of primary flow Loss of offsite power (both PSPs/ISPs), single PSP trips, single PSP locked rotor Loss of heat removal Loss of Nuclear Island Salt System (NSS)/Energy Island, loss of 1 intermediate sodium loop Preliminary Analyses 57

Inadvertent continuous withdrawal of a single control rod during full power operating conditions

Reactor scrams on either high high power range neutron flux, high high power-to-flow ratio, or high high positive power range neutron flux rate

Rod withdrawal inhibit SSC fails

Safe shutdown is achieved with IAC non-passive mode providing decay heat removal and fuel performance acceptance criteria are met.

General modeling conservativisms are used for this event.

Reactivity Transient Overview 58

SUBJECT TO DOE COOPERATIVE AGREEMENT NO. DE-NE0009054 Copyright © 2025 TerraPower, LLC. All Rights Reserved Beyond Design Basis Event: Loss of offsite power with gravity rod insertion failure (DHP-LOOP-3)

CRDM receive scram signal; rods fail to insert from gravity. CRD driveline scram follow occurs and drives rods in at motor speed

System thermal hydraulic analysis performed in SAS (SAS4A/SASSYS-1). Figures of merit fail screening criteria indicating detailed fuel performance analysis necessary

Fuel performance code determined 2/3 core failure (fresh/once burned fuel doesnt fail)

Analysis performed with best-estimate plus uncertainty approach; however, several conservatisms are still retained for this event.

Loss of Primary Flow Overview 61

Loss of heat removal from one intermediate sodium loop Modeled as instantaneous loss of heat transfer to one IHX Reactor scram on high high cold pool temperature PSPs and ISPs trip on high high cold pool temperature, and the PSPs coast down Thermal capacity of the piping, components, and intermediate sodium in the remaining intermediate sodium loop are assumed to be available On scram, NSS isolated (SHX heat removal lost for intact intermediate sodium loop) and parasitic IAC heat removal lost Safe shutdown is achieved with RAC providing decay heat removal and fuel performance acceptance criteria are met.

General modeling conservativisms are used for this event.

Loss of Heat Removal Overview 64

SUBJECT TO DOE COOPERATIVE AGREEMENT NO. DE-NE0009054 Copyright © 2025 TerraPower, LLC. All Rights Reserved ANS - American Nuclear Society AOO - Anticipated Operational Occurrence ASME - American Society of Mechanical Engineers BDBE - Beyond Design Basis Event CATT - Core Assembly Transfer Tube CCF - Common Cause Failure CFR - Code of Federal Regulations CP - Construction Permit CPA - Construction Permit Application CRD - Control Rod Drive System CRDM - Control Rod Drive Mechanism DBA - Design Basis Accident DBE - Design Basis Event DID - Defense In Depth DF - Decontamination Factor DL - Defense Layer EAB - Exclusion Area Boundary EPRI - Electric Power Research Institute EPZ - Emergency Planning Zone EVHM - Ex-Vessel Handling Machine F-C - Frequency-Consequence FHE - Ex-Vessel Fuel Handling System FFV - Fueling Floor Valves HAA - Head Access Area IAC - Intermediate Air Cooling System IE - Initiating Event IDP - Integrated Decision-Making Process IDPP - Integrated Decision-Making Process Panel IHX - Intermediate Heat Exchanger ISP - Intermediate Sodium Pump KU1 - Kemmerer Unit 1 LBE - Licensing Basis Event LPZ - Low Population Zone LWR - Light Water Reactor MST - Mechanistic Source Term NEI - Nuclear Energy Institute NHV - Nuclear Island Heating, Ventilation, and Air Conditioning System NST - Non-Safety-Related with No Special Treatment NSRST - Non-Safety-Related with Special Treatment NSS - Nuclear Island Salt System OL - Operating License OQE - Other Quantified Event PFCB - Primary Functional Containment Boundary PIE - Postulated Initiating Event PIRT - Phenomena Identification and Ranking Tables POS - Plant Operating State PRA - Probabilistic Risk Assessment PSAR - Preliminary Safety Analysis Report PSF - PRA Safety Function PSP - Primary Sodium Pump QHO - Quantitative Health Objectives RAC - Reactor Air Cooling System RC - Radiological Consequences RES - Reactor Enclosure System RG - Regulatory Guide RR - Radionuclide Retention RXB - Reactor Building SCG - Sodium Cover Gas System SPS-P - Primary Sodium Processing System SR - Safety-Related SSC - Structures, Systems, and Components TEDE - Total Effective Dose Equivalent Acronyms 68

ML25281A200

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