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ACRS CPA Presentation - Oct 21 Open (RCC Cra CRD)
	ML25293A258
Person / Time
Site:	Kemmerer File:TerraPower icon.png
Issue date:	10/21/2025
From:	; TerraPower
To:	; Office of Nuclear Reactor Regulation
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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 Kemmerer Unit 1 ACRS Subcommittee Meeting Natrium Design ACRS Subcommittee Meeting October 21, 2025

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 Fuel and Core Design Reactor Core System Overview

RCC is composed of removable assemblies and is designed to sustain a nuclear chain reaction for fission heat generation within the thermal-mechanical constraints of the components.

Function ID Function Description Safety Classification DL3-RC1 Scram - Gravity Driven Absorber Insertion by Latch Release SR DL3-RR2 Cladding Barrier SR DL3-HR5 Natural Circulation of Sodium in Primary System SR DL4-RC3 Control Rod Drive System Driveline Scram Follow NSRST The RCC also provides a SR structural support load path function for SR components as well as SR passive heat removal functions

Title Description Fuel Assembly Contains heavy metal mass that contributes to the production of fission neutrons within the reactor core and the generation of nuclear heat.

Primary and Secondary Control Rod Assembly Contains neutron-absorbing material for managing reactivity adjustments and reactivity suppression Reflector Assembly Reduces heavy metal mass loading in the reactor core and contains materials and components with favorable neutron scattering behavior.

Shield Assembly Contains neutron absorbing material for the net reduction of neutron flux at the interface between the reactor core and other fixed structural components within the Reactor Enclosure System, including the core barrel and in-vessel storage.

Neutron Source Assembly Produces neutrons when the reactor core is in a subcritical configuration for the measurement of source range signals.

Simulated Core Assembly Occupies reactor core positions for hot functional testing and debris filtering. These core assemblies may also be used to for core mining activities during refueling in the case of stuck core assemblies.

Compressive Assembly A mechanically actuated core assembly, which interfaces with the In-Vessel Transfer Machine at refueling conditions to provide reliable net negative radial feedbacks during normal and transient conditions.

Other assembly types include lead demonstration, lead test, and material surveillance assemblies

Core Map

Assembly Layout

Reactivity feedback mechanisms include fuel temperature (Doppler) effects, fuel axial expansion and contraction, primary sodium coolant density, control rod driveline axial expansion, and radial distortion feedbacks.

The reactor core is designed such that the net effect of the prompt acting components of these feedback mechanisms is negative in the power operating range.

These feedback mechanisms tend to compensate for a rapid increase in reactivity.

Reactivity Coefficients

The compressive assembly provides core compression force, reducing deflection of the core.

The general science and concept of the compressive assembly is understood but the specific requirements have not been defined for the design.

The specific components required for the compressive assembly remain to be defined with requirements or drawings and testing must be performed in a relevant environment.

R&D-Compressive Assemblies

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 Reactivity Control System Overview Control Rod Assemblies and Control Rod Drive System

There are 9 primary control rod assemblies and 4 secondary control rod assemblies which function in conjunction with the CRD to position neutron absorber material to appropriately control and terminate the nuclear reaction.

Absorber pins contain cladded, helium-bonded, Boron Carbide absorber pellets.

Overview-Control Assemblies 12

To provide design diversity to limit common cause failures in compliance with PDC 26, the preliminary design includes both primary and secondary control assemblies, with geometric differences, which are described in TerraPower, LLC (TerraPower) Natrium Topical Report: Fuel and Control Assembly Qualification, NAT-2806.

Either bank is capable of achieving safe shutdown independent of the other bank

The secondary control assemblies provide a regulating function to manage small reactivity changes.

Overview-Control Assemblies 13

Control Rod Drives are identical for Primary and Secondary CRAs

CRDM Housings perform a primary coolant boundary function and are constructed per ASME Section III, Division 5

Upon signal from the RPS, CRD releases the CRAs to initiate a scram by gravity drop into the reactor core

The CRD also provides scram-follow motor drive-in of the CRAs as a diverse scram for defense-in-depth

Scram follow minimum speed as modeled in safety analysis is 9 in/min.

The design with incorporate adequate margin to protect the capability target.

Electro-Pnuematic Scram Valve Assembly provides 2-out-of-3 voting at CRDM for CRA release.

CRD positions the CRA within the reactor core for reactivity control

Utilizes motor and ball screw for vertical positioning

Includes redundant indication on the CRDM ball screw position

CRA position is determined by RMC system, which commands individual drives to effectuate movements

RMC includes numerous interlocks and limits for CRD movement

SUBJECT TO DOE COOPERATIVE AGREEMENT NO. DE-NE0009054 Copyright © 2025 TerraPower, LLC. All Rights Reserved CRD - System Safety Functions 17 Function ID Function Description Safety Classification DL3-RC1, RC2 Scram - Gravity-driven absorber insertion by latch release SR DL4-RC3 CRD Driveline Scram Follow NSRST DL3-RR1 Primary Coolant Boundary SR

SUBJECT TO DOE COOPERATIVE AGREEMENT NO. DE-NE0009054 Copyright © 2025 TerraPower, LLC. All Rights Reserved ASME - American Society of Mechanical Engineers CRA - Control Rod Assembly CRD - Control Rod Drive System CRDM - Control Rod Drive Mechanism NCB - Nuclear Island Control Building NSRST - Non-Safety-Related with Special Treatment PDC - Principal Design Criteria RCC - Reactor Core System RMC - Rod Monitoring and Control System RPS - Reactor Protection System SR - Safety-Related UIS - Upper Internal Structure Acronyms 19

ML25293A258

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