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ACRS CPA Presentation - Oct 22 Open (SS SSC Design Pht Iht Rac Iac RES Scg Rwg)
	ML25293A256
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Site:	Kemmerer File:TerraPower icon.png
Issue date:	10/22/2025
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 22, 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 Safety-Significant SSC Design Requirements

PDC establish necessary design, fabrication, construction, testing, and performance requirements for safety-significant SSCs

Summaries of PDC implementation in PSAR Section 5.3 and Chapter 7

PDC were developed in accordance with RG 1.232, Developing Principal Design Criteria for Non-Light Water Reactors

Topical report NATD-LIC-RPRT-0002-A, Principal Design Criteria for the Natrium Advanced Reactor, contains the methods and PDC development for Kemmerer Unit 1

Implementation of NEI 18-04 develops plant level functional and SSC level design criteria in a systematic manner, and are traceable to PDCs for implementation of design and performance requirements Principal Design Criteria

DBHL definition - design specification of level of severity or intensity of hazard for which SR SSCs are designed to withstand with no adverse impact on their capability to perform their RSFs (Ref. NEI 18-04, NEI 21-07)

SR SSCs are protected from DBHLs by design features such as barriers or designed to withstand hazard loading

NSRST SSCs may be protected from hazards at different level of severity or intensity than DBHL

CP stage selection of SR SSCs and DBAs is based on PRA that includes internal events but has not yet been expanded to address external hazards

Since SR SSCs are required to be capable of performing RSFs in response to DBHLs, no new DBAs are expected to be introduced by external hazards at OL stage Design Basis Hazard Levels (DBHLs)

External Hazards

Site characterization performed to meet requirements in 10 CFR 100, 10 CFR 50 and PDC 2 using established guidance

Site characterization results used to inform hazards and hazard magnitudes incorporated into safety-significant SSC design bases

Supplemented by NUREG-0800 Chapter 3, established regulatory guidance, and industry codes and standards

Internal Hazards

Selected to meet requirements of 10 CFR 50 and PDC 4 using established guidance

PRA hazards screening analysis also performed using established guidance to identify plant specific hazards (PSAR Table 3.1-3)

Will be evaluated further at OL stage Hazards Characterization

External DBHL:

Wind and tornado Seismic External flooding Extreme winter precipitation Internal DBHL:

Internal flooding Missiles Rupture of piping Internal fire DBHLs

NSRST and NST SSCs are designed such that DBHLs will not cause NSRST or NST SSC to adversely impact ability of SR SSC to perform SR function

Failure of non-SR SSC does not cause non-SR SSC to strike SR SSC

Failure of non-SR SSC does not adversely impact ability of SR SSC to perform an SR function

Non-SR SSC is analyzed and designed to prevent failure under DBHL conditions

Application of interaction prevention design requirement to interaction source SSC does not affect safety classification of source SSC

At CP stage, interaction prevention design requirements are developed for seismic and tornado hazards (see PSAR Section 6.1.3)

Interaction prevention design requirements for other DBHLs will be developed at OL stage DBHL Interaction Requirements for Non-SR SSCs

Provide increased assurance beyond normal industrial practices that safety-significant SSCs perform their design basis functions

Selected using systematic process considering PRA safety functions and safety-significance, risk significance, and equipment type of SSC

Also supplemented through IDP action

Once reliability and capability targets are confirmed, special treatments provide reasonable confidence that levels of reliability, availability, and capabilities of functions of SSCs assessed in the PRA and DID adequacy evaluation are met

Special treatments for safety-significant SSCs are described in PSAR Chapter 7 Special Treatments

Programmatic special treatments:

Quality Assurance Program Description

Design Reliability Assurance Program

Reliability and Integrity Management Program

Equipment Qualification Program

Testing Program

Inservice Testing Program

Comprehensive Vibration Assessment Program

Human Factors Engineering Program

Post-Construction Inspection, Testing, and Analysis Program Codes and standards:

Nuclear codes and standards (e.g., ASME Section III, ACI 349)

Modifications to industrial standards to address service conditions (e.g., elevated temperature, hazard loading)

Seismic special treatments are considered in the form of seismic classifications Special Treatments

SUBJECT TO DOE COOPERATIVE AGREEMENT NO. DE-NE0009054 Copyright © 2025 TerraPower, LLC. All Rights Reserved Seismic Classification Seismic Design Parameters SCS1 Seismic Demand SSE Design: Codes and standards consistent with SC-I SSCs described in RG 1.29 Rev. 6 Qualification: Reasonable assurance of function under seismic loads consistent with SC-I SSCs described in RG 1.29 Rev. 6 SCS2 Seismic Demand SSE Design: Codes and standards consistent with SC-I SSCs described in RG 1.29 Rev. 6 Qualification: Reasonable confidence of function under seismic loads consistent with commercial standards of ASCE 7 Seismic Classifications 10

Maximum Considered Earthquake Ground Motion SSE Seismic Risk Category IV Importance Factor, I = 1.5 Structural Design: IBC 2021 Non-structural components:

Commercial design codes applicable to SSC type Designated seismic system requiring functional qualification SCN2 Seismic Design Parameters:

Maximum Considered Earthquake Ground Motion SSE Seismic Risk Category III Importance Factor, I = 1.25 Structural Design: IBC 2021 Non-structural components:

Commercial design codes applicable to SSC type Designated seismic system requiring functional qualification SCN3 Seismic Design Parameters:

Maximum Considered Earthquake Ground Motion SSE Importance Factor, I = 1.0 Structural Design: SCN3 is not applicable to structures Non-structural components:

Commercial design codes applicable to SSC type Seismic Classifications 11

SUBJECT TO DOE COOPERATIVE AGREEMENT NO. DE-NE0009054 Copyright © 2025 TerraPower, LLC. All Rights Reserved 12 Initial seismic classifications are assigned at CP stage and will be confirmed or adjusted for OL stage based on risk-informed process and use of seismic PRA

SCS1 is initially assigned to SR SSCs

SCS2 is assigned to SR SSCs if seismically induced failure of the SR SSC does not adversely affect the safety significant function CP Stage Seismic Classification Assignments

Initial seismic classification for NSRST SSCs is based on various factors:

SSC function

Importance to life safety consistent with commercial building code

Potential contribution to events with dose consequences

SCN3 is assigned as minimum initial seismic classification for NSRST SSCs and initial seismic classification is increased to SCN2 or SCN1 as appropriate based on above factors

SCN2 or SCN1 are assigned as appropriate to meet minimum building code requirements

SCN1 is assigned for SSCs identified as having high potential contribution to seismic risk and to impose seismic qualification for active components CP Stage Seismic Classification Assignments

SUBJECT TO DOE COOPERATIVE AGREEMENT NO. DE-NE0009054 Copyright © 2025 TerraPower, LLC. All Rights Reserved 14 Area review is performed to identify interaction source and target pairs based on zones of influence Seismic interaction prevention design requirements are applied to non-SR SSCs as indicated by results of seismic interaction review

Design per ASCE 7-16 at level consistent with SCN1 seismic classification

Additional design evaluations demonstrate that NSRST or NST seismic interaction source SSC will withstand SSE at seismic performance level greater than or equal to seismic interaction target SSC with acceptance criterion of moderate inelastic deformation

Design evaluations apply response parameters that correspond to ASCE 43-19 Limit State B (target performance for collapse prevention for any SSC that is identified as seismic interaction hazard to an SSC with required safety function)

Application of interaction prevention design requirement to interaction source SSC does not affect safety classification of source SSC Seismic Interaction

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 Primary Heat Transport System &

Intermediate Heat Transport System Overview

- System Overview 17

At power, PHT transfers heat from core to IHT, with PSPs providing flow and IHXs transferring heat to IHT

Upon PSP trip, PSPs initially provide coastdown flow to core and subsequently, system transitions to natural circulation flow

Natural circulation is SR core cooling mechanism where heat is passively transferred from PHT to RES to RAC

PHT-RAC passive heat transfer is always on, it does not need any action (manual or automatic) to be placed in operation

Primary sodium in RV

3x pools (hot, warm, cold)

2x IHXs

2x PSPs

IHXs are shell-and-tube heat exchangers

PSPs are vertical centrifugal pumps

Reactor is pool-type with sodium pools and blanketed by near atmospheric pressure cover gas (argon)

SUBJECT TO DOE COOPERATIVE AGREEMENT NO. DE-NE0009054 Copyright © 2025 TerraPower, LLC. All Rights Reserved PHT - System Safety Functions 20 Function ID Function Description Safety Classification DL3-HR1 PSP Coastdown SR DL3-HR2 PSP Trip on High High Primary Sodium Temperature SR DL3-HR5 Natural Circulation of Sodium in Primary System SR DL3-RR1a IHX Primary System Barrier SR DL3-RR1d Primary Sodium Pump Seal SR DL4-HR1 IAC Passive Mode Operation NSRST DL4-HR2 PSP Trip Automatic Backup NSRST DL4-HR6 Manual PSP Trip NSRST

System Overview 22

At power, IHT transports heat from primary coolant to NSS for electrical power generation and energy storage

During reactor start-up and shutdown operation, IHT transports heat from primary coolant to IAC for rejection to atmosphere

When ISPs are not available, IHT provides natural circulation of intermediate coolant for reactor decay heat removal through IAC AHXs

IHT includes equipment within 2 intermediate sodium loops

IHT equipment per loop includes:

1x ISP

Array of SHXs

Interconnecting piping

Supporting equipment includes expansion tanks and drain subsystem

SUBJECT TO DOE COOPERATIVE AGREEMENT NO. DE-NE0009054 Copyright © 2025 TerraPower, LLC. All Rights Reserved Function ID Function Description Safety Classification DL3-HR3 ISP Trip on High High Primary Sodium Temperature SR DL3-HR12 ISP Trip on High High Primary Sodium Level SR DL2-HR2 ISP Trip on Low IHT Level NSRST DL4-HR7 Manual ISP Trip NSRST DL4-HR1 IAC Passive Mode Operation NSRST DL4-HR3 ISP Trip Automatic Backup NSRST DL4-DID1 Intermediate Leak Guard Piping NSRST IHT - System Safety Functions 24

This R&D item is focused on prevention or mitigation of a sodium/salt interaction in the Intermediate Heat Transport System Sodium-Salt Heat Exchanger.

Analysis of options resulted in selection of an etched diffusion bonded heat exchanger, which is expected to be designed such that there are no credible failures that could result in a sodium-salt reaction.

To advance beyond R&D, further analysis and development of leak detection capabilities is required.

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 Reactor Air Cooling System &

Intermediate Air Cooling System Overview

System Overview 28

Supports passive reactor decay heat removal by natural convection air flow and heat rejection to atmosphere

Provides long-term emergency core cooling function in conjunction with PHT and RES

Continuously in operation and requires no automatic or manual actuations or operator action to perform the heat removal safety function

Consists of 4 inlet and 4 outlet stacks, Collector Cylinder Assembly (CCA),

and associated inlet and outlet ducting

Integrated into RXB substructure design

Stack outlets are at higher elevation than stack inlets to provide separation of air flow streams to drive natural circulation and limit potential for recirculation

Inlet stacks inlet openings are in horizontal orientation and protected by louver assemblies configured to prevent wildlife ingress and to minimize precipitation and debris entry

Drains at base of inlet stacks allow drainage of water resulting from precipitation entry

Design of inlet louvers includes provisions for temporary installation of fine screens in event of severe small debris or dust conditions

Stack outlets are vertically oriented and protected by chimney cowl configured to mitigate wind effects and prevent rain, large wind-blown debris, and animal ingress

Instrumentation is provided to monitor inlet temperature, outlet temperature, and outlet stack mass flowrate to monitor heat removal performance

Required to meet its heat removal capability per TS

2x 100% capacity back-up methods of decay heat removal, IHT/IAC, are available

RXB is ~60 ft north-to-south RAB is ~139 ft north-to-south 32 11 12

SUBJECT TO DOE COOPERATIVE AGREEMENT NO. DE-NE0009054 Copyright © 2025 TerraPower, LLC. All Rights Reserved RAC - System Safety Functions 33 Function ID Function Description Safety Classification DL3-HR4 Inherent RAC Operation SR DL5-PAM1 Post-Accident Monitoring NSRST

An R&D item exists to ensure adequate heat transfer performance

Potential solutions include design changes to increase surface emissivities

Items to be completed to advance beyond R&D:

Ion irradiation testing of candidate coatings

Refinement of analyses

Selection of final design solution

These activities will be completed before the end of construction activities RAC R&D

System Overview 35

IAC transfers heat from intermediate sodium to atmosphere

IAC is primary and preferred means of reactor heat removal during low power and shutdown conditions

Heat may be rejected in Active Mode (normal operation), Blower Mode (off-normal operation), and Passive Mode (emergency operation)

IAC passive mode provides DID to the RAC decay heat removal; no manual operator actions or electrical power are required to initiate passive mode

IAC is available in standby while plant is at power

Air dampers above and below AHXs are closed to limit heat loss from intermediate sodium

Dampers fail open upon loss of power

IHT provides intermediate sodium flow to IAC

Heat transfer at IHX is necessary to transport heat to the AHX

In AHX, heat is transferred from intermediate sodium to atmosphere

IAC components are housed within 2 ASE structures located in plant yard area on either side of RAB

Each ASE contains:

1x AHX

1x chimney structure

1x air blower

Dampers

Air heater & recirculation blower

Weather cap and screens

Provisions for sodium catch pans and leak detection

AHXs are connected in series within each intermediate loop

Intermediate sodium flows on tube-side of AHX and ambient air on shell-side

Elevation differences between the IHX and the AHX drive natural circulation flow

SUBJECT TO DOE COOPERATIVE AGREEMENT NO. DE-NE0009054 Copyright © 2025 TerraPower, LLC. All Rights Reserved IAC - System Safety Functions 39 Function ID Function Description Safety Classification DL4-HR1 IAC Passive Mode Operation NSRST

IHT is designed to provide natural circulation of intermediate sodium for reactor decay heat removal through AHXs

Natural convection airflow is induced in air stack by decreased density of heated air in AHX

Ambient air is drawn in through low-elevation air intake and heated air exits through elevated air stack exhaust openings

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 Reactor Enclosure System Overview

Reactor Vessel

Guard Vessel

Reactor Head

Rotatable Plug Assembly

Reactor Fixed Internals

Core Barrel Structures

Reactor Support Structures

Low (near atmospheric) operating pressure

No penetrations in the Reactor Vessel

Fully enclosed, integral Primary Heat Transport system

Seismically isolated from the Reactor Building Substructure

Subgrade location increases external hazard protection

Passive emergency core cooling

SUBJECT TO DOE COOPERATIVE AGREEMENT NO. DE-NE0009054 Copyright © 2025 TerraPower, LLC. All Rights Reserved RES - Fundamental Safety Functions 44 During normal and off-normal conditions, the RES supports:

Radionuclide Retention Provides majority of primary coolant boundary and primary functional containment boundary components.

Reactivity Control Maintains reactor control assembly positions relative to control rod drive components for control rod alignment and insertion.

Decay Heat Removal Establishes flowpaths for primary coolant circulation within the reactor vessel and provides external surface area for heat rejection to atmosphere.

Primary coolant boundary component

Contains all primary sodium coolant and provides inert (argon) cover gas space

Safety related load path for in-vessel equipment, including:

Reactor Fixed Internals

Core Support Structures

Primary Heat Transport components

Surrounds Reactor Vessel with inert (argon) gas annulus for Defense-in-Depth functional containment

Maintains core cooling capability in the unlikely event of a Reactor Vessel leak

Surface area and surface enhancements promote passive heat rejection to Reactor Air Cooling system

Primary coolant boundary component

Sealed penetrations for interfacing system equipment and instrumentation

Safety related load path for:

Reactor Vessel

In-vessel equipment

Head mounted equipment

Assembly comprised of primary coolant boundary and reactor internal components (such as the Upper Internal Structure)

Provides in-vessel access for Reactor Core and In-Vessel Fuel Handling systems

Maintains primary coolant boundary and functional containment during refueling

Supports and positions Control Rod Drive components

Reactor internals and core supports

Establishes primary coolant flowpaths and maintains barriers between sodium pools

Supports and maintains alignment of reactor internals and reactor core components

Surrounds reactor core with Fixed In-Vessel Shielding

Provide safety related load path from internals to Reactor Vessel wall

Provides safety related load path for all RES loads to the Reactor Building Substructure

Integrated Seismic Isolation System provides site specific, seismic hazard protection

Seismic Isolation System Qualification Methodology Topical Report NAT-8922 -

NRC Staff audit and technical review complete

SUBJECT TO DOE COOPERATIVE AGREEMENT NO. DE-NE0009054 Copyright © 2025 TerraPower, LLC. All Rights Reserved RES - System Safety Functions 51 Function ID Function Description Safety Classification DL3-RC1 Scram - Gravity driven absorber insertion by latch release - maintains alignment SR DL3-HR4 RAC Operation - promotes adequate heat transfer SR DL3-HR5 Natural Circulation of Sodium in Primary System SR DL3-RR1 Primary Coolant Boundary SR DL4-RR1 HAA Barrier, GV Seals support Leak Prevention Function NSRST

Follow up discussion from Oct 9th subcommittee

Role of SSCs contributing to HAA boundary

HAA NHV isolation function Head Access Area (HAA) Barrier and Performance Criteria

Reference:

KU1 PSAR Section 1.3.2.1 Barrier or set of barriers that effectively limits transport of radioactive material to the environment.

SUBJECT TO DOE COOPERATIVE AGREEMENT NO. DE-NE0009054 Copyright © 2025 TerraPower, LLC. All Rights Reserved 53 Functional Containment Overview Head Access Area (HAA) Barrier and Performance Criteria Power Operation Configuration Major SSCs:

Concrete walls, floor, and ceiling

(~ 4ft thick)

Floor plugs at RXB grade level Penetration seals for piping, instrumentation, and cabling IHT piping clamshell Isolation of NHV bubble tight dampers Below grade structure Not accessible during power operations Ladder access via floor plugs in RXB grade level Function-specific classification (KU1 PSAR 7.8.1.1.2)

SR for structural support of RES NSRST for radionuclide retention (DL4-RR1a)

Approximate Dimensions:

60 ft (L) x 80 ft (W) x 40 ft (H)

Isolated leakage rate is set to ensure RSF performance criteria is met with margin across core release BDBEs.

HAA

SUBJECT TO DOE COOPERATIVE AGREEMENT NO. DE-NE0009054 Copyright © 2025 TerraPower, LLC. All Rights Reserved Functional Containment Performance 54 Power Operation Configuration Refueling Configuration Fuel Inventory Sodium Coolant Cover Gas Head Access Area Fuel Cladding Failure (instantaneous release)

Reactor Vessel &

Vessel Head (1% CG vol per day w/ SCG isolation)

Concrete Structure, Hatches, Penetrations and Seals (10% HAA vol per day w/ NHV isolation)

EAB Dose Criteria:

10 CFR 50.34 limits for DBAs

F-C Targets for DBEs and BDBEs Environment Barrier Rad Retention Classification Performance (leakage)

RES Safety-Related 1% cover gas volume per day (SCG isolated)

HAA NSRST 10% HAA volume per day (NHV isolated)

RXB Superstructure NST No established leakage performance Barrier Rad Retention Classification Performance (leakage)

RES + FHE Safety-Related 1% cover gas + EVHM volume per day (SCG isolated)

RXB Superstructure NST No established leakage performance

Activated SCG releases do not challenge DBA limits or F-C target curve - no additional HAA RR performance.

Activated SPS-P releases mitigated by hermetically sealed guard pipe - no additional HAA RR performance.

Intermediate sodium activity is below radionuclide screening threshold.

Head Access Area (HAA) Barrier Performance Functional Containment Performance 55 Event/Source PFCB HAA Barrier Representative Dose (LBE ID)

Dose Criteria In-vessel failed fuel event (DBA)

Intact and isolated (1% cover gas vol per day)

Not credited (100% HAA vol per day)*

0.96 rem 30-day TEDE (LFF-SAO-CN) 25 rem 30-day TEDE and worst 2-hr period (10 CFR 50.34)

In-vessel failed fuel event (1 assembly)

(DBE)

Intact and isolated (1% cover gas vol per day)

Not credited (100% HAA vol per day)*

0.237 rem 30-day TEDE (LFF-SAO-1)

Target 1 rem 30-day TEDE (F-C target curve)

In-vessel failed fuel event (2/3 core)

(BDBE)

Intact and isolated (1% cover gas vol per day)

Isolated (10% HAA vol per day) 0.406 rem 30-day TEDE (DHP-LOOP-3)

Target 25 rem 30-day TEDE (F-C target curve)

(*) Post-CP stage analyses will confirm whether the results are sensitive to this barrier performance and ensure it is adequately classified and appropriately applied in analyses.

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 Auxiliary Reactor Systems Overview

SCG supplies and controls gas flows to various systems and monitors cover gas for composition for fuel pin breaches

Supply and exhaust piping form portion of primary coolant boundary and primary functional containment boundary

Monitors RV/GV annulus for indication of RV leaks

SUBJECT TO DOE COOPERATIVE AGREEMENT NO. DE-NE0009054 Copyright © 2025 TerraPower, LLC. All Rights Reserved SCG - System Safety Functions 59 Function ID Function Description Safety Classification DL3-RR1c SCG Primary System Barrier SR DL3-RR7 Reactor Enclosure System Pressure Relief SR DL3-RR10 SCG Isolation SR DL4-HR1 Intermediate Air Cooling Passive Mode Operation NSRST DL2-RR10 Primary SCG Barrier NSRST DL4-RR4 SCG Cells Barriers NSRST DL4-RR4a Automatically Close SCG Isolation Valves on Leak Detection NSRST DL4-RR4c Vapor Trap Cell Isolation on Overpressure NSRST DL5-PAM1 Post Accident Monitoring NSRST

SCG contributes to functional containment

Portion of SCG from RV up to and including first isolation valve are part of primary functional containment boundary

Utilizes enveloping barriers to prevent releases

Additional SCG functional containment features includes:

Vapor trap cell (enveloping barrier)

Secondary enclosures for monitoring cabinets held below atmospheric pressure

Argon pressure delivered to RES barriers Functional Containment / Radionuclide Retention

Reference:

KU1 PSAR Section 1.3.2.1 Functional Containment

SUBJECT TO DOE COOPERATIVE AGREEMENT NO. DE-NE0009054 Copyright © 2025 TerraPower, LLC. All Rights Reserved Gaseous Radwaste System (RWG) - System Overview 63 SCG removes sodium vapors and sends cover gas to RWG RWG processes cover gas by providing holdup for decay of short-lived isotopes, filtration for particles, and enhanced delay via adsorption for long-lived isotopes prior to discharge RWG discharge to plant stack is diluted by airflow from NHV The combined exhaust is monitored and recorded for compliance with dose limits

SUBJECT TO DOE COOPERATIVE AGREEMENT NO. DE-NE0009054 Copyright © 2025 TerraPower, LLC. All Rights Reserved RWG - System Safety Functions 64 Function ID Function Description Safety Classification DL2-RR4 Retain Radionuclide - RWG Radionuclide Boundary NSRST

System Overview 66

SPS monitors and removes impurities of primary coolant

Sodium is pumped from cold pool to ex-vessel equipment where:

Cold traps remove oxygen, hydrogen, and most solutes

Cesium traps remove cesium from fuel pin breaches

Plugging temperature indicators monitor overall cleanliness by measuring temperature at which precipitation begins

Radiation and hydrogen levels are monitored online

Sodium sampling allows for extended chemistry and particulate content evaluation

Portions of SPS, including SPS ex-vessel piping that penetrates RES, form part of the primary coolant boundary and the primary functional containment boundary

SUBJECT TO DOE COOPERATIVE AGREEMENT NO. DE-NE0009054 Copyright © 2025 TerraPower, LLC. All Rights Reserved SPS - System Safety Functions 67 Function ID Function Description Safety Classification DL3-HR11 SPS Pump Trip on Low Primary Sodium Level SR DL3-RR1b SPS Primary System Barrier SR DL3-RR4 Ex-Vessel Storage Tank Barrier SR DL4-HR1 Intermediate Air Cooling Passive Mode Operation NSRST DL2-RR7 Primary SPS Barrier NSRST DL2-RR8 Intermediate Cold Trap SPS Barrier NSRST DL4-RR8 Manual SPS Pump Trip on Low Primary Sodium Level NSRST DL4-RR3 SPS Cells Barrier NSRST DL4-RR3a SPS Supply Valve Isolation on Leak Detection NSRST DL4-RR3b SPS Pump Trip on Leak Detection NSRST DL4-RR3c SPS Cells Barrier Isolation on Leak Detection NSRST DL4-PAM1 Post Accident Monitoring NSRST

SPS contributes to functional containment

Primary SPS piping up to and including first isolation valve forms part of the primary functional containment boundary and utilizes enveloping barriers

Additional SPS functional containment includes:

DL2-RR7 - Primary SPS Barrier components

DL4-RR3 - SPS Cells Barrier components Functional Containment / Radionuclide Retention

SUBJECT TO DOE COOPERATIVE AGREEMENT NO. DE-NE0009054 Copyright © 2025 TerraPower, LLC. All Rights Reserved AHX - Sodium-Air Heat Exchanger AOO - Anticipated Operational Occurrence ASCE - American Society of Civil Engineers ASE - Air Stack Structures and Equipment ASME - American Society of Mechanical Engineers BDBE - Beyond Design Basis Event CATT - Core Assembly Transfer Tube CCA - Collector Cylinder Assembly CFR - Code of Federal Regulations CP - Construction Permit CRD - Control Rod Drive System DBA - Design Basis Accident DBHL - Design Basis Hazard Level DBE - Design Basis Event DID - Defense In Depth EVHM - Ex-Vessel Handling Machine F-C - Frequency-Consequence FHE - Ex-Vessel Fuel Handling System FFV - Fueling Floor Valves FTL - Fuel Transfer Lift GV - Guard Vessel HAA - Head Access Area IAC - Intermediate Air Cooling System IDPP - Integrated Decision-Making Process Panel IHT - Intermediate Heat Transport System IHX - Intermediate Heat Exchanger ISP - Intermediate Sodium Pump IVTM - In-Vessel Transfer Machine LBE - Licensing Basis Event NEI - Nuclear Energy Institute NHV - Nuclear Island Heating, Ventilation, and Air Conditioning System NRC - Nuclear Regulatory Commission NSS - Nuclear Island Salt System NST - Non-Safety-Related with No Special Treatment NSRST - Non-Safety-Related with Special Treatment NSS - Nuclear Island Salt System OL - Operating License PDC - Principal Design Criteria PHT - Primary Heat Transport System PRA - Probabilistic Risk Assessment PSAR - Preliminary Safety Analysis Report PSP - Primary Sodium Pump RAB - Reactor Auxiliary Building RAC - Reactor Air Cooling System RES - Reactor Enclosure System RFDC - Required Functional Design Criteria RG - Regulatory Guide RIM - Reliability and Integrity Management RPA - Rotatable Plug Assembly RR - Radionuclide Retention RSF - Required Safety Function RV - Reactor Vessel RWG - Gaseous Radwaste Processing System RXB - Reactor Building SCG - Sodium Cover Gas System SFR - Sodium Fast Reactor SHX - Sodium-Salt Heat Exchanger SPS-P - Primary Sodium Processing System SR - Safety-Related SSC - Structures, Systems, and Components SSE - Safe Shutdown Earthquake TEDE - Total Effective Dose Equivalent TS - Technical Specifications Acronyms 71

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