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NAT-2954-NP In-Vessel Events Without Fuel Failure Evaluation Model Development Non-Proprietary (Public)
	ML23081A535
Person / Time
Site:	99902100
Issue date:	03/22/2023
From:	Cornelious Banks; NRC/NRR/DANU/UAL1
To:	; TerraPower
References
	DE-NE0009054 NAT-2954
	Download: ML23081A535 (1)
	v • d • e

NAT-2954 In-Vessel Events without Fuel Failure Evaluation Model Development a TerraPower & GE-Hitachi technology

Natrium'Reactor Overview

The Natrium project is demonstrating the ability to design, license, construct, startup and operate the Natrium plant within a timeframe established for the Advanced Reactor Demonstration Project.

Pre-application interactions are intended to reduce regulatory uncertainty and facilitate the NRCs understanding of the Natrium design and its safety case.

2

Natrium Safety Features 3

Control Contain Cool

Pool-type Metal Fuel SFR with Molten Salt Energy Island

- Metallic fuel and sodium have high compatibility

- No sodium-water reaction in steam generator

- Large thermal inertia enables simplified response to abnormal events

Simplified Response to Abnormal Events

- Reliable reactor shutdown

- Transition to coolant natural circulation

- Indefinite passive emergency decay heat removal

- Low pressure functional containment

- No reliance on Energy Island for safety functions

No Safety-Related Operator Actions or AC power

Technology Based on U.S. SFR Experience

- EBR-I, EBR-II, FFTF, TREAT

- SFR inherent safety characteristics demonstrated through testing in EBR-II and FFTF Control Motor-driven control rod runback Gravity-driven control rod scram Inherently stable with increased power or temperature Cool In-vessel primary sodium heat transport (limited penetrations)

Intermediate air cooling natural draft flow Reactor air cooling natural draft flow -

always on Contain Low primary and secondary pressure Sodium affinity for radionuclides Multiple radionuclides retention boundaries

4 Rx Building Fuel Building Fuel Aux. Building Rx Aux. Building NI Power Distribution Center & Controls Control Building Warehouse

& Admin Standby Diesels Firewater Shutdown Cooling Inert Gas Steam Generation Turbine Building TI Power Distribution Center Energy Storage Tanks Demin Water Salt Piping

Plant Overview 5

Reactor Aux. Building Intermediate Sodium Hot Leg Intermediate Sodium Cold Leg Reactor and Core Intermediate Air Cooling Head Access Area Refueling Access Area Reactor Air Cooling / Reactor Cavity Reactor Building Fuel Handling Building Reactor Air Cooling Ducts Spent Fuel Pool (water)

Sodium Int. loop Sodium/Salt HXs Salt Piping to/from Thermal Storage System Ground Level

Agenda 6

In-Vessel Events Envelope Presentation Objectives EM Development Principles EMDAP Element 1 Evaluation Model Capability Requirements & Phenomena Identification and Ranking Tables (PIRTs)

EMDAP Element 2 Scaling Analysis, Legacy Test Data and TerraPower Tests, Assessment Matrix for Validation EMDAP Element 3 Selection of Primary Safety Analysis Computer Code, EM structure, Closure Models

EMDAP Element 4 Evaluate the Model Adequacy (Top-Down and Bottom-Up)

In-Vessel Events Envelope 7

All QE by Radiation Source In-Vessel Events Ex-Vessel Events Events w/o Release Tools: System Model (SAS4A/SASSYS-1) and Fuel Performance Model Time at temperature criteria met OR Fuel performance shows no release Events w/ Release Tools: System Model or Mechanistic Evaluation, Fuel Performance Model, Mechanistic Source Term, Atmospheric Dispersion Events with fuel failure predicted Events w/o Release Tools: Mechanistic Evaluation and Fuel Performance Model Release prevented from selected Radiation Source by an identified barrier Fuel Performance model used for fuel Events w/ Release Tools: Mechanistic Evaluation, Fuel Performance Model, Mechanistic Source Term, Atmospheric Dispersion Fuel handling events Radionuclide containing SSCs Clad Failure 1st Barrier Failure

Initiating Event Screening Meets F-C Target 8

All Events PRA Modeled Events (QHOs Calculated here)

Quantified Events (Assigned a Consequence)

Licensing Basis Events AOO DBE BDBE DBA Other Quantified Events EPZ/Cliff Edge Normal Ops Screening Residual Region DID Only Decreasing Frequency Meets 10 CFR 50.34 dose limits Derived from DBE, no frequency assigned Demonstrates DID adequacy or other important safety feature Evaluates potential for cliff edge and events contributing to EPZ evaluation In-Vessel Events Envelope Event Type Line Diagram by Frequency

To share what has been done and what is planned to develop TerraPowers EM for in-vessel events without fuel failure

To receive comments on EM development to date:

- Appropriateness of complying with RG 1.203 (EMDAP)

- Legacy test data selected for EM assessment Note: Available legacy test data is limited 9

Presentation Objectives

In-Vessel Events Without Fuel Failure EM Development 10

Comply with the basic principles of EMDAP

- 4 Elements with 20 Steps Most steps in Element 1 through Element 3 have been performed

- Additional work is Planned for Step 6 (scaling analysis), Step 8 (Evaluation of IET distortions and SET scaleup capability), and Step 9 (Experimental uncertainties)

Most steps in Element 4 are in development RG. 1.203

Element 1 - Evaluation Model Capability Requirements Step 1: Analysis Purpose To demonstrate that the Natrium Reactor has enough safety margin for AOOs, DBEs, and BDBEs, and will meet construction permit and operating license expectations 11 Element 1 Establish Requirements for Evaluation Model Capability

1. Specify analysis purpose, transient class, and power plant class

2. Specify figures of merit

3. Identify systems, components, phases, geometries, fields and processes that should be modeled

4. Identify and rank phenomena and processes Step 2: Figures of Merit Cladding temperature history, coolant temperature, and thermal creep strain Step 3: EM Characteristics (Eight ingredients)

Systems o Natrium Plant Subsystems o RCC, RES, PHT, IHT, IAC, CRD, & RAC Modules o Physical components within the subsystems such as reactor vessel, IHX, etc.

Subsystem Name RCC Reactor Core and Core Components RES Reactor Enclosure System PHT Primary Heat Transport System IHT Intermediate Heat Transport System IAC Intermediate Air Cooling CRD Control Rod Mechanism System RAC Reactor Air Cooling System

Element 1 - Evaluation Model Capability Requirements 12 Step 3: EM Characteristics (Eight ingredients) (cont.)

- Constituents o Sodium, air, & argon gas

- Phases o Liquid sodium and gas

- Geometrical configurations o Liquid sodium flowing upwardly, downwardly, and horizontally, air flowing through the riser of the RAC, argon gas in stagnant condition at the top of the hot pool

- Fields o Mass, momentum, and energy transportation of liquid sodium, air, and argon gas, Thermal energy of heat structure

- Transport processes: Many mechanisms that determine the transport of and interactions between constituent phases o Transport properties defining inter-nodal mass, momentum, and energy of liquid sodium, air, and argon gas o Other transport processes

Step 4: Phenomena Identification and Ranking Table (PIRT)

- PIRT Development o Separate PIRTs developed to reflect ongoing Natrium design changes (1) Internal Panelists (9/2021); (2) External Panelists (8/2022) o Representative Events Loss Of Offsite Power: Scenarios for internal and external PIRTs Rod Withdrawal At Power: Scenarios for internal and external PIRTs Loss Of Heat Sink: Scenario for external PIRTs

- Combined PIRT o The rankings were combined with conservativeness for each phenomena Importance ranking: Higher ranking chosen (H > M > L)

Knowledge level ranking: Lower ranking chosen ( L > M > H)

- Further revision to the PIRT is expected to reflect Natrium design changes 13 Element 1 - Evaluation Model Capability Requirements

14 Questions?

Acronym List 15 AOO - Anticipated Operational Occurrence LBE - Licensing Basis Event BDBE - Beyond Design Basis Event NI - Nuclear Island CRD - Control Rod Drive PHT - Primary Heat Transport System DBA - Design Basis Accident PIRT - Phenomena Identification and Ranking Table DBE - Design Basis Event PRA - Probabilistic Risk Assessment DID - Defense in Depth QE - Quantified Event EBR - Experimental Breeder Reactor QHO - Quantitative Health Objective EM - Evaluation Model RAC - Reactor Air Cooling System EMDAP - Evaluation Model Development and Application Process RCC - Reatcor Core and Core Components EPZ - Emergency Planning Zone RES - Reactor Enclosure System F-C - Frequency-Consequence RX - Reactor FFTF - Fast Flux Test Facility SET - Separate Effect Test HX - Heat Exchanger SFR - Sodium-Cooled Fast Reactor IAC - Intermediate Air Cooling TI - Turbine Island IET - Integral Effect Test SSC - Structures, Systems, and Components IFR - Integral Fast Reactor TREAT - Transient Reactor Test Facility IHT - Intermediate Heat Transport System IHX - Intermediate Heat Exchanger

ML23081A535

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