Development of a DesignStage PRA for the Xe-100

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1 Development of a DesignStage PRA for the Xe-100 PSA 2017 Pittsburgh, PA, September 24 28, 2017 Alex Huning* Karl Fleming Session: Non-LWR Safety September 27th, 1:30 3:10pm 2017 X Energy, LLC, all rights reserved Nuclear Energy. Reimagined.

2 Outline Introduction Motivation for a Design-Stage PRA Scope Challenges and Unique Features Path Forward 2

3 X Energy Who Are We? A World Leader in High Temperature Gas Cooled Reactor (HTGR) Technology Design Engineering Company - Designing a family of HTGRs (the Xe-100 Series) - Fuel to power our reactors (UCO-TRISO Fuel) Product Lines - Xe-100 series of pebble bed HTGR s - TRISO-based pebble fuel Corporate Funding Sources and Commitment 3

4 Innovating on a Proven Foundation The Xe-100 is a revolutionary design for a nuclear reactor that builds on over 70 years of research, testing, and demonstration USA China USA Japan Germany 2005 Present USA 1998-Present HTTR Germany USA Fort St. Vrain 2000-Present HTR THTR AVR UK Peach Bottom USA Dragon 1944 ORNL Extensive testing of reactor core and pebbles to temperatures, pressures and failure modes have validated the safety performance of High Temperature Gas-Cooled Nuclear Reactors (HTGRs) 2017 X Energy, LLC, all rights reserved Nuclear Energy. Reimagined. 4

The Xe-100 Reactor Control rods Graphite top reflector Pebble bed Graphite side reflector Graphite bottom reflector Core barrel Pressure vessel Helium Flow Path Thermal Output Reactor ~4.

5MPa ~76MWe Circulators Steam collection manifold Helical coil tubes (not shown) Feed water inlet Technology The Xe-100 is a 200MWth/76MWe helium cooled power plant that features a 15.

6 The Xe-100 Reactor Control rods Graphite top reflector Pebble bed Graphite side reflector Graphite bottom reflector Core barrel Pressure vessel Helium Flow Path Thermal Output Reactor ~4.88 Meters Xe-100 Reactor Specifications Steam Temperature ~20 Meters Steam Generator Steam Pressure Electric Output 200MWth 565 o C 16.5MPa ~76MWe Circulators Steam collection manifold Helical coil tubes (not shown) Feed water inlet Technology The Xe-100 is a 200MWth/76MWe helium cooled power plant that features a 15.5% LEU fuel cycle Small size and modular construction result in relatively low cost single reactor plant of <$1B, expandable to 8 reactors on plant site On-line fueling allows for continuous operations with minimal down times for maintenance and refurbishment Benefits The Xe-100 has the ability to perform rapid load following in real time with the power range of % and can replace and supplement other fuel sources (coal, wind, solar) to leverage existing transmission and distribution infrastructure The heat source is based on pebble bed technology which has a proven meltdown proof core The Xe-100 is a C0 2 -free nuclear thermal power source that can be utilized for power generation, process heat applications, and water desalination 6

U.S. Department of Energy Endorsement DOE Cooperative Agreement X-energy began activities

Department of Energy focused on: Furthering the Xe-100 reactor design Establishing pebble

source term development roadmap Structural graphite selection criteria summary Pebble

7 U.S. Department of Energy Endorsement DOE Cooperative Agreement X-energy began activities July 1, 2016 on a 5-year, $53M cooperative agreement with the U.S. Department of Energy focused on: Furthering the Xe-100 reactor design Establishing pebble fuel manufacturing capability NRC engagement Milestones Completed to Date Mechanistic source term development roadmap Structural graphite selection criteria summary Pebble matrix graphite analysis summary First fuel form pebbles produced at ORNL, Fall 2016 Prototype mold and first pebble 7

8 Outline Introduction Motivation for a Design-Stage PRA Scope Challenges and Unique Features Path Forward 8

9 Goals for a Design-Stage PRA Provide a systematic examination of dependencies and interactions and the role that SSCs and operator actions play in the development of each event sequence; Improve system and plant safety design Provide risk insights to trade studies and design alternatives; Improve system and plant safety design Provide risk insights to the selection of License Basis Events (LBEs) and Design Basis Accidents (DBAs) Reduce uncertainty Provide risk insights to the safety classification of SSCs and special treatment requirements; Improve economics Input to application for license submittal (~Year 2021) Reduce regulatory uncertainty AND OTHERS: - Tech. Specs. - Op. Actions - E.P. 9

10 PRA Full Scope Roadmap 10

11 PRA Roadmap, Cont. 11

12 PRA Roadmap, Cont. 12

13 Challenges and Features Design-Stage PRA Development: Challenge: Balance of work scopes and integration of new design information Feature: Structured integration and clearly defined documentation approach 13

14 Integration of Specialized Engineering Disciplines Design for Performance System Requirements Develop Design Solution Verify Design Solution Primary Rqmt s Derived Rqmt s Additional Requirements Eng. Discipline #1 Goals Evaluate Design Solution Meet ED #1 Goals No Yes Eng. Discipline #2 Goals Evaluate Design Solution Meet ED #2 Goals No Yes Eng. Discipline #n Goals Discipline Engineering Evaluate Design Solution Meet ED #n Goals Yes No 14

15 PRA Design Integration 15

16 Challenges and Features Design-Stage PRA Development: Challenge: Balance of work scopes and integration of new design information Feature: Structured integration and clearly defined documentation approach Multi-Module and Non-reactor Source Risks: Challenge: Spectrum of possible releases from different units, spent fuel storage, and cogeneration facility initiating events Feature: Explicit modular plant model using RISKMAN 16

17 Plant Model 17

18 Multi-Module Endstates W 1 X 1 Y 1 - z 1 4 W 2 X 2 Y 2 - z 2 W 3 X 3 Y 3 - z 3 W 4 X 4 Y 4 - z 4 Rigorous Coding Scheme Simplified Coding Scheme 18

19 Challenges and Features Design-Stage PRA Development: Challenge: Balance of work scopes and integration of new design information Feature: Structured integration and clearly defined documentation approach Multi-Module and Non-reactor Source Risks: Challenge: Spectrum of possible releases from different units, spent fuel storage, and cogeneration facility initiating events Feature: Modular and explicit plant model in RISKMAN Level 3 PRA, MST/Consequence Calculations for Risk Estimation: Challenge: Lack of mechanistic tools and source term data Feature: AGR experiments, INL collaboration, XSTERM Code Suite Development 19

into XSTERM computational domain (see the next slide) for 30 axial nodes.

20 Xe-100 Mechanistic Source Term Code Suite (XSTERM) XFP - TRISO Fuel Particle Failure Mechanisms INITIALIZE: (a) Imports the input files such as VSOP [1] calculated flux, broad-group cross sections, multi-pass burnup / fluence / sphere power and then maps them into XSTERM computational domain (see the next slide) for 30 axial nodes. (b) Runs XTDYN module to calculate all the temperatures in the core and radial components, including fuel spheres (Pebbles), TRISO-coated particles, reflectors, barrel, RPV for 30 axial nodes. 20

21 XSTERM Code Descriptions Module Description XDM XRAD XMC XTDYN XFP XGAS XSOL XDUST XHPB manages data among the XSTERM code modules. performs mass balance calculations for radionuclides throughout the plant. performs Monte Carlo statistical analysis for a wide range of variables in the reactor such as TRISO particle layer thicknesses and densities, power and coolant flow variations, etc. calculates detailed temperature distributions in fuel elements (Pebbles/Compacts), TRISO-coated fuel particles and all the core components such as reflectors, barrel and RPV during normal and accident conditions. Temperature profiles are used by all other modules to calculate parameters such as failure fractions and diffusion coefficients. is a coated particle fuel performance code and calculates TRISOcoated particle failure fractions, which are used in XGAS and XSOL to calculate the release rates from TRISO-coated particles and fuel elements. calculates gaseous fission product release from TRISO-coated fuel particles and fuel elements during normal and accident conditions. calculates metallic (solid) fission product release from TRISOcoated fuel particles and fuel elements during normal and accident conditions. is a graphite dust production code in the helium pressure boundary (HPB). calculates dust particles, fission and activation product transport, suspension, plateout and re-entrainment behavior in HPB during normal and accident conditions. 21

22 Challenges and Features Design-Stage PRA Development: Challenge: Balance of work scopes and integration of new design information Feature: Structured integration and clearly defined documentation approach Multi-Module and Non-reactor Source Risks: Challenge: Spectrum of possible releases from different units, spent fuel storage, and cogeneration facility initiating events Feature: Modular and explicit plant model in RISKMAN Level 3 PRA, MST/Consequence Calculations for Risk Estimation: Challenge: Lack of mechanistic tools and source term data Feature: AGR experiments, INL collaboration, XSTERM Code Suite Development Licensing: Challenge: NUREG-800, are LWR centric (core damage/lerf) Feature: Large body of previous experience (MHTGR, PBMR, NGNP) and industry standards (Non-LWR PRA standard, ANSI/ANS 53.1) 22

23 ANSI/ANS nuclear safety design process for modular helium-cooled reactor plants Bulk of conceptual design PRA development effort Frequency (LBE Category) Legend, per-plant-year F(AOO) > F(DBE) > F(BDBE) 10-6 F(cutoff) < AOO DBE BDBE cutoff Example Frequency Consequence (F-C) Curve 23

24 Path Forward Near Term: PRA/Design cross-cutting activities: System design evaluations, dependency analysis Support and safety system functional design Evaluation of system operator actions, success criteria Planned activities: System model construction as design information becomes available Fault tree construction Notebook documentation Plant transient analysis (thermal-fluid data, support event sequence analysis and success criteria) Mechanistic source term cases 24

25 Thank You! Questions? Contact info: Alex Huning Karl Fleming 25

The Next Generation Nuclear Plant (NGNP)

The Next Generation Nuclear Plant (NGNP) Dr. David Petti Laboratory Fellow Director VHTR Technology Development Office High Temperature, Gas-Cooled Reactor Experience HTGR PROTOTYPE PLANTS DEMONSTRATION