Reactors with Molten-Salts: Heat Transport Options and Missions H2 Dr. Charles Forsberg AHTR Oak Ridge National Laboratory P.O. Box 2008; Oak Ridge, TN 37831 E-mail: [email protected] Tel: (865) 574-6783 Frederic Joliot & Otto Han Fusion Summer School on Nuclear Reactors Off-gas Cadarache, France System Primary Secondary Salt Pump Coolant Salt August 25–September 3, 2004 (Clean) Salt Pump Graphite Moderator (Bare) Electricity Heat Exchanger The submitted manuscript has been authored by a contractor of the U.S. Government under Reactor Fuel Salt contract DE-AC05-00OR22725. Accordingly, the U.S. Government retains a nonexclusive, - Dissolved Uranium Freeze royalty-free license to publish or reproduce the published form of this contribution, or allow Plug - Fission Products others to do so, for U.S. Government purposes. File: France2004.MoltenSaltOptionsView MSR Critically Safe, Passively Cooled Dump Tanks (Emergency Cooling and Shutdown) 1 Contents • Introduction to molten salts • Applications − Heat transport − Advanced high-temperature reactor − Molten salt reactor − Fusion • Molten salt characteristics • Power cycles 2 Introduction Molten Fluoride Salts A High-Temperature Coolant There Has Been a Rebirth of Interest in High-Temperature Nuclear Reactors Brayton power cycles that efficiently convert heat to electricity (vs. steam cycle limits at ~500ºC) Thermochemical hydrogen production: Requires high temperatures: 700 to 850ºC H2 Increased availability of carbon- carbon composites and other high-temperature materials 4 Only Two Coolants Have Been Demonstrated to be Compatible with High-Temperature Operations Helium Molten Fluoride Salts (High Pressure/Transparent) (Low Pressure/Transparent) 5 Mankind has Large-Scale Experience with Only 3 High-Temperature Liquids Iron, Glass, and Fluoride Salts) Molten Fluoride Salts Were Used in Molten Salt Reactors with Fuel in Coolant (AHTR Uses Clean Salt and Solid Fuel) Molten Fluoride Salts Have Been Used for a Century to Make Aluminum in Graphite Baths at 1000°C 6 Reactor Peak Temperatures and Power Outputs 1000 Molten Salt Systems (Low Pressure) Thermo- Brayton • Heat Transport Systems chemical • Advanced High-Temperature Reactor (Solid Fuel) (Helium or Cycles 800 • Molten Salt Reactor (Liquid Fuel) Nitrogen) • Fusion Reactors 600 Helium-Cooled VHTR (High-Pressure) Liquid Metal Fast Reactor (Low Pressure) 400 Rankine Temperature (°C) (Steam) Light Water Reactor (High Pressure) 200 General Electric ESBWR European Range of Hydrogen Pressurized-Water Plant Sizes Reactor Electricity Hydrogen 0 Application 0 1000 2000 Electricity (MW) 03-243R2 7 Molten Salt Nuclear Applications Molten-Salt Nuclear Applications High-temperature heat transport→ from nuclear reactors to thermochemical hydrogen facilities H2 ←Advanced high-temperature reactor with solid fuel and a molten-salt coolant Off-gas System Primary Secondary Salt Pump Coolant Salt (Clean) Salt Pump Graphite Moderator Molten salt reactor (MSR)→ (Bare) Electricity Heat Exchanger Reactor with fuel dissolved in a molten salt Fuel Salt - Dissolved Uranium Freeze Plug - Fission Products Critically Safe, Passively Cooled Dump Tanks (Emergency Cooling and Shutdown) ←Fusion: Molten salt coolant for heat transfer and tritium breeding 9 High-Temperature Heat Transport Heat Transport From Nuclear Reactors to Thermochemical Hydrogen Facilities Heat Transport Systems for Hydrogen Production (Heat + Water → Hydrogen + Oxygen) Nuclear Thermochemical Reactor Hydrogen Production System Oxygen Heat Exchanger H2 Water • Heat must be transported from the reactor to the hydrogen production plant [1000s of MW(t)] • Significant transport distances are involved because of the size of the chemical plants and safety (100s of meters) • Temperature of delivered heat: 700 to 850ºC • Other molten salts used in the chemical industry to 600ºC 11 03-153 Molten Salts Have Superior Capabilities for the Transport of Heat Number of 1-m-diam. Pipes Needed to Transport 1000 MW(t) with 100ºC Rise in Coolant Temperature Water Sodium (PWR) (LMR) Helium Molten Salt Pressure (MPa) 15.5 0.69 7.07 0.69 Outlet Temp (ºC) 320 540 1000 1000 Coolant Velocity (m/s) 6 6 75 6 03-258 12 Molten Salt Intermediate Heat Exchangers (IHXs) have Lower Temperature Drops, Smaller Heat Exchangers, and Less Power Consumption than Helium IHXs 100 60 600 MW(t) He-to-He 50 10 A B He-to-MS 40 1 He-to-He P, MW He- 30 V , m 3 to-MS HX 0.1 B 20 MS-to-MS A 0.01 10 MS-to-MS 0.001 0 0 20406080100 LMTD, K Optimized Compact Off-set Strip-Fin IHX 13 High-Temperature Heat-Transport Research-and-Development Challenges • Materials of construction, if operating temperatures are above 750ºC • Optimized choice of salt • System engineering of salt with a freeze point between 350ºC and 500ºC 14 The Advanced High- Temperature Reactor (AHTR) Solid Fuel Clean Molten Salt Coolant The Advanced High-Temperature Reactor Combining Existing Technologies in a New Way General Electric S-PRISM Passively Safe Pool-Type Reactor Designs GE Power Systems MS7001FB High-Temperature, High-Temperature Low-Pressure Brayton Power Cycles Coated-Particle Transparent Molten- Fuel Salt Coolant 16 The Advanced High-Temperature Reactor Passive Decay Heat Exchanger Brayton Heat Removal Reactor Compartment Power Cycle Hot Air Out Control Hot Molten Salt Air Inlet Rods Heat Fuel Pump Exchanger (Coated-Particle, Generator Graphite Matrix) Reactor Vessel Pump Recuperator Guard Vessel Helium or Nitrogen Graphite Partly Gas Decouples Salt Compressor and Vessel Wall Temperature Molten Salt Coolant Cooling Water 03-239R 17 AHTR Fuels and Coolant Graphite-Matrix, Coated Particle Fuel Clean Molten-Salt Coolant The AHTR Uses Coated-Particle Graphite Fuel Elements (Peak Operating Temperature: 1250ºC; Failure Temperature: >1600ºC) Same Fuel as Used in Gas-Cooled Reactors • Fuel particle with multiple coatings to retain fission products • Fuel compact contains particles • Compacts inserted into graphite blocks − Several options for graphite geometry (prismatic, rod, pebble bed, etc.) − Base design uses prismatic; other options are viable • Graphite blocks provide neutron moderation and heat transfer to coolant 19 Molten Salt Coolant Reduces AHTR Temperatures and Equipment Sizes Relative to Helium Reactors 100 60 He-to-He 50 10 A ←Better Heat Transfer B He-to-MS 40 (Smaller Temperature Drops in Heat 1 He-to-He Exchanger with Lower Peak P, MW He- 30 V , m3 to-MS HX Temperatures) 0.1 B 20 MS-to-MS A 0.01 10 Number of 1-m-dia. Pipes Needed MS-to-MS To Transport 1000 MW(t) 0.001 0 With 100ºC Rise 0 20406080100 In Coolant Temperature LMTD, K Smaller Pipes, Valves, Heat Exchangers, and Water Sodium (PWR) (LMR) Helium Molten Salt Other Components→ Pressure (MPa) 15.5 0.69 7.07 0.69 Outlet Temp (ºC) 320 540 1000 1000 Coolant Velocities (m/s) 6 6 75 6 20 Liquids Remove Heat More Effectively than Gas: Cooler Fuel for the Same Coolant Exit Temperatures coolant channel graphite fuel compact GT-MHR → coolant channel graphite fuel compact AHTR → 1160 Helium (600 MW, 6.6 W/cc) 1140 Temperature Profile at Core Outlet for Average Channel 1120 LiF-BeF2 (2400 MW, 8.3 W/cc) 1100 1080 LiF-BeF2 (600 MW, 6.6 W/cc) 1060 Temperature (°C) 1040 1020 1000 980 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Coolant Channel Distance (cm) Fuel Compact Centerline Centerline 21 AHTR Facility Design A Low-Pressure, High-Temperature Liquid-Cooled Reactor Proposed AHTR Facility Layouts are Based on Sodium-Cooled Fast Reactors Low Pressure, High Temperature, Liquid Cooled General Electric S-PRISM 23 AHTR 9.0-m Vessel Allows 2400-MW(t) Core 102 GT-MHR fuel columns 222 Additional fuel columns Elev. 0.0 m Reactor Closure 324 Total fuel columns Floor Slab Elev. -2.9 m Cavity Cooling Channels Cavity Liner Cavity Cooling Baffle Coolant Pumps Siphon Breakers Control Rod Drives Elev. -9.7 m Guard Vessel Reactor Vessel Graphite Liner Outer Reflector Reactor Core Inner Reflector Elev. -19.2 m Elev. -20.9 m Elev. -21.1 m Power density = 8.3 MW/m3 (26% larger than 600-MW GT-MHR) 24 03-155 In an Emergency, Decay Heat is Transferred to the Reactor Vessel and then to the Environment • Similar to GE S-PRISM (LMR) ~50º C Difference Hot Air Out Control in Molten Salt Air Rods • Liquid transfers heat from fuel to Temperatures Inlet wall with small temperature drop (~50ºC) Fuel (Similar to • Argon gap: Reactor to guard vessel MHTGR) − Heat transfer: ~T4 Core Reactor Vessel − Thermal switch mechanism Argon Gap Guard • Heat rejection: Vessel temperature Vessel dependent Insulation − LMR: 500-550ºC [~1000 MW(t)] Decay Heat Decay Heat from − AHTR: 750ºC [~2400 MW(t)] from Core to Vessel to Vessel Liner Environment • Other decay heat cooling options 04-039 25 2400-MW(t) AHTR Nuclear Island is Similar in Size to 1000-MW(t) Sodium-Cooled S-PRISM Plant • Differences from S-PRISM Turbine Hall With MS-Gas HX Reactor facility layout: Cavity − No SNF storage in vessel No heat exchanger inside vessel Cooling − − Molten salt-to-gas heat Ducts exchanger in turbine hall • Same vessel size (low pressure) − Space for 2400-MW(t) AHTR Spent core with low power density Fuel Storage • Similar equipment size − Molten salt volumetric heat capacity > than that for sodium • Higher-capacity decay heat MS-MS Heat removal system Exchanger Reactor − 750ºC vessel under accident Core conditions for nominal 1000ºC salt exit temperature • Higher electrical output − S-PRISM: 380 MW(e) − AHTR: >1200 MW(e) 26 The Preliminary Economic Analysis Indicates Capital Costs of 50 to 60% per kW(e) Relative to S-PRISM and MHTGRs • Economics of scale − 2400 MW(t) vs.