MOLTEN SALT REACTORS Back to the future LOUISIANA NUCLEAR SOCIETY ROWLAND LINFORD MARCH 19, 2019 What is a molten salt reactor? A molten salt reactor (MSR) is a type of nuclear reactor that uses liquid fuel instead of the solid fuel rods used in conventional nuclear reactors. Why Are They Such a Hot Topic? High temperature operation for hydrogen generation and other process heat. Low pressure operation making radiation containment easier during transient conditions. Generate less high level waste. No fuel manufacturing. Potential to burn fuel wastes and use alternate fuels easily. Better stability and safety

History Aircraft Applications first major scale experiment Aircraft Reactor Experiment late 1940s Extremely long range bombers in the air at all times Very high power density and power levels needed for thrust ARE reactor operated for 100 hours (1954) Na-Zr-U molten fuel pumped though Be blocks Sodium secondary fluid Inconel piping and structural material Achieved temperatures of 8600 C and 100 MWh energy Operating reactor (89 flights) flown in a Convair B-36 aircraft (not as an engine) Key issues were weight and crew shielding Other reactor tests run in INEL produced successful engines ICBM capability and development killed the aircraft nuclear programs Molten Salt Reactor Experiment Operated at Oak Ridge 1965 to December 1969 Follow-on effort from ANP to develop commercial MSR power plants Alvin Weinberg key leader in the effort at ORNL Design

10-MW power - thermal spectrum core (actually 8MW due to design error) Single carrier fluid design Mixture of enriched LiF-BeF2-ZrF4(flibe) Combined with ThF4 and/or UF4 fuel Unclad pyrolytic graphite moderator Structural and piping was Hastelloy-N (nickel alloy) Secondary coolant was molten LiF-BeF2 No online fuel processing MSRE Schematic MSRE Operating Experience MSRE was a successful experiment Operation was reliable Radioactive liquids and gases were contained Corrosion could be limited effectively with Hestalloy UF salts were stable and compatible with other materials Single-fluid system worked Operation was acceptable with 233U, 235U or 239Pu

U could be removed completely by fluoridation Did not include online reprocessing What happened next Modest effort until 1980 1000 MWe MS Breeder was designed LiF-BeF2 ThF4 - UF4 fuel salt Secondary coolant NaF-NaBF4 Effort stopped to focus on LMFBR ANP Engine at EBR-1 Site Current Day Overview Decisions, decisions, decisions What applications and options are important

Who is involved What is the cost? How is it financed/developed? What are limiting issues for full-scale application? What is a comprehensive safety analysis? What are the problems for site rehabilitation after end-of-life. Non-proliferation issues. What fuel, Th or U? May be an issue independent of MSR One of several concepts: Brayton cycle 40-44% efficiency Brayton Cycle Operation High Temperature yields better efficiency and more applications MSR Advantages Walk-away safe

The core is already melted Negative temperature and void coefficients Lower fissile and radioactive inventory Low pressure operation - near atmospheric Freeze plugs melt at high temperatures dumping the core to subcritical tanks No operator action needed for fuel dumping High temperature operation Broadens process applications such as hydrogen generation Raises efficiency to 40-44% range compared to LWRs at ~32-34% Can be used to burn existing spent fuel (about 96% of the waste for LWRs) Smaller amount of waste material More efficient nuclear fuel usage No solid fuel assembly

Online refueling Waste not useful for future weapons applications Fuel conversion and breeding easier with continuous reprocessing Important Features of MSRs Radiotoxic Waste Perspective Thorium Conversion Single Salt Concept Development Issues and Design Questions Molten salt reactor (MSR) verses high temperature reactor (FHR) FHR

Has a solid core structure with fluorine salt coolants Achieves higher temperatures than the MSR Higher power densities than gas cooled high temperature designs Requires fuel fabrication Retains the passive safety features What fuel design: TRISO pebbles or rodded fuel MSR Operates in broad range of neutron energy spectrum (burns, converts and breeds) Minimized wastes from fission but serious irradiation of components by circulated fuel Burns actinides in spent fuel as a recycled fuel function No fuel assembly required Two salt system verses single salt system for conversion or breeding advantages

Development Issues and Design Questions Salt types Lithium salts require enriched Li-7 to eliminate tritium generation Good news natural lithium is 92.4% Li-7 Bad news it still needs to be enriched to 99.99% Worse news US would need to scale up production or purchase abroad (Russia or China?) Fluoride salts

Good heat transfer, better energy retention than water, low vapor pressure at temperature, inert to key metals Require close monitoring to remain in a reduced state and avoid corrosion Have small neutron cross sections Melts at about 4590C and boils at about 14300C LiF-NaF-KF melts at 4540C and boils at 15700C but absorbs more neutrons Cl may be a good replacement for F but requires almost pure Cl 37 Beryllium Toxicity is not desirable Avoiding it would require higher temperatures Full scale system may turn up other corrosion issues Development Issues and Design Questions oMobile fission products plating out inventory accountability issues oRemote maintenance required due to high temperatures and high radiation oHow to control tritium production elimination oSome fairly complex chemistry to remove actinides (cleanup of bred fuel for reuse) oOnline fuel processing development oThorium or Uranium Cycle development

World Supplies of Uranium and Thorium Thorium tonnes Brazil 632,000 Uranium Kazakhstan tonnes 842,200 % 14% Australia

595,000 Canada 514,400 8% USA 595,000 Russia 485,600 8% Egypt 380,000

Namibia 442,100* 7% Turkey 374,000 South Africa 322,400 5% Venezuela 300,000

China 290,400 5% Canada 172,000 Niger 280,000* 5% Russia 155,000 Brazil

276,800 5% Uzbekistan 139,200* 2% Ukraine 114,100 2% Mongolia 113,500

2% Botswana 73,500* 1% Tanzania 58,200* 1% USA 47,200 1% Jordan

43,500 1% Other 280,600 4% South Africa 148,000 China 100,000 Norway 87,000 Greenland

86,000 Finland 60,000 Sweden 50,000 Kazakhstan 50,000 Other countries 1,725,000 World total 6,355,000 World total

6,142,600 Breeding New Thorium Fuel Non-proliferation issue of breeding new fuel (also an issue with Uranium-Plutonium cycle) Thorium fuel application requires breeding or conversion since 233U does not exist in nature 233 U is produced from 232th by a neutron absorption becoming 233Pa that decays to 233U ( 232th 233Pa+ 233U) Pa removal highly desirable due to high absorption cross section 233 Pa decays with a 27 day half-life before becoming 233U Pure 233U is a ready-made nuclear weapons grade material Inventory tracking of fissile isotopes is difficult due to the core circulation and plate-out of of the fuel

actinides NOT A PROBLEM FOR OPERATIONAL TRANSIENTS OR FOR BURNING OR CONVERSION WHERE THE 233U STAYS IN THE FUEL! Who is playing and What Designs China SINAP and US cooperation on solid fuel designs China MSR design Russia actinide recycler and transmuter (MOSART/MARS) European community/Netherland SAMOFAR US AHTR and FHR and LFTR, Thorcon, Southern Co MCFR, GE Hitachi UK MOLTEX SSR Canada Terrestrial Energy Transatomic Power TAP Japan Fuji Denmark Seaborg SWaB Elysium Industries US/Canadian India MSBR Chinese Program (SINOP)

Technology R&D Includes fuel fab, online salt reprocessing, technology of pyro processing Corrosion and material lifetime evaluation for development reactors Reactor design development for experimental and demo systems Develop design, safety analysis and technical standards Develop high temperature applications and hydrogen production Very complete R&D to develop the design, design processes and manufacturing of MSRs About 400 staff level Developing two test reactors TMSR-Sf1 and TMSR-LF1 for solid fuel and liquid fuels SF1 Design Parameters Power 10MWt

Lifetime 20year Operation time 100 EFPD for single batch of fuel Average power density 4.0 MW/m3 Fuel element / abundant / 235U load 6cm ball / 17.0% /15.6 kg Coolant 1stloop 2ndloop FLiBe 99.99%Li7 FLiNa K Structure material N alloy, graphite Reactor coolant inlet temperature 6000C Reactor coolant outlet temperature 6500C Vessel temperature / pressure design 7000C / 0.5MPa (abs.) Vessel upper cover temperature designed <3500C 1st/2ndloop coolant flow rate 84 kg/s / 150kg/s Cover gas/ pressure Ar/ 0.15MPa(abs.) European Community Program

o Safety Assessment of the Molten Salt Fast Reactor (SAMOPAR) o Prove safety concepts of Thorium in the breeding mode o Advanced experimental and numerical methods o Break though in safety and optimal waste management o Only one in which the Pa-233 can be stored in a hold-up tank to let it decay to U-233. o 11 participants and is mainly undertaken by universities and research laboratories US Design and Development: FHR FHR a high-temperature reactor that can conceptually have an outlet temperature of 1000 C Core design can be graphite prismatic blocks or graphite pebble form but is designed to be a burner Operates with liquid salt coolant Pebble form of the fuel is called TRISO

TRISO Fuel Pebble Spherical fuel pebble with several regions Center is uranium oxide, carbide or UCO covered by layers of carbon materials There are four layers of carbon, a dense layer of pyrolytic carbon and finally silicon carbide surrounding the uranium fuel Advantages High temperature Low Pressure operation High power density High thermal efficiency Passive safety systems Better retention of fission products if an accident occurs FHR Reactor

Liquid Fluoride Thorium Reactor and FLiBe LFTR Both designs are two-fluid MSRs One fluid is the fuel and the other is the fertile fluid Rapid power changes possible so they can load follow Inexpensive to build and operate LFTR Breeding is done in a blanket with FLiBe and ThF as fertile material Pa-233 captured and allowed to decay to U-233 U-233 converted to fuel and returned to the reactor FLiBe LFTR Uses FLiBe as the salt for both fuel and breeding Breeding salt includes Th Fuel salt circulates through graphite logs Secondary loop coolant is BeF2-NaF ThorCon Underground siting

Scale up of the MSRE reactor Block assembly in a factory and shipped to site Four year change-out cycle of key components Walk-away safety by draining fuel during an accident Closed steam cycle for higher efficiency The ThorCon Nuclear Island. This entire structure is underground Terrestrial Energy IMSR Graphite-moderated thermal reactor Fuel enrichment lower than 5% Core and moderator replaced as a unit every 7 years U235 fuel (UF4) in a fluoride carrier salt Secondary fluid is ZrF4-KF Completed the first of three phases in the Canadian Nuclear Safety Commission's pre-licensing vendor design review Three size units 80 MWt, 300 MWt and 800 MWt

Aim is first operation by 2030 First Business Casualty Transatomic Power announced it is shutting down operations 9/25/2018 Did not believe they can catch up to the leaders Will provide all design information as open source Summary We are at the gold rush stage Early stage development Effort is more software and concepts Less expensive stage of evolution Overly optimistic aura in the excitement of great new things There will be an inevitable shake-out of ideas, providers and demonstrations Now is the time for clear thinking and serious process development

Big issues looming Regulatory process Design process Operations process Thorium potential Breeding and non-proliferation resolution Expect development money and support will be a big factor Hang on: this next generation will be very interesting

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