LIQUID FLUORIDE THORIUM REACTORS Zack Draper | Physics 486 February 22, 2016

Works cited "Nuclear Fission - Fission Reaction." Nuclear Power. Web. 14 Feb "Pressurised Water Reactor VS Boiling Water Reactor." Clpgroup.com. Web. 14 Feb David, Sylvain, Elisabeth Huffer, and Hervé Nifenecker. "Revisiting the Thorium-uranium Nuclear Fuel Cycle." Europhysics News 38.2 (2007): Web. 14 Feb "How Do Fast Breeder Reactors Differ from Regular Nuclear Power Plants?" Scientific American. 17 July Web. 14 Feb "How Nuclear Power Works." Union of Concerned Scientists. Web. 14 Feb Kharecha, Pushker, and James Hansen. "National Aeronautics and Space Administration." NASA GISS: Science Brief: Coal and Gas Are Far More Harmful than Nuclear Power. NASA, Apr Web. 14 Feb LeBlanc, David. "Potential of Thorium Fueled Molten Salt Reactors." 12 May Web. 14 Feb Niiler, Eric. "Nuclear Power Entrepreneurs Push Thorium as a Fuel." Washington Post. The Washington Post, 20 Feb Web. 14 Feb "Nuclear Energy." National Geographic Education. 24 May Web. 14 Feb "Nuclear Power." Union of Concerned Scientists. Web. 14 Feb "Pros and Cons of Nuclear Energy - Conserve Energy Future." ConserveEnergyFuture. 07 Mar Web. 14 Feb Sorensen, Kirk. Lessons for the Liquid-Fluoride Thorium Reactor (from History). 20 July Web. 14 Feb Stenger, Victor. "LFTR: A Long-Term Energy Solution?" The Huffington Post. TheHuffingtonPost.com. Web. 14 Feb "Could Thorium Make Nuclear Power Safe?" 28 Mar Web. 14 Feb

Nuclear energy If handled correctly, nuclear power is environmentally friendly – sustainable – low operation costs – almost zero greenhouse gas emissions Not used to its full potential

Incentive for advances Nuclear power comes with challenges Nuclear fuels are radioactive Reactors produce long lived radioactive waste Several well known catastrophes Nuclear weapons and reactors go hand in hand LFTRs could decrease risk Nuclear waste storage

Fission is the process of breaking apart nuclei Gamma rays and nucleus fragments carry energy About 80% (170 MeV) is kinetic energy Combined mass of new smaller nuclei is less than mass of original nucleus E = mc 2 Nuclear fuels millions of times more energy dense than chemical fuels How fission works

Fission as a power source Not efficient to wait for radioactive decay Neutron fired at nucleus gives energy to overcome strong force When split, more neutrons are produced These neutrons can fission other nuclei Thermal energy can boil water, turn a turbine, and create electricity

Cross section depends on neutron energy Usually much larger at low energies Moderators slow down neutrons, increasing probability of fission Low mass nuclei are most effective Water is used as a coolant and moderator LFTRs use graphite rods as a moderator Thermal reactors

Do not use moderators to slow down neutrons Average speed of thermal neutrons is around 2200 m/s Average speed of fast neutrons is around 9 million m/s (3% speed of light) Fast reactors use higher fuel enrichment to sustain chain reaction Fast neutrons can release energy from U-238 Fast reactors

Controlling the reaction Control rods regulate the fission rate Composed of materials which absorb neutrons (e.g. boron, silver, indium or cadmium) Attached by electromagnets If power fails control rods fall and stop the reaction LFTRs can include a freeze plug which is cooled by a small fan If power fails the plug melts and fuel drains and cools

Uranium fuel cycle Only 0.7% of natural uranium is fissile U-235 Traditional reactors require enriched uranium as fuel Once fissioned, more needs to be enriched and added to core

Breeder reactors Breeders contain fissile and fertile fuel Fissile material releases two or three neutrons Some neutrons split fissile material, continuing chain reaction Others are absorbed by fertile fuel, which transmutes into fissile material A reactor that creates more fissile material than it consumes is called a breeder reactor

The thorium fuel cycle Uranium-233 fissions producing two or three neutrons Thorium-232 is bombarded with neutrons and transmuted to protactinium-233 Protactinium decays to uranium-233, a fissile material Uranium is extracted from blanket and put in core Earth's crust contains much more thorium than uranium Enough thorium to provide energy for hundreds of thousands of years

LFTRs were first investigated in 1960s Helping create weapons was a benefit of using U- 235 Potential to create weapons is now a disadvantage Thorium decreases need to enrich uranium Reduces plutonium created Thallium-208 makes it difficult to create bombs Preventing proliferation

Diminishing nuclear waste Conventional reactors transmute U-238 to Pu-239 (half life of 24,000 years) Containment vessels must withstand high temperature, radioactive decay, and weathering Using thorium, little waste is transuranic The rest has a half-life of only 30 years Radiotoxicity will reach safe levels in 300 years

Pressurized water reactors Pressurized water reactors keep water at high pressure to prevent boiling Heat is transferred to a second water reservoir outside core Here, it is allowed to boil, produce steam, and power a turbine

Boiling water reactors Boiling water reactors use one water supply Water in core is pumped around reactor in a closed cycle Water boils and powers turbine before condensing and being recycled

Benefits of molten salt coolants Water coolant can rapidly expand as it boils Water can produce explosive hydrogen Molten salts have boiling points much higher than water and cannot form hydrogen gas Radioactive materials are trapped in fluoride salt Explosive hydrogen gas at Fukushima

The future of LFTRs Very few molten salt reactors have been built Technology must be developed further Critics argue the benefits are not enough Significant cost of replacing or converting existing reactors Japan, China, the UK, and private companies are investing in new reactors

Conclusion Public perception of nuclear energy is a significant obstacle Catastrophic events are remembered, but other forms of energy kill silently Replacing fossil fuels with nuclear energy saved 1.8 million lives between 1971 and 2009 LFTRs offer solutions to the downsides of nuclear energy Would offer cost-effective, plentiful energy while combating climate change