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August 20, 2013

Summary of Safety and Design of Molten Salt Reactors

Backup slide information from David LeBlanc presentation on Molten Salt Reactors at TEAC 5

What factors differentiate between various Molten Salt designs?
• R and D required and level of technological uncertainty
• Amount and type of startup fissile load and thus deployability
• Whether fission product removal is used and if so, its degree of difficulty
• Reactivity coefficients
• Degree of Proliferation Resistance

Advantages of all Molten Salt Reactors Safety

• No pressure vessel
• No chemical driving forces(steam build up or explosions, hydrogen production etc)
• Almost no volatile fission products in salt
– They are passively and continuously removed
– Both Cesium and Iodine stable within the salt
• No excess reactivity needed
– Even control rods are optional
• Very stable with instantly acting negative temperaturereactivity coefficients
• Passive Decay Heat removal



Advantages of all Molten Salt Reactors Long Lived Waste
• Fission products almost all benign after a few hundred years
• The transuranics (Np,Pu,Am,Cm) are the real issue and reason for “Yucca Mountains”
• All designs produce less TRUs and can be kept in or recycled back into the reactor to fission off

Advantages of all Molten Salt Reactors Resource Sustainability
• Once started breeder designs only require minor amounts of thorium(about 1‐10 tonne per GWe year)
– 30 k$ of thorium= 500 M$ electricity
– Must include processing costs though
• Converter designs are far simpler and only require modest amounts of uranium
– Typically 35 tonnes U per GWe‐year versus 200 tonnes for LWRs
– Annual Fuel cycle cost ~ 0.1 cents/kwh

DMSR Extremely High Proliferation Resistance
• Plant does not process the fuel salt
• Uranium always denatured, at no stage is it weapons usable
• Any Pu present is of very low quality, very dilute in highly radioactive salt and very hard to remove
– About 3 times the spontaneous fission rate
of LWR Pu and 5 times the heat rate (72.5 W/kg)
• No way to quickly cycle in and out fertile to produce fissile

The World Needs Nuclear
• LWRs and HWRs mature technology but little area for improvements and widespread adoption unlikely
• Supercritical Water
– Extremely challenging material science,still many years off
• Gas Cooled Prismatic or Pebble Beds
– Good safety case, economic smarginal
– Must co‐develop fuel fabrication and Brayton turbines
• Fast breeders
– Decades and billions later,still unproven economics
• Small Modular LWR or FBRs
– Fine for niche markets, unlikely a base load competitor
• Molten Salt Reactors have the potential to be true game changers

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