Molten Salt Reactors: Removing the risk of meltdown Molten salt reactors use fluoride salts as coolant and differ from standard pressurized water reactors in a number of significant areas- stemming from the differing thermodynamic properties of the salt. Salt, melts at 460deg.C and boils at 1400deg.C- this means that MSRs have extremely high safety margins with regard to meltdown, as operating temperatures are far below the boiling temperature. As well as this, molten salt does not require pressurisation to prevent boiling, unlike water which is pressurised at 150 atmospheres in PWRs. The implications of this are that explosions of pressure as seen in previous disasters are impossible. The lack of pressurisation also means that expensive primary and secondary containments are not necessary, greatly reducing the cost of construction. If a rupture forms, release is greatly restricted by the fact that the salt will solidify once its temperature drops below its melting point- preventing rapid release of radioactive material. In the case of a nuclear disaster in which an emergency shutdown takes place, the coolant and fissile material may easily be immobilised due to the freezing of the salt below the high melting point. Molten salt reactors may either be operated with solid or liquid fuel, dissolved in salt. However both forms benefit from the high operating temperatures of the salt, as thermal efficiencies are significantly higher, often ~45% maximum efficiency. This results in lower fuel expenditure and lower operating costs. Due to the ease of gas removal such as of Xenon, the MSRs have the potential to respond to changes in load much more quickly, meaning they can increase or decrease power in a matter of minutes, greatly increasing profitability by providing peak power on demand. The greatest passive safety advantage of salt as a coolant is its negative temperature reactivity feedback. This means that as it is heated, its reactivity decreases, hence slowing heating and heat transfer. This makes runaway meltdowns impossible. MSRs of various designs are also capable of using thorium derived fuels, which are 4 times as abundant as natural uranium and produce much less long life waste. This will be discussed in depth in future posts. Liquid Fluoride Thorium Reactors and Molten Salt Reactors can match or better the safety, economy, compactness and sustainability of current third and three and a half generation Pressurized Water Reactors [1] The images represent future designs of Fluoride High-temperature Reactors whose modular design mean that they may see use in a wide range of applications, as well as a summary of safety designs incorporated. [1] formatex.info/energymaterialsbook/book/761-768.pdf#sthash.QT03vv3L.dpuf [2] https://engineersaustralia.org.au/sites/default/files/engineers_australia_molten_salt_reactor_talk_v0.5.pdf
Posted on: Mon, 12 Jan 2015 09:59:25 +0000
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