Supercritical CO2

If you have been reading about advanced nuclear reactors, including molten salt reactors, it won’t be long before you start hearing about supercritial CO2.

After I explain what is meant by supercritical CO2, you will understand why they are a match made in heaven.

Supercritical CO2 is just carbon dioxide at a temperature and pressure where it continues to act like a gas, but has the density of a liquid.

Watch this video for the first 30 seconds and then at 3:30 for a minute

Why is this property of CO2 important?

Because it means that turbo-machinery that uses CO2 can be made much smaller than conventional steam turbines.Rankine vs Brayton turbine_0

The low pressure section of a typical steam turbine is about 12 feet in diameter, while a similar power supercritical CO2 turbine would be about 1 foot in diameter.  You can imagine the precision metallurgy in both turbines, with a lot less material in the supercritical CO2 turbine!

Nuclear power plants produce heat that is turned into mechanical energy usually by heating water into steam, which then spins a turbine connected to a electrical generator.

Coal-fired power plants produce heat by combusting carbon with atmospheric oxygen to produce heat.  The heat is turned into mechanical energy and then electrical energy using the same technology of steam turbine and electrical generator.

The maximum conversion efficiency of heat to mechanical energy is limited by Carnot’s theorem

Efficiency = 1 – Tc/Th, where Tc is the cold temperature where heat is exhausted and Th is the hottest temperature in the turbine (without getting into a lot of geek talk)

Since molten salt reactors operate hotter than most typical solid fueled reactors, they can turn more of the heat into useful energy. This coupled with much smaller supercritical CO2 turbines can lead to considerable savings and increased efficiency.

Check out this video of research that Sandia is conducting:

Energy from Thorium also as a good explanation of supercritical CO2.



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