The current fleet of nuclear plants run continuously and are refueled, typically one third of the fuel is replaced, after a period of about 2 years. The very high energy density of uranium, which accounts for the environmental superiority of nuclear power, means that at 3000 MWth plant run on plutonium - my favorite nuclear fuel - would consume about 3 kg of fuel a day, since the energy density of plutonium is approximately 80 TJ/kg.
There are no commercial energy systems in the world other than nuclear plants themselves, that can match this mass efficiency. A 3000 MWth coal plant requires trainloads of fuel per day.
At the end of fuel life, used nuclear fuel typically contains about 4% fission products, meaning that about 4% of the actinides have been consumed. This means that the actinides are available for recovery and reuse after removal of the fission products, or with minor mechanical reprocessing as in the DUPIC fuel cycle.
Unfortunately the current fleet of nuclear reactors, dominated, albeit not completely, by PWR and BWR operate at low thermal efficiency, as they are largely Rankine type steam plants. These typically operate at 33% thermal efficiency. This is unfortunate, because nuclear fuel is extremely hot during plant operation. In theory this allows for very high thermal efficiency. Modern materials science has developed options for exploiting high temperatures to increase efficiency, notably with thermal barrier coatings developed for jet engines (Brayton cycle devices) and combined cycle devices.
I have convinced myself that heat networks can be built using nuclear fuels which may reach, even exceed, 70% thermal efficiency, exceeding the best thermal efficiencies achieved by dangerous natural gas fueled combined cycle plants, which can approach 60%. Some of the 70% thermal efficiency would involve the direct conversion of heat into chemical energy, captive hydrogen to make fuels, but the thermodynamic penalty normally associated with storing energy, would not matter since it would represent energy normally rejected to the environment as waste heat.
Although I'm not an MSR kind of guy - I don't oppose MSRs, I just think there are better options - the use of heat networks are very possible for MSRs. The Wyoming hybrid reactor being build by Terrapower will apparently store thermal energy in molten salts. I'm OK with that; it's not the best option, but it's certainly a good option. It will however not use molten salt fuels, but molten salt heat transfer, something I regard as a very, very, very, very good option. The options I recommend to my son will involve some salt based heat transfer.
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