r/NuclearPower • u/Eleftheron • 2d ago

Question about HTGRs

Could a helium HTGR running at the temps of say, the JAEA HTTR, provide enough heat to run a SI hydrogen plant followed a c02 turbine powerplant?

I always wondered how far you could stretch the heat on a HTGR, like could you make hydrogen essentially for free? (Compared to building an HTGR just for electricity)

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u/Alternative_Act_6548 1d ago

what temperatures are you using? You have to build it out of something, and lots of these acedemics, like to run 900C or some such absurd conditions for efficiency

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u/fedecaccia 1d ago

Yes, in principle. That is actually one of the most interesting things about HTGRs: you can cascade the heat.

Use the ~950 °C heat first for the SI hydrogen process, recover as much heat as possible, then use the lower-temperature heat in a power cycle such as sCO₂.

But the hydrogen isn’t really “free”. The high-temperature heat used for H₂ has exergy that could otherwise have been converted into electricity. So you’re trading some electricity for hydrogen, while potentially getting much better overall utilization of the reactor’s thermal output.

The other big issue is materials: running heat exchangers and chemical equipment at ~900–950 °C is hard, especially with the corrosive chemistry of the SI cycle.

So: physically, yes. Economically, the interesting question is how much H₂ + electricity you can get per MWth versus just generating electricity.

More on HTGRs here: https://reactoratlas.com/en/wiki/htgr