TRISO sounds like another example of solving the wrong problem. Nuclear's big problem isn't safety, it's cost.

TRISO will also make dealing with spent fuel more difficult, as the dry casks are going to have to be much larger.

But the high cost of nuclear power is probably due to the extraordinary (and perhaps very excessive) safety procedures, no? It's not like the raw material or basic principles are very expensive. So I presume the idea is to hope that having a more intrinsically safe fuel will allow those expensive safety procedures to be relaxed (although, given the sclerotic nature of nuclear regulation, probably not).

The safety procedures don't help the cost, but even the non-nuclear part of a nuclear power plant is expensive. The "nuclear island" is just 1/3rd the cost of a nuclear power plant. All externally heated thermal power plants have become uncompetitive now. Not just nuclear, but also coal, geothermal, and concentrating solar thermal.

So, TRISO is depending not just on the nuclear island being cheaper, but the non-nuclear part somehow becoming less expensive. This probably involves very high temperature, for example for nuclear air Brayton. But any time you go to higher temperature material problems rapidly accumulate.

In any case, there will always be a cost premium to the nuclear part of a nuclear power plant, if only because it has to be very reliable because it can't be repaired if something serious breaks. In (say) a coal fired power plant one can send workers into the guts of the shut down plant to fix or replace things. In a reactor, I don't think that's possible, even if the fuel has been removed. The residual radioactivity is too high.

Thanks.

> All externally heated thermal power plants have become uncompetitive now. Not just nuclear, but also coal, geothermal, and concentrating solar thermal

Are you saying that an externally heated power plant is unlikely to be cost competitive even if the source of energy is free? If not, your overall comment doesn't make sense to me. If so, that's an extraordinary that could very well be true, but I haven't heard anyone argue it and I'd be extremely interested in further reading/links/citations.

Yes, that is the direction things are going in. The remaining thermal power technology that's still (for the moment) viable is combustion turbines, which are internally heated (combined cycle does have an externally heated bottoming cycle, but only 1/3 the power output goes through that, and it shares the generator with the combustion turbine proper.) But even combustion turbine sales are falling; that's what's gotten General Electric in such trouble lately.

Much appreciated! Are there any forward-looking doc's you can recommend that discuss this in more depth, especially any that try to get at the basic physics or economics? It's truly startling to me, and to the extent it's true it really changes the way people should think about future energy tech.

Yes this is the idea. Cost in nuclear is completely coupled to safety. The hypothesis of triso is to reduce costs by improving safety.

Also, triso allows temperatures that allow nuclear heat to be used directly in industrial processes and thermal energy storage. These can also improve economics.

The FHRs seem like a nice combination of the safety of Triso fuel and the higher power density and low pressure of MSRs. Wonder why they haven't been studied more..

It is a pretty new reactor idea, and has lots of benefits. It was popularized recently by MIT Professor (formerly of ORNL) Charles Forsberg. Here's a full presentation showing the case from 2012 [1].

[1] https://whatisnuclear.com/assets/FHR_Project_Presentation_Ja...