Chinese modular high temperature nuclear reactors reach full power and 42% thermal efficiency.

[NNadir]

5. These are excellent questions John, and would apply to Triso fuel using air as a working fluid.

The other issue would be oxidation of the TRISO itself.

It's not at all what I have in mind however. The system I envision would not be exposed to a neutron flux, but rather to gamma radiation as part of a heat exchange network. It's a very different system. It would take a very long time to describe the details; I've been working to get these ideas into my son.

(Again, I'm not a TRISO kind of guy.)

I would never dream of creating carbon-14 in air, although I have no problem with it in fuel. In many ways, carbon-14 is a potentially useful material, particularly when the world runs out of helium, which it will. Carbon-14 does not have a neutron capture cross section of zero like helium, but to my knowledge, it has the lowest capture cross section of any other nuclide except helium; close to deuterium, but, if memory serves me well, slightly lower than deuterium across most of the neutron spectrum. It thus has a remarkable potential for high neutron efficiency, a key issue if humanity chooses to scale nuclear energy rapidly, as it must do to have any chance to function at a decent level in a sustainable world.

The other issue you raise, nitrogen oxides - albeit not nitrous oxide directly - are of course issues with other devices using compressed air, including jet engines. At high temperatures nitrous is an oxidant; it will support combustion. What is formed in hot compressed air, for example in a diesel or Otto engine, is nitric oxide (NO) and (mechanistically via oxidation of NO) nitrogen dioxide, NO2. These are thermodynamically unstable compounds actually, and can be (and are in automotive catalysts) destroyed by catalysis with palladium, rhodium, and ruthenium, all of which are components of used nuclear fuels. (Palladium will be slightly radioactive, unless it is obtained from the decay of ruthenium 106.)

The brilliance of Per Peterson's design, although, again, it's not the kind of reactor I would choose to build in a fantasy world where my opinion was sought, is to remove the issue of gas flow. It's a FLIBE system as I understand it. I don't like FLIBE for a number of reasons, but even if it's not ideal (to my mind), it is still excellent compared to say, burning dangerous fossil fuels. I like the KAIROS reactor overall, mostly because it will be built. However, I consider it a local maximum, not a global maximum. I'm a fast neutron spectrum kind of guy.

Thank you for your excellent remarks.