Ideal PLAN submarine

A glow? No, I didn't :-S <- MSN emoticon.

A turbo-electric drive sounds okay then.... it gives you greater flexible between your plant and shaft. You shouldn't need gears at all here since electric motors have good torque and can change speeds quickly and independent of the plant which needs to run all the time.

Not sure by what you mean by incompatible. I was thinking of 2 independent reactors. (But nevermind, you don't really need 2 reactors on a SSN.)

Anyway, any comments or faults on the "Orca hole" (The hydrojet propulsion and location of stern sonar)?

Yes, with a turbo electric, the sub design can be independent of the power plant. An electric motor does not appear to produce the same kind of mechanical noises a reduction gear would. By far most nuclear subs use a reduction gear except for the experimental USS Narwhal.

As for having 2 independent nuclear reactors, actually by standard, most Soviet nuclear subs are double reactors, in order to produce the power they need and to have some redundancy. Soviet reactors are not as reliable as the Western counterparts so that is a factor. Only one US sub ever had a double reactor and that was the Trident.

Despite this I don't really see the point of having two reactors one HTGR and one liquid lead. The HTGR does not produce the same amount of power per size, and this kind of set up requires volume consuming systems that offsets the main advantage of using a liquid metal reactor, which is for size. There is no point really in having a second reactor to run just to keep the lead hot and liquid, or pump huge amounts of electricity to keep the lead liquid hot via battery, fuel cell or external power grid. You might as well do the obvious, which is to keep the reactor running anyway in a low power "idling" state.

As for the Orca hole or any other form of water jet propulsion, that is surely going to create much noise and to add on top of that, a huge wake.