Maybe 600kW?Are there any good guesses how much power such a system should generate ?

If I'm not wrong, "normal" AIP systems generate a few hundred KW of power.

A reactor for a "normal" SSN would generate at least 5MW of usable power (shaft/electric) which would be >15MW thermal (for a rather "underpowered" SSN).

I guess a "nuclear AIP" should fit the following demands:

- enough power to be worth the trouble (at least as much power as a "normal AIP")

- significantly smaller and cheaper than "real nuclear propulsion"

- lower maintenance needs than "real nuclear propulsion", perhaps some way to change the whole "power pack" at once after opening a big hatch

- no need for "nuclear engineers" in the crew (or at least significantly reduced compared to "real nuclear propulsion")

Could something like a 500KW (electric) reactor (perhaps 2MW thermal) fit these requirements ?

There is an estimate of 38KW required for a stationary Yuan.

Then there is the smaller Gotland submarine which has 150KW of Stirling Engines for a sustained speed of 5knots.

And the Type-212 has a total of 600KW of fuel cells. It did a 2800km journey in 2weeks at 4-5knots as well.

Plus the Soviets tested 600KW VAU-6 auxiliary reactors on their diesel-electric submarines.