Turbo-Electric drive on nuclear subs?

Well, you’d still need redundancy for survivability, but it sure is tempting. The British FASM (Future Attack Submarine) was to get integrated full-electric propulsion, but it is now unclear what will happen after Astute.

When you say Turbo-Electric is “slower”. Why is it slower? Is it because of reduced efficiency? Or because you can’t push that much power through an electric motor?
Turbo-Electric is converting mechanical energy to electric current, then back to mechanical. So there is a higher loss of energy than direct mechanical connection.
Turbo-Electric seems like such a natural system for nuclear subs. You would only need a single drive system and no additional generators. Right now, a nuclear sub needs mechanical propulsion and a generator set and an emergency electric motor. If it were turbo-electric I would think you could do with a single system that provides propulsion and all electric power.
Maybe that only makes sense when the military requirement of speed and stealth are taken out of the equation.

Barracuda (the new French SSN) will have a reduction gear for high speeds and retain a turbo-electric drive for low speed.

Turbo electric drive is slower. The Americans experimented with it with Tubilee in the 60s and later Glenard P Lipscomb in the early 70s but the speed penalty always ruled it out. The French never had the speed requirements of the U.S, hence turbo electric drive was a technologically much easier way to achieve quietness and with SSBNs in particular speed was not much of an issue. Remember even the Ohio was not designed for speed, hence the use of a natural circulation reactor in its design. Remember this was the Cold War and U.S Submarines had become slower and slower to obtain quieting from Skipjack to Permit to Sturgeon which could make roughly only 26 knots. When Rickover killed Conform, one of the reasons he cited was the need for high operational speeds to escort carriers. Turbo electric drive was clearly incompatable with the speed requirement of Los Angeles and later developments like natural circulation, or the ability for a reactor to circulate coolant without pumps at low speeds using convection (available at low speeds on Trafalgar, Los Angeles, Akula, Sierra), meant you could have silence at low speed and high speed when you needed it which was operationally more desired than covertness at the cost of high speed capability. Natural circulation clearly held much promise to the Americans which was later vindicated in the all natural circulation reactor of the Ohio, its use in Los Angeles to allow very quiet, sprint, drift operations and of course Seawolf which boasted the previously low speed natural circulation range to over 20 knots. Additionally though turboelectric drive reduced noise of gearing, improvements in manufacturing tolerances meant gear teeth could be made finer and with it, the noise of gearing much reduced so the appeal of turbo electric (remove loud gearing) became much reduced. By way of example, the Soviets estimated that the Delta IV could not match Ohio in covertness largely because they could not making gearing to such fine tolerances as the Americans. So the path to quietness could be reached without the speed penalty by a combination of natural circulation, better gearing tolerances, rafting improvements (double rafting in Seawolf, Akula), better and quieter coolant circulation pumps when at high speed and later tiles. Remember this was era of the high speed Alfa, Sierra and Mike threats. Now, of course natural circulation is available up to 20/ 25 knots (Seawolf tactical speed) and pumps are much quieter (big improvements were made with 688 Improved class) so you can have speed without the speed loss of turbo electric drive.