Russian Navy Nuclear-Powered combat AUVs?
Flag If the robotics revolution pushes us towards uncrewed nuclear subs, will Russia have an advantage? This would be because of their ongoing research into unattended underwater nuclear power plants. Based on a Forbes article (here).
Russian Navy Nuclear-Powered combat AUV - Covert Shores

The current generation of submarines are designed around humans. One of the reasons that U.S. Navy and Royal Navy submarines operate so effectively is because of their large crews. With over 100 people aboard they can deal with emergencies and keep the submarine at sea for months on end. Russian attack subs typically have higher levels of mechanical automation and thus smaller crews. But crew fatigue remains a problem, as does underway maintenance, so they generally don’t stay at sea for as long.

Autonomous underwater vehicles (AUVs) are a hot topic. As well as spy missions, they are increasingly being considered to fulfill missions currently requiring manned submarines. These can include being a cruise missile launch platform or sowing minefields. And they could also carry torpedoes, provided that the risks of friendly fire can be mitigated. This is anyway the case with the latest generation of mobile mines. (See article on low-cost armed XLUUV concept).

The U.S. Navy's Orca XLUUV (extra large unmanned underwater vehicle) pushes the boundaries of AUV technology into the traditional submarine space. But Orca is a long way short of the current front line fast attack submarines. Largely this is because it relies on a diesel engine to power itself. Proper submarines, at least in the US / UK context, are nuclear powered. This gives them greater power and virtually unlimited range. And they do not have to come near the surface to recharge their batteries. This, generally, makes them harder to detect and gives them a better chance of escaping if they are detected.

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So could a nuclear-powered attack submarine be fully automated? For the Russians, maybe it could. They have been investing in fully autonomous underwater nuclear power plants. The first which comes to mind powers the ginormous Poseidon inter-continental nuclear-powered nuclear-armed autonomous torpedo. In artists' impressions this was initially drawn as an AUV with multiple torpedo tubes:
Poseidon / Kanyon artworks - Covert Shores
Artist's impressions of Poseidon ('KANYON') showing an AUV with torpedo tubes. The left one appears to be from Russian sources, and the right one from Western sources.

Yet despite often being described as a drone, it's a weapon. It's designed for a one-way trip and doesn't have many of the features normally associated with regular submarine operations.
Poseidon / Kanyon artwork - Covert Shores

But Russia has another type of autonomous underwater reactor intended for continuous operation. The Autonomous Nuclear Turbine Generator (ATGU) is to power seabed infrastructure under the ice cap. And the Malachite design bureau has proposed using it in regular submarines intended for under-ice operations. The ‘Service Submarine’ would still have a crew, but that is for the rest of its mission. The ATGU itself and the propulsion machinery is completely unattended.
Autonomous Nuclear Turbine Generator (ATGU) - Covert Shores

A similar, but physically larger, design is the 'Gidropress’ (ГИДРОПРЕСС) 'Underwater Uninhabited Nuclear Power Modules' (ПНАЭМ = PNAE). This is designed by OKBM and is a scalable 10-50MW reactor. It uses a lead-bismuth cooled fast reactor based on technology developed for the famous Project 705K ALFA Class submarine.
'Gidropress’ (ГИДРОПРЕСС)  'Underwater Uninhabited Nuclear Power Modules' - Covert Shores
So Russia could combine the ATGU or PNAE with drone technology to create the world’s first uncrewed nuclear-powered attack submarine.

Removing humans from the equation doesn’t just save space, it massively reduces the power requirements. According to Rachel Pawling, who teaches naval architecture at University College London, upwards of 30% of a submarine’s power consumption, besides propulsion, is devoted to keeping its crew alive. That spans life support to lighting to frozen food.

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And we could ask ourselves how much of the necessary underway maintenance which a submarine crew is needed to perform is actually caused by systems to support the humans? Without a crew there would be far fewer systems to go wrong (?). This doesn't remove the underway maintenance problem but it could partly mitigate it.

Such an autonomous attack submarine would likely be limited compared to current nuclear powered attack submarines. They'd likely be slower thanks to their less powerful reactors. And noisier due to having less space for sound cancellation layers.

The torpedoes or other weapons would have to be loaded ready-to-fire and not require maintenance while underway. This is anyway the direction torpedoes are headed.

But it would benefit from unlimited endurance (as long as nothing malfunctions), lower cost and, to an extent, it would be expendable. They would only need to return to port for repairs or periodic maintenance. And it would be inherently more powerful than even the largest non-nuclear AUVs are likely to be.

How long it will take the West to develop such technology? Current Western submarine nuclear reactors were built for crewed submarines. That influenced their design in lots of ways, so a completely new reactor project would be needed. And new projects would have to overcome funding and human resourcing challenges. Not to mention a likely environmental backlash of putting unattended nuclear reactors into the world's oceans. Russia doesn't seem to care about that.

So whether completely unattended nuclear reactors on autonomous submarines is a good idea or not, it’s something you are likely to see in the Russian Navy long before any western power.

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