Russian designers propose hybrid powerplant concept for small nuclear submarine

Nikolai Kirillov, a designer from St. Petersburg, Russia, has proposed a powerplant concept for a small nuclear submarine, envisioning a combination of a diesel engine, a small nuclear reactor, and an electric motor to provide the submarine with three operating modes: diesel surface cruising, electric submerged navigation, and sustained nuclear power generation.

Under this concept, the submarine is powered by the diesel engine while surface cruising. The diesel engine drives a fixed-pitch propeller through a gearbox and a dedicated propeller shaft, allowing the diesel to operate as close to its rated conditions as possible to reduce equipment wear.

In submerged conditions, the diesel engine is shut down, and propulsion is provided by a separate electric motor. This motor is paired with a controllable-pitch propeller and draws power from a battery bank.

The core of the concept lies in a small water-cooled nuclear reactor. This reactor does not directly drive the propeller; instead, it converts energy into electricity through an organic Rankine cycle and a generator, maintaining battery charge across different operating modes. Kirillov believes this design can reduce the required power of the diesel engine, cut fuel reserves, and shrink the overall size of the powerplant.

The related patent documents also propose a dual-loop configuration with low coolant pressure. The designer anticipates that, compared with a single-loop design, this arrangement helps reduce the mass and dimensions of the system while lowering radiological risks.