I admit to being amused because, if you put "BOREY Class Russian SSBN" into a search engine, you get a lot of stuff about Putin's dangerous new submarine and other domesday assessments until you come to the following 10 July 17 posting highjacked from this website with unusual dispatch.
The BOREY Class Russian SSBN: You Get What You Pay For
As previously discussed, BOREY Class Russian SSBNs should not be described as a “fourth-generation” nuclear submarines. They are – at best – modified third-generation hulls that employ 30+ year-old propulsion and hull components from scrapped AKULA and OSCAR hulls with a Rube Goldberg approach to noise reduction: the use of a turbo-electric (TE) capability for slow-speeds.
The objective of the TE capability is to reduce the acoustic vulnerabilities of the GTZA (Geared Turbine Assembly) OK-9VM produced by the two-stage epicyclic design reduction gear that is difficult to effectively quiet because the design requires the use of gear-tooth combinations that insure the repeated contact (wear) of the same teeth on meshing gears, and because of gear-float due to inferior gear-cutting technology then available.
As also previously discussed, the main propulsion turbine and integral gear system cannot be shut-down during TE mode operations because - if needed for high-speed operations - the GTZA must be brought on-line slowly to avoid uneven heating and shape distortion of turbine blades; hence, it must be kept basically idling during TE mode operations which means that turbine blade-rates, and gear system mesh-rate and hobbing error components are still exploitable.
The following (unclassified) discusses how the US delt with a related issue with S5W reactor systems: (quote) Place the Main Propulsion Turbines “on the jack” to allow even heating during startup. “On-the-Jack” is a term for a small electric motor that keeps the main turbines and the propulsion Bull Gear slowly rotating during engineering plant startup. (end quote)