I did some research on Vega sub systems, based on our knowledge of Bismarck class battleships taken from Gas Miners Guild, adopted with the latest reconstruction of the Vega. Though most of the ship was heavily reconstructed, primarily systems of the reactor weren't changed, only adopted to PHWR type, to bring maximum efficiency with less changes in the mechanism.
The PHWR system is a common and reliable technology that has been used for centuries. With all advantages such as low maintenance price, simplicity in repairs and durability is under the air, per turbine maintenance and rods replacement ship is required for high-end service on the shipyard, which, in my opinion, is a bad practice for our fleet.
The big advantage comes with its ability to avoid enriched fuel but in time life expiration I would suggest replacing it with a different type of reactor, which will affect ship persistence. I'm saying about nuclear reactor that Mr. Henrik mentioned previously. While at first impression it seems like technology that wouldn't be able to fulfill ship requirements, the good thing is about its size. It could offer the modularity of the power plant section. Which could extend the non serviceable ship period. In case of reactor replacement it would be possible in open space, without having a shipyard in the backyard. While reactors bay would serve as main source of the energy, each section also can have mounted own second-circle reactors, which could be used per significant damage for main reactor section, to offer incredible vitality even compare to the Hyperion
Further investigation is required, but it depends more on Livadia Shipyard current capacity in rebuilding a ship of such size and current status of the Vega PHWR systems. Oh, and on the side note I heard that engineers on the Livadia almost made it possible to extract coordinates of the beacon coordinates launch. The origin is no longer under the question, it was sent by Vega emergency program.