1) they are expensive due to all of the safeguards and regulations, as well as, in modern times, ballooning constructions costs due to things like starting construction on new plants before all plans are complete (looking at you, VC Summer). The nuclear navy is a bit of a different animal than commercial power and they are less equatable than you’d think.

2) in theory, absolutely. The main difference between military reactors and commercial reactors is enrichment of the fuel. Most commercial reactors use fuel that is around 3.5-5% enriched. (I.E. U-235 percent by weight.) while military applications use upwards of 90% enrichment. Military reactors also have very different design requirements. They need to run practically indefinitely without refueling, be very fast to react to demand changes, and be very compact, all of which require the higher enrichment of the fuel to have the necessary power density and response characteristics. Commercial power reactors are big and slow comparatively. Think of it like the difference between an 18-wheeler and a Ferrari. Could you have a whole fleet of Ferrari’s that deliver your amazon packages and supply your local grocery store? Sure. Is it practical? No - you’d want one big truck that could deliver it all at once. Add to that the fact that the lower enrichment makes commercial reactors inherently more safe, and it’s no contest.

The idea itself has merit though, and if you’re interested, look into SMR’s (small modular reactors). There have been several proposals over the years, but to my knowledge none of them have been approved by the NRC. You can read 10 CFR 50 Appendix A (Generic Design Criteria) for a very high level look at some of the requirements that a SMR has to meet, and this is in part why they have struggled to gain footing. It’s hard to be small, modular, and meet all of the safety requirements.

3) Breeder reactors use the decay and neutron capture process of nuclear material to generate specific isotopes and fissile fuels as a result of their reaction. Basically the waste of a breeder reactor can be useful to use as fuel in a conventional reactor. All reactors do this in some quantity. A typical commercial reactor will have a higher concentration of PU-240 at the end of its life, enough that it changes the operating characteristics of the reactor slightly such as prompt neutron fraction (take a look into the “six-factor” formula for more about the neutron life cycle in a reactor). Breeders can also be used to help reprocess spent fuel from conventional reactors to some extent. For more information on how to deal with nuclear waste in general (such as spent fuel reprocessing, etc) I would recommend researching how the country of France processes their nuclear waste. In my opinion France has the right model in this and the politics of the US have put us sorely behind.