Secrecy isn't the obstacle here. Naval reactors are optimized for combat performance, costs be damned. They aren't economically efficient for commercial power generation.

At least Russia is doing fine with SMRs, thought the fuel enrichment level is around 20%. They are building new reactors all the time and they seem pretty efficient. E.g. they have even floating nuclear plant: https://en.wikipedia.org/wiki/Akademik_Lomonosov