>>1885300>Why are modern submarines powered by nuclear reactors?Because a nuclear reactor is extremely well optimized for energy density compared to alternative options (electric batteries, hydrogen fuel cells, storing both combustants and oxidizers). In submarine doctrines that involve spending long durations underwater, the energy density of the nuclear reactor becomes the highest priority.
There are alternative submarine doctrines where that may not be the case. For example, a coastal-defense submarine fleet does not have the same pressure to remain underwater for days at a time and can usually surface and hide in a safe area to recharge their batteries. In these fleets, electric propulsion using batteries is frequently quieter than an equivalently engineered nuclear propulsion system (though there are debates about what the acoustics of cutting-edge modern nuclear propulsion systems are like, given they'd be classified).
Sorry but I don't feel like googling the other two.
