Nuclear Submarine Reactor (S6G/PWR2)

S6G and PWR2 are naval pressurized-water reactor designs that power attack and ballistic-missile submarines. The S6G (S = submarine, 6 = sixth core generation, G = General Electric) drove the US Los Angeles-class SSN. PWR2 is the Rolls-Royce reactor in the Royal Navy’s Vanguard-class SSBN and Astute-class SSN, designed for a core life long enough to last the boat without refueling. A PWR uses the reactor heat to raise steam in a separate loop that turns the propulsion turbines, giving the boat near-unlimited submerged endurance limited only by food and crew.