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Nuclear
reactors are basically heat engines. As uranium fissions, the breaking
apart of atoms releases energy, much of it in the form of heat, which can
then be used to do work. In a nuclear-powered submarine, reactor heat
produces steam to drive the turbines that provide the submarine's actual
power. The development of compact, safe, and highly reliable pressurized
water reactors for naval use in the early 1950s was the major
technological achievement that made nuclear-powered submarines
possible.
How
Reactors Work
Naval pressurized-water reactors include a primary
coolant system and a secondary coolant system. The primary system
circulates water, which is pressurized to keep it from boiling, in a
closed loop. As water passes through the reactor, it is heated. It then
goes through the steam generator, where it gives up its heat to generate
steam in the secondary system. Finally, it flows back to the reactor to be
heated again. Inside the steam generator, heat energy is transferred
across a watertight boundary to the secondary system, also a closed loop.
The unpressurized water in the secondary system turns to steam when
heated. The steam, in turn, flows through the secondary system to the
propulsion turbines, which turn the propellers, and to the turbine
generators, which supply electricity. As it cools, it condenses to water
and is pumped back to the steam generator.