Savannah has a pressurized light-water reactor (PWR). The reactor core contains fuel assemblies which are cooled by high pressure water (1750 PSIA), which is circulated by electrically powered pumps (the primary cooling system). The amount of heat generated is controlled by the position of the control rods (boron steel rods that can be raised or lowered between the fuel rods) and the temperature of the primary cooling loop water (higher temperature yields lower power).
Inside Reactor Containment Vessel Forward of Reactor can be seen the large reactor pressure vessel (painted in orange). Inside the reactor are the fuel and control rods that are used to generate heat and control the nuclear chain reaction. Around the rods circulates the high pressure, high temperature (around 500 degree) water of the primary cooling loop.
On the port side is one of the two steam generators on top connected to its heat exchanger at the bottom by downcomers and risers (all painted in purple). The primary loop water circulates through small tubes in the heat exchanger. Around it is the water that is heated to create steam that powers the turbines in the engine room. Forward of reactor and steam generators is the base of the pressurizer (in grey), It is a large tank to allow room for the expansion and contraction of the water in the primary loop. Forward on port is an effluent condensing tank (in white.)
In the illustration above the primary (high pressure, radioactive) water cooling loop is in red. The secondary (low pressure, non-radioactive) water and steam loop is in blue.