15.43. The reactor core, pressure vessel, and steam generator arrange­ment is shown in Fig. 15.4. Major design specifications are summarized in Table 15.3. In the vessel, the helium coolant flows downward through the core, where it is heated to an average temperature of 687°C, then flows through an inner portion of a coaxial cross duct to the steam generator. The gas flows downward through a helical heat exchange bundle in which steam is produced in the tubes. This cooled gas then flows upward in an annulus compartment to the main circulator integral to the top of the steam generator vessel. Compressed cool gas returns to the reactor vessel through an outer annulus in the cross duct, then flows upward through another annulus between the core and vessel wall to the top of the core to complete the circuit.

15.44. Decay heat during shutdown may be removed either using the main heat transport loop or through a separate shutdown cooling system driven by a circulator at the bottom of the reactor vessel. In this system, heat is transferred to service water in a separate helium to water exchanger.