The system utilizes twin counter-rotating turbines and alternators and a balanced thrust exhaust system. The system layout is shown in Fig. 1. Figure 2 shows the system schematic and again illustrates the configuration common to the open cycle systems. The schematic notes the two pass flow configuration of the core in which the hydrogen enters the reactor and flows up through the outer annulus of fuel pins to the upper plenum, reverses direction, and then flows down through the center array of fuel pins. Reactor. The Boeing concept uses a British Rolls Royce designed reactor, hydrogen cooled with a fuel pin core. The fuel pins are contained within hexagonal modules of triangular pitch. Reactor control is maintained with movable beryllium control wings on the outside of the pressure vessel. Figure 3 shows the reactor and Fig. 4 shows a cross section through the core. Figure 3 shows the flow path of the two pass core. Design operating temperature at the reactor outlet is 1200 K. Turbine. Boeing chose an 8 stage turbine operating at 15 000 rpm. Figure 5 shows the basic layout of the turbine. Generator. The generator for the Boeing design is a brushless wound rotor machine chosen for its reliability and operational efficiency. Figure 6 shows the overall features of the generator. General Electric System description. General Electric has designed a reactor system in the 10s of MW range using a derivative of the reactor (the 710 reactor) designed for the PLUTO program in the 1960s. This reactor is a hydrogen cooled open Brayton cycle and the system configuration is shown in Fig. 7.
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