salt-to-helium heat exchangers. Hot helium then flows to turbines of the Brayton rotating unit (three, with one generator each). Six recuperator modules surround the turbomachines. The helium- to-liquid metal (NaK) heat exchangers (coolers) are located in the recuperator housings. NaK accumulators (volume make-up) and pumps are located between the recuperators and the fuel process carousel. High and low temperature NaK and electrical power pass through the interface to the powersat main frame (on left). A small flow of molten salt is continuously circulated through the fuel process module, which accomplishes the following: • Removes protactinium (which decays to uranium) • Removes other wastes • Removes bred fuel • Accepts fertile fuel • Adjusts salt mixture The fuel process module is located on a continuously rotating carousel; the resultant inertial forces simulate gravity and permit operation of the countercurrent separation columns. Module servicing (e.g., waste removal) is accomplished through the docking port on the right. The battery stack on the right is part of the system which allows the reactor module to separate and operate as an independent spacecraft. Propulsion and attitude control systems are located at the left, delta velocity capability is nominally 100 m (328 ft/sec) which allows a malfunctioning reactor system to be undocked and separated a safe distance from the powersat which continues to operate at a reduced power level. In Section 4.9 reasons were given for consideration of a rotating particle bed reactor (RPBR). Two approaches to implementing the RPBR are given in Figure 5-29: 1. Rotate the reactor itself about its vertical axis. This is the type reactor system examined by the Brookhaven National Laboratory. This concept is shown on the left; note that a rotating seal is required in the gas loop. In this configuration 64 individually rotating reactors would be used in a 20 GW ground output unit. This concept does not require a rotary joint of the transmitter. Fig. 5-29. RPBR Approaches 2. Locate the reactor in a rotating assembly to produce a conventional "gravity" field in the reactor. This way the same type reactor can be used in space and on earth. The reprocessing plant, and other reactor systems, could be located in the same rotating assembly. For this configuration a 1 g level at the reactors is produced by rotation at 3 rpm. This means that the rotary joint to the transmitter rotates at this rate—a possible problem. A potential rotating particle bed reactor configuration is shown in Figure 5-30. Fig. 5-30. Simplified RPBR Configuration The circular element is the radiator system, a planar array made up of panels, headers and manifolds as in the solar Brayton configuration. The projected area is 4.71 km^ (1.82 mile^). The transmitter and power generating systems are located at the center of the radiator.
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