Thermionic reactor converters

The NPPs based on thermionic reactor converters may also become the basis for nuclear power propulsion systems. There are two possible development lines ... 

A thermionic reactor is composed of an array of thermionic fuel elemerrts (TFEs) in which mtdtiple thermionic converters are connected in series inside an electrically instdating tube, much like cells in a flashhght. In principle, it is possible to design reactor systems with the thermionic converters out of core. This... 

The feasibility of the thermionic reactor system has been demonstrated by in-core converter and TFE tests in the United States, France, and Germany. As of the mid-1970s, four TOPAZ thermionic reactors had been built in Russia and tested at outputs of up to 10 kWe (kilowatts electrical). 

When rhenium is added to other refractory metals, such as molybdenum and tungsten, ductility and tensile strength are improved. These improvements persist even after heating above the rccrystallization temperature. An excellent example is the. complete, ductility shown by a molybdenum-rhenium fusion weld. Rhenium and rhenium alloys have gained some acceptance in semiconductor, thermocouple, and nuclear reactor applications. The alloys also axe used in gyroscopes, miniature rockets, electrical contacts, electronic-tube components, and thermionic converters. 

The record holder for converter life is LC-9, a converter built for NASA by General Atomic as part of the in-core nuclear space reactor program. LC-9 operated with perfectly stable performance for over five years at an emitter temperature of 1970 K. As shown in Figure 12 ( ), LC-9 had an electrode efficiency of 17%, and generated 8 W/cm of output power (80 KW /m ). The converter was still performing stably when tests were terminated for programmatic reasons. This test illustrates well the long life capability of the thermionic converter process. 

Historically, the primary motivation for the development of thermionic converters has been their potential application to nuclear power systems in space, both reactor and radioisotope. In addition, thermionic converters are attractive for terrestrial, solar, and combustion applications. 

The merits of thermionic converters lie in the fact that they operate at higher temperatures, have smaller dimensions and higher efficiency. They may be located inside the reactor core as their cathodes may serve as claddings of fuel elements making a thermionic fuel element (TEE). In this case, the high-temperature coolant loop is eliminated. These designs were developed in the USSR. 

The system based on the bimodal reactor in which electric power is generated in a thermionic converter and thrust is produced by hydrogen expelled through the core (TFE) will allow significantly shorter time of delivery to high-altitude orbits. 

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