Thermionic conversion for space power application
Efforts to develop thermionic conversion for space power application are discussed. Tungsten,
niobium and Al2O3 were selected as the emitter, collect and insulator
materials for the converter. Uranium carbides and uranium oxide were
selected as candidates for the nuclear fuel. A total of 36 fueled
thermionic converters and
fuel elements were life-tested during 1965 to
1972. These tests, supported by a dozen converter tests and several
material irradiation tests, provided the base
of the in-core thermionic
technology. Unfueled converters demonstrated a life of five years or
more, while fueled converter fuel elements have been operated for one to
one and one-half years. The major limiting factors for converter life
and
performance were: component diffusion through cladding and emitter
cracking for carbide-fueled converters, and emitter swelling for the
oxide-fuel converters.
Various means for mitigating the fuel effects on
converter life and performance were proposed but they were not
thoroughly evaluated.
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