Life tests of a thermionic converter

The ES-6-3 six-element thermionic assembly has been tested in a reactor for 2670 h. During the tests the electrical power of the assembly decreased from 550 W, corresponding to a specific power of ∼7 W/cm2, to 75 W. A stepwise decrease in assembly power was observed following any reduction in reactor power; this is attributed to short-circuiting of individual elements, to irreversible increase in temperature of the collectors, and to possible increase in heat loss from the emitter.