Experiments with a fission-heated plasma diode

An account is given of the general arrangement and construction of two in-pile thermionic convertors. The cathode material was sintered uranium carbide-zirconium carbide in solid solution of composition 67%UC, 33%ZrC by weight. The experiments were conducted in the Pluto reactor at AERE, Harwell. Space-charge neutralisation was achieved by arranging for caesium vapour to be present in the cathode/anode interelectrode space. The two convertors differed only in the method used to control the caesium vapour pressure and anode temperature. Cathode temperatures were varied up to values of the order of 2000°C with stainless-steel anode temperatures of 700°C, the anode rejecting heat through a helium gas gap to the reactor heavywater coolant. A maximum current of 132A at 0.3V was obtained from a 10cm2 emitter feeding into an unmatched load. Current variations were observed during a 36 h life test.