Effect of cesium vapor on the bulk conductivity of plasma-sprayed spinel. Final report
The potential advantages of using magnesium aluminate spinel (MgAl{sub 2}O{sub 4}) in the thermionic fuel elements (TFEs) of nuclear heated space reactors have been described in a previous report. In particular, its apparent resistance to radiation damage is attractive. In ref. (1) it was demonstrated that the surface electrical conductivity of single crystal spinel in cesium (Cs) vapor was of a similar magnitude, but in fact somewhat lower than that of sapphire. On this basis the authors concluded that, from the point of view of surface electrical degradation in Cs, single crystal spinel would be suitable for use as the insulator in the metal-ceramic seals in a TFE. The question then arises as to the possibility of using spinel, in plasma-sprayed form, as the collector insulator, instead of alumina (the material presently used). The potential benefits of spinel are, if anything, even greater here since the combined effects of radiation, temperature and high electric fields are most severe for this insulator. Under normal operating conditions this insulator is not exposed to Cs vapor. However if a metal-ceramic seal should leak then Cs can diffuse into the helium gap between the collector and the NaK coolant channel and coat the outside of the plasma-sprayed insulating layer. In a previous report (2) the authors have demonstrated that Cs vapor is able to penetrate the bulk of plasma-sprayed (ps) alumina and increase its electrical conductivity by many orders of magnitude. In this report they describe the results of a number of similar experiments performed on ps spinel. The experimental techniques have been described in ref. (2) and will not be repeated here.
- Research Organization:
- AEA Technology PLC, Materials and Chemistry Div., Didcot (United Kingdom)
- OSTI ID:
- 350682
- Report Number(s):
- AD-A-360066/XAB; CNN: Contract F61708-95-C0002; TRN: 91310268
- Resource Relation:
- Other Information: PBD: 6 Aug 1995
- Country of Publication:
- United States
- Language:
- English
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