Effect of cesium vapor on the bulk conductivity of plasma-sprayed alumina. Final report
The thermionic fuel elements (TFEs) of the TOPAZ-II space nuclear power system sit in cylindrical channels in the reactor core and are separated from the NaK coolant channels by a 50 microns gap filled with helium at around 100 Torr. Ideally there would be no contact between the outer metallic surface of the TFE collector and the coolant channel. However in practice mechanical forces and thermal expansion make it difficult to maintain the 50 microns gap over the full length of the TFE. Therefore in order to maintain electrical isolation of the collector from the reactor body the outside of the molybdenum collector is coated with a thin layer of plasma-sprayed (ps) alumina, around 150 microns thick. Under normal operational conditions this insulating layer has a temperature of around 900 K and must hold off a maximum of 15 V. Under non- standard conditions this may rise to 30 V. Thus the insulator may be exposed to electric fields up to 2{times}10{sup 5} V/m. In a nuclear heated system this combination of temperature, high electric fields and radiation may be a cause of some concern in the light of recent investigations of the so-called RIED` effect (radiation induced electrical degradation). In the present work the authors wish to consider the possibility of another potential failure mechanism for this insulator, that of cesium penetration.
- Research Organization:
- AEA Technology PLC, Materials and Chemistry Div., Didcot (United Kingdom)
- OSTI ID:
- 350683
- Report Number(s):
- AD-A--360096/XAB; CNN: Contract F61708-95-C0002
- Country of Publication:
- United States
- Language:
- English
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