Radioisotope Thermoelectric Generators Design Research Articles

Impedance spectroscopy characterization of neutron irradiated thermoelectric modules for space nuclear power

The European Space Agency is currently supporting the research and development of advanced radioisotope power systems utilising thermoelectric modules. The performance of thermoelectric modules following exposure to neutron radiation is of significant interest due to the likely application of radioisotope thermoelectric generators in deep space exploration or planetary landers requiring prolonged periods of operation. This study utilises impedance spectroscopy to characterise the effects of neutron irradiation on the performance of complete thermoelectric modules, as opposed to standalone material. For a 50 We americium-241 radioisotope thermoelectric generator design, it is estimated that the TE modules could be exposed to a total integrated flux of approximately 5 × 1013 neutrons cm-2 (>1 MeV). In this study, an equivalent neutron dose was simulated experimentally via an acute 2-hour exposure in a research pool reactor. Bi2Te3-based thermoelectric modules with different leg aspect ratios and microstructures were investigated. Gamma-ray spectroscopy was initially used to identify activated radionuclides and hence quantify irradiation induced transmutation doping. To evaluate the thermoelectric properties pre- and post-irradiation, impedance spectroscopy characterization was employed. Isochronal thermal annealing of defects imparted by the irradiation process, revealed that polycrystalline based modules required significantly higher temperature than those with a monolithic microstructure. Whilst this may indicate a greater susceptibility to neutron irradiation, all tested modules demonstrated sufficient radiation hardness for use within an americium-241 radioisotope thermoelectric generator. Furthermore, the work reported demonstrates that impedance spectroscopy is a highly capably diagnostic tool for characterising the in-service degradation of complete thermoelectric devices.

Analysis of contact through finite element gaps

A numerical technique is described for analyzing contact of disconnected structures through the use of finite element gaps. A special gap element is used, together with a stress invariance principle, to model the contact process. The solution is achieved through an iterative procedure which adjusts the modulus of the gap elements. The numerical procedure is described and results are given for two problems of differing complexity. The first is a classical Hertz problem involving contact between a sphere and a rigid plane. The second problem is concerned with the thermostructural analysis of the beat shield for a Radioisotope Thermoelectric Generator design.