Processing and Characterisation of Metal Foams as Filters for Space Radioisotope Power Systems

Abstract

The University of Leicester is designing and building a Radioisotope Thermal electric Generator (RTG) and Radioisotope Heater Unit (RHU) with a consortium of companies and collaborative network. Both the RTGs and RHUs have a similar inner containment architecture in which they include a containment vessel that encompasses the radioisotopic ceramic fuel, known as the cladding. To stop the vessel from failing due to over pressurisation due to gaseous helium and oxygen release from the fuel, a frit vent is employed. The frit vent uses a porous material to stop radioactive fines from escaping the containment vessel while also releasing the internal gases at a specific flow rate. The work presented in this thesis was undertaken to determine a suitable material and manufacturing route for the frit vent, to complete the next phase of the ESA ISO scale. This was achieved through the manufacture and characterisation of surrogate frit vents. Copper frit vents were manufactured by employing two different methodologies: the space holder and loose powder sintering route. A systematic frit vent characterisation was undertaken through the development of a bulk sample image analysis tool for determination of filtration performance, and design and manufacture of a helium pressure-drop rig for testing against the helium flow criterion. Frit vents were initially manufactured via the traditional loose powder sintering route, in which they successfully passed the filtration criteria but failed the critical RTG helium flow criterion by around an order of magnitude. An experimental powder mixing study was undertaken to determine the mixing conditions required to attain uniformly dispersed PMMA space holder, resulting in the development of a dispersion image analysis tool. Through the utilisation of the space holder route, frit vents were successfully manufactured to meet filtration and helium flow criterion determined from previous US RTG studies for a fixed frit geometry.</p