Development Concept for a High-Efficiency Cascaded Thermoelectric Radioisotope Power System

Since the 1960s there have been numerous development activities on high-impact material and device-level technologies that could be integrated into current or future radioisotope power systems ( RPS) to enhance their performance. One recent concept study proposed cascading thermoelectrics to convert some of the waste heat from the Multi-Mission Radioisotope Thermoelectric Generator ( MMRTG) into electrical power. The first-order evaluations of the concept study suggested that performance improvements to beginning-of-life ( BOL) and end-of-design life ( EODL) power could be achieved by integrating bismuth telluride ( Bi2Te3) thermoelectric modules into the MMRTG design. This paper discusses a proof of concept development approach to determine the BOL and EODL performance gains that could potentially be obtained by employing Bi2Te3 thermoelectric modules in an RPS as a second stage in a cascaded architecture. The principal efforts embedded in this approach entail an iterative modeling and analytical process to arrive at a Stage 2 module design coupled with a heat rejection system design that enables the cascaded thermoelectric system to operate at satisfactory performance levels. This paper addresses some of the design considerations that will need to be addressed at the system level. For the purposes of this study the MMRTG characteristics and properties are employed as the basis for this paper.