AMTEC Cell Optimization for Advanced Radioisotope Power System (ARPS) Design 1999-01-2655

An AMTEC cell optimization study investigated various cell design performance tradeoffs for an AMTEC cell operating in a 4-GPHS (General Purpose Heat Source) ARPS using 16 AMTEC cells per system. The design objective was to generate 141 watts at beginning-of-mission (BOM), 112 watts at 6-year end-of-mission (EOM), and 99 watts at 14-year EOM from the 4-GPHS/16-cell system at a system voltage of 28 volts (cell voltage 3.5 volts). Cell performance predictions on a system-level compared the effect of BASE tube number, BASE tube sizing, electrode performance parameters, thermal shield design, and condenser emissivity on cell-level and system- level performance. The selected reference cell design is 2 inches diameter, 4 inches length using electrodes characterized by a B=120 A-K^1/2/m²-Pa and G=10, one cylindrical and 21 conical thermal radiation shields, and eight BASE tubes having a 0.40 inch diameter and 1.0 inch active length. The reference design is projected to produce a system power output of 140-143 watts at 28 volts from the 4-GPHS, 16-cell system configuration. Cell power output at a cell voltage of 3.5 volts is projected to be 8.76 - 8.95 watts/cell. The cell is capable of producing a peak power of 9.0-9.25 watts at approximately 4.0 volts per cell, so the power penalty at 3.5 volts is minimal. Equally important, the maximum BASE tube temperatures are projected to be about 818-821°C, well below the 850°C maximum specification, and evaporator temperatures are predicted to be 788-790°C for electrodes characterized by B=120 A-K^1/2/m²-Pa and G=10. These relatively low temperatures will greatly alleviate material compatibility and material degradation issues within cell components.