Performance analysis of coated plutonia particle fuel compact for radioisotope heater units

Coated plutonia particle fuel has been proposed recently for use in radioisotope power systems and radioisotope heater units for a variety of space missions requiring power levels from milliwatts to tens or even hundreds of watts. The 238PuO2 fuel kernels are coated with a strong layer of ZrC designed to fully retain the helium gas generated by the radioactive decay of 238Pu. A recent investigation has concluded that helium retention in large-grain ( > 200 mu m) granular and polycrystalline fuel kernels is possible even at high-temperatures (> 1700 K). Results of performance analysis showed that this fuel form could increase by 2.3-2.4 times the thermal power output of a light weight radioisotope heater unit. These figures are for a single-size (500 mu m) particles compact, assuming 10% and 5% helium gas release respectively, and a fuel temperature of 1723 K, following 10 years of storage. A binary-size (300 and 1200 mu m) particles compact increases the thermal power output of the RHU by an additional 15%.