An analysis of coated particles fuel compact-general purpose heat source (CPFC-GPHS)

Abstract

The C oated P articles F uel C ompact (CPFC) offers performance advantages for use in the Radioisotope Heater Unit (RHU) and General Purpose Heat Source (GPHS) for Advanced Radioisotope Power Systems (ARPSs), generating a few milliwatts or a few hundred watts of electrical power, respectively, for future planetary exploration. It comprises 238PuO 2 fuel kernels with 5-μm thick PyC inner coating and a strong ZrC outer coating, dispersed in a graphite matrix. The fuel kernels in the compact could be either of a single size (≤ 1200 μm) or binary sizes (300 and 1200 μm) for particles' volume compaction of 62.5% and 72%, respectively. The ZrC coating serves as a pressure vessel for containing the fuel kernels and the helium gas generated by the radioactive decay of 238Pu during storage time before launch and the mission lifetime (15–25 years). The thickness of the ZrC coating and hence, the specific thermal power of the CPFC depend on the estimated maximum fuel temperature during reentry following a launch accident, the storage time before launch and mission duration, and the helium release fraction from the fuel kernels. This paper investigates, the advantage of replacing the four iridium-clad 238PuO 2 fuel pellets, the two floating graphite membranes, and the two graphite impact shells in current State-Of-the-Art (SOA) GPHS with CPFC. The mass, thermal power, and specific thermal power of the CPFC-GPHS are calculated as functions of the helium release fraction from the fuel kernels, up to a full release, and the maximum compact temperature during reentry, from 1500 K to 2400 K. For the same mass and volume, the single-size particles CPFC-GPHS could generate 260 W at Beginning-Of-Mission (BOM), following 10 years of storage, versus 231 W for SOA GPHS. For an additional 10% higher mass, the CPFC-GPHS could generate 340 W at BOM at a specific thermal power of 214 W/kg, which are 47% and 34% higher than those of SOA GPHS, respectively.