AN ANALYSIS OF COATED PARTICLES FUEL COMPACT-GENERAL PURPOSE HEAT SOURCE (CPFC-GPHS)

摘要

The Coated Particles Fuel Compact (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 ~(238)PuO_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 ~(238)Pu 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 ~(238)PuO_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.