Modeling of Am-241 as an alternative fuel source in a radioisotope thermoelectric generator

Abstract

Radioisotope thermoelectric generators (RTGs) have been utilized in the USA to power satellites and space exploration equipment for over half a century. In our preceding paper, Dustin and Borrelli (2021), we assessed the performance of 241Am as an alternative to 238Pu by modeling the specific decay-heat and gamma spectra of several potential radioisotopes in SCALE-ORIGEN, and comparing these with 238Pu An analysis of heat output, heat stability, safety, availability and required mass showed that of the isotopes reviewed, 241Am had the greatest potential for replacing 238Pu, with additional design considerations. In our current work, we have assessed radiation transport for two configurations of an 241Am powered Multi-Mission Radioisotope Thermoelectric Generator (MMRTG), due to the potential health effects for operators, fabricators, and others with the potential to be exposed to neutrons and lower energy gamma rays. We have modeled the use of americium as a fuel source replacement for plutonium in current MMRTG designs. The assessment has been performed using MCNP6, in terms of neutron and gamma emissions that might interfere with sensitive equipment and power system production. The radiation transport behavior in terms of dose rate of the 241Am fueled models is compared with that of a 238Pu fueled model. Additional work was performed to validate modeling simplifications with regards to thermocouple material configurations.