Abstract
Radioisotope thermoelectric generators (RTGs) have been utilized in the USA to power
satellites and other space exploration equipment for over half a century. RTGs are essential
for deep space exploration where solar energy is negligible. 238Pu is the current fuel source
for RTGs due to several favorable properties, such as high decay heat and minimal gamma
radiation emission. The supply of 238Pu is dwindling rapidly, but 241Am has emerged as a
potential substitute.
We have assessed the performance of 241Am as an alternative to 238Pu by modeling
the specific decay-heat and gamma spectra of several potential radioisotopes in SCALEORIGEN, and comparing these with 238Pu. An analysis of half-life, paired with decay heat
and gamma output demonstrated that, of the isotopes reviewed, 241Am had the greatest
potential for replacing 238Pu, with additional design considerations. 241Am had a specific
decay heat about 1/5th that of 238Pu, and emits gamma radiation at about 50 keV. This
leads to additional mass requirements for fuel and possibly shielding.
Due to the potential health effects for operators, fabricators, and others with the potential to be exposed to these lower energy gammas, as well as impacts on sensitive electronics,
we assessed radiation transport for an 241Am powered Multi-Mission Radioisotope Thermoelectric Generator. 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 gamma emissions that might interfere with sensitive equipment and consequently
the potential for additional shielding needed to mitigate such interference. The radiation
transport of the 241Am fueled model is compared with that of a 238Pu fueled model.