The three most important americium isotopes, 241Am, 242mAm, and 243Am originate in the nuclear fuel of pressurized water reactors (PWRs), fast reactors (FRs), or accelerator-driven systems (ADSs) in a ratio of 241Am/243Am between ~0.45/0.55 to ~0.85/0.15. The content of 242mAm in the spent fuel of PWRs, FRs, and ADSs is relatively small and varies between 0.08 and 4.5%. Only by dedicated breeding in 241Am fuel and blanket assemblies could this 242mAm content be increased to ~7%. Only the isotope 241Am has a relatively high alpha-particle heat production whereas the isotopes 242mAm and 243Am have a relatively small alpha-particle heat production. All three americium isotopes are spontaneous fission neutron emitters.

In this paper the different isotopic compositions of the three americium isotopes, 241Am, 242mAm, and 243Am are assembled for a number of fuel cycle strategies for PWRs, FRs and ADSs. Then, the critical masses, spontaneous fission neutron sources, and alpha-particle heat power of these different americium compositions are calculated. In a preignition analysis for gun systems and implosion systems, it is shown that only the implosion system would be applicable to the considered americium isotopic compositions. A subsequent thermal analysis with assumptions for the geometry and choice of materials of so-called hypothetical nuclear explosive devices (HNEDs) shows that the high alpha-particle heat power in the fissile reactor americium part would lead to such high temperatures that the surrounding chemical high explosives would melt and self-explode, and the americium metal would melt.

Such HNEDs on the basis of reactor americium as fissile material would be technically unfeasible.