Proliferation Resistance of Americium Originating from Spent Irradiated Reactor Fuel of Pressurized Water Reactors, Fast Reactors, and Accelerator-Driven Systems with Different Fuel Cycle Options

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.