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AGA: Arbeitsgruppe Physik und Abrüstung

AGA 6: Nuclear Fuel Cycle and Proliferation

AGA 6.2: Vortrag

Donnerstag, 21. März 2024, 17:00–17:30, PTB HS HvHB

Unusual fissile materials in nuclear weapons — •Matthias Englert¹ and Friederike Frieß² — ¹Institute for Applied Ecology, Rheinstr. 95, 64283 Darmstadt — ²Institute of Safety and Risk Sciences, BOKU Vienna

Today's nuclear arsenals typically utilize fissile materials such as uranium - enriched to over 90% in uranium-235 - and plutonium with an isotopic composition exceeding 93% plutonium-239. It has been long established that lower enrichments of uranium or different isotopic variations of plutonium, like reactor-grade plutonium, can still be employed in nuclear weapons. However, their use comes with drawbacks that render them suboptimal for military purposes. All plutonium containing Pu-239 as well as uranium-235 are categorized as 'special fissile material' under the International Atomic Energy Agency (IAEA) safeguards system. Additionally, uranium-233 is considered a special fissile material, produced through neutron capture in a thorium-uranium fuel cycle and subsequently fissioned in a thorium-fueled reactor to generate energy. IAEA defines U-233, uranium enriched beyond 20% U-235, and plutonium with less than 80% Pu-238 as 'direct use' materials, encompassing their compounds such as irradiated reactor fuel (spent fuel) and mixtures like mixed oxide (MOX) fuel. Not as widely recognized are alternative nuclear materials, specifically higher actinoids formed in nuclear reactors through neutron reactions. Neptunium-237, a fissile material reportedly used in a nuclear test explosion, along with isotopes of americium, fall into this category. While these materials are not currently extensively utilized or separated in the nuclear fuel cycle, future plans for alternative reactor designs addressing nuclear waste transmutation could increase the accessibility of these materials and technologies for their separation.

Keywords: Fissile Materials; Highly Enriched Uranium; Plutonium; Nuclear Weapons; Thorium