Evaluation of Self-Protection of 20% Uranium Denatured with ²³²U Against Unauthorized Reenrichment

In the opinion of some experts in problems of nuclear nonproliferation, the threat that subnational terrorist groups may become owners of gas centrifuges is real. If enrichment of feeding uranium increases from 0.7 to 20%, then the scope of separative works and amount of the feeding uranium needed for uranium enrichment up to the weapons-grade level decreases by many times. In this connection it can be expected that a potential nuclear proliferator will use gas centrifuges for illegal reenrichment of 20% uranium, taken from export deliveries for research reactors or from any other sources, up to weapons-grade quality and then manufacture a crude nuclear explosive device. These reasons indicate that besides reduction of uranium enrichment to 20% ²³⁵U, other measures may also be required to upgrade self-protection of 20% uranium against its unauthorized reenrichment.

Denaturing of 20% uranium due to the admixture of small ²³²U amounts (~0.1%) creates an effective barrier against its renrichment up to the weapons-grade level because in the reenriching process the following occurs: (a) the content of ²³²U increases; (b) the internal source of alpha radiation intensifies; (c) UF₆ molecules are destroyed by alpha particles from decays of ²³²U with generation of low-volatile uranium fluorides and free fluorine; and (d) the neutron emission rate intensifies too, and this results in a cardinal reduction of energy yield from the chain fission reaction (CFR) by three orders of magnitude. So, uranium denatured with ²³²U becomes quite unattractive for potential nuclear proliferators.

The authors are continuing the studies on the effects induced by the ²³²U admixture on the radiation resistance of UF₆ and on the energy yield of CFR in reenriched uranium.