Kessler G. Proliferation-Proof Uranium-Plutonium and Thorium-Uranium Fuel...2017

Textbook in PDF format

Chapters 9-14 of the first edition dealt with plutonium from the commercial nuclear fuel cycle as a proliferation problem. As a result of scientific analyses these chapters provided ranges for the isotopic concentration of Pu-238 above which reactor grade plutonium is proliferation-proof.
This second edition deals, in addition, with the possibility of re-enrichment of <20% U-235 enriched uranium of research and test reactors to weapons type high enriched uranium in relatively small cascades of gas ultra-centrifuges. Kryuchkov et al. of Moscow Engineering Physics Institute (MEPHI) in a publication in Nuclear Science and Engineering Vol. 162, p.208-213 (2009) suggested to dope the <20% U-235 enriched fuel with 0.1% of the uranium isotope U-232. This uranium isotope U-232 has a very high alphaparticle activity and, therefore, a higher internal heat source than Pu-238. It also has a relatively high spontaneous neutron activity. In addition, the U-232 isotope is by three atomic mass units lighter than the isotope U-235. During re-enrichment in gas ultracentrifuges it, therefore, would be enriched from 0.1% U-235 enrichment to 11%, whereas U-235 is enriched from <20% U-235 enrichment to about 70%. As will be shown in chapters 15 and 16 this will make <20% U-235 proliferation-proof in several ways.
U-233 originating from the conversion/breeding process in the thorium/U-233 fuel cycle is always contaminated by the uranium isotope U-232. Enrichment of <12% U-233 uranium in gas ultra-centrifuges to weapons type high enriched U-233 (proliferation problem) would similarly lead to higher enrichment of the contaminant U-232. However, U-232 is only one atomic mass unit lighter than U-233. Therefore, this factor of U-232 enrichment differs not as strongly as in the above case of U-235.
For Light Water Reactors operating in the thorium/U-233 fuel cycle the contamination of their fuel by U-232 is sufficiently high after a fuel burnup of 20,000-30,000 MWd/t to make such fuel proliferation-proof against enrichment in gas ultra-centrifuges. This is also valid for the fuel of Fast Breeders having a burnup > 100,000 MWd/t. This is shown in chapters 17 and 18. INTERNET links in chapters 15 through 18 refer to the publishing year 2016