New Publication: Utilizing neutronics modelling to predict changing Pu ratios in UO₂ in the presence of Th

The Nuclear Futures Institute is very pleased to announce a new publication led by Dr Lee Evitts and co-authored by Dr Simon Middleburgh, Prof Bill Lee and Dr Marcus Dahlfors of the Nuclear Medicine Research Group. Lee’s publication can be found in the international journal Progress in Nuclear Energy.

The isotopic fractions of plutonium produced in a reactor are of significant value as nuclear forensic signatures, and the mechanisms of their production and alteration should be investigated thoroughly.

In the production of plutonium in a nuclear reactor, the isotopic composition of the plutonium has been shown to be heavily dependent on the neutron energy spectrum experienced by the uranium under irradiation.

A series of neutronics calculations were made on a typical UO2 PWR setup, introducing (Th,U)O2 MOX rods gradually, to investigate how the presence of Th affects the 240Pu/239Pu and 242Pu/239Pu ratios in the remaining UO2 fuel rods. A relationship is found that links the percentage change in these ratios, with the burnup and Th content in the configuration. In an extreme case, it was found that the presence of Th may increase the ratio of 242Pu/239Pu by as much as 3.5% at low burnup.

Further details of the calculations and results may be found in the full publication available online here.

The ratio of 242Pu/239Pu in the 3% enriched UO2 fuel rods that are exposed to different Th weightings of the MOX fuel, at a burnup of 10 MWd/kgU.
L.J. Evitts, M.R. Gilbert, S.C. Middleburgh, W.E. Lee, M. Dahlfors, Utilizing neutronics modelling to predict changing Pu ratios in UO2 in the presence of Th, Progress in Nuclear Energy, 137.