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J.M. Osborn, T.M. Coles, and S.S. Chirayath, "Trace Fission Product Ratios for Nuclear Forensics Attribution of Weapons-Grade Plutonium Separated from Fuel Irradiated in Thermal and Fast Reactor Types," 55th Annual Meeting of the Institute of Nuclear Materials Management, Atlanta, Georgia, 20-14 July 2014.


A computational and experimental nuclear forensics study on weapons-grade plutonium produced in a fast and thermal reactor neutron environment is in the final stages at Texas A&M University. The main objective of the project is to reliably predict and measure unique intrinsic physical characteristics of separated weapons-grade plutonium. The study is on plutonium that could be separated from low fuel burnup of about 1 MWd/kg. It is anticipated that the differences in neutron energy spectra in these two reactor types as well as the fission yield differences between the fuels used in them would result in variations in isotopes of plutonium, minor actinides, and fission products. The radiation transport code, MCNPX-2.7 is used to model the reactor cores, perform fuel burnup simulations and to estimate actinides and trace elements composition in the discharged fuel at low burnup. Isotopes selection was done based on the amount of isotope production, half-life, activity, probability of detection, and the isotope's Plutonium Uranium Recovery by EXtraction (PUREX) decontamination factor. Ratios of the selected isotopes' concentrations and activities per 1 kg of total plutonium, with a decontamination factor (10^6) applied, were calculated for both the reactor types. A comparison of results between the two reactor types was done to identify isotopes with reactor dependencies. A suite of isotopic ratios were then selected which would be useful for quick and accurate nuclear forensics attribution of the source reactor for interdicted weapons-grade plutonium. An uncertainty analysis on the isotope concentration due to the use of Monte Carlo methodology was completed. Fuel sample neutron irradiation for the fast reactor case was conducted at the Oak Ridge National Lab-High Flux Isotope Reactor (ORNL-HFIR), by modifying its thermal neutron spectrum at the sample location to a fast neutron spectrum. Bench scale PUREX process on these neutron irradiated samples is in progress at the Texas A&M Radiochemistry laboratory to separate plutonium from fission products and uranium. The experimental data will become available in the latter half of this investigation for comparison and verification of the computational results. Logistics arrangements for the uranium sample irradiation in the thermal neutron spectrum are in progress.

Associated Project(s):

  • Plutonium Fingerprinting for Forensics (PuFF) Project

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