A study is in progress at Texas A&M University to utilize computational models and experimental methods to reliably predict the unique intrinsic signature in the weapons-grade plutonium separated from a low burned CANDU (CANada Deuterium Uranium) thermal reactor fuel. This unique intrinsic signature will be compared with the experimental measurements consisting of Plutonium URanium EXtraction (PUREX) reprocessing of natural UO2 samples irradiated in the Oak Ridge National Lab-High Flux Isotope Reactor (ORNL-HFIR). The CANDU reactor can produce weapons-grade plutonium, if the fuel is discharged intentionally at low burn-up (1,000 MWD/MTU). CANDU core modeling is made using MCNPX-2.7 radiation transport code. MCNPX-2.7 burn-up calculations can determine the resulting isotopic makeup of actinides, fission products and trace elements in the discharged fuel. The specific isotopes for the analysis were chosen based upon their half-lives, activity, and the fuel reprocessing decontamination factor. The discharged fuel of interest was a single bundle of natural UO2, which saw a burn-up of 1,000 MWD/MTU. During the CANDU reactor core burn-up simulation, certain fuel channel bundles were replaced with fresh ones to simulate the process of on-line refueling of the reactor; however it was later determined that utilizing a single bundle computational model with reflective boundary conditions on all sides was sufficient. The single bundle was burnt to the desired burn-up and the final fuel composition of that bundle was used in the isotopic analysis. The signature of separated plutonium along with fission product contamination in the CANDU reactor will be compared to that produced from a fast breeder reactor (FBR). This paper presents the modeling efforts and analysis of the CANDU-type reactor and a separate paper is submitted in this meeting's proceedings on the FBR modeling and analysis. The differences in the neutron energy spectrum of the reactors can cause variations in the isotopes of plutonium, fission products and other minor actinides produced between the two reactor types. Correlations between the findings from the two different reactor types will be investigated, along with being compared to the experimental data (in future). The goal is, if smuggled weapons-grade plutonium is caught, analysis of intrinsic isotope signature associated with it should be able to ascertain the type of reactor that produced it. The experimental data is not yet available and will become available in the latter half of this project.
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