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5/17/2017  |   1:30 PM - 1:55 PM   |  1

Evaluation of thermophysical properties and microstructure of U-Pu-Zr metallic fuels

Featuring high burn-up, high fissile and fertile isotopic density, inherent safety characteristics, and favorable thermal response, actinide transmutation metallic fuels are considered to be among the most promising fuel classes for next generation fast nuclear reactors. During reactor operation, it is anticipated that fluctuations in chemical potential along the temperature gradient will lead to migration and redistribution of constituents between radial zones of the cylindrical fuel pin, resulting in inhomogeneities in both composition and thermophysical properties, and hence unpredictable fuel performance. Owing to limited experimental fuel performance data in which to ultimately select and certify a transmutation fuel type, different compositions of options uranium-plutonium-zirconium (U-Pu-Zr) alloys have been investigated. Complementary techniques were employed to characterize the phase distribution, microstructure, and thermophysical properties of unirradiated U-Pu-Zr fuels in both the as-cast and annealed condition. These techniques include differential scanning calorimetry (DSC), laser flash diffusivity (LFD), and scanning and transmission electron microscopy (SEM and TEM, respectively). DSC measurements did not reveal the expected, individual phase transitions predicted by the ternary phase diagram but showed two convoluted transitions upon heating and three upon cooling of the alloy. Transition temperatures, enthalpies of transition, and diffusivity data are reported and correlated with SEM and TEM microstructural analysis. Heat Capacity (Cp) values were calculated using the Ratio method and second order polynomial fit expressions were determined as a function of temperature. The measured Cp, diffusivity and density values were multiplied to calculate the conductivity of the different compositions.

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Scott Middlemas (POC,Primary Presenter), Idaho National Laboratory,;
Cynthia Papesch (Co-Author), Idaho National Laboratory,;
Assel Aitkaliyeva (Co-Author), Idaho National Laboratory,;

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