Abstract
The miscibility, lattice parameter, and thermophysical properties of (Th0.2U0.8)N and (Th0.5U0.5)N have been investigated. It is shown that additions of thorium nitride (ThN) to uranium nitride (UN) increases the thermophysical performance of the mixed nitride fuel form in comparison to reference UN. In the more dilute limit, additions of ThN serve as a burnable neutronic poison and reduces the change in keff over the lifecycle of the fuel. At higher concentrations, additions of ThN serve as a significant fertile source of 233U. Where appropriate, comparisons to previous work on UN + PuN mixtures are made, as this is a comparable fuel form for potential fast reactor concepts, and a suitable point of contrast in the possible design space afforded by mixed (ThxU1 − x)N fuel forms. The data from this work are the input parameters for finite element modeling of the temperature distribution in a compact reactor. The results of modeling and simulation of this core design are shown for the case of steady-state operation and during double, adjacent heat pipe failure.
Highlights
Thermal conductivity, which is highly dependent on temperature, chemistry, and crystal structure, is an important factor of nuclear fuel performance under irradiation
Following recent work on the characterization of uranium nitride (UN) and thorium nitride (ThN), this study extends our research to mixed (ThxU1-x)N ceramics.[12]
While the value of heat capacity as a function of temperature is found to be similar in magnitude in ThN and UN, notable differences arise and are attributed to differences in the proportion of thermal transport carried by electrons
Summary
Thermal conductivity, which is highly dependent on temperature, chemistry, and crystal structure, is an important factor of nuclear fuel performance under irradiation. In the more dilute limit, x 1⁄4 0:2, Parker, Newman, Fallgren, and White thorium serves as a burnable neutronic poison and reduces the change in keff over the lifecycle of the fuel, while simultaneously providing significant increases in the thermophysical properties of the mixed nitride fuel form At this composition, the relative enrichment of fissile isotopes of uranium (i.e., 233U or 235U in a matrix of 238U) may be assumed to be low enriched (19.7%) or high enriched (> 20%). A set of samples of (Th0.5U0.5)N and (Th0.2U0.8)N with dimensions suitable for measurement of thermophysical properties were produced by cold pressing and high-temperature sintering (2000 K) in flowing argon with 6%. Reported diffusivity values were determined by fitting the temperature rise signal with a pulse-corrected Cape–Lehman model
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