The development of metallic, low-enrichment uranium fuels requires accurate prediction of their neutron transport properties and reactivity parameters, which in turn require thermal neutron scattering data. Accurate prediction of thermal neutron scattering data, including thermal cross sections, requires knowledge of the phonon scattering properties of the medium, but such matrix binding effects in next-generation fuels such as U-Mo, U-Zr, and U-Si are typically neglected because these effects are often difficult to measure or calculate. Using molecular dynamics simulations with previously published interatomic potentials, we calculate the phonon dispersion relations and phonon densities of states for U andU in the α and γ phases. The performance of these potentials was evaluated using published ab initio simulation data and inelastic neutron scattering data. The phonon densities of states obtained by each potential were then utilized to calculate the thermal neutron scattering cross sections of U andU at 1113 K using the NJOY program. The resulting thermal neutron scattering cross sections are assessed by comparison to data obtained from available experimental densities of states. The cross sections generated show how the addition of binding effects decreases the cross section by up to a factor of six over the free-atom model. A definite effect on reactivity is also demonstrated by the use of these thermal libraries on a simple core model. As a consequence, the cross sections generated in this work provide a better description of the true cross section than the free-atom data currently available. We also discuss the sensitivity of the thermal scattering cross sections to the phonon density of states.
La interacción del hidrógeno molecular [H2] con rccc metil- y fluor-pirogalol[a]arenos funcionalizados con cationes Li+ [Li-R-Pyg[4]Ar] fue estudiado teóricamente por medio de cálculos cuanto-mecánicos DFT al nivel de teoría B3LYP/6-311G (d,p). En una primera etapa de estudio, la estabilidad del catión Li+ dentro de la cavidad de los R-Pyg[4]arenos fue analizada inspeccionando el ambiente local del ion adsorbido y los mapas de densidad total de carga así como de potencial electrostático de los complejos. En una siguiente etapa de trabajo, se determinó la posición óptima del H2 en la cavidad de los R-Pyg[4]arenos puros, y con litio. Una vez obtenida la geometría de equilibrio, la energía de amarre libre de ESFB fue calculada para varios complejos H2/R-Pyg[4]Ar. Los resultados muestran que la capacidad de adsorción de los R-Pyg[4]arenos mejora de manera significativa por la presencia del catión Li+ dentro de su cavidad.
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