Thermal behavior and kinetic modeling of (NH4)4UO2(CO3)3 decomposition under non-isothermal conditions

The thermal behavior and kinetic analysis of ammonium uranyl carbonate decomposition has been studied in inert gas, O₂, and 90%Ar–10%H₂ atmospheres under non-isothermal conditions. The results showed a dependence on specific surface area with the decomposition temperature of ammonium uranyl tri-carbonate (AUC). Specific surface area increases and reaches a maximum between 300 and 400 °C and decreases at T > 400 °C. The reaction paths of AUC decomposition under the three atmospheres were proposed. The integral methods Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS) were used for the kinetic analysis. The activation energy averages are 58.01 and 56.19 kJ/mol by KAS and FWO methods, respectively.

     

Fluid-structure interaction with an application to a body immersed and anchored in a fluid flow

In this paper, an implicit coupling algorithm for fluid–structure interaction problems with under-time steps for the solid is presented. Its implementation on two configurations is achieved by using the CASTEM finite-elements code. First, the free oscillations of a cylinder in an annular fluid domain where its movement is determined by the coupled fluid–solid action is considered in the case of viscous fluid. It should be noted that the implicit coupling algorithm gives the best prediction of the structure oscillations. The under-time steps for the solid are introduced in order to obtain better results. Then, an application whose final objective is to model a floating barrage is studied. The main goal of this application is to predict the displacements of a ring completely immersed and anchored by a cable to the lower boundary of the fluid domain. The finite-element discretization of the Navier–Stokes equations in the ALE formulation is used