NuFuel & MMSNF 2015

First Workshop on Research into Nuclear Fuel in Europe
and Materials Modeling and Simulation for Nuclear Fuels Workshop
Karlsruhe, Germany, November 16th to 18th, 2015

Updated: Tue 08 Dec 2015, 14:27

Talk 4.2: Inverse method for calculating thermo- physical properties of nuclear materials up to their melting point

Tsvetoslav Pavlov1,2, Luka Vlahovic1, Dragos Staicu1, Paul Van Uffelen1, Mark Wenman2 and R. W. Grimes2
  • 1: European Commission, Joint Research Centre, Institute for Transuranium Elements (ITU), Hermann-von-Helmholtz Platz 1, PO Box 2340, DE–76125 Karlsruhe, Germany
  • 2: Centre for Nuclear Engineering, Imperial College London, Royal School of Mines, London, SW7 2AZ, England

Abstract

The proposed method uses experimental thermograms obtained via laser- flash heating of a disc-shaped sample in combination with finite element analysis and parameter optimization. The experimental part involves heating samples to a steady state temperature via two lasers (on the back and front sides) and subsequently subjecting the front sample surface to a short laser pulse, resulting in a temperature transient (thermogram). A thermal camera records the temperature transients at equally spaced points along the radius of the rear surface of the sample. The noisy thermograms are filtered via Fast Fourier Transforms and a total variation minimization algorithm.

Subsequently, an optimization technique known as the Levenberg-Marquardt method is applied, whereby multiple parameters (emissivity, heat transfer coefficient, heat capacity and thermal conductivity) can be optimized and used as inputs in a finite element model. The parameters are changed until the least square difference between the numerical and experimental thermograms reaches a minimum. The calculated properties at each of the radial points correspond to different temperatures along the surface of the sample and thus temperature dependent expressions of these properties are obtained as well.

The method has been tested using both simulated and experimental data. Both heat capacity and thermal conductivity are in good agreement with literature data for POCO AXM–5 graphite.