Investigating the microstructure and mechanical behaviour of simulant “lava-like” fuel containing materials from the Chernobyl reactor unit 4 meltdown

C.Paraskevoulakos, J.P.Forna-Kreutzer, K.R.Hallam, C.P.Jones, T.B.Scott, C.Gausse, D.J.Bailey, C.A.Simpson, D.Liu, C.Reinhard, C.L.Corkhill, M.Mostafavi - Interface Analysis Centre, School of Physics, University of Bristol, Bristol BS8 1TL, UK - Bristol Composites Institute, Department of Aerospace Engineering, University of Bristol, Bristol BS8 1TR, UK - Immobilisation Science Laboratory, Department of Materials Science and Engineering, University of Sheffield, Sheffield S13JD, UK - Department of Mechanical Engineering, University of Bristol, Bristol BS8 1TR, UK - School of Physics, University of Bristol, Bristol BS8 1TL, UK - Diamond Light Source, Harwell Science and Innovation Campus, Didcot OX11 0DE, UK

Decommissioning of the damaged Chernobyl nuclear reactor Unit 4 is a top priority for the global community. Before such operations begin, it is crucial to understand the behaviour of the hazardous materials formed during the accident. Since those materials formed under extreme and mostly unquantified conditions, modelling alone is insufficient to accurately predict their physical, chemical and, predominantly, mechanical behaviour. Meanwhile, knowledge of the mechanical characteristics of those materials, such as their strength, is a priority before robotic systems are employed for retrieval and the force expected from them to be exerted is one of the key design questions. In this paper we target to measurement of the standard mechanical properties of the materials formed during the accident by testing small-scale, low radioactivity simulants.

A combined methodology using Hertzian indentation, synchrotron X-ray tomography and digital volume correlation (DVC), was adopted to estimate the mechanical properties. Displacement fields around the Hertzian indentation, performed in-situ in a synchrotron, were measured by analysing tomograms with DVC. The load applied during the indentation, combined with full-field displacement measured by DVC was used to estimate the mechanical properties, such as Young’s modulus and Poisson’s ratio of these hazardous materials.

How Amira-Avizo Software is used

  • Avizo was subsequently used for further data processing including 3D visualization, volume/length measurements and material segmentation.
  • The threshold values separating the different phases in the gray-scale intensity range were determined using the “Line-Probe” module in Avizo.
  • Using Avizo segmentation and analysis tools, general porosity, pore size distribution, U-rich and Fe/Zr-rich phase volume fractions were determined using the pre-loaded datasets; results are presented in Fig. 6
  • Pore size distribution analysis, performed by combining the “Material Statistics” and “Label Analysis” Avizo modules, generated the histogram shown in Fig. 11
  • The Avizo “XDigital Volume Correlation” extension module was employed to quantify the loading-induced deformation on the samples tested.