Photon Factory Activity Report 2018 #36 (2019)

BL-27B/2017G187

Characterisation of simulant Chernobyl nuclear meltdown materials

Shi-Kuan Sun*, Martin Stennett, and Neil Hyatt
Immobilisation Science Laboratory, Department of Materials and Science Engineering, The
University of Sheffield, Sheffield.
1 Introduction
In order to support decommissioning operation at theChernobyl nuclear power plant (NPP) work is being
conducted to understand the properties of materials
formed during nuclear meltdowns. In this study smallscale batch samples of lave-like fuel containing materials(LFCM) have been prepared and characterized by X-ray
absorption spectroscopy (XAS). XAS is a powerful
technique for investigating local physicochemical
properties, such as valence state and local coordination
environment, which will have an influence on importantmaterial characteristics such as the durability.
Comparison is made with data acquired from material
retrieved from the Chernobyl NPP to provide someinsight into the suitability of these synthetic samples assimulants.
2 Experiment
Synthetic LFCM was prepared from reagent grade
precursor to match bulk chemical analyses reported in theliterature [1-3]. The sample was melted in an alumina
crucible under reducing conditions (5% H2 – 95% N2) at1500 °C for 4 hours and annealed at 720 °C for 72 hours.
U LIII edge XANES spectra of the synthetic LFCM sample
was measured in transmission mode on BL-27 at thePhoton Factory (Tsukuba, Japan). To aid the analysis
4+standards with known oxidation state (UO2 – U ;5+
6+
Yb0.5U0.5Ti2O6 – U ; CaUO4 – U ) were also measured.
All the samples were prepared by mixing finely groundpowders with polyethylene glycol (PEG) and pressing
into 13mm diameter disks. Subsequent data reduction
and analysis was performed using the Athena software
package [4].
3 Results and Discussion
Figure 1 shows the U LIII edge XANES data for thesynthetic LFCM sample. For comparison the data fromthe standards are also shown. The position of theabsorption edge (determined as the energy position at anormalised absorption of 0.5) was similar to the value
measured from the UO2 standard which suggested that theaverage uranium oxidation state in both samples is closeto four (Figure 2). There are also marked similarities inthe features in the post edge range which indicated thatthe local coordination environment of uranium in thesynthetic LFCM sample was similar to that in UO2 (VIIIfold). Previous studies on real LFCM particles has
indicated that the uranium tended to partition into zircon
crystals often referred as chernobylite (Zr1-xUxSiO4) [5, 6].
The local structural environment around the Zr cations inzircon is VIII-fold [7], which is consistent with thefindings in this study, suggesting that our synthetic
sample is a promising analogue for real LFCMs.

Fig. 1: Uranium LIII edge XANES data for synthetic LFCM,
with reference to uranium standards of known oxidation state.

Fig. 2: Linear regression of the extracted normalised edge
position of standards and LFCM sample.

Acknowledgement
We acknowledge Dr. Y. Okamoto from JAEA for his
assistance during beamtime. S.K Sun and M. Stennett are
grateful for financial support from Daiwa Foundation.
References[1] P. Poml et al., Journal of Nuclear Materials, 439, 21(2013).
[2] B. E. Burakov et al., Materials Research Society
Proceedings, 465, 1309 (1997).
[3] A. S. Baev et al., Radiochemistry, 39, 169 (1997).
[4] B. Ravel et al., Journal of Synchrotron Radiation, 12,537 (2005).
[5] V. N. Bondarenko et al., Atomic Energy, 102, 304(2007).
[6] V. S. Krasnorutsky et al., Problems of Atomic Scienceand Technology, 65, 60 (2010).
[7] K. Robinson et al., American Mineralogist, 56, 782(1971).
* shikuan.sun@sheffield.ac.uk