Synthesis of simulant ‘lava-like’ fuel containing materials (LFCM) from the Chernobyl reactor Unit 4 meltdown

Abstract

A preliminary investigation of the synthesis and characterization of simulant ‘lava-like’ fuel containing materials (LFCM), as low activity analogues of LFCM produced by the melt down of Chernobyl Unit 4. Simulant materials were synthesized by melting batched reagents in a tube furnace at 1500 °C, under reducing atmosphere with controlled cooling to room temperature, to simulate conditions of lava formation. Characterization using XRD and SEM-EDX identified several crystalline phases including ZrO2, UOx and solid solutions with spherical metal particles encapsulated by a glassy matrix. The UOX and ZrO2 phase morphology was very diverse comprising of fused crystals to dendritic crystallites from the crystallization of uranium initially dissolved in the glass phase. This project aims to develop simulant LFCM to assess the durability of Chernobyl lavas and to determine the rate of dissolution, behavior and evolution of these materials under shelter conditions.

Safely probing the chemistry of Chernobyl nuclear fuel using micro-focus X-ray analysis

“…Brown LFCM contained more zircon than black LFCM, 12 and contained larger crystallites, indicating that zircon formation was more favourable in the former composition. Analysis of the local coordination of U in the glass matrix found that in simulant brown LFCM, U was present in a U(IV)O 6 -type environment, while in the simulant black LFCM it was in a UO 8 -type environment, similar to the coordination in coffinite, the U-end member of the U-zircon solid solution (Zr 1Àx U x SiO 4 ).…”

“…Such zoning is attributed to differential growth rates of crystal faces during cooling. 38 Previous analysis of the simulant brown LFCM showed very faint zoning throughout the crystallite, 12 however, only two zones were apparent in the m-XAS analysis. Since the temperature of U-rich zircon formation in this simulant material was found to be similar to chernobylite in real LFCM (crystallites were formed at $1245 AE 5 C and estimates made from analysis of real LFCM gave a range of between 1000-1250 C), 13,37 the differences observed between the simulant and real samples are most likely due to differences in the cooling regime.…”

“…Analysis by X-Ray Diffraction (XRD) and Scanning Electron Microscopy, coupled with Energy Dispersive X-ray Spectroscopy (SEM/EDS), demonstrated that the simulant LFCMs accurately reected the phase assemblage, microstructure and mechanical properties of real brown and black LFCM. [12][13][14] Thermal characterisation of the simulants conrmed that the crystallisation temperatures were consistent with those of naturally-occurring versions of the LFCM minerals. 13 Furthermore, the corrosion rates of U from the simulant LFCMs were found to be similar to those determined from limited studies of real LFCM.…”

“…excluding ssion products, were synthesised and characterised. [12][13][14] Detailed bulk analysis of these simulant materials was reported and the morphology and mineralogy were found to closely approximate those of real LFCMs. In the present study, micro-focus synchrotron X-ray analysis was used to investigate several representative regions of these materials.…”

Synthesis, characterisation and corrosion behaviour of simulant Chernobyl nuclear meltdown materials

“…To overcome this lack of information, past attempts to simulate lowactivity LFCMs (i.e., containing no fission products, only depleted uranium) have been made to help understand the conditions within the reactor during the accident, however, this work was unable to accurately approximate the microstructure, morphology and mineralogy of LFCM. [19][20][21][22] One important aspect of LFCM behaviour that has not yet been investigated in detail is its corrosion behaviour within the reactor building. It is known that, due to the condensation of water inside the roof of the original Chernobyl sarcophagus (as a result of the temperature differential within and outside the structure), and the presence of holes in the sarcophagus roof, a significant proportion of water has dripped onto the LFCM causing it to corrode.…”