Analysis of the Secondary Phases Formed by Corrosion of U₃Si₂-Al Research Reactor Fuel Elements in the Presence of Chloride Rich Brines.

Andreas Neumann,Martina Klinkenberg,Hildegard Curtius

doi:10.3390/ma11071121

Andreas Neumann, Martina Klinkenberg + Show 1 more

Open Access

https://doi.org/10.3390/ma11071121

Copy DOI

Abstract

Corrosion experiments with non-irradiated U3Si2-Al research reactor fuel samples were carried out in synthetic MgCl2-rich brine to identify and quantify the secondary phases because depending on their composition and on their amount, such compounds can act as a sink for the radionuclide release in final repositories. Within the experimental period of 100 days at 90 °C and anoxic conditions the U3Si2-Al fuel sample was completely disintegrated. The obtained solids were subdivided into different grain size fractions and non-ambient X-ray diffraction (XRD) was applied for their qualitative and quantitative phase analysis. The secondary phases consist of lesukite (aluminum chloro hydrate) and layered double hydroxides (LDH) with varying chemical compositions. Furthermore, iron, residues of non-corroded nuclear fuel (U3Si2), iron oxy hydroxides and chlorides were also observed. In addition to high amorphous contents (>45 wt %) hosting the uranium, the quantitative phase analysis showed, that LDH compounds and lesukite were the major crystalline phases. Scanning electron microscopy (SEM) and energy dispersive -Xray spectroscopy (EDS) confirmed the results of the XRD analysis. Elemental analysis revealed that U and Al were concentrated in the solids. However, most of the iron, added as Fe(II) aqueous species, remained in solution.

Highlights

Due to considerable long-term impacts on the environment and society the waste management of spent nuclear fuel (SNF) is one of the most challenging issues for which sustainable disposal solutions must be found [1,2,3]
This study focuses on the identification and quantification of secondary phases which were retrieved by corrosion of non-irradiated U3 Si2 -Al research reactor fuel elements in MgCl2 rich brine
Elemental analysis (ICP-OES and Liquid Scintillation Counter (LSC)) showed that aluminum and uranium were quantitatively found in the secondary phases

Summary

Introduction

Due to considerable long-term impacts on the environment and society the waste management of spent nuclear fuel (SNF) is one of the most challenging issues for which sustainable disposal solutions must be found [1,2,3]. This study focuses on the identification and quantification of secondary phases which were retrieved by corrosion of non-irradiated U3 Si2 -Al research reactor fuel elements in MgCl2 rich brine (which accounts for a repository in salt formations) Such investigations are important due to the fact that corrosion of aluminum dispersed fuels exhibit higher degradations rates than those being determined for UO2 fuels of commercial nuclear power plants. The radio analytical investigations of the secondary phases of the U3 Si2 -Alirr /UAlx -Alirr fuel sample corrosion showed that the long-lived 234 U, 238,239,240 Pu and 241 Am isotopes were immobilized by the solids [21] This is observed for MgCl2 rich brine and for Mont Terri clay pore water as well. Efforts were taken and unique experimental equipment was applied to prevent the secondary phases from alteration by oxidation during retrieving, treatment, and analysis

Setup of the Corrosion Experiments and Sample Pre-Treatment

X-ray Diffraction Analysis

X-ray Analysis of the Secondary Phases

Background

Conclusions