Redox response of actinide materials to highly ionizing radiation

Cameron L Tracy,Christina Trautmann,Maik Lang,Dmitry Popov,Daniel Severin,John M Pray,Changyong Park,Vladimir A Skuratov,Markus Bender,Rodney C Ewing,Fuxiang Zhang

doi:10.1038/ncomms7133

Abstract

Energetic radiation can cause dramatic changes in the physical and chemical properties of actinide materials, degrading their performance in fission-based energy systems. As advanced nuclear fuels and wasteforms are developed, fundamental understanding of the processes controlling radiation damage accumulation is necessary. Here we report oxidation state reduction of actinide and analogue elements caused by high-energy, heavy ion irradiation and demonstrate coupling of this redox behaviour with structural modifications. ThO2, in which thorium is stable only in a tetravalent state, exhibits damage accumulation processes distinct from those of multivalent cation compounds CeO2 (Ce(3+) and Ce(4+)) and UO3 (U(4+), U(5+) and U(6+)). The radiation tolerance of these materials depends on the efficiency of this redox reaction, such that damage can be inhibited by altering grain size and cation valence variability. Thus, the redox behaviour of actinide materials is important for the design of nuclear fuels and the prediction of their performance.

Highlights

Energetic radiation can cause dramatic changes in the physical and chemical properties of actinide materials, degrading their performance in fission-based energy systems
Relating trends in radiation tolerance to the dynamic process of radiation damage accumulation is difficult due to the complex nature of defect production and recovery, both of which occur at nanometric length scales, femto- and picosecond timescales, and extremely high energy densities[8]
We have investigated the effects of highly ionizing radiation on actinide materials using heavy ions accelerated to velocities ranging from 5% to 10% the speed of light

Summary

Introduction

Energetic radiation can cause dramatic changes in the physical and chemical properties of actinide materials, degrading their performance in fission-based energy systems. We report oxidation state reduction of actinide and analogue elements caused by high-energy, heavy ion irradiation and demonstrate coupling of this redox behaviour with structural modifications. Relating trends in radiation tolerance to the dynamic process of radiation damage accumulation is difficult due to the complex nature of defect production and recovery, both of which occur at nanometric length scales, femto- and picosecond timescales, and extremely high energy densities[8]. The effects of highly ionizing radiation are generally less well understood than those of displacive radiation, but fission fragments, which fall into this high-energy regime, are known to significantly degrade the performance of nuclear fuels[12]. To better understand the physics of damage production by ionizing radiation, a comprehensive approach, in which structural modifications are considered alongside coupled electron delocalization and redox processes, is necessary. Any relationship between radiation tolerance and redox behaviour would have important implications for the technologically important light actinide (Th-Cm) oxides, as their partially delocalized 5f orbitals cause significant variation in the accessible stable electronic configurations across this series[21]

Methods

Results

Conclusion