Molecular-Dynamics Simulation of Displacement Cascades in Zircon (ZrSiO4)

ABSTRACTZircon (ZrSiO4) is of great interest for the nuclear industry as it is one of the new crystalline waste form considered for the disposal of actinides, for example weapons' plutonium in USA. In this study the effects of displacement cascade due to α-decay has been modelled from an atomistic point of view by molecular dynamics simulation using Born-Mayer-Huggins empirical potential. The numerical values of the parameters of this potential have been fitted on structural equilibrium properties of the crystal and on atomic arrangements.Displacement cascades are reproduced by accelerating one of the atoms of the cell, thus modelling the effect of the α-decay recoil nucleus. Kinetic energies up to 2 keV have been introduced. The unfolding of the cascades and the final structures have been studied in detail. The centre of the displacement cascade exhibits an amorphous zone where the zircon structure is completely lost. It contains an assembly of distorted SiO4 tetrahedra and disordered zirconium polyhedra. The zirconium ions (originally surrounded by 8 oxygen atoms) exhibit a decrease in their coordination number to 7 or 6 in agreement with what is observed for zirconium ions in amorphous zircon, zirconia or glasses. The size of the amorphous zone and the number of atoms displaced have been estimated for different recoil energies.The energy stored during the cascade has been calculated. It exhibits an overall good agreement with the available experimental data at complete amorphization.The existence of an amorphous track in our calculated cascades shows that the correct model for the amorphisation process should take into account the existence of a direct impact amorphous zone.

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Molecular Dynamics Simulation of Recoil Nucleus Displacement Cascade in Zircon

MRS Proceedings ◽

10.1557/proc-540-343 ◽

1998 ◽

Vol 540 ◽

Cited By ~ 1

Author(s):

Jean-Paul Crocombette ◽

Dominique Ghaleb

Keyword(s):

Molecular Dynamics ◽

Molecular Dynamics Simulation ◽

Molecular Simulations ◽

Recoil Nucleus ◽

Dynamics Simulation ◽

Local Temperature ◽

Displacement Cascades ◽

Displacement Cascade ◽

Temperature And Pressure

AbstractThe results of molecular simulations of a-recoil nucleus displacement cascades in zircon (ZrSiO4) are presented. The local temperature and pressure are found to increase dramatically during the cascade. The structure of the cascade tracks is amorphous. Its shape has been analyzed in terms of disordered and distorted cations. SiO2 nanophase are found to exist in the tracks consistently with what is observed in the experiments.

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Displacement cascade initiated with the realistic energy of the recoil nucleus in UO2 matrix by molecular dynamics simulation

Journal of Nuclear Materials ◽

10.1016/j.jnucmat.2006.01.020 ◽

2006 ◽

Vol 354 (1-3) ◽

pp. 28-35 ◽

Cited By ~ 51

Author(s):

L. Van Brutzel ◽

M. Rarivomanantsoa ◽

D. Ghaleb

Keyword(s):

Molecular Dynamics ◽

Molecular Dynamics Simulation ◽

Recoil Nucleus ◽

Dynamics Simulation ◽

Displacement Cascade

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Molecular dynamics simulation of the α-recoil nucleus displacement cascade in zirconolite

Journal of Nuclear Materials ◽

10.1016/s0022-3115(02)01134-0 ◽

2002 ◽

Vol 306 (1) ◽

pp. 61-72 ◽

Cited By ~ 31

Author(s):

L. Veiller ◽

J.-P. Crocombette ◽

D. Ghaleb

Keyword(s):

Molecular Dynamics ◽

Molecular Dynamics Simulation ◽

Recoil Nucleus ◽

Dynamics Simulation ◽

Displacement Cascade

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Molecular Dynamics Simulation of the Alpha-Recoil Nucleus Displacement Cascade in Zirconolite

Volume 3: Hazardous Waste; Engineered/Geological Barriers in Disposal Systems; L/ILW; Radioactive Waste From Research/Industries; Spent Fuel/HLW Disposal; Public Involvement; Remediation of Uranium Mining/Milling; LL/ILW; Clearance/Exemption Levels; Mgmt. of Fissile Material; HLW; Dismantling; Reversible/Irreversible Disposal; Waste Avoidance/Minimization; Decontamination; Liquid Waste; Radioactive Waste Processing; Transport of Spent Fuel/HLW; Solid HLW Confinement; QA/QC ◽

10.1115/icem2001-1290 ◽

2001 ◽

Author(s):

L. Veiller ◽

JP. Crocombette ◽

C. Meis ◽

D. Ghaleb

Keyword(s):

Molecular Dynamics ◽

Structural Changes ◽

Md Simulations ◽

Recoil Nucleus ◽

Dynamics Simulation ◽

Α Decay ◽

Cell Parameters ◽

Displacement Cascades ◽

Pair Potentials ◽

High Level

Abstract Zirconolite (CaZrTi2O7) has been proposed as a crystalline ceramic host for the long-term disposal of actinides extracted from high-level nuclear waste (e.g. France) and from excess weapons-grade plutonium (e.g. USA). The disintegration of radionuclides induces modifications of the crystalline structure. During α-decay of actinides, localized cascades of displaced atoms occur primarily because of ballistic collisions in the material from the emitted α-recoil nuclei. Under α-decay irradiation, zirconolite undergoes a crystalline to amorphous transformation, which is associated to a volume expansion. We have focused our study on the understanding of radiation-induced structural changes at the atomic level in this ceramic. Molecular Dynamics (MD) has been used in the simulation of displacement cascades in zirconolite. Original Buckingham pair potentials have been established for zirconolite to characterize the two body short-range interactions between different ionic pairs. We present the potential parameters fitted to the structural equilibrium properties of the crystal. This fitting reproduces the characteristics of the cell parameters of zirconolite within 4% and gives reasonable values for the bulk modulus and the specific heat. The MD method is applied to determine the threshold displacement energies for the various sublattices. Finally, we have modelled the effects of displacement cascades in zirconolite, due to the α-recoil nuclei. For that purpose, two MD simulations of high recoil kinetic energies (2 and 6 keV) were performed. The preliminary results show that the complex matrix zirconolite tends to a structural disordering for high PKA energy values although a partial recrystallization step is observed during the energy dissipation.

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