Why a steady state void size distribution in irradiated UO2? A modeling approach

NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS

卷:374

Article

Maillard, S.¹  Martin, G.^1,2  Sabathier, C.¹ 

[1] CEA, DEN, SESC LLCC, F-13108 St Paul Les Durance, France

[2] CEA, DEN, SPRC, LECy, F-13108 St Paul Les Durance, France

关键词: Fission gas bubbles;    UO2;    Irradiation effects;    Object Kinetic Monte Carlo;    Multi-scale modeling;   

DOI  :  10.1016/j.nimb.2015.09.068

来源: Elsevier

【 摘 要 】

In UO2 pellets irradiated in standard water reactor, Xe nano-bubbles nucleate, grow, coarsen and finally reach a quasi steady state size distribution: transmission electron microscope (TEM) observations typically report a concentration around 10(-4) nm(-3) and a radius around 0.5 nm. This phenomenon is often considered as a consequence of radiation enhanced diffusion, precipitation of gas atoms and ballistic mixing. However, in UO2 thin foils irradiated with energetic ions at room temperature, a nano-void population whose size distribution reaches a similar steady state can be observed, although quasi no foreign atoms are implanted nor significant cation vacancy diffusion expected in conditions. Atomistic simulations performed at low temperature only address the first stage of the process, supporting the assumption of void heterogeneous nucleation: 25 keV sub-cascades directly produce defect aggregates (loops and voids) even in the absence of gas atoms and thermal diffusion. In this work a semi empirical stochastic model is proposed to enlarge the time scale covered by simulation up to damage levels where every point in the material undergoes the superposition of a large number of sub-cascade impacts. To account for the accumulation of these impacts, simple rules inferred from the atomistic simulation results are used. The model satisfactorily reproduces the TEM observations of nano-voids size and concentration, which paves the way for the introduction of a more realistic damage term in rate theory models. (C) 2015 Elsevier B.V. All rights reserved.

【 授权许可】

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