Rate Theory Study On The Anti-irradiation Properties Of BCC Metals Under Steady/Non-steady State

The design of high anti-irradiation materials in fission and fusion environment is one of the key problems in the development of nuclear energy.The research on the damage behavior and anti-irradiation mechanism of materials under irradiation field can provide theoretical support for experiment.Based on the steady state rate theory model and multi-scale cluster dynamics model constructed by rate theory,this paper systematically studies the general law of anti-irradiation behavior of BCC metal under steady and non-steady state,puts forward the influence of diffusion and absorption bias on the irradiation tolerance of BCC metals,and simulates the defect retention behavior of aluminum under He ion irradiation.The main contents are as follows:1)Different materials would exhibit discrepant behaviors of radiation tolerance under energetic particle irradiation,due to the effect of intrinsic features(like defect migration energy and sink strength of grain boundaries)and extrinsic conditions(like irradiation rate and temperature)on defect accumulation.We wonder what the general rules of radiation tolerance are in body-centered cube(BCC)transition metals.Based on the steady state chemical rate theory,the influence of these intrinsic features and extrinsic conditions on vacancy accumulation is thus investigated in typical BCC metals including V,Cr,Fe,Nb,Mo,Ta and W.It shows that V,Cr,Fe and Nb exhibit obvious advantage in radiation resistance than that of Ta,Mo and W under typical service conditions,due to their higher vacancy diffusivities.In addition,the smaller grain size and lower irradiation rate,the higher anti-irradiation ability of BCC metals.Therefore,we propose that,under practical irradiation rates and temperatures,BCC metals with low vacancy migration energy and small grain size should be recommended in the selection of new nuclear materials,at least in the view of steady state.2)In the actual irradiation environment,the material is always in an unsteady state.The nuclear material will produce serious displacement damage after long-time and high-energy neutron irradiation.Therefore,it is necessary to systematically explore the general mechanism of irradiation resistance of BCC transition metals(V,Cr,Fe,Nb,Mo,Ta and W)with different grain sizes under unsteady state.The effects of grain size and temperature on vacancy accumulation in nanocrystalline metals under neutron irradiation were systematically simulated by using the method of cluster dynamics under unsteady state.The results show that nanocrystalline V,Cr,Fe and Nb have good irradiation resistance at room temperature,while nanocrystalline Ta,Mo and W had no obvious irradiation resistance advantage even at high temperature.It is their lower vacancy energy compared with Mo,Ta and W,smaller diffusion and absorption bias that are the main reasons why the accumulation of defects in V,Cr,Fe and Nb reduces and thus eventually improve the anti-irradiation ability of these nanocrystalline materials.The higher temperature,the smaller diffucion and absorption bias.Our results indicate that only nanocrystalline V,Cr,Fe and Nb can be used at low temperature in the selection and design of nuclear structural materials.3)Aluminum has been widely used in nuclear reactions.It is necessary to understand the influence of helium on the surface damage of plasma-facing materials as well as the self-irradiation damage of plutonium.Therefore,we study the defect dynamic and aggregation behavior of helium in aluminum under keV-He ion irradiation by using a cluster dynamics model.Through the quantitative analysis of the concentration of He by different traps(clusters,grain boundaries and dislocations)we find that most of He atoms are absorbed in grain boundaries,which is the main contribution to embrittlement of Al under low irradiation fluence.With irradiation energy increasing,the position of He retention peak becomes deeper.However,with ion fluence increasing,the amount of He retention in Al becomes more,while the position of retention peak remains unchanged.The results show that the effect of grain boundaries plays a key role in the distribution of He retention and the behavior of embrittlement in Al,which is also helpful for understanding the dynamic behavior of He and the distribution of damages in metals.