International Topical Meeting on Nuclear Research Applications and Utilization of Accelerators

4-8 May 2009, Vienna

A Study of Diffusion Behaviour of Silicon in D9 Steel

C. David, J. Arunkumar, K.G.M. Nair, B.K. Panigrahi, C.S. Sundar, and B. Raj

Indira Gandhi Centre for Atomic Research, Kalpakkam, India

Corresponding Author: davec in@yahoo.co.uk

Silicon is an essential solute element in D9 steel, which is envisaged for use as fuel cladding and wrapper materials in the Indian fast breeder reactor (FBR). The effectiveness of silicon in extending the transient regime of void swelling is well known, but an understanding of the underlying mechanism is still lacking. Any quantitative modelling of the irradiation effects in alloys requires knowledge of the diffusion behavior of the constituent atomic species due to their considerable redistribution during irradiation. In this paper we experimentally investigate the thermal diffusion behavior of silicon in D9 steel. D9 steel samples are implanted with 500 keV Si³⁰ to a fluence of 3 x 10¹⁶ atoms cm ^-2. The implanted Si³⁰ profile which resides at a depth of ~280 nm serves as the marker layer and its broadening can be used for following the diffusion of silicon in D9 steel samples. Depth profiling of Si³⁰ was carried out by the Resonance Nuclear Reaction Analysis (RNRA) using Si³⁰ (ρ, γ) resonance at 942 keV. The range and straggling of the room temperature implant determined by the RNRA is in agreement with that computed from the TRIM program. The D9 alloy samples were isochronally annealed for 30 minutes at temperatures of 320, 390, 460, and 530K. After every annealing step the sample was quenched and RNRA was carried out to probe the diffusion of silicon atoms. The diffusion constant is obtained from the profile broadening and the Arrhenius plot shows a linear behavior. An activation energy of 0.34 eV for diffusion was obtained. At temperatures of 600K and above there is a tendency for the FWHM of the diffusion profiles to shrink and approach that of the as implanted profile. Also, a shift in the vertex of the diffusion profile towards the peak damage position is observed. From our previous studies on the annealing behavior of D9 alloy using positron annihilation spectroscopy it was found that the vacancies in the alloy start migrating at temperatures above 500K. Therefore at temperatures above 600K silicon atoms may be diffusing by a vacancy mechanism. The movement of silicon atoms in a direction opposite to the direction of the vacancy migration has resulted in the shrinking of the diffusion profile. The above results are discussed in the light of irradiation induced point defects acting as vehicles for solute atom diffusion.