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The nuclear industry produces a wide range of radioactive waste in terms of hazard level, contaminants and material. For metallic equipment like steam generators, the radioactivity is mainly located in the oxide surface. In order to study and develop safe techniques for dismantling and for decontamination, it is important to have access to oxide layers with a representative distribution of non-radioactive contaminants. In this paper we propose a method for the creation of oxide layers on stainless steel 304L with europium (Eu) as contaminant. This technique consists in spraying an Eu-solution on stainless steel samples. The specimens are firstly treated with a pulsed nanosecond laser after which the steel samples are placed in a 873 K furnace for various durations in order to grow an oxide layer. The oxide structure and in-depth distribution of Eu in the oxide layer were analyzed by scanning electron microscopy coupled to an energy-dispersive X-ray microanalyzer, as well as by glow discharge optical emission or mass spectrometry. The oxide layers were grown to thicknesses in the range of 200 nm–4.5 μm depending on the laser treatment parameters and the heating duration. These contaminated oxides had a ‘duplex structure’ with a mean concentration of the order of 6 × 1016 atoms/cm2 (15 μg/cm2) of europium in the volume of the oxide layer. It appears that europium implementation prevented the oxide growth in the furnace. Nevertheless, the presence of the contamination had no impact on the thickness of the oxide layers obtained by preliminary laser treatment. These oxide layers were used to study the decontamination of metallic surfaces such as stainless steel 304L using a nanosecond pulsed laser.

The nuclear industry produces a wide range of radioactive waste in term of level of hazard, contaminants and material. For metallic equipment like steam generators, the radioactivity is mainly located in the oxide surface. In order to study and develop techniques for dismantling and for decontamination in a safe way, it is important to have access to oxide layers with a representative distribution of non-radioactive contaminants. We propose a method of formation of oxide layer on stainless steel 304L with europium (Eu) as contaminant marker. In this method, an Eu-solution is sprayed on the stainless steel samples. The specimen are firstly treated with a pulsed nanosecond laser and secondly the steel samples are exposed to a 600°C furnace for various durations in order to grow an oxide layer. The oxide structure and in-depth distribution of Eu in the oxide layer are analysed by scanning electron microscopy coupled with energy dispersive X-ray microanalyzer, and by glow discharge optical emission or mass spectrometry. The oxide layers were grown to thicknesses in the range of 200 nm to 4.5 μm regarding to the laser treatment parameters and the heating duration. These contaminated oxides have a ‘duplex structure’ with a mean weight percentage of 0.5% of europium in the volume of the oxide layer. It appears that europium implementation prevents the oxide growth by furnace but has no impact on laser heating. These oxide layers are used to study the decontamination of metallic surfaces such as stainless steel 304L using a nanosecond pulsed laser.

A simplified procedure of lock-in thermography was developed and applied for characterization of nuclear materials. The possibility of thickness and thermal diffusivity measurements with the accuracy better than 90% was demonstrated with different metals and Zircaloy-4 claddings.

A near-field laser ablation system was developed for the analysis of inorganic solid samples in the nanometer resolution range. The instrument is based on the coupling of a nanosecond Nd:YAG laser with an atomic force microscope. The technique uses a tip enhancement effect obtained by the interaction of laser radiation with the conductive tip of the AFM maintained at a few nanometers above the sample surface. By applying this technique to conducting gold and semiconducting silicon samples, a lateral resolution of 100 nm was demonstrated. With a single laser pulse, craters of about 100 nm in diameter and a few nanometers in depth were obtained. A multi-parametric study was carried out in order to understand the effect of different experimental parameters (laser fluence, tip-to-sample distance, sample and tip nature) on the near-field laser ablation efficiency, crater dimensions and amount of ablated material. Numerical simulations of the localized heating with a home-made 3-D code presented a good explanation for the nanometer-sized crater diameters obtained in our experiments. [ABSTRACT FROM AUTHOR]

We investigate the plasma produced by the interaction of ultraviolet nanosecond laser pulses with a carbon fiber composite tile from the inner wall of a fusion reactor. The experiments are carried out in argon at a pressure of 5 × 104 Pa. Fast imaging is used to characterize the plume expansion dynamics and excited plasma species are followed by time- and space-resolved emission spectroscopy. The measurements show that ionized and highly excited plasma species are located in the front of the expanding plume, whereas neutral atoms and lower excited species dominate in the plasma core. By measuring the excitation temperature of metallic ions and neutral atoms, we evidence the existence of a temperature gradient that appears during the early expansion stage and remains up to delays typically used in material analysis via laser-induced breakdown spectroscopy. The knowledge of the spatial distribution of the plasma properties is then used to model the plasma emission spectrum. Assuming two plasma zones in local thermodynamic equilibrium of different temperatures and electron densities, we calculate the spectral radiance and compare it to the spatially integrated spectrum recorded with an Echelle spectrometer. From the best agreement between measured and computed spectra we deduce the elemental concentrations of carbon, hydrogen and metal impurities. The validity of the model is critically discussed and the measurement uncertainties are evaluated. The present approach is foreseen to improve the accuracy of analysis via laser-induced breakdown spectroscopy in many applications, in particular when materials of elements with significantly different ionization potentials are investigated. [ABSTRACT FROM AUTHOR]