Study of amorphous alumina coatings for next-generation nuclear reactors: High-temperature in-situ and post-mortem Raman spectroscopy and X-ray diffraction.

The present work focuses on the investigation of the thermal stability and structural integrity of amorphous alumina coatings intended for use as protective coatings on cladding tubes in Generation IV nuclear reactors, specifically in the Lead-cooled Fast Reactor (LFR) type. High-temperature Raman spectroscopy and high-temperature X-ray diffraction analyses were carried out up to 1050 °C on a 5 µm coating deposited by the pulsed laser deposition (PLD) technique on a 316L steel substrate. The experiments involved the in-situ examination of structural changes in the material under increasing temperature, along with ex-situ Raman imaging of the surface and cross-section of the coating after thermal treatments of different lengths. As it was expected, the presence of α-alumina was detected with the addition of other polymorphs, γ- and θ-Al2O3, found in the material after longer high-temperature exposure. The use of two structural analysis methods and two lasers excitation wavelengths with Raman spectroscopy allowed us to detect all the mentioned phases despite different mode activity. Alumina analysis was based on the emission spectra, while substrate oxidation products were identified through the structural bands. The experiments depicted a dependence of the phase composition of oxidation products and alumina's degree of crystallization on the length of the treatment. Nevertheless, the observed structural changes did not occur rapidly, and the coating's integrity remained intact. Moreover, oxidation signs occurred locally at temperatures exceeding the LFR reactor's working temperature, confirming the material's great potential as a protective coating in the operational conditions of LFR nuclear reactors.

Effect of Nitrogen Atmosphere Annealing of Alloyed Powders on the Microstructure and Properties of ODS Ferritic Steels.

Oxide Dispersion Strengthened (ODS) ferritic steels are promising materials for the nuclear power sector. This paper presents the results of a study on the sintering process using the Spark Plasma Sintering (SPS) technique, focusing on ODS ferritic steel powders with different contents (0.3 and 0.6 vol.%) of Y2O3. The novelty lies in the analysis of the effect of pre-annealing treatment on powders previously prepared by mechanical alloying on the microstructure, mechanical, and thermal properties of the sinters. Using the SPS method, it was possible to obtain well-densified sinters with a relative density above 98%. Pre-annealing the powders resulted in an increase in the relative density of the sinters and a slight increase in their thermal conductivity. The use of low electron energies during SEM analysis allowed for a fairly good visualization of the reinforcing oxides uniformly dispersed in the matrix. Analysis of the Mössbauer spectroscopy results revealed that pre-annealing induces local atomic rearrangements within the solid solution. In addition, there was an additional spectral component, indicating the formation of a Cr-based paramagnetic phase. The ODS material with a higher Y2O3 content showed increased Vickers hardness values, as well as increased Young's modulus and nanohardness, as determined by nanoindentation tests.

Mechanical and Thermal Properties of W-Ta-B Coatings Deposited by High-Power Impulse Magnetron Sputtering (HiPIMS).

We present the deposition and characterization of tungsten-tantalum diboride (W,Ta)B2 coatings prepared by the high-power impulse magnetron sputtering technique. We evaluated the influence of pulse duration and substrate bias on the properties of (W,Ta)B2 films. A high hardness of up to 35 GPa measured by nanoindentation was simultaneously obtained with good elastic properties. Changing the pulse duration greatly affected the B/(W+Ta) atomic ratio, which influenced the properties of the coatings. The deposited films are thermally stable at up to 1000 °C in vacuum and are able to withstand oxidation at 500 °C.

Round Robin into Best Practices for the Determination of Indentation Size Effects.

The paper presents a statistical study of nanoindentation results obtained in seven European laboratories which have joined a round robin exercise to assess methods for the evaluation of indentation size effects. The study focuses on the characterization of ferritic/martensitic steels T91 and Eurofer97, envisaged as structural materials for nuclear fission and fusion applications, respectively. Depth-controlled single cycle measurements at various final indentation depths, force-controlled single cycle and force-controlled progressive multi-cycle measurements using Berkovich indenters at room temperature have been combined to calculate the indentation hardness and the elastic modulus as a function of depth applying the Oliver and Pharr method. Intra- and inter-laboratory variabilities have been evaluated. Elastic modulus corrections have been applied to the hardness data to compensate for materials related systematic errors, like pile-up behaviour, which is not accounted for by the Oliver and Pharr theory, and other sources of instrumental or methodological bias. The correction modifies the statistical hardness profiles and allows determining more reliable indentation size effects.

High resolution SEM characterization of nano-precipitates in ODS steels.

The performance of the present-day scanning electron microscopy (SEM) extends far beyond delivering electronic images of the surface topography. Oxide dispersion strengthened (ODS) steel is on of the most promising materials for the future nuclear fusion reactor because of its good radiation resistance, and higher operation temperature up to 750°C. The microstructure of ODS should not exceed tens of nm, therefore there is a strong need in a fast and reliable technique for their characterization. In this work, the results of low-kV SEM characterization of nanoprecipitates formed in the ODS matrix are presented. Application of highly sensitive photo-diode BSE detector in SEM imaging allowed for the registration of single nm-sized precipitates in the vicinity of the ODS alloys. The composition of the precipitates has been confirmed by TEM-EDS.

Manufacturing and characterization of molybdenum pellets used as targets for 99mTc production in cyclotron.

The method of 100Mo metallic target preparation for production of 99mTc by proton irradiation in 100Mo(p,2n)99mTc reaction was demonstrated. For this purpose, pressing of molybdenum powder into pellets and their subsequent sintering in reductive atmosphere were applied. The influence of parameters such as molybdenum mass and time of both pressing and sintering on the 100Mo target durability was investigated. Under the optimized conditions, 100Mo metallic pellet targets with density of 9.95±0.06g/cm3 were obtained. Morphology and structure of pressed pellets before and after sintering were studied by using standard optical microscope and Scanning Electron Microscope (SEM). Nanoindentation technique was used to investigate the mechanical properties such as nanohardness and Young modulus. Prepared 100Mo pellets were successfully irradiated with protons and 99mTc was efficiently isolated.