Sapphire is best known for its hardness that makes it ideal for many mechanical and optical applications, but its resistance to radiation damage and its optical properties, combined with metallic nano-particles, make it promising for future opto-electronic and plasmonic devices. In this paper, we present an overview of our work on the fabrication of metallic nano-particles embedded in synthetic sapphire by means of ion implantation, thermal annealing and high energy ion irradiation. We show that we can have control over the amount and size of the nano particles formed inside the matrix by carefully choosing the parameters during the preparation process. Furthermore, we show that anisotropic nano particles can be obtained by an adequate high energy ion irradiation of the originally spherical nano particles. We also have studied the linear and non-linear optical properties of these nano-composites and have confirmed that they are large enough for future applications.

The effects of thermal treatments on the thermoluminescent (TL) signal of NaCl (ACS reagent) induced by gamma radiation were investigated. Samples of NaCl were thermally treated at 500, 800 and 1000 °C and characterized by X-Ray diffraction and scanning electron microscopy. After their exposure 0.1 to 150 Gy of gamma radiation from a gamma-ray source of 60Co, a TL curve for each temperature of treatment was obtained. We observed a different TL behavior on the irradiated samples as a function of the temperature applied during the thermal treatments. For the sample treated at 500 °C, three peaks centered at 102, 133 and 228 °C were observed. Samples treated at 800 and 1000 °C showed two main peaks at 128 and 220 °C and 136 and 219 °C, respectively; however, the highest TL intensity signal was observed for the sample at 800 °C. All samples showed a linear dependency of the integrated TL intensity from the signal emitted as function of the irradiation time. This is an important advantage because NaCl could be applied as a very low cost thermoluminescent dosimetric material. A comparison between the TL signal induced by gamma radiation in pure and Eu doped NaCl is also reported.

The TRISO (tristructural isotropic) coated fuel particle is made of a uranium oxide kernel coated with three layers of pyrolytic carbon and one of silicon carbide. This fuel, originally used in High Temperature Reactors, has been proposed as accident tolerant fuel for Light Water Reactors after the accident in Fukushima. Although this fuel is capable of retaining fission products within the particle up to 1600°C, little is known on the origin of this temperature limit. Therefore, in order to increase the safety of this type of fuel, it is necessary to understand the origin of the degradation of the materials that compose this fuel. We have studied the effect of temperature on the microstructure and diffusion of silver in pyrolytic carbon coatings produced by fluidized bed chemical vapor deposition. Samples were heat treated at 1000°C, 1400°C and 1700°C for 200 hrs. under inert atmosphere. The effect of temperature on the microstructure and silver diffusion behavior were analyzed by Raman spectroscopy, X-Ray diffraction, optical microscopy, SEM and TEM. We observed that the microstructure of PyC changed drastically above 1400°C, showing the increase in anisotropy and the re-orientation of the graphene planes. The diffusion of silver appears to be also correlated with this change in microstructure.

The insertion of reprocessed fuel spiked with thorium in a typical PWR fuel element considering (TRU-Th) cycle was simulated using different fissile materials that varied from 5.5% to 7.0%. The reprocessed fuels were obtained using the ORIGEN 2.1 code from a burned PWR standard fuel (33,000 MWd/tHM burned), with 3.1% of initial enrichment, which was remained in the cooling pool for five years and then reprocessed using UREX+ technique. The kinf, hardening spectrum and the fuel evolution during the burnup were evaluated. This study was performed using the SCALE 6.0

Recently, the research team synthesized some scandium- and titanium-based oxide compounds, in order to analyze their thermoluminescent (TL) response [1-2]. The oxides mixture Sc2TiO5:Eu2Ti2O7:Sc2O3 was synthesized in equilibrium phase by solid state reaction at 1100 °C / 48 h. The structural characterization was performed by XRD and SEM. The TL properties of this oxide mixture were examined after exposing it to gamma radiation from a 60Co source. The glow curve showed two main glow peaks at 151 °C and 260 °C, yet the curve shape looks quite complex, revealing that it is composed by overlapped individual TL peaks, which was confirmed with the Tstop preheat method performed [3]. The linear dose-response between 150 to 600 Gy was obtained, followed by a slow saturation stage. The intensity of the glow curves increases as the radiation dose increases, and their maxima remain at the same temperature values, which indicates that the TL phenomenon follows first-order kinetics [4]. After ten irradiation-TL readout cycles at 500 Gy, good stability (SD 2.02 %) between TL integrated response and the exposure dose was found. It is concluded that Sc2TiO5:Eu2Ti2O7:Sc2O3 is a promising material to use as high-dose dosimeter.

The displacement per atom (dpa) has been a specific issue to evaluate the damage in the first wall of the Tokamak. Two different first wall materials were evaluated. In this study, MCNP5 code was used to obtain the neutron flux, the energy deposition and the main reaction rates, on the inboard and outboard first wall. The damage calculations were performed by the SPECTER code using the neutronic parameters obtained by MCNP5. The Tokamak reactor modeled has similar dimensions to the ITER. Tungsten and beryllium alloys were simulated on the outboard first wall. The results indicate which material has a higher resistance to be damage and dpa values for the analyzed material.

This contribution presents a critical review about some materials used in dosimetry and the interest that has emerged on topaz recently. In addition, results about the feasibility for synthesizing topaz by the HYSY-CVD route using Na2SiF6 and Al2O3 are shown. Synthesis tests in nitrogen atmosphere were conducted varying temperature (700 and 750°C) and time (60 and 90 min) while maintaining constant the amounts of Al2O3 and Na2SiF6. The microstructural characterization by XRD, SEM and EDS revealed the succesful formation of topaz and aluminium fluoride.

Silicon carbide (SiC) has a potential to replacement zircaloy as fuel cladding material due to its high temperature tolerance, chemical stability and low neutron affinity. These characteristics may improve the economic and safety of nuclear reactors. Previous work has examined the possible use of SiC as a fuel cladding material in a PWR (Pressurized Water Reactor) environment. However, the advantage thermo mechanical and neutronic analysis replacement zircaloy cladding is not clear. Literature reviews has been done to predict the thermo mechanical behavior of SiC in high temperatures. The neutronic analysis was made using the SCALE 6.0 (Standardized Computer Analysis for Licensing Evaluation) code. This codes system is widely accepted and used worldwide for safety analysis and criticality of nuclear reactors has been utilized to model a typical fuel element of a PWR. It was used the CSAS6 and TRITON modules. The goals are to evaluate the behavior of the infinite multiplication factor (kinf) and neutron flux using SiC as a fuel cladding material.

Integrity and lifetime of reactor pressure vessels are practically determined by their material resistance against fast/non-ductile failure and consequently by their radiation damage resulting in irradiation embrittlement and hardening. Mechanism of irradiation embrittlement of RPV materials depends on selected materials and operation conditions but their values depend in a large extent on reactor design, i.e. on neutron flux/fluence depending on RPV wall. Generally, new RPV design allows smaller neutron fluences but absolute value of irradiation embrittlement still depends on a choice of RPV material. Even though radiation damage (especially irradiation embrittlement) is important for RPV behavior, integrity and lifetime depends, in principle, on final value of applied fracture mechanics parameter –transition temperature. Thus, its initial value as well as its shift due to irradiation embrittlement is of interest but only the embrittlement can be affected during operation.

The principles of Stress Corrosion Cracking (SCC) are supported in the behavior of the oxide film formed into a crack; in fact the active dissolution of metal atoms after a film rupture and until fill repassivation is the base of slip dissolution model which is a good model to justified the crack tip advance in stainless steels (SS) used in vessel internal components for the nuclear industry. This paper shows the analyzed made at the oxide film formed on samples of 304L SS sensitized and non sensitized, under autoclave conditions (288°C, 8MPa) with and without crevice geometric formation, using SEM, XRD and Raman Spectra.

The crevice and no crevice condition allow establish the difference of an oxide formed on a free surface (no crevice) and the oxide formed on the wall in a crack (crevice); the chemical and physical properties of oxide film can alter the mechanism and kinetics of SCC process, so the difference between these two conditions will give more information about the behavior of the oxide film.

Currently, the research team is systematically studying the oxide compounds present in the ternary system In2O3-TiO2-MgO in order to analyze its thermoluminescent (TL) response. The oxide Mg1.5InTi0.5O4 present in this system was synthesized by a solid state reaction at 1350 °C in air. The X-ray powder diffraction pattern showed a spinel-type structure for this compound. In this work, this spinel, as well as its TL properties when exposed to beta particles, are being reported for the first time. The glow curve is simple and wide with a TL maximum located at 203 °C at 21.33 Gy. The peak shows a shift to lower temperatures and it increases its intensity, as the irradiation dose increases. The lineal behavior was observed between 10.66 to 341 Gy, and no saturation signs were observed. The relative sensitivity variation was 2.7% and standard deviation after ten consecutive irradiation - TL readout cycles was 1 %. The minimum detectable dose was 5.65 Gy for this spinel-type oxide [3]. These results suggest the possible application of Mg1.5InTi0.5O4 in dosimetry.