Radiocarbon AMS determination of the biogenic component in CO2 emitted from waste incineration

The thermal utilization of waste for energy production is gaining importance in European countries. Nevertheless, the combustion of waste leads to significant CO₂ emissions in the atmosphere which, depending on the fraction of biogenic and fossil materials, have to be only partially accounted for the national greenhouse gas inventory. For this reason the development of proper methodologies for the measurement of the biogenic fraction in the combusted waste is an active research field. In fact the determination of the radiocarbon concentration in the carbon dioxide stack emissions allows to have a direct indication of the biogenic component in the burned fuel. We present the results of the AMS radiocarbon analyses carried out on carbon dioxide sampled at the stack of three power plants located in Northern Italy burning natural gas, landfill biogas and SRF (Solid Recovered Fuel) derived from MSW (Municipal Solid Waste). The sampling apparatus and the applied processing protocols are described together with the calculation procedures used to determine, from the measured radiocarbon concentrations, the proportion of biogenic and fossil component in the flue gas and in the combusted fuel. The results confirm the high potentialities of this approach in the analysis of industrial CO₂ emissions.     

Corrosion resistance of ceramics SiC and Si3N4 in flowing lead-bismuth eutectic

A corrosion test was conducted to investigate the corrosion characteristics of SiC and Si₃N₄ in a flowing lead-bismuth eutectic (Pb-Bi) with a fluid temperature of 550 °C, a velocity of 1 m/s, and an oxygen concentration of 1 × 10⁻⁶ wt% for an exposure time of 2000 h. The weight losses of the SiC and Si₃N₄ specimens were lower than those of corrosion-resistant steels tested under the same condition. The specimens showed excellent resistance against an element dissolution and an oxidation in the Pb-Bi flow. The surface was slightly damaged due to some stresses of the Pb-Bi flow and/or those generated by adhered Pb-Bi in the test procedure.     

Molecular-sieving effect of zeolite 3A on adsorption of H2, HD and D2

Synthetic zeolite 3A has the molecular-sieving windows of nominal diameter 0.3 nm in its crystal lattice framework, which obstruct the crystalline adsorption of molecules of diameter larger than 0.3 nm, except water, hydrogen and helium. The window's diameter slightly varies with temperature, however, that is endorsed in experimental results that hydrogen cannot be adsorbed at the liquid-nitrogen temperature. Authors measured the range of temperature where zeolite 3A permits hydrogen adsorption, and revealed the temperature difference of several degrees in appearance of molecular sieving for H₂ and D₂. This difference is important because from a H₂–D₂ mixture one isotope could be isolated by adsorption if operated at a temperature regulated between the molecular-sieving appearance temperatures. We have reported large values of D₂/H₂ separation factor obtained from molecular-sieving experiments. In this study, the effect of sieving for the hybrid-atomic isotope HD is examined using a H₂–HD–D₂ mixture. We here report the experimental HD/H₂ separation factor evaluated between the D₂/H₂ factor and unity. This result is significant because where the effective molecular diameter concerning the sieving mechanism is suggested. From this knowledge, the isotopic effect of sieving for HT and DT can be predicted.     

Comparative study of silicate glasses containing Bi2O3, PbO and BaO: Radiation shielding and optical properties

The radiation shielding and optical properties of xBi₂O₃:(100-x)SiO₂, xPbO:(100-x)SiO₂ and xBaO:(100-x)SiO₂ glass systems (where 30 ? x ? 70 is the composition by weight%) have been investigated. Total mass attenuation coefficients (μ_m) of glasses at 662 keV were improved by increasing their Bi₂O₃ and PbO content, which raised the photoelectric absorption in glass matrices. Raising the BaO content to the same fraction range, however, brought no significant change to μ_m. These results indicate that photon is strongly attenuated in Bi₂O₃ and PbO containing glasses, and but not in BaO containing glass. The results from the optical absorption spectra show an edge that was not sharply defined; clearly indicating the amorphous nature of glass samples. It is observed that the cutoff wavelength for Bi₂O₃ containing glass was longer than PbO and BaO containing glasses.     

Interaction of energetic clusters (Au3, Au400 and C60) with organic material and adsorbed gold nanoparticles

Using molecular dynamics simulations (MD), this contribution compares the interaction of three energetic clusters (Au₃, Au₄₀₀ and C₆₀) with a hybrid surface of crystalline polyethylene (PE) covered by a layer of gold nanoparticles. This model system mimics the situation encountered in metal-assisted secondary ion mass spectrometry. The chosen impact points are representative of the PE surface, the metal particles and the frontier between the metal and the polymer. The simulations show the differences between the impact over the Au nanoparticle and the polymer surface, in terms of projectile penetration, crater formation and sputtering yield of PE and gold species. For C₆₀ and Au₃ projectiles, a simple correlation is found between the quantity of energy deposited in the top polymeric layers and the quantity of sputtered polymer material, including all the impact points. The results obtained with Au₄₀₀ do not fit on this line, indicating that other physical parameters are prevalent. The mechanistic view of the interaction provided by the MD helps explain the differences. In short, while C₆₀ and Au₃ quickly break apart, creating energetic recoils and severing many bonds in the surface, Au₄₀₀, with the largest total momentum by far (∼10 times larger than the others) and the lowest energy per atom (25 eV), tends to act and implant in the solid as a single entity, pushing the polymeric material downwards and breaking few bonds in the surface.     

Chlorination of UO2, PuO2 and rare earth oxides using ZrCl4 in LiCl-KCl eutectic melt

A new chlorination method using ZrCl₄ in a molten salt bath has been investigated for the pyrometallurgical reprocessing of nuclear fuels. ZrCl₄ has a high reactivity with oxygen but is not corrosive to refractory metals such as steel. Rare earth oxides (La₂O₃, CeO₂, Nd₂O₃ and Y₂O₃) and actinide oxides (UO₂ and PuO₂) were allowed to react with ZrCl₄ in a LiCl-KCl eutectic salt at 773 K to give a metal chloride solution and a precipitate of ZrO₂. An addition of zirconium metal as a reductant was effective in chlorinating the dioxides. When the oxides were in powder form, the reaction was observed to progress rapidly. Cyclic voltammetry provided a convenient way of establishing when the reaction was completed. It was demonstrated that the ZrCl₄ chlorination method, free from corrosive gas, was very simple and useful.     

Chemical state and distribution of iodine deposits on 17% Cr/12% Ni steel oxidised in CO2/CH3I gas mixtures

Iodine-131 is one of the most important volatile fission product elements with respect to radiobiological impact, and the characterisation of its chemical state and distribution on reactor surfaces is required for reactor safety assessments. To this end, duplicate samples of Type 316 (17%Cr/12% Ni) stainless steel oxidised in CO₂/CH₃I gas mixtures and previously characterised using X-ray photoelectron spectroscopy have been examined using Raman spectroscopy. The aim is to improve our understanding of the way in which iodine is distributed throughout the oxide scale and to identify its chemical state. In this paper we present Raman spectra recorded from a series of stainless steel specimens together with spectra recorded from a number of standard iodine compounds. It is demonstrated that the technique is well suited as a fingerprint method of species identification, can differentiate between the chemical state of iodine as iodide and iodate and can analyse thin oxide films (5–50 nm). Identification of iodine deposits in these oxide films at concentrations of 2 at% was not achieved however, there being insufficient iodine present to distinguish any peaks present from the background signal. It is concluded that local concentrations of iodine in oxide inclusions of different composition/morphology on the steel surface does not occur to any extent.     

Determination of Electron Swarm Parameters in Pure CHF3 and CF4 by a Time-Resolved Method

The density-normalized effective ionization coefficient (α-η)/N (α and η are the ionization and attachment coefficients respectively), the electron drift velocity V e and density-normalized longitudinal diffusion coefficient ND L in trifluoromethane (CHF3 ) and carbon tetrafluoride (CF4 ) were measured using a pulsed Townsend technique over a wide E/N range. From the plots of (α-η)/N, we have derived the limiting field strength, (E/N) lim , which is valid for the analysis of insulation characteristics and applications to power equipment. Comparisons of the electron swarms parameters between CHF3 and CF4 have been performed, and the global warming potential (GWP) is also taken into account.