C. Alvani

Small field behavior of critical current in Y1Ba2Cu3O7 sintered samples

Critical currents carried by sintered Y1Ba2Cu3O7 superconducting samples have been measured at different temperatures close to the critical temperature Tc. The effects of an applied magnetic field perpendicular to the current direction have been investigated. A strong reduction of the dc current for field values smaller than the lower critical field Bc1 has been observed. The magnetic field dependence is discussed in terms of weak coupling between grains. The experimental data show an excellent agreement, at low field values, with the theoretical dependence valid for an array of Josephson junctions.

Li2TiO3 pebbles reprocessing, recovery of 6Li as Li2CO3

Abstract A process for obtaining Li 2 CO 3 from Li 2 TiO 3 powder by wet chemistry was developed. This is considered useful in view of the recovery of the 6 Li isotope from lithium titanate breeder burned to its end of life in a fusion reactor. The process was optimized with respect to the chemical attack of titanate and the precipitation of carbonate from aqueous solutions to get a powder with chemical and morphological characteristics suitable for its reexploitation in the fabrication of Li 2 TiO 3 pebbles. Reprocessing was also planned to adjust the 6 Li concentration to the desired value and to obtain a homogeneous distribution in the powder batch. Further development concerning reprocessing of sintered Li 2 TiO 3 pebbles is in progress exploiting the results obtained with lithium titanate powders.

Improvement of sintered density of Li2TiO3 pebbles fabricated by direct-wet process

Abstract The application of Li2TiO3 pebbles (diameter: 0.2–2 mm, density: 80–85%T.D., grain size:

Fabrication of Porous LiAlO2 Ceramic Breeder Material

AbstractThe gamma-LiAlO2 ceramic material is the reference candidate for the solid breeder option of the Next European Torus Program. The experiments and methodologies developed in Italy to produce high surface area gamma-LiA102 powders to be compacted by cold pressing and sintering at 70 to 90% of the theoretical density, keeping a near fully open porosity is presented. The lithiating step was assessed for the Li2CO3 and Li2O2 precursors reacting with Al2O3 having submicron grain size. Sol-gel methodologies were also developed for the gamma-LiAlO2 preparation by which very high surface area ceramic grade powders were obtained.

Tritium removal from various lithium aluminates irradiated by fast and thermal neutrons (COMPLIMENT experiment)

Abstract Within the frame of the COMPLIMENT experiment, γ-LiAlO 2 specimens with different microstructures (grain size distributions) were tested in the same environmental conditions to compare the effects caused by 6 Li(n, α)T reaction and by fast neutron scattering, the damaging dose being held at about the same level (1.6–1.8 dpa). The tritium retention times were obtained by the tritium removal of isothermal annealing under He + 0.1% H 2 sweeping gas. In spite of the different Li burnups (2.5% and 0.25%) and the residual tritium concentrations which were found in the irradiated specimens (4.3 Ci/g and 0.09 Ci/g, respectively, for specimens held at 450°C during the irradiations), the kinetics of tritium removal was not found to be discriminated by the two different irradiations. Moreover, the results were found to agree with those previously obtained by the “in-situ” TEQUILA experiment, performed on the same type of Li ceramics. Hence, the apparent first order desorption mechanism has been confirmed to control the kinetics of tritium removal from the porous fine grain γ-LiAlO 2 ceramics.

Reactive Pellets for Improved Solar Hydrogen Production Based on Sodium Manganese Ferrite Thermochemical Cycle

Hydrogen production by water-splitting thermochemical cycle based on manganese ferrite/sodium carbonate reactive system is reported. Two different preparation procedures for manganese ferrite/sodium carbonate mixture were adopted and compared in terms of material capability to cyclical hydrogen production. According to the first procedure, conventionally synthesized manganese ferrite, i.e., high temperature (1250°C) heating in Ar of carbonate/oxide precursors, was mixed with sodium carbonate. The blend was tested inside a temperature programed desorption reactor using a cyclical hydrogen production/material regeneration scheme. After a few cycles, the mixture resulted rapidly passivated and unable to further produce hydrogen. An innovative method that avoids the high temperature synthesis of manganese ferrite is presented. This procedure consists in a set of consecutive thermal treatments of a manganese carbonatel sodium carbonateliron oxide mixture in different environments (inert, oxidative, and reducing) at temperatures not exceeding 750°C. Such material, whose observed chemical composition consists of manganese ferrite and sodium carbonate in stoichiometric amounts, is able to evolve hydrogen during 25 consecutive water-splitting cycles, with a small decrease in cyclical production efficiency.

Superconducting properties of Y-Ba-Cu-O thin films grown in situ by laser ablation

Abstract Thin films of YBa 2 Cu 3 O y have been grown in situ on (100) SrTiO 3 and (100)MgO, by pulsed excimer laser evaporation from a stoichiometric target. The substrate temperature was adjusted at 750°C by using a CO 2 laser as the heating source and the oxygen partial pressure during the deposition was about 0.3 mbar. The samples have been patterned in the shape of lines 0.2 mm long and of widths between 5μm and 20μm. DC transport critical currents have been investigated as a function of temperature and of applied magnetic field up to 6T.

In-situ tritium release (CORELLI-2 experiment) and ex-reactor ionic conductivity of substoichiometric LiAlO2 breeder ceramics

LiAlO2 pellets with about 5% Li deficiency, prepared by a “wet” and a “dry” route were tested in situ for tritium release properties in nearly the same environmental conditions (CORELLI-2 experiment). Both the “wet” and “dry” route specimens were characterized by 80% of theoretical density (TD), almost fully open porosity and grain size ≤ 0.5 μm. The tritium removal rate evolution, following temperature or sweep gas changes during the irradiation, were observed to be nearly the same for both materials, in spite of their different preparation routes and impurities concentration. The ionic conductivities, as determined by impedance spectroscopy, were also similar. The presence of LiAl5O8 spinel phase in both samples apparently influenced the defect structure related transport properties of both lithium and tritium in these materials.

Effect of purge gas oxidizing potential on tritium release from Li-ceramics and on its permeation through 316L SS clads under irradiation (TRINE experiment)

Abstract The effect of red—ox potential of helium purge gas (variously doped with H2, H2O and O2) was examined on tritium release from Li-ceramics (LiAlO2 and Li2ZrO3 pellets) and on its permeation rate through the 316L stainless steel clads (bare and coated) held at 500°C. Decreasing the H2 content from 1000 vpm (reference ‘R’ gas mixture) to 100 vpm, and substituting H2O for H2, the tritium permeation rate (ca. 1.41010 atoms cm−2 s−1 in R-gas) increases. Tritium inventories in the Li ceramics were increased too. When a strong oxidizing purge (1000 vpm O2 added to He containing 100 vpm H2O) was used, a retention time (τ) of two days at 400°C was measured for Li2ZrO3. In this oxidizing environment the tritium permeation loss dropped by a factor five for the uncoated capsules while an aluminide coating became a very effective tritium barrier: tritium permeation flux at 550°C fell below the measurable limit.

Progress in Understanding Factors Governing the Sodium Manganese Ferrite Thermochemical Cycle

The mixed sodium manganese ferrite thermochemical cycle for sustainable hydrogen production is reviewed. Both the hydrogen production step and the reaction that leads to the regeneration of initial reactants are described as multistep reactions. The chemical cyclability of the reactive system has been demonstrated at 750°C.