S. Casadio

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:

EXOTIC-7: Irradiation of ceramic breeder materials to high lithium burnup

Abstract The EXOTIC-7 irradiation experiment in the high flux reactor (HFR) has been completed. Its aim has been to investigate the effects of high lithium-burnup on the mechanical stability and tritium release characteristics of candidate ceramic breeder materials, originating from the fusion programmes of CEA, FZK, ENEA, AECL and ECN. The tested ceramic breeder materials were pellets of Li 2 ZrO 3 , LiAlO 2 and Li 8 ZrO 6 and pebbles of Li 4 SiO 4 and Li 2 ZrO 3 , with a variety of characteristics, like grain size and porosity. The test matrix provided the simultaneous irradiation of eight independent capsules with on-line tritium monitoring. Two capsules contained a mixture of Li 4 SiO 4 and beryllium pebbles. The experimental design, sample loading and main irradiation parameters are described. Some PIE results and analysis of in-situ tritium release behaviour are presented.

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.

The behaviour of ceramic breeder materials with respect to tritium release and pellet/pebble mechanical integrity

In situ tritium release experiments from several candidate fusion blanket ceramic breeder materials have been performed in the High Flux Reactor (HFR) at Petten over the last few years. The sixth experiment, EXOTIC-6, contained pellets of LiAlO2, Li2XrO3, Li6Xr2O7 and Li8ZrO6 and pebbles of Li4SiO4 and Li2ZrO3 which were irradiated up to a lithium burnup of 3%. A large number of temperature transients and purge gas composition changes were performed. From the temperature transients tritium residence times have been determined. Some preliminary results were presented at the 17th Symposium on Fusion Technology (SOFT) held in Rome in 1992. In the present paper results of a further analysis of the residence times are presented together with some postirradiation examination results. The LiAlO2 pellets showed a better mechanical stability than the Li-zirconates pellets. The pebbels remained intact. The tritium residence times determined from the tritium inventories were in good agreement with those previously determined from temperature transients. The tritium release characteristics of the materials investigated remain substantially unchanged up to the maximum lithium burnup achieved in this experiment.

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.

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.

Kinetics of tritium release from irradiated Li2TiO3 pebbles in out-of-pile TPD tests

Abstract The rate of tritium release from Li 2 TiO 3 pebbles was examined by post irradiation thermal desorption spectroscopy (the Temperature Programmed Desorption (TPD) method). Pre-treatments before and even after irradiation were found useful to gain insight on the behavior of these pebbles at different temperatures, as good spectrum de-convolution is achieved and kinetic parameters for the rate determining pseudo-first-order steps can be estimated. We show the results concerning Li 2 TiO 3 pebbles bed specimens developed in the frame of the European fusion technology program.

Inorganic Sol-Gel Preparation of Medium Sized Microparticles of Li2TiO3 from TiCl4 as Tritium Breeding Material for Fusion Reactors

Microspheres of Li2TiO3 were fabricated by a classical, inorganic sol-gel process from commercially available TiCl4. Elaborated process consists of the following main steps: (1) dissolving of TiCl4 in concentrated aqueous HCl and addition of LiOH; (2) formation of sol emulsion in 2-ethylhexanol-1 containing the surfactant SPAN-80 (EH); (3) gelation of emulsion drops by extraction of water with partially dehydrated EH; (4) impregnation of gel to Li:Ti molar ratio MR = 2; (5) thermal treatment at 1200°C in order to receive chloride free product. This temperature can be significantly lowered (to 750°C) by dechlorination starting solution TiCl4 by chemical treatment of the with nitric acid to form of nitrate-stabilized titania sols. Tritium release from sol-gel made Li2TiO3 microspheres were found very close to that observed for other traditional materials, however for the first sample process starts slightly earlier.