T. Kurasawa

Correlation behavior of lithium and tritium in some solid breeder materials

Abstract Tritium behavior in candidate solid breeder materials such as Li 2 O, Li 2 SiO 3 or γ-LiAlO 2 has been clarified to have a close relation with the diffusion of lithium by the analysis of spin-lattice relaxation with nuclear magnetic resonance and ionic conductivity. The conductivity measurement is a simple and brief technique and can be performed even in a in situ condition under irradiation.

In-pile tritium release behavior from lithium aluminate and lithium orthosilicate of the VOM-23 experiment

Abstract Lithium aluminate from CEN/Saclay and lithium orthosilicate from KfK/Karlsruhe were irradiated in separate capsules in the VOM-23 experiment as a part of the IEA breeder exchange matrix (BEATRIX). The behavior of tritium release from lithium orthosilicate was observed to be similar to that of lithium aluminate in spite of differences in grain size, density and specific surface area. The tritium release kinetics was strongly influenced by the content of hydrogen isotopes in the purge gas. Tritium release was enhanced in purge gases with higher hydrogen contents which is indicative of a significant contribution from the surface adsorption-desorption process. The tritium release behavior in both materials appeared to be governed by both diffusion and surface adsorption-desorption mechanisms. A model including both mechanisms was developed to analyze the data from this experiment.

The time dependence of in-situ tritium release from lithium oxide and lithium aluminate (VOM-22H experiment)

An in-situ tritium recovery experiment was conducted in the JRR-2 reactor on Li 2 O and LiAlO 2 spheres. A technique for obtaining tritium diffusion coefficients from the time dependency of tritium release after incremental temperature changes was developed. The tritium retention in LiA1O 2 was higher than in Li 2 O for the same temperature. The apparent diffusion coefficients for LiAlO 2 at temperatures up to 900°C was one order magnitude higher than the previous, lower temperature TRIO data.

Electrical conductivity of a sintered pellet of octalithium zirconate

Abstract The conductivity of a sintered pellet of Li 8 ZrO 6 was measured in dry or wet argon atmosphere by the two-terminal technique with an AC Wheatstone bridge in the temperature range 350–1050 K. The temperature dependence of conductivity multiplied by temperature (σT) of Li 8 ZrO 6 in a dry environment had two transition points at 426 and 833 K. The activation energies of conductivity in high, middle and low temperature regions were 103.2, 52.1 and 37.4 kJ/mol, respectively. The activation energies of conductivity agreed well with those obtained by temperature dependence of spin-lattice relaxation time T 1 of 7 Li with pulsed nuclear magnetic resonance.

Mechanical properties of HIP bonded joints of austenitic stainless steel and Cu-alloy for fusion experimental reactor blanket

Abstract Tensile, fatigue and impact properties have been measured for hot isostatic pressing (HIP) bonded joints of type 316 austenitic stainless steel (SS316)/SS316, and of SS316/Al2O3 dispersion strengthened copper (DSCu). The HIP bonded joints of SS316/SS316 had almost the same tensile and fatigue properties as those of the base metal. The HIP bonded joints of SS316/DSCu had also almost the same tensile properties as those of the base metal of the DSCu, though total elongation and fatigue strength were slightly lower than those of the DSCu base metal. Further data accumulation, even with further optimization of fabrication conditions, is required, especially for HIP bonded SS316/DSCu joints, to confirm above data and reflect to blanket/first wall design.

In situ tritium recovery experiment from lithium oxide under high neutron fluence

In situ measurement of tritium release during irradiation provides a more realistic understanding of the tritium release mechanism than that obtained by the post-irradiation annealing method. The tritium release curves reached saturated values after irradiation of a few days at the reactor operation of 10 MW. The saturated values were in good agreement with the predicted values of the tritium generation rate obtained from neutronics calculation. Temperature dependence of tritium release under the temperature of 550°C at the pellet center was interpreted by the decomposition of LiOH(T) at the pellet surface. The ratio of tritium gas and tritiated water (HT/HTO) was strongly affected by the moisture generated from the piping system and the pellet. The retained tritium in Li2O was 0.5–0.9 wppm after the final stage of the irradiation of 760°C and the burnup of 0.24% of total Li.

Infrared spectroscopic analysis of OH− and OD− in crystalline Li2O as a function of chemical treatment☆

Infrared spectroscopy has been used to study the chemical form and approximate concentration of OH− and OD− in Li2O single crystals as a function of chemical treatment. Infrared absorption maxima at (3671±0.5) cm−1and (2711±3.3) cm−1 were observed for OH− and OD−, respectively. The absorption coefficient for OD− was determined to be 4.0±0.4 absorbance units per mol part per million OD− per mm of sample thickness. Vacuum baking of Li2O crystals reduced the OH− and OD− concentrations to <50 mppm; baking in a low moisture-level D2 environment at 600 to 800°C appeared to lead to volatilization of LiD from the Li2O crystals; and baking in D2 containing (350±50) mppm D2O at 600 to 800°C produced a measurable quantity of LiOD. In all cases, the observed spectra indicated the presence of only one distinguishable form of OH− or OD− in the Li2O lattice. Because of the close correspondence of the observed absorption maxima to reported values for pure LiOH and LiOD, the most consistent (although not conclusive) interpretation is that the OH− and OD− are present as a separate LiOH or LiOD phase at room temperature. Only limited conclusions can be drawn regarding the chemical state of OH− and OD− during the elevated temperatures exposures. An estimate of the approximate value for the solubility of tritium in Li2O at 800°C was made using data from D2/Li2O isothermal exposure experiments — this value was ⩾ 25 wppm.

Tritium release kinetics of solid lithium ceramics with irradiation defects

For the assessment of tritium release behaviors of lithium oxide under irradiation, a model reaction scheme was developed, which was based on the interactions of irradiation-induced defects with tritium. F0 centers (oxygen vacancy trapping two electrons) and their partners, O2 molecules, were considered to be produced under the blanket conditions. The model predictions were compared with the results of an in situ tritium recovery experiments with Li2O, called BEATRIX-II, and the observed tritium release behaviors were successfully interpreted by the present model. The reactions were discussed, of which the equilibrium constant and rate constant were to be determined for the further development of the model.

Electrical resistivities of the uranium carbides

Abstract Electrical resistivities of arc-melted uranium carbides, UC, UC2, U2C3 and UC + UC2, were measured over the temperature range between 4 and 1900 K. The monocarbide, dicarbide and the mixture of carbides showed metallic character in their resistivity dependence on temperature above 30 K, while below this the resistivities were constant. U2C3 showed a knee in the resistivity curve at 54.0 K corresponding to a magnetic transition. Above 1100 K, the resistivity of U2C3 did not vary with temperature. The resistivity of the mixture (UC + UC2 with U2C3 precipitates) showed an arrest between 800 and 950 K.

Reaction of several iron and nickel based alloys with sintered Li2O Pellets

Abstract The reaction of type 316 stainless steel, Incoloy 800, Hastelloy X-R, Inconel 600 and pure Ni with sintered Li 2 O pellets has been studied between 800 and 1100°C under dynamic vacuum. The reaction products were analyzed by means of metallographic, microprobe and X-ray diffraction methods. The reactions proceeded measurably between 800 and 950°C and appreciably at 1000°C, being greatest with Incoloy 800 and least with Hastelloy X-R. Among the primary alloy constituents, chromium was exclusively attacked by lithium and oxygen diffusing from the Li 2 O into the alloys to form LiCrO 2 . This phase grew into a reaction zone (subscale) of uniform thickness beneath the surface of each alloy. Preferential growth of LiCrO 2 along the grain boundaries was observed only in the case of Inconel 600 below 950°C. On the other hand, iron diffused toward the Li 2 O pellets to form volatile Li 5 FeO 4 . However, any reaction product associated with Ni was not detected and Ni metal was little attacked by the Li 2 O pellet over the whole range of reaction temperature.