Li Mass Loss Research Articles

Long‐term thermal stability of Li4TiO4–Li2TiO3 core–shell breeding pebbles under continuous heating in H2/Ar atmosphere

AbstractThe long‐term thermal stability of tritium breeding materials during service is a key factor to ensure efficient tritium release. In this study, the long‐term thermal stability of advanced Li4TiO4–Li2TiO3 core–shell breeding pebbles under continuous heating in 1%H2/Ar at 900°C was investigated for the first time. The results show that this core–shell material loses 3.4% Li mass after heating for 30 days, resulting in a reduction in Li density to .415 g/cm3, which is still significantly higher than other breeding materials. The moisture in the sample bed will determine the form of Li volatilization and thus affect the rate of Li mass loss. The core–shell pebbles maintain favorable phase stability during long‐term heating, and the grain sizes of the Li2TO3 shell and Li4TiO4 core after 30 days of heating are 6.5 ± 1.5 and 6.9 ± 2.5 μm, respectively. Moreover, the samples did not crack or collapse during long‐term heating and still had a satisfactory crushing strength of 37.61 ± 7.13 N after 30 days of heating. Overall, the high Li density and good thermal stability during long‐term heating demonstrate that the Li4TiO4–Li2TiO3 core–shell breeding pebbles are a very reliable tritium breeding material for long‐term service under harsh operating conditions.

Influence of Lithium Mass Transfer on Tritium Behavior in Pebbles of Li2TiO3 with Excess Lithium

• Li 2 TiO 3 with excess Li was heated at 900 °C for 30 days in 1000 Pa H 2 /Ar flow. • Li mass loss was 0.7 wt%, grain size increased and BET surface area decreased. • The majority of evaporative Li was lost by first 3 days. • The influence of the 30 days heating on tritium behavior was not large. • Tritium recovery by isotope exchange with H 2 was effective at 600 °C and 900 °C. Tritium breeding ceramic materials are placed at high temperatures for a long period in a fusion DEMO reactor. Therefore, the understanding of Li mass loss phenomena and its influence on tritium behavior are important. In this study, the pebbles of Li 2 TiO 3 with excess Li were heated at 900 °C for 30 days in a 1000 Pa H 2 /Ar flow and tritium sorption and recovery experiments were carried out. Li mass loss by the heating was evaluated to be 0.7 wt%. The value of Li mass loss was almost same as that for 3 days heating at the same condition. Tritium sorption capacity for the heated pebbles at 600 °C and 900 °C were almost same as that for the pebbles as received. Tritium sorbed in the pebbles could not be recovered effectively by the 1000 Pa H 2 /Ar purge at room temperature and 300 °C but it could be recovered at 600 °C and 900 °C. The influence of the long-time heating on the behavior of tritium sorbed in the pebbles was not large.

Li mass loss and structure change due to long time heating in hydrogen atmosphere from Li2TiO3 with excess Li

Abstract Solid tritium breeding materials are used in a high temperature condition for a long time in a fusion reactor blanket. It is expected that a certain amount of Li will be evaporated and the pebble structure will be changed. Understanding of Li mass transfer behavior in the blanket is an important issue from viewpoints of establishment of tritium cycle and tritium safety. In this work the pebbles of Li2TiO3 with excess Li were heated at 900 °C in 1000 Pa H2/Ar flow for a long time (72, 240, 720, 1200 h). The amount of Li mass loss under the hydrogen atmosphere was 0.665 wt% which was less than that under the water vapor atmosphere observed in the previous study. No significant Li mass loss was observed after 240 h. By heating for 240 h, the grain diameter increased from 1.8 to 3.1 μm and the specific surface area decreased from 0.72 to 0.20 m2/g. After 240 h, no significant grain growth and no significant decrease in the specific surface area were observed. From these results, it seems that there is a relation between Li mass loss and grain growth.

Evaluation of Li mass loss from Li2TiO3 with excess Li pebbles in water vapor atmosphere

Understanding of Li mass transfer behavior in a tritium breeding blanket is an important issue from viewpoints of establishment of tritium cycle and tritium safety. In this work, weight reduction property of Li2TiO3 with excess Li pebbles, which were fabricated by National Institutes for Quantum and Radiological Science and Technology, was investigated and the amount of Li mass loss and the rate of Li mass loss in water vapor atmosphere at elevated temperatures were evaluated. The Li mass loss proceeding at 900 °C with a relatively high rate was limited. The Li mass loss of Pebble210 (Li/Ti = 2.10) was 1.2 wt% and that of Pebbe211 (Li/Ti = 2.11) was 1.4 wt%, eventually. The rate of the Li mass loss increased with increasing temperature and it seemed to increase proportionally to a square root of water vapor pressure. An empirical formula for the Li mass loss was proposed as a function of temperature, heating time and water vapor pressure in a purge gas.

Li mass loss from Li2TiO3 with excess Li pebbles fabricated by optimized sintering condition

Understanding of Li evaporation properties is important because Li mass transfer decreases tritium breeding ratio and influences tritium behavior possibly. In QST, the pebbles of Li2TiO3 with excess Li were fabricated by the optimized sintering condition recently and it was confirmed that the pebbles have a good tritium release property. In this work, the weight reduction of the pebbles at elevated temperatures was investigated considering the releases of water vapor and CO2 from the pebbles. Furthermore the mechanism of Li mass loss from Li2TiO3 with excess Li pebbles was discussed by comparing the difference between the pebbles formed by the optimal fabrication method, Pebble210 and ones formed by the previous fabrication method, Pebble211. The release behaviors of water vapor from Pebble210 and Pebble211 were almost same except a small peak at 350°C. A large amount of CO2 was released from Pebble211 at over 700°C which is close to the melting point of Li2CO3. On the other hand, the release of CO2 from Pebble210 was not observed. The weight reduction excluding the contribution of water vapor for Pebble210 was smaller than that for Pebble211. The difference of weight reduction between Pebble210 and Pebble211 are caused by the presence of Li2CO3.

Water vapor concentration dependence and temperature dependence of Li mass loss from Li2TiO3 with excess Li and Li4SiO4

In this study, weight reduction of Li2TiO3 with excess Li and Li4SiO4 at elevated temperatures under hydrogen atmosphere or water vapor atmosphere was investigated. The Li mass loss for the Li2TiO3 at 900°C was 0.4wt% under 1000Pa H2 atmosphere and 1.5wt% under 50Pa H2O atmosphere. The Li mass loss for the Li2TiO3 increased proportionally to the water vapor pressure in the range from 50 to 200Pa at 900°C and increased with increasing temperature from 700 to 900°C although Li mass loss at 600°C was significantly smaller than expected. It was found that water vapor concentration dependence and temperature dependence of Li mass loss for the Li2TiO3 and the Li4SiO4 used in this work were quite different. Water vapor is released from the ceramic breeder materials into the purge gas due to desorption of adsorbed water and water formation reaction. The released water vapor possibly promotes Li mass loss with the formation of LiOH on the surface.

Mass loss of Li2TiO3 pebbles and Li4SiO4 pebbles

It has been known that water vapor is released from ceramic breeder materials into the purge gas due to desorption of adsorbed water under dry atmosphere and due to the water formation reaction under hydrogen atmosphere. However, an effect of water vapor in the purge gas to Li mass loss has not been understood. In this study, mass loss of Li2TiO3 (NFI) and Li4SiO4 (FzK) under hydrogen atmosphere (1000Pa H2/Ar), and mass loss of Li2TiO3 (NFI) and Li2TiO3 with additional Li which is in a developmental stage (JAEA) under water vapor atmosphere (50Pa H2O/Ar) were compared, respectively. It was found that under hydrogen atmosphere Li mass loss of Li4SiO4 and Li2TiO3 is same degree although the amount of water vapor released from Li4SiO4 is larger than that from Li2TiO3. It was clarified with regard to Li2TiO3 that Li mass loss in water vapor atmosphere is larger than that in hydrogen atmosphere. Mass loss of Li2TiO3 with additional Li (JAEA) was larger than that of Li2TiO3 (NFI). It was observed by X-ray analysis that Li deposits formed on the inner wall of the quartz tube contain Li2SiO3.

Li Enrichment, Mass Loss, and CN Abundances in High Rotating K Giants

High rotating low-mass K giants can be considered as interesting new “laboratories” for studies of the mixing process and mass loss. By means of high spectral resolution observations of some rapidly rotating K giants we found a series of connections between rotation, stellar activity, high Li abundance and mass loss. These giants show low 14N and high 13C enrichment. Nearly half of them are Li rich. This frequency is much higher than the ~ 2% corresponding to common, low rotating K giants. They are also the most suitable objects to test new models of rotation-induced mixing or planet engulfing scenarios.