Thermodynamic considerations for the use of vanadium alloys with ceramic breeder materials

Fusion energy is considered to be an attractive energy form because of its minimal environmental impact. In order to maintain this favorable status, every effort needs to be made to use low activation materials wherever possible. The tritium breeder blanket is a focal point of system design engineers who must design environmentally attractive blankets through the use of low activation materials. Of the several candidate lithium-containing ceramics being considered for use in the breeder blanket, Li{sub 2}O, Li{sub 2}TiO{sub 3}, are attractive choices because of their low activation. Also, low activation materials like the vanadium alloys are being considered for use as structural materials in the blanket. The suitability of vanadium alloys for containment of lithium ceramics is the subject of this study. Thermodynamic evaluations are being used to estimate the compatibility and stability of candidate ceramic breeder materials (Li{sub 2}O, Li{sub 2}TiO{sub 3}, and Li{sub 2}ZrO{sub 3}) with vanadium and vanadium alloys. This thermodynamic evaluation will focus first on solid-solid interactions. As a tritium breeding blanket will use a purge gas for tritium recovery, gas-solid systems will also receive attention

Tritium release from irradiated lithium aluminate, can it be improved?

Lithium aluminate is an attractive material (in terms of its chemical, mechanical and irradiation properties) for breeding tritium in fusion reactors; however, its tritium release characteristics are not as good as those of other candidate materials. To investigate whether tritium release from lithium aluminate can be improved, we have studied the tritium release from irradiated samples of pure lithium aluminate, lithium aluminate doped with Mg, and lithium aluminate with a surface deposit of platinum. The release was studied by the temperature programmed desorption (TPD) method. Both the platinum coating and magnesium doping were found to improve the tritium release characteristics, as determined by TPD. Tritium release shifted to states with lower activation energies for the altered materials

Desorption activation energies for tritium release from ceramic breeders

Desorption has been identified as an important process in determining the kinetics of tritium release from ceramic tritium breeder materials considered for use in fusion reactors. However, details of the desorption of tritium from ceramic materials are mostly unknown. Models of tritium release have treated desorption as a simple process with desorption occurring from one type of site with one activation energy. Recent measurements of the rates of water uptake by LiAlO/sub 2/, and evolution of water from LiAlO/sub 2/ exposed to water, indicate the presence of multiple types of desorption sites. Estimates of desorption activation energies were obtained from these data and from data in the literature suggesting multiple types of desorption sites for desorption from Li/sub 2/O and Li/sub 4/SiO/sub 4/. 15 refs., 4 figs

Tritium release from irradiated lithium aluminate, can it be improved

Lithium aluminate is an attractive material (in terms of its chemical, mechanical and irradiation properties) for breeding tritium in fusion reactors; however, its tritium release characteristics are not as good as those of other candidate materials. To investigate whether tritium release from lithium aluminate can be improved, we have studied the tritium release from irradiated samples of pure lithium aluminate, lithium aluminate doped with Mg, and lithium aluminate with a surface deposit of platinum. The release was studied by the temperature programmed desorption (TPD) method. Both the platinum coating and magnesium doping were found to improve the tritium release characteristics, as determined by TPD. Tritium release shifted to states with lower activation energies for the altered materials

Modeling of tritium behavior in ceramic breeder materials

The model described in this paper considers diffusion and desorption as the rate-controlling mechanisms for tritium release from a ceramic breeder material. This model was used to predict the tritium release from samples of Li/sub 2/SiO/sub 3/ and LiAlO/sub 2/, given the temperature history of the samples. The diffusion-desorption model did a better job of predicting the tritium release for these samples under pure helium purge gas than did a pure diffusion model using the best values for the diffusivity of these materials available. The activation energies of desorption found from the best fit of the predicted tritium release to the observed release were 105-108 kJ/mol for Li/sub 2/SiO/sub 3/ and 85.7 kJ/mol for LiAlO/sub 2/. These values are in fair agreement with activation energies reported in the literature. 13 refs., 6 figs

Reforming petroleum-based fuels for fuel cell vehicles : composition-performance relationships.

Onboard reforming of petroleum-based fuels, such as gasoline, may help ease the introduction of fuel cell vehicles to the marketplace. Although gasoline can be reformed, it is optimized to meet the demands of ICEs. This optimization includes blending to increase the octane number and addition of oxygenates and detergents to control emissions. The requirements for a fuel for onboard reforming to hydrogen are quite different than those for combustion. Factors such as octane number and flame speed are not important; however, factors such as hydrogen density, catalyst-fuel interactions, and possible catalyst poisoning become paramount. In order to identify what factors are important in a hydrocarbon fuel for reforming to hydrogen and what factors are detrimental, we have begun a program to test various components of gasoline and blends of components under autothermal reforming conditions. The results indicate that fuel composition can have a large effect on reforming behavior. Components which may be beneficial for ICEs for their octane enhancing value were detrimental to reforming. Fuels with high aromatic and naphthenic content were more difficult to reform. Aromatics were also found to have an impact on the kinetics for reforming of paraffins. The effects of sulfur impurities were dependent on the catalyst. Sulfur was detrimental for Ni, Co, and Ru catalysts. Sulfur was beneficial for reforming with Pt catalysts, however, the effect was dependent on the sulfur concentration

No persisting effect of partial sleep curtailment on cognitive performance and declarative memory recall in adolescents

Growing evidence indicates that sleep facilitates learning and memory processing. Sleep curtailment is increasingly common in adolescents. The aim of this study was to examine the effects of short‐term sleep curtailment on declarative memory consolidation in adolescents. A randomized, cross‐over study design was chosen. Twenty‐two healthy subjects, aged 14–16 years, spent three consecutive nights in the sleep laboratory with a bedtime of 9 h during the first night (adaptation), 4 h during the second (partial sleep curtailment) and 9 h during the third night (recovery). The control condition consisted of three consecutive nights with bedtimes of 9 h. Both experimental conditions were separated by at least 3 weeks. The acquisition phase for the declarative tests was between 16:00 and 18:00 hours before the second night. Memory performance was examined in the morning after the recovery night. Executive function, attention and concentration were also assessed to control for any possible effects of tiredness. During the 4‐h night, we observed a curtailment of 50% of non‐rapid eye movement (non‐REM), 5% of slow wave sleep (SWS) and 70% of REM sleep compared with the control night. Partial sleep curtailment of one night did not influence declarative memory retrieval significantly. Recall in the paired‐associate word list task was correlated positively with percentage of non‐REM sleep in the recovery night. Declarative memory consolidation does not appear to be influenced by short‐term sleep curtailment in adolescents. This may be explained by the high ability of adolescents to compensate for acute sleep loss. The correlation between non‐REM sleep and declarative memory performance supports earlier findings