Influence of Framework Silica-to-Alumina Ratio on the Tritiated Water Adsorption and Desorption Characteristics of NaX and NaY Zeolites

The fixed-bed adsorption process has been studied as one of the promising processes for the recovery of tritiated water in the field of nuclear fusion. The influence of the framework SiO₂/Al₂O₃ ratio ranging from 2.0 to 10.0 on the tritiated water adsorption and desorption characteristics in the H₂O-HTO binary systems was systematically examined using NaX and NaY zeolites. A large difference in isotherm was observed by changing the SiO₂/Al₂O₃ ratio from 7.0to 10.0. The framework SiO₂-to-Al₂O₃ ratio has a slight effect on the isotope separation factor. The capacity of removable water from NaY10.0 around room temperature is approximately four times larger than that from NaA2.0 even though both zeolites have nearly the same capacity for absorbable H₂O at nearly P=P0= 1:0. The weaker interaction generates the isotope effect on desorption. The HTO dehydration ratio has a strong interrelation with the accumulative amount of purge gas. Dehydration is independent of the flow rate of the purge gas. On the design side of the water adsorption process with multi-absorber systems, the size of the water absorber such as a dryer or dehumidifier can be downscaled with NaY10.0 as the adsorbent since the consideration of the heating and cooling periods necessary for the temperature swing desorption process is not required in the NaY10.0 column.     

Adsorption Characteristics of Water Vapor on Gamma-Lithium Aluminate

Lithium aluminate (LiAl0₂) is one of the probable candidates for tritium breeding material because of its potential to give a fair tritium breeding ratio, stability at high temperature and stability in atmosphere containing water vapor. Clarification of the adsorption performances of water on LiAl0₂ is important for optimization of the way to recover bred tritium from LiAl0₂ and for estimation of the tritium inventory in the breeding blanket and for quantification of the hydrogen isotope exchange reaction. The amount of water captured on LiAl0₂ was studied in the temperature range of 373~1,100K using the breakthrough curve method, and adsorption isobar and isotherm of water on LiAl0₂ were proposed based on the data obtained. The water capture phenomena of LiAl0₂ was attributed to the dissociative chemisorption, and the apparent activation energy was determined to be 32.2 kJ/mol.K. The tritium inventory by sorption for LiAl0₂ was compared with that for Li₂0.     

The Influence of ZrO2 Treatment on the Electrochemical Behavior of Oxygen and Hydrogen on Type 304 Stainless Steels in High Temperature Water

For enhancing the effectiveness of hydrogen water chemistry (HWC) in boiling water reactors (BWRs) in the aspects of lower hydrogen consumption and of a more effective reduction in electrochemical corrosion potential (ECP), the technique of inhibitive protective coating on structural materials was brought into consideration. The application of inhibitive treatment is aimed at deterring the reduction reactions of oxidizing species occurring on metal surfaces and the oxidation reaction of metals. In the current study, electrochemical polarization analyses at 288°C were conducted to characterize the electrochemical properties of ZrO₂ treated and untreated 304 stainless steel specimens in pure water with dissolved oxygen or hydrogen. The polarization results showed that the treated specimens exhibited lower corrosion potentials, corrosion current densities, exchange current densities, and cathodic current densities than the untreated one in high temperature pure water with dissolved oxygen. For the environment with dissolved hydrogen only, reductions in anodic current density and exchange current density were observed, indicating that the ZrO₂ treatment also deterred the oxidation reaction of hydrogen. However, in comparison with the data obtained, the ZrO₂ treatment seemed to be relatively more effective in inhibiting the oxygen reduction reaction than inhibiting the hydrogen oxidation reaction. One additional beneficial outcome was that the anodic current density of the metal was also decreased, leading to a much lower overall corrosion current density of the ZrO₂ treated specimen.     

Mist Formation in a Water Vapor Cold Trap and Evaluation of Its Removal Rate

Mist formation conditions in a mixture of non-condensable gas (nitrogen or helium) and water vapor, mass transfer rates onto a cooled wall under the mist formation and choking time are determined in a case of a laminar flow in a vertical round tube cooled from the outside at constant temperatures of 77K to 263 K. This is a basic study of a cold trap for a fusion fuel clean-up (fcu) system. If mist is formed in the trap, it makes tritium spikes at the trap outlet, and consequently it causes tritium leakage to the outlet. The limiting condition of mist formation in the present system is quantitatively expressed by the critical supersaturation model (CSM). When the inlet vapor concentration is within the CSM mist formation condition, the outlet concentration is very high immediately after the gas supply and, afterward, it drops very quickly. When within the no-mist formation condition, the outlet concentration is almost constant throughout the frosting time. The trap shows a good removal performance for a long time until choking. This difference in the time variations is successfully explained by the relaxation of the mist formation condition with an increase in the thermal resistance of frost formed on cooled surfaces.