A. Sagara

A. Tanaka

J. Yagi

T. Muroga

National Institute for Fusion Science (NIFS-Repository)

    Hydrogen transport characteristic of liquid breeding material is still important issue to be clarified because it has great influence on the blanket system design, especially for the tritium recovery and the permeation leakage reduction. In particular, hydrogen transport phenomena around the liquid/solid (tubing wall etc.) surface including that in thin fluid film are very important. Thus using the experimental device constructed in FY2012, hydrogen transport though thin FLiNaK (LiF-NaF-KF mixed molten salt ) film was investigated. The experimental setup is similar to our previous work performed in FY2012 in which liquid Li-Pb eutectic alloy was used. In this time, 1.0 mm FLiNaK film was sandwiched with pure Ni plates(2 and 1 mm thick) whose outer surfaces were exposed to decompressed hydrogen gas (100~3000 Pa) and evacuated by a high vacuum system respectively. Temperature of the system was kept to be 823 K. Fig.1,2 shows the overview of the experimental system and an example of the hydrogen permeation breakthrough. The transient permeation decrease and increase just after the start and the stop of hydrogen gas supply are due to the thermal balance change by the gas supply.   Fig. 1. Overview of the experimental system  Fig. 2. Example of hydrogen permeation breakthrough.  Hydrogen permeation at steady state, shown in Fig.2, is summarized in Fig.3. The permeation flux increases with the 0.65 power of the hydrogen feeding pressure. This result indicates that both of hydrogen diffusion by atomic state H (in Ni) and diffusion by molecular state H2 (in FLiNaK) are included as a rate-determining process.  For further discussion, 1D diffusion model was constructed assuming the equilibrium hydrogen distribution at the Ni/FLiNaK boundary, hydrogen molecular diffusion in FLiNaK, and no permeation resistance at all boundaries (adsorption, recombination, etc.). Fitting with this model showed good agreement in some cases as shown in Fig.4, though much improvement is necessary. Permeability of FLiNaK estimated with the model was close to the reported data. This system is planned to be used in FY2014 for the similar experiment with FLiNaK mixed with metal powder to increase the practical hydrogen solubility  Fig. 3. Steady state hydrogen permeation through Ni/FLiNaK/Ni system at 823 K.   Fig. 4. Breakthrough curve of hydrogen permeation at 823 K with its fitting result by diffusion model            Fusion material researches related to liquid breeding materials, such as hydrogen recovery process, corrosion of structure materials, and function of ceramic coatings have been widely performed so far. However experiments performed in an enough flowing condition with a temperature difference in the system, they are appreciated from a practical point of view, are very few because such experimental system is usually very large and expensive. In this fiscal year, we designed and fabricated a new small liquid loop driven by a gas pressure difference whose schematic is shown in Fig.1. Three tanks for liquid are connected via valves, whose cover gas pressures are 1atm (compression tank), decompressed to be 0.2~0.9atm (decompression tank), and controlled to be equal to that of other 2 chambers alternatively (adjustment tank). Driven by the cover gas pressure difference, continuous flow is generated from the compression tank to the decompression tank. The valve between tanks is opened only when the both tanks have the same cover gas pressure, transporting fluid from the decompression tank to the adjustment tank and from adjustment tank to compression tank due to the level difference.  Fig. 1. Schematic of the loop system.  The main flowing path, from compression tank to decompression tank, is made of 1/8 inch SUS316L tube (I.D. 1.755mm) and the length is adjusted to have an appropriate pressure drop as shown in Table I. In this system, fast flow velocity is achievable though flow volume is limited. Moreover, supplying atmospheric pressure to the compression tank enables samples (as well as fluid) to be sampled out through a gate valve on the top of the tank, where a portable glove box is to be connected.  The test section is connected to the main flow path through a heat exchanger (and additional heating) unit, to increase the fluid temperature and to make temperature difference in the loop. Required heat to make the temperature difference is also calculated as Table I, while actual heater power requirement will be decreased below 2~300W by a heat exchanger, whose conceptual design was also completed in FY2013. The test section and the heat exchanger unit is to be made of ferritic steel (for Li and Li-Pb) or Ni alloy (for FLiNaK) considering the compatibility at high temperature. Construction of the major part of the loop was completed as shown in Fig.2. Flowing test with water, fabrication of the heat exchanger unit will be completed in FY 2014 followed by the campaign using the actual liquid breeding material.  Table I. Summary of the pumping and heating parameter                             Fig. 3. View of the liquid tanks with pneumatic valves (upper) and the gas control system (lower) Fluid Li Flinak LiPb waterI.D. mm 1.755Length m 2 1.5 2Flow rate 2 cc/s (0.83 m/s)Pressure drop kPa 8.6 52 82 15Liquid head m 1.75 2.6 0.84 1.6Tank temperature K 500 750 550 RTTemperature difference K 300 200 300 -Required heat W 1260 1520 1140 -325§6. Design and Construction of Gas Pressure Driving Loop for Liquid Breeding MaterialsYagi, J., Tanaka, A., Muroga, T., Sagara, A.2

Design and Construction of Gas Pressure Driving Loop for Liquid Breeding Materials

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Design and Construction of Gas Pressure Driving Loop for Liquid Breeding Materials

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