مطالعه تجربی و شبیه سازی در جذب ایزوتوپهای هیدروژن بر روی MS5A در 77 K

Extraction of tritium from the sweep gas of the ITER Helium Cooled Pebble Bed (HCPB) Test Blanket Module is proposed to be carried out in a two-step process: trapping of water in a cryogenic cold trap, and adsorption of hydrogen isotopes (H2, HT, T2) in a Cryogenic Molecular Sieve Bed (CMSB) at 77 K. A CMSB mock-up in a semi-technical scale (1/6 of the flow rate of the ITER-HCPB) was designed and constructed at the Forschungszentrum Karlsruhe. In this work, the adsorption isotherms of hydrogen and deuterium on the MS5A adsorbent were investigated by the volumetric method. The correlation of the experimental adsorption isotherms of hydrogen and deuterium on the MS5A adsorbent were performed. To validate the cryogenic adsorption process, breakthrough experiments were performed using the CMSB mock-up. The experimental breakthrough curves obtained were analyzed with model mass balance equations, and scale-up numerical simulations were carried out.

To validate design concepts of tritium breeding blankets used for the generation of fuel in fusion machines such as ITER and DEMO, experimental investigation and tests of these concepts are necessary. According to the design concepts, ceramic breeder materials such as lithium orthosilicate generate tritium via nuclear reaction between the neutrons and the lithium atoms. The tritium produced in the breeder material has to be removed by means of a Tritium Extraction System (TES) in which a helium sweep gas containing 0.1% of hydrogen is used to assist the tritium release from the breeder materials via isotope exchange reactions. The TES foreseen for the ITER Helium Cooled Pebble Bed (HCPB) Test Blanket Module (TBM) will remove all tritiated species present in the He sweep gas in a two-step process such as (1) trapping of water in a cryogenic cold trap and (2) adsorption of all hydrogen isotopes (H2, HT, T2) in a Cryogenic Molecular Sieve Bed (CMSB) operating at liquid nitrogen temperature [1] and [2]. In a first series of experiment, the efficiency of a semi-technical scale cold trap (1/6 of the ITER operating conditions) has been demonstrated, which can remove efficiently water vapor from the He stream [3] and [4]. Then, the second part of the extraction process for removal of all hydrogen isotopes was validated. A CMSB mock-up in a semi-technical scale (1/6 of the flow rate of the ITER-HCPB) has been designed and manufactured in the Forschungszentrum Karlsruhe and was installed in an experimental rig at the Tritium Laboratory Karlsruhe (TLK). The adsorbent container filled with 20 kg of molecular sieve (MS5A) was arranged inside a liquid nitrogen-cooled vacuum-isolated vessel. During the operation of the bed, the MS5A adsorbent is uniformly cooled down to 77 K. To comply with the ITER requirements and to save the amount of He consumed, the CMSB presently installed at TLK has been implemented within a close loop, which allows He to be continuously circulated with flow rates up to 2 m3/h. The details of the experimental set-up facility have been reported in a previous literature [5]. In this work, the adsorption isotherms of hydrogen and deuterium on the MS5A adsorbent were investigated by the volumetric method. The correlation of the experimental adsorption isotherms of hydrogen and deuterium on the MS5A adsorbent were performed using several models of adsorption equilibrium. To validate the cryogenic adsorption process, breakthrough experiments were performed using helium containing hydrogen of up to 0.2% in volume. The experimental breakthrough curves obtained were analyzed with model mass balance equations, and scale-up numerical simulations were carried out.

Adsorption isotherms of hydrogen isotopes were investigated by the volumetric method. The experimental adsorption isotherms were successfully correlated with the vacancy solution model formulated with the NRTL equation. The performance of the CMSB was tested in a closed loop with the process gas flow rates up to 2 m3/h and hydrogen concentrations up to 2000 vppm. The results of breakthrough experiment were analyzed with the numerical calculation code and the effective pore diffusivity of H2 was determined. The scale-up simulation of CMSB was performed and the result suggests that CMSB properly works for the adsorption of H2. The scale-up numerical simulation was also carried out for binary adsorption, and the result of calculation indicates that the coexistent H2 substantially affects the breakthrough behavior of D2.