Myunghwa Shim

Disproportionation Characteristics of a Zirconium-Cobalt Hydride Bed Under ITER Operating Conditions

Abstract Quantitative assessment of a disproportionation in the ZrCo-hydrogen system under ITER-relevant operating conditions was performed by means of experimental tests and a theoretical calculation. In the static temperature experiments with equilibrium hydrogen pressures, a 10% disproportionation of ZrCoHx (x = 2.0 and 2.5) was observed in 5.5 h at 415° (~78 kPa), 9 h at 400° (~72 kPa), 172 h at 380° (~51 kPa), and 1626 h at 350° (~28 kPa). An experimental formula [log τ = 17 268/T (K) - 25.814, where τ is the reaction time (day) of 10% disproportionation] was derived from these experiments. Experiments with a temperature cycling of up to 125 cycles (from room temperature to 350 to 360°) proved that no enhancement of a disproportionation occurs in the ZrCoHx (1.7 < x ≤ 2.0). Typical operation conditions of the ZrCo hydride bed for the D-T gas storage delivery system were proposed based on the ITER FDR 2000 plasma operation scenarios. The disproportionation rate estimated conservatively by the theoretical model indicates that a disproportionation in the ITER basic performance phase can be reduced by <4% even when there is a direct supply from the fuel storage and delivery system beds for all the D-T pulses and by <0.1% when the supply is from the hydrogen isotope separation system.

INITIAL TEST RESULTS OF A FAST HEAT TRANSFER RESPONSE ZrCo HYDRIDE BED

Abstract We are developing an innovative ZrCo hydride bed design, which is characterized by a large cylindrical filter, very thin cylindrical metal hydride powder packed layer, and large relative heating area per unit weight of ZrCo powder for ITER fuel cycle application. To validate this design concept, two ZrCo bed models each loaded with 127 g of ZrCo were tested by using H2 gas. In the first model, ZrCo powder was packed into the 3 mm gap between the filter cylinder and the vessel, and mold heater elements were attached to the outer surface of the vessel. The second model consisted of a layer of ZrCo powder packing (7 mm thickness), coiled cable heaters attached independently to the outer surface of the primary vessel and the inner surface of the filter cylinder. This paper presents detailed design features of the ZrCo bed models, and test results of the beds performances, i.e., temperature transient of the ZrCo packed bed during fast heating, hydriding rate up to 90-99% recovery, and 90-98% delivery fraction.

EXPERIMENTAL STUDY ON THE DELIVERY RATE AND RECOVERY RATE OF ZrCo HYDRIDE FOR ITER APPLICATION

Abstract To investigate the key design aspects of the storage and delivery system (SDS) bed in ITER, rates of a hydriding, dehydriding and isotope effects on the H/D composition during a rapid delivery were experimentally investigated by using small tube-type reactors with different packing heights. Hydrogen recovery times for a shorter packing-height bed (20~40mm) decreased exponentially with an increasing initial hydrogen pressure, but increased by approximately two orders of a magnitude in a longer packing-height bed (145mm). Dehydriding rate increases exponentially with an increase in the relative heating area per unit weight of ZrCo powder and decreases in the packing-height of ZrCo hydride. Continuous isotopic compositional change inevitably occurs during the entire delivery time due to the known isotope effect in the metal-hydrogen systems. To overcome the isotope effect during a delivery from the SDS beds, an alternative operation method was suggested for the fuel supply from the SDS.

Korea's activities for the development of ITER tritium storage and delivery systems

Abstract The ITER fuel cycle plant is composed of various subsystems such as a long term tritium storage system (LTS), a fuel storage and delivery system (SDS), a tokamak exhaust processing system, a hydrogen isotope separation system, and a tritium plant analytical system. Korea shares in the construction of the ITER fuel cycle plant with the EU, Japan and US, and is responsible for the development and supply of the SDS and LTS. The authors thus present details on the development status of the tritium transport container, the long term tritium storage beds, the short-term delivery system T2, DT, and the D2 storage beds, the calorimetry system, and the associated He-3 recovery loop, the over pressure protection systems, and the gas analysis manifold connected to the tritium plant’s analytical systems.

KOREA'S ACTIVITIES FOR THE DEVELOPMENT OF A DETRITIATION SYSTEM

Tritiated gas and water should be properly treated to minimize an environmental tritium emission in nuclear fusion research facilities. Tritiated gas is usually treated in two steps: it is first oxidized to a tritiated water vapor by a catalyst and then the vapor is adsorbed in a molecular sieve drier. We have used a 1wt.% Pt/SDBC polymer catalyst and Zeolite 13X for the tritiated gas removal system. We confirmed that the decontamination factor of the equipment was more than 100 under a gas flow rate of 90 liters/hr and at a temperature of 65-80 °C.Furthermore we have developed a tritiated organic liquid treatment process. We have used a 0.5wt.% Pd/Al2O3 catalyst to oxidize an organic liquid. The simulated organic liquid was converted to water by over 99%. We have also developed a small scale CECE (Combined Electrolysis and Chemical Exchange) process by combining an LPCE (Liquid phase Catalytic Exchange) catalytic column with SPE (Solid Polymer Electrolyte) electrolysis. The experimental results of the CECE process produced a decontamination factor of 13-20. We used the electrolyte Nafion 117 which was coated with Pt as a cathode catalyst and IrO2 as an anode catalyst. We also tested a palladium alloy membrane for a purification of the hydrogen in the detritiation process.

PARAMETER ESTIMATIONS FOR THE KINETICS OF DEHYDRIDING REACTION BETWEEN ZIRCONIUM-COBALT AND HYDROGEN

Abstract The dehydriding reaction between ZrCo and hydrogen is the most important role of delivering hydrogen isotopes for fusion energies. Many researchers experimented in various conditions and estimated the relationship between ZrCo and hydrogen. In this study the kinetic approaches are performed using numerical simulations between ZrCo and hydrogen. Two kinds of parameter estimations are performed for the equilibrium pressure and the kinetics modeling and those are validated by the good agreement between predicted and experimental data. Based on the numerical simulation with obtained parameters, more rapid rates of dehydriding reaction can be achieved with lower pressure and higher temperature.