[en] An aggressive low aspect ratio scoping fusion reactor design indicated that a 2 GW(e) reactor can have a major radius as small as 2.9 m resulting in a device with competitive cost of electricity at 49 mill/kWh. One of the technology requirements of this design is a high performance high power density first wall and blanket system. A 15 MPa helium-cooled, V-alloy and stagnant LiPb breeder first wall and blanket design was utilized. Due to the low solubility of tritium in LiPb, there is the concern of tritium migration and the formation of V-hydride. To address these issues, a lithium breeder system with high solubility of tritium has been evaluated. Due to the reduction of blanket energy multiplication to 1.2, to maintain a plant Q of > 4, the major radius of the reactor has to be increased to 3.05 m. The inlet helium coolant temperature is raised to 436 C in order to meet the minimum V-alloy temperature limit everywhere in the first wall and blanket system. To enhance the first wall heat transfer, a swirl tape coolant channel design is used. The corresponding increase in friction factor is also taken into consideration. To reduce the coolant system pressure drop, the helium pressure is increased from 15 to 18 MPa. Thermal structural analysis is performed for a simple tube design. With an inside tube diameter of 1 cm and a wall thickness of 1.5 mm, the lithium breeder can remove an average heat flux and neutron wall loading of 2 and 8 MW/m(2), respectively. This reference design can meet all the temperature and material structural design limits, as well as the coolant velocity limits. Maintaining an outlet coolant temperature of 650 C, one can expect a gross closed cycle gas turbine thermal efficiency of 45%. This study further supports the use of helium coolant for high power density reactor design. When used with the low aspect ratio reactor concept a competitive fusion reactor can be projected at 51.9 mill/kWh

[en] The objective of this task is to develop the required data base and demonstrate the performance of a liquid lithium-vanadium advanced blanket design. The task has two main activities related to vanadium structural material and liquid lithium system developments. The vanadium alloy development activity included four subtasks: (1.1) baseline mechanical properties of non irradiated base metal and weld metal joints; (1.2) compatibility with liquid lithium; (1.3) material irradiation tests; and (1.4) development of material manufacturing and joining methods. The lithium blanket technology activity included four subtasks: (2.1) electrical insulation development and testing for liquid metal systems; (2.2) MHD pressure drop and heat transfer study for self-cooled liquid metal systems; (2.3) chemistry of liquid lithium; and (2.4) design, fabrication and testing of ITER relevant size blanket mockups. A summary of the progress and results obtained during the period 1995 and 1996 in each of the subtask areas is presented in this report

[en] The tritium transport and inventory in Li₂O solid breeder of the fusion blanket have been affected by the oxygen bearing molecules in the purge gas as well as the solubility of tritium in Li₂O as LiOT. The capability of predicting the LiOT precipitation and the effect on tritium inventory were tested using a new version of MISTRAL code. However, the recent tritium inventory analyses in Li₂O solid breeder under steady state and pulsed operating conditions shows significant differences between the code predictions and thermodynamic correlation. In this study, a logic for predicting LiOT formation and decomposition in Li₂O solid breeder is developed and integrated in the MISTRAL code based on the available thermodynamics and kinetics data. The logic is based on comparison between the local concentration of tritium in the grain and the LiOT solubility limit at the breeder temperature. With this logic, the code is used to analyze tritium inventories in Li₂O under steady and transient conditions. Using a transient temperature scenario in which breeder temperature varied over a wide range from 600 deg C to 100 deg C and several tritium generation rates in the range of 1 x 10¹⁸ to 1 x 10²¹ atoms/m³-s, the temperature limits for formation and decomposition of LiOT and the temperature regimes, over which each of the three forms of tritium inventory (grain, surface and precipitation) is dominant, are determined as a function of tritium generation rate. (author)

[en] Convective heat transfer in MHD laminar flow through rectangular channels in the plasma-facing components of a fusion reactor has been analyzed numerically to investigate the effects of channel aspect ratio, defined as the ratio of the lengths of the plasma-facing side to the other side. The adverse effect of the nonuniformity of surface heat flus on Nusselt number (Nu) at the plasma-facing side can be alleviated by increasing the aspect ratio of a rectangular duct. At the center and corner of the plasma-facing side of a square duct, the Nu of non-MHD flow are 6.8 and 2.2, respectively, for uniform surface heat flux. In the presence of a strong magnetic field, Nu at the center and corner increases to 22 and 3.6, respectively. However, when the heat flux is highly nonuniform, as in the plasma-facing components, Nu decreases from 22 to 3.1 at the center and from 3.6 to 3.1 at the corner. When the aspect ratio is increased to 4, Nu at the center and corner increase to 5 and 4.7. Along the circumference of a rectangular channel, there are locations where the wall temperature is equal to or less than the bulk coolant temperature, thus making the Nu with conventional definition infinity or negative. The ratio between Nu of MHD flow and Nu of non-MHD flow for various aspect ratios is constant in the region of Hartmann number of more than 200 at least. On the other hand, its ratio increases monotonously with increasing the aspect ratio

[en] Numerical simulations are presented on the flow and heat transfer characteristics of an impinging round jet of argon plasma with atmospheric pressure. The target slab with finite thickness upon which plasma jet impinges is assumed to be as SiC which is a candidate material for plasma facing material of fusion reactor. The plasma jet is treated by use of a magnetohydrodynamics model that takes its two-temperature non-equilibrium state into account. The rear side of the target slab is assumed to be cooled by a gas-solid suspension impinging round jet. The result shows that the plasma is in non-equilibrium state in which the electron temperature is higher than the heavy particle in the outer region of plasma jet core and that the heat flux to the target slab is over 8 MW/m² in the region of the plasma jet core contacts. (author)

[en] The high heat flux component cooling by means of a gas-solid suspension impinging jet is proposed, especially for the fusion power reactor. Though the heat transfer performance by using a single nozzle gas-solid suspension impinging jet was demonstrated by authors, the effective cooling area was restricted within a narrow region near the stagnation point. In order to spread the effective cooling area, the multiple jets are required. However, no data concerning the multiple gas-solid suspension impinging jets exists. So that, in this study, experiments by using the confined multiple impinging jet were carried out and the uniformity of heat transfer coefficients was examined. The jets were arranged in staggered rows and spent holes were set in the center of three jets. In the case of the gas-solid suspension flow, the heat transfer coefficient in the overall region was improved in comparison with a single-phased flow case. (author)

[en] To develop a tritium breeding blanket for a fusion reactor, irradiation tests in fission reactors must be conducted to obtain data on tritium production / release / recovery performance of the blanket. In-situ various irradiation tests have been carried out in Japan (JMTR) and Europe (HFR) to investigate tritium release characteristics from ultra-small Li₂TiO₃ pebble (1 mm dia) bed. Tritium performance irradiation tests presently focus on Li₂TiO₃ ceramic considered promising as a new strong candidate for breeding material. This report shown the present status of in-situ irradiation tests carried out throughout the world. An in-situ irradiation test program on tritium release for partial breeding blanket module is presented. (author)

[en] Regeneration operation is a very important operation, because it is the most influential factor for deciding the net operation cycle time and the minimum dimension of Cryogenic Molecular Sieve Bed (CMSB). However, the experimental data of CMSB regeneration operation was not so sufficient that even the optimum regeneration procedure could not be decided yet. This work was focused on getting the primary information about various regeneration procedures. (author)

[en] A large-scale helium refrigerator/liquefier has been developed to provide reliable and safe operation for the Large Helical Device (LHD). The refrigerator is required to satisfy four different types of cooling methods: forced-flow supercritical helium, a pool boiling method, two-phase helium flow and forced-flow low-temperature (40-80 K) helium gas. The forced-flow supercritical helium is widely used in modern large-scale superconducting magnets. This method requires a much more complex refrigeration system than does pool boiling because of the circulation of low-temperature helium within a very long cooling path. The overall refrigeration system is fairly complicated because of these multi-refrigeration requirements. As a matter of fact, it is not likely to find this type of refrigeration plant in the world. The helium refrigerator has a total refrigeration capacity of 5.65 kW at 4.4 K and 20.6 kW at 80 K and 650 l/h liquefaction. The refrigerator was designed to have high processing efficiency since the construction expense is much less than the operating cost. In order to achieve this, the refrigerator has two precooling cycles (300 to 80 K and 80 to 20 K) and has two turboexpanders running in parallel with different temperature levels at the cold end. To achieve a high mass flow rate in a low-temperature regime, eight screw-type compressors are operated at room temperature. There are two compressor groups, group A and group B, to reduce the overall work load. Each group consists of 1st and 2nd stage compression processes. The total mass flow rate becomes 960 g/s at 1.864 MPa. This article reviews the basic characteristics of a 10 kW class helium refrigerator/liquefier and a simple refrigeration cycle. (author)

[en] The Vacuum Vessel, which is a core component of International Thermonuclear Experimental Reactor (ITER), is required to be exchanged remotely in a case of accident such as superconducting coil failure. The in-vessel components such as blanket and divertor are planned to be exchanged or fixed. In these exchange or maintenance operations, the thick wall welding and cutting are inevitable and remote handling tools are necessary. The thick wall welding and cutting tools for blanket are under developing in the ITER R and D program. The design requirement is to weld or cut the stainless steel of 70 mm thickness in the narrow space. Tungsten inert gas (TIG) arc welding, plasma cutting and iodine laser welding/cutting are selected as primary option. Element welding and cutting tests, design of small tools to satisfy space requirement, test fabrication and performance tests were performed. This paper reports the tool design and overview of welding and cutting tests. (author)