Enhancement of the separation factor in a separation cell has been desired a s one means of reducing the cascade scale required for a radioactive rare gas membrane separation. I t is already known that the separation factor of the separation cell increases as cut increases. Hence, in a series-type separation cell which consists of two-unit cells, an appropriate selection of cuts for each unit cell can be expected to provide a marked improvement in separation factor under symmetric separation. T h i s paper presents analytical and experimental results for separation characteristics of a series-type separation cell whose separation factors are far from unity. It was found that the seriestype separation cell has a larger separation factor than other types of separation cells, such as recycle separation cell and conventional separation cell. T h e series-type separation cell requires less power consumption and membrane area than the recycle separation cell while it requires more than the conventional separation cell. As both the two-unit series-type separation cell and the conventional separation cell have individual merits and demerits, a comparison is also made between the cascade consisting of series-type separation cells and that of conventional separation cells. T h e cascade of series-type separation cells requires fewer stages and less power consumption but somewhat more membrane area than that of conventional separation cells. Based on results of this study, the scale of a cascade can be reduced by using series-type separation cell.

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In Japan, increase of nuclear plant unit capacity has been promoted to take advantage of economies of scale while further enhancing safety and reliability. As a result, more than 50 units of nuclear power plants are playing important role in electric power generation. However, the factors, such as stagnant growth in the recent electricity demand, limitation in electricity grid capacity and limited in initial investment avoiding risk, will not be in favor of large plant outputs. The reactor concept considered in this paper has a small power output, a compact containment and a simplified BWR configuration with comprehensive safety features. The Compact Containment Boiling Water Reactor (CCR), which is being developed with matured BWR technologies together with innovative systems/components, will provide attractiveness for the energy market in the world due to its flexibility in energy demands as well as in site conditions, its high potential in reducing investment risk and its safety feature facilitating public acceptance. The flexibility is achieved by CCR’s small power output of 300 MWe class and capability of long operating cycle (refueling intervals). The high investment potential is expected from CCR’s simplification/innovation in design such as natural circulation core cooling with the bottom located short core, internal upper entry control rod drives (CRDs) with ring-type dryers and simplified ECCS system with high pressure containment concept. The natural circulation core eliminates recirculation pumps as well as needs for maintenance of such pumps. The internal upper entry CRDs shorten the height of the reactor vessel (RPV) and consequently shorten the primary containment vessel (PCV). The safety feature mainly consists of large water inventory above the core without large penetration below the top of the core, passive cooling system by isolation condenser (IC), passive auto catalytic recombiner and in-vessel retention (IVR) capability. The large inventory increases the system response time in case of design base accidents including loss of coolant accidents. The IC suppresses PCV pressure by steam condensation without any AC power. The recombiner decreases hydrogen concentration in the PCV in case of a severe accident. Cooling the molten core inside the RPV if the core should be damaged by loss of core coolability could attain the IVR. The Compact Containment Boiling Water Reactor (CCR) has possibilities of attaining both economical and safe small reactor by simplified system and compact PCV technologies.

LSBWR (Long operating cycle Simplified BWR) is a modular, direct cycle, light water cooled, and small power (100–300MWe) reactor. The design considers requirements from foreign utilities as well as from Japanese. LSBWR is currently being developed by Toshiba Corporation and Tokyo Institute of Technology. Major characteristics of the LSBWR are: 1) Long operating cycle (target: over 15 years), 2) Simplified systems and building, 3) Factory fabrication in module. From the perspective of economic improvement of nuclear power plant, it is needed to shorten the plant construction period and to reduce building volume. In designing LSBWR building, a new building structure, where the hull structure of a ship is applied to floors and walls of LSBWR has been studied. Since the hull structure is manufactured at a shipyard, building module that includes plant equipment becomes possible. The application of the hull structure, which can make large modules at a shipyard, is an effective solution to the lack of laborer and economic improvement. LSBWR is a small size BWR, turbine is smaller size and lighter weight than medium or larger size plant. Then, it has been studied to install a reactor and a turbine in the same building for decreasing building volume. From the view point of standardization, whole building is supported by three dimensional seismic isolation mechanism.