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[en] The general position with regard to nuclear power and fast reactors in the UK during 1996 is described. The main UK Government-funded fast reactor research and development programme was concluded in 1993, to be replaced by a smaller programme which is mainly funded and managed by British Nuclear Fuels plc. The main focus of this programme sustains the UK participation in the European Fast Reactor (EFR) collaboration and the broader international links built-up over the previous decades. The status of fast reactor studies made in the UK in 1996 is outlined and, with respect to the Prototype Fast Reactor at Dounreay, a report of progress with the closure studies, fuel reprocessing and decommissioning activities is provided. (author)

[en] Fast reactor activities in Brazil have the objective of establishing a consistent knowledge basis which can serve as a support for a future transitions to the activities more directly related to design, construction and operation of an experimental fast reactor, although its materialization is still far from being decided. Due to the present economic difficulties and uncertainties, the program is modest and all efforts have been directed towards its consolidation, based on the understanding that this class of reactors will play an important role in the future and Brazil needs to be minimally prepared. The text describes the present status of those activities, emphasizing the main progress made in 1996. (author)

[en] The economics of LMR is largely dependent on the construction cost of the power plant, and the fuel cycle options usually constitute 20 to 30 % of total electricity generation cost. The choice of fuel cycle technology and the fuel type is important in order to develop a LMR with better economics, performance and safety. The LMR fuel types, whose performances have been proven up to 15 at% burnup, are MOX and IFR metal fuel. The base alloy, binary (U-10% Zr) metal fuel with HT9 is used as structural materials of KALIMER. The design concept of KALIMER fuel has been established through the investigation of technical feasibilities on the fuel and recycle systems for MOX and IFR metal fuel. According to the results of comparative analysis for MOX and metal fuel, metal fuel is better than MOX in view of safety, in-reactor performance, nuclear characteristics, economics and non-proliferation, while MOX fuels have advantages in the developmental status and technical cooperation potential. The overall performance of binary (U-10% Zr) metal fuel with HT9 cladding, which is a potential start-up fuel for KALIMER, is not only superior to that of MOX fuel, but also has enough technical feasibility in its high-burnup performance, safety and economics. (author). 54 ref., 13 tabs., 20 figs

[en] A study on safety measures of LMR coolant showed the results as follows: 1. Sodium fire characteristics. A. Sodium pool temp., gas temp., oxygen concentration calculated by flame combustion model were generally higher than those calculated by surface combustion model. B. Basic and detail designs for medium sodium fire test facility were carried out and medium sodium fire test facility was constructed. 2. Sodium/Cover gas purification technology. A. Construction and operation of calibration loop. B. Purification analysis and conceptual design of the packing for a cold trap. 3. Analysis of sodium-water reaction characteristics. We have investigated the characteristics analysis for micro and small leaks phenomena, development of the computer code for analysis of initial and quasi steady-state spike pressures to analyze large leak accident. Also, water mock-up test facility for the analysis of large leak accident phenomena was designed and manufactured. 4. Development of water leak detection technology. Detection signals were appeared when the hydrogen detector is operated to Ar-H₂ gas system. The technology for the passive acoustic detection with respect to large leakage of water into sodium media was reviewed. And water mock-up test equipment and instrument system were designed and constructed. (author). 19 refs., 45 tabs., 52 figs

[en] Thermal stratification phenomena are observed in an upper plenum of liquid metal fast breeder reactors (LMFBRs) under reactor scram conditions, which give rise to thermal stress on structural components. Therefore it is important to evaluate characteristics of phenomena in the design of the internal structure in an LMFBR plenum. The phenomena is a stable stratified flow and shear layer is formed by bringing two streams of fluid. Previous many experiments and numerical simulations have the layer is dominated by large, spanwise coherent vortex structures and the structures have an important effect on mixing. In this study, to evaluate numerical model and its constants for the thermal stratification phenomena, numerical analyses were carried out for a shear flow test with water. The test that had no temperature difference was analyzed with direct numerical simulation code. The numerical results could indicate the large spanwise coherent vortex structures with vortex growing and pairing. The analyses with different mesh arrangement, inlet velocity distribution and two dimensional and three dimensional arrangement were carried out and the numerical velocity, velocity fluctuation and Reynolds stress were compared with the experimental results. Through the comparison, the difference of mesh arrangement or the velocity distribution in inlet boundary not caused distinction of the velocity, velocity fluctuation and Reynolds stress at 0.9 meter away from separator. Velocity fluctuations in the depth was very small in the three dimensional analysis and no difference was found in the comparison of the results with two dimensional analysis. The numerical velocity and velocity fluctuation in horizontal direction were well agreed with measured velocity, but the velocity and fluctuation in vertical direction were higher than measured value. (author)

[en] Uranium-plutonium mixed nitride and carbide for advanced fast reactor fuels were irradiated at JRR-2, and the fission gas release from these fuels were determined. It is confirmed from the irradiation tests that the application of the cold fuel concept to these fuels on the basis of their advantageous thermal properties may realize low fission gas release. Furthermore, the introduction of the thermal stable pellets with dense matrix and relatively large pores can lower the fission gas release to a few percent up to the burnup of 5.5% FIMA. In spite of the retention of fission gas release in the thermal stable pellets, no significant enhancement of the fuel-clad mechanical interaction was observed in the examined range of burnup. It is also suggested that the open porosity would strongly influence the fission gas release from nitride and carbide. (author). 18 refs, 6 figs, 6 tabs

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