A numerical technique for solving liquid metal MHD problems has been developed as a design tool of fusion reactor blankets. The present code can analyze the effect of field non-uniformity on the velocity profile in a straight circular pipe perpendicular to the magnetic field. Under the very strong field, the perpendicular current components in the fluid to the field are uniform in the field direction. The field directional distributions of the electric potential and the velocity can be expressed by simple algebraic functions. Therefore, these values in a certain plane perpendicular to the field well represent those in the whole duct even when the field is non-uniform. Thus we can replace the three-dimensional problem with the two-dimen-sional one as we could in the case of uniform magnetic fields. The similar procedure to the previous code was used in the present code, and we could get the solution which satisfied all the governing equations. The solution was compared with analytical results, which showed the reliability of the code.

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Simultaneous measurements of fast neutron and prompt γ-ray albedos were performed by nominal 14-MeV neutrons for the type 304 SS and the limestone concrete. Both neutrons and γ-rays were detected by an NE-213 scintillator with the aid of the n-γ discrimination circuit. The time-of-flight method was used to obtain neutron spectra, whereas the unfolding method was applied to analyze γ-ray pulse-height data of the scintillator. The measured data were compared with those calculated by the MCNP code with the ENDF/B-IV data. The calculation reproduced the measured secondary γ-ray differential albedo data well for both materials. For neutrons, apparent disagreement was seen in the albedo data of the 304 SS between the calculation and the experiment. This was due to some inaccuracies in the chromi-um cross sections in the ENDF/B-IV. The agreement of the neutron data was better for the limestone concrete than for the 304 SS.

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A multielement position sensitive proportional counter was developed for the measurement of ³H labeled gas movement in a pipe by internal counting. The counter consists of an outer cylindrical pipe with an inner diameter of 40 mm, seven resistive stainless steel anode wires with a diameter of 22μm, and 24 cathode wires with a diameter of 120μm. These wires divide the radial cross section of the pipe into seven regions. Since each region independently works as a position sensitive proportional counter and the seven resistive anode wires are connected in series through lump resistors, the region and the axial position where a β-decay event occurred can be known by a simple operation upon the charge signals obtained from two preamplifiers. The axial position resolution for ³H β-rays was 9 mm FWHM. Demonstrative experiments were performed for the flow and diffusion of 3H labeled ethane in the counter pipe.

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Reflood phenomena of 2-loop PWR with upper-plenum-injection (UPI) type ECCS was studied by examining CCTF experimental data. The major conclusions about the effects of asymmetric UPI and single low-pressure-coolant-injection (LPCI) pump failure on reflood phenomena are as follows : (1) Single failure assumption of LPCI pump is more conservative (worse core cooling) than no failure assumption of LPCI pump under UPI condition. This is consistent with current guide line for reactor safety evaluation. (2) The asymmetric UPI promoted a radial ununiformity of the core cooling, although even symmetric UPI lead to the radial ununiformity of the core cooling. (3) The asymmetric UPI did not give a local degradation of core cooling in comparison with symmetric UPI but gave an enhancement of core cooling in the upper part of core after the initiation of water fall back. (4) The enhancement of core cooling is considered to be caused by increased upward fluid flow due to water fall back and water fall back itself, which are promoted by asymmetric UPI. (5) Initiation of water fall back can be predicted with Bankaff's correlation under UPI condition when the fluid temperature is saturated.

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The influences of reaction time, temperature and NH4NO3 concentration on the reaction of solid β-UO₃ with aqueous NH₄NO₃ were experimentally studied. Both type I(UO₃•2H₂O) and type II(3UO₃-NH₃-5H₂O) uranyl compounds were observed in the X-ray diagrams of reaction product. High temperature (80°C) and long reaction time (2 h) favor the formation of type II uranyl compounds and generation of uranyl nitrate. Based on the experimental results, two possible models were proposed. The model that assumed pseudohomogeneous reactions conforms to the experimental data better than the model that assumed noncatalytical solid-fluid heterogeneous chemical reaction. The dependence of uranyl nitrate generation rate on reaction time, temperature and NH₄NO₃ concentration can be calculated from the pseudohomogeneous reaction model.

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A simple model for analysis of fuel rod ridging is proposed. In this model, a piece of radially cracked pellet is considered as a beam, and cladding as a tube shell, allowing fuel rod ridging to be analyzed by applying the beam and shell theories. Ridging height and contact force between the pellet piece and the cladding tube are expressed in a relatively simple form as a function of elastic constants of the pellet and cladding, temperatures, dimensional param-eters, etc. Effects of fuel design parameters on the fuel rod ridging are evaluated using this model.

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A new method of isotope detection and separation based on transport phenomena of ions in gases, which consist of a drift tube, is proposed and the analytical expression of resolution power of the method has been derived from a diffusion equation. The expression shows that the resolution power increases with the square root of the voltage supplied to the tube. A simple drift tube was constructed and natural Li was isotopically separated in Ne 100 Torr with the maximum resolution power, about 2. The variations of the resolution power with the applied voltage were measured by using the ion source of 6Li and 7Li separately and compared with calculations.

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The catalytic oxidation and adsorption method is considered to be a potential and reliable measure to recover tritium released into room air in fusion power plants. The activity of precious metal catalysts that are expected to be useful in recovery of tritium released into the -oom air is affected by moisture in the air, and tritium in the gas phase can be captured into :he catalyst substrate not only through adsorption but also through isotopic exchange reaction. The simulation study on tritium behavior in the catalyst bed was carried out quantitatively on :he basis of experimental results. It is confirmed by the simulation study that the installation A the preadsorption bed decreases water vapor before the gas is passed through the precious metal catalyst bed; this is an effective countermeasure against the deterioration of the catalytic oxidizing performance caused by moisture. It is also shown that large amounts of tritium :an be captured by the catalyst itself when the preadsorption bed is introduced.

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Groeneveld-Stewart's minimum film boiling temperature correlation was incorporated into the RELAP5/MOD2 code in order to explicitly define the minimum film boiling temperature. The transition boiling curve in the code was also modified. The Loss-of-Fluid Test (LOFT) experiment, Experiment LP-02-06 which was a cold-leg double-ended break LOCA experiment with minimum emergency core coolant injection, was analyzed with the modified RELAP5/ MOD2 code. The modified RELAP5/MOD2 code well calculated system transients including the rod surface temperature transient. The temporary rewetting of rods in the early phase of blowdown, which had not been predicted by the original RELAP5/MOD2 and other codes, was predicted by the modified RELAP5/MOD2 code.

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Several factors affecting the track registration performance of CR-39 detectors were studied, adopting as intermediate criterion of detector performance the diameters of etch pits left by normally-incident α-particles. Measures that have been proposed for enhancing detector per-formance, such as stirring and by ultrasonic vibration applied during etching have proved not to be effective : While these measures increased the etch pit diameters to some extent, the same measures were found to accelerate in keeping also the bulk etching rate, so that the increase observed in the etch pit diameters could not be attributed to enhancement of track registration sensitivity, which is the ultimate criterion of detector performance. Contamination of detector surface with finger grease transferred upon manipulation with bare hand proved not to influence even the intermediate criterion of etch pit diameter. Nor was this criterion influenced by the presence in etchant solution of etched products up to a concentration of 5 g/l. On the other hand, the etch pit diameters were found to be influenced beyond negligible extent by environ-mental factors such as humidity and temperature even within the range of normal variations occurring in the natural environment, and these factors thus require taking into account in order to ensure consistent measurements with CR-39 detector.

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