A study is performed on 14.5 MeV-neutron induced fission of ²³⁸U by means of three-parameter experiment in which the energies of both fragments and the time-of-flight of one fragment are measured. A mosaic-arrayed surface barrier detector of large sensitive area is used at the remote end of a flight tube. The pre- and post-neutron-emission frag-ment mass distributions are obtained, together with the average total kinetic energy of fragment as a function of its mass. The average number of neutrons emitted from an individual fragment and the average total number of emitted neutrons are also derived as a function of fragment mass. The results agree well with those calculated by the method developed in our laboratory for medium-excitation fission. The average number of emitted neutrons and the mass distribution of fission fragment are derived for the re-spective reactions of first-, second- and third-chance fission.

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Experimental study was made to investigate the controlling factors on the vapor de-position rate on reactor rotating shield plug annulus, which is exposed to the vapor entrained cover gas during reactor operation. Two simulated test assemblies having annuli were made for this purpose and were installed into a small test vessel. In the experiment, the average deposition rates on the annular walls of the test assemblies were measured for various pool temperatures, and their dependents upon such parameters as pool temprature T_s (or the saturated vapor pressure P_s at pool surface), cover gas pres-sure P_G, and temperature drop ΔT_G across cover gas, were studied.
The results revealed that the dominant controlling factor was the vapor pressure P_s at pool surface. Dependent of the average deposition rate φd upon the above parameterswas simply expressed by : φ_d=Bρ_sD_sΔT_G, where, ρ_s is the saturated vapor concentrationat pool surface, D_s the vapor diffusion coefficient, and B the proportional constant.
To these experimental results, the previously published evaporation rate data and the theoretical evaporation rate equation based on Epstein & Rosner's theory were reviewed. Then correlation between the deposition and the evaporation rates was dis-cussed.

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The objective of this study is the establishment of the thermo-hydrodynamic model of the reactor core during reflood phase of LOCA.
Based on the quench model proposed by the author, and assuming a reflood model including a flow model and a set of the thermo-hydrodynamic correlations, a reflood an-alysis code named "REFLA-1D" was developed.
Considerably close agreement between PWR-FLECHT tests and the results calculated by REFLA-1D code for the critical Weber number We_c=1 was obtained for fuel clad temperature histories and the quench time and the quench temperature except for the quenching from the top of the fuel rod. It was found that the errors of calculated quench time and temperature are within ±20% under the following conditions: (1) pressure 4.51.5kg/cm²•a or core inlet velocity 154.8 cm/s, (2) inlet subcooling more than 30°C. In the transition flow region, the calculated tendency of the temperature histories is different from the measured. This reflood model appears to be reasonable but some modifications on the low flooding quench model and the transition flow are necessary.

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Heads and tails separation factors α, β are multiplicative measures of separation concerning the desired material's enriched and depleted streams. The function trans-forming multiplicative quantities to additive ones is a logarithm, and additive measures of separation concerning the desired material become In α and In (1/β) for the enriched and depleted streams, respectively. The additive measure of separating element is the weighted sum of them and the weights are selected to be portions of the desired material moving towards the enriched and depleted streams η and η:
which equals to the separative power relevant to the desired material per unit flow rate. Similarly, the additive measure relevant to the undesired material becomes
Thus, the functions representing separative power wt, and cos are additive measures of separating element relevant to the desired and undesired materials, respectively. More-over, ψ_b and ψ_a are equivalent and distinguished only by the selection of the desired material in the two components in a binary mixture.

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A computer code MIRA-PB for predicting the iodine removal by containment spray in LOCA was prepared on the basis of MIRA-P/MIRA-B code developed in Battelle Columbus Laboratories. MIRA-PB considers behavior of inorganic iodine, organic iodide, and iodic aerosol and simultaneous removal by natural deposition, liquid-film absorption, spray washout, filtration and leakage to the environment. The iodine removal by the containment spray systems in LOCA of PWR and BWR is calculated with the MIRA-PB.

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A cooling system of a stationary target for the Fusion Neutronics Source (FNS) has been designed to satisfy the structural, thermal and hydraulic requirements. Two square tubes for ion beam and for cooling water were concentrically placed and the target was mounted on the top of the beam guide tube. The end plate of the outer tube was devised to be removable for easier replacement of the target. In order to test the cooling capability of the system, dummy target assemblies with electical heaters were used in the experiment of heat transfer in place of using an accelerator. Correlations of heat transfer and head loss were obtained experimentally as a function of Reynolds number. The extrapolation of the data has shown that for the present target system, about 2.3 kW is the maximum power for the beam in diameter of 15 mm. This value was sufficiently large compared with the required heat load of FNS.

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A thin film thermometer with high sensitivity and small response time has been developed. A nickel film was deposited in a vacuum on a backing plate of stainless steel 0.05 mm thick. The pattern of nickel film was so designed to provide sufficient accuracy. A small heat flux of 0.5 W/cm² is measurable with a response time of less than 1 ms. The thermometer was applied to radiation loss measurement in JFT-2 tokamak. The power loss due to the radiation was found to be about 30% of the total power input.

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