In order to prepare the γ-ray data library requested in a design of fission and fusion reactors, γ-ray production cross sections and spectra of Al, Si, Ca, Fe, Ni, Cu, Nb, Ta, Au and Pb have been obtained at the neutron energies of 120 MeV, using a spin-dependent multi-step evaporation model. Calculations include dipole and quadrupole transition without the distinction between electric and magnetic process, and take explicit account of the role of yrast levels. The effects of the yrast levels and γ-ray strength function upon γ-ray production are also investigated in relation to particle emission, At the incident neutron energies where (n, n'γ) and/or (n, 2nγ) reactions are dominant, the present model is shown to be able to predict the production of secondary γ-rays (<9.0 MeV) from medium-heavy to heavy nuclei with reasonable accuracy.

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The density wave instability in a parallel boiling channel system heated electrically has been studied experimentally and analytically by the authors, In our country, the steam generator for LMFBR has been investigated with Power Reactor and Nuclear Fuel Devel-opment Corp. as the central figure for its development, and many results of this instability were reported. Their results were different from our ones as regard to the governing factor of the period of flow oscillation in the unstable region and to the effect of the slip ratio on the stability in analysis. A new linear analytical model is proposed in this paper and the analytical results are compared with ones of two-phase analyses based on the same linear method as this model. Subsequently, the effect of the slip ratio on the stability is studied analytically by this model. The parallel boiling channel system is studied experi-mentally and analytically, using Freon-113 as test fluid heated by hot water as simulation of the SG for LMFBR. The governing factor of the period of flow oscillation is made clear.

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A program control method is formulated and discussed with respect to typical program control of a tokamak machine. This formulation determines the preprogramming voltages in the poloidal coil power supplies which are necessary for control of plasma current, posi-tion and cross section. The plasma dynamics used are described by a tokamak circuit model consisting of circuit equations for the plasma current and poloidal field coil currents, and equilibrium equations for the plasma position and cross section. The program control method presents the ideal preprogramming voltages which realize desired values for the controlled variables, when coil voltages are not restricted. This method is also applicable to problems where restrictions are imposed on the coil voltages.

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Dose rates obtained in a cylindrical vessel filled with gaseous ⁸⁵Kr source were measured using blue cellophane dosimeter. Besides obtaining the dose rate distribution within the vessel, the dose rate at vessel center was correlated to the ⁸⁵Kr pressure, to the shape and size of the vessel, and to the material forming the inner wall surface. The ⁸⁵Kr source used in the experiment amounted to 300 Ci (11. 1 TBq), with a radioactive concentration of 35.9 mCi/ml NTP (1.33 GBq/m/ NTP).
The dose rate in the vessel was found to rise in direct proportion to the ⁸⁵Kr pressure, and also to increase in keeping with the size of the irradiation vessel and with the atomic number of the material lining the inner wall. Fairly good uniformity of the dose rate was noted, a ratio of only 1. 33 being registered between the values obtained at the locations of maximum and minimum dose rate. The observed relationship between the dose rate and ⁸⁵Kr pressure agreed fairly well with a theoretical expression derived for spherical β source. A dose rate of 4.8 X 10⁷ rad/h (480 kGy/h) can be expected to be realized with a ⁸⁵Kr source charged to 760 Torr (1. 01 X 10⁵ Pa) in a vessel measuring 1, 710 mm X 570 mm diameter, lined with Pb.

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A new approach for a highly sensitive effluent monitor is presented. The free flow type monitor, which consists of a straightener, nozzle, monitoring section and γ-ray detector, is demonstrated to be effective in providing long term stability.
The 160 start-and-stop cycles of effluent discharge were repeated in a 120-h testing period. Results showed a background increase was not observed for the free flow type monitor. The background count rate was calibrated to the lowest detection limit to be 2.2 X 10^-2 Bq/ml for a 300 s measurement time.

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This study investigates the effects of partial flow blockage due to ballooning of fuel cladding on the core heat transfer during reflood phase in a PWR loss-of-coolant accident, in particular, the effects of coolant bypass flow at flow blockage and the effects of major parameters in a wide core with a bundlewise flow blockage.
Forced-feed reflood tests were carried out with the Slab Core Test Facility, in which 8 simulated fuel bundles are arranged in a row with two out of these designed as blockage bundles with about 60 % blockage ratio. The test results which were obtained under most probable coolant injection conditions were investigated with respect to quench and heat transfer coefficients. As the results, the following were revealed. (1) The effects of flow blockage appear only downstream of flow blockage at the flow blockage bundles with promoted cooling of rods. (2) Effects of coolant bypass flow due to flow blockage are insignificant. (3) Flooding velocity by accumulator injection has a predominant effect on promoted cooling of rods downstream of flow blockage.

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The vaporization of SUS 304L stainless steel was studied by using a mass spectrometer attached with a molybdenum Knudsen cell. The partial vapor pressures and chemical activities of principal components of SUS 304L austenitic steel were determined in the tern-perature range of 1, 3001, 430 K (for Fe and Cr each) and 1, 0701, 230 K (for Mn). Activity coefficients, partial free energies of mixing and excess partial free energies of the com-ponents Mn, Fe and Cr were computed from the measured partial pressures and chemical activities. The thermodynamic functions obtained are discussed especially in regard of the chemical state of Cr at the surface of SUS 304L stainless steel.

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A numerical analysis is presented of the flow of a binary gas mixture of UF₆ and N₂ in a rotating cylinder. The equations for flow and the diffusion equation are solved simul-taneously for the binary mixture in static state, taking account of viscosity and compres-sibility, using a modified version of the Newton method, commonly applied to rotating fluid flow. An appropriate model is assumed for a centrifuge provided with scoop and baffle plate. Computations are carried out with the N₂ to UF₆ mixing ratio adopted as parameter.
At small values of mixing ratio, the pressure distribution of UF₆ in the radial direction is little influenced by the presence of N₂. The N₂ pressure distribution is close to that at equilibrium of N₂ itself in zones inside cylinder of relatively slow gas travel. In the zones of faster gas travel, conversely, the N₂ pressure distribution deviates from that of its equi-librium and approaches that of UF₆.
The pressure distribution of UF₆, on the other hand, is strongly influenced by the presence of N₂ when the mixing ratio is above 0.2. The resulting radial distribution along a section close to the exit scoop presents a peculiar concave configulation with a shallow valley appearing in the intermediate zone, and this significantly lowers the concentration of UF₆ extracted through the scoop. The separation efficiency obtained between the two gases is extremely low, but this is due to the mass flow rate having been chosen to opti-mize the separation efficiency between UF₆ isotopes.

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Precise measurements of total neutron cross sections are proposed by using an Fe-filtered beam and a proton-recoil counter. An accuracy of 0.3% was realized for the 24-keV cross sections of Be and C.
It is important that an Fe-filtered beam has a low contamination of both backgrounds of other energy neutrons and γ-rays of all energies. The backgrounds were accurately determined by a Ti-filter of 4 cm in thickness.

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