The three quench modes based on the observation with an outside-heated quartz tube experiment, i.e. (1) liquid column type, (2) dry out type and (3) droplet-rewetting type are discussed quantitatively to provide correlations for a reflood analysis code. For the quench velocity of liquid column type and dry out type, using the data of PWR-FLECHT experiments, a correlation is obtained. This correlation is compared with experimental data and found that it can predict the inverse quench velocity within ±20% accuracy under the following conditions. pressure 1.04.1 kg/cm² a, quench temperature 370510°C, local subcooling 030°C, flow rate 525 cm/sec. For the quench temperature of droplet-rewetting type, a correlation is derived and the prediction from it gives the qualitative agreement with few available data.

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For gas-liquid two-phase flow, two kinds of fundamental equations have been pro-posed by the methods of hydrodynamics and hydraulics. The hydrodynamic equation, to avoid analytical difficulties, does not deal with two-phase flow itself, but with a hypo-thetical liquid flow which has actual physical quantities in the region wherethe liquid phase really exists and has the imaginary physical quantities of liquid in the region where the gas exists, for each instant, and with a hypothetical gas flow similarly. The hydraulic equation differs from the usual form in the treatment of friction term or interaction, and has better physical insight. These equations are analyzed mathematically and some relationship between physical quantities centering void fraction arediscussed. Hydrodynamic equation shows the void fraction distribution to have relation to pressure loss and velocity distributions, and, for the case of laminar two-phase flow with axial symmetry, explicit expression is presented. By hydraulic equation, the relation between void fraction and other variables are discussed. For the upward two-phase flow with constant flow area, gas-liquid interaction force is discussed theoretically and experi-mentally.

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Thermal neutron spectra in the graphite bulk of slab geometry with boron carbide were measured at temperatures from 20 to 800°C by the time-of-flight method, using a 100 MeV electron linear accelerator. The results were compared with calculation based on the multi-group S₈ method using Young-Koppel's scattering law. Fairly goodagree-ment is obtained between the calculated and measured spectra except in a limited range of energy just above the peak of the thermal spectra. Considering the uncertainty in the spectrum calculations, the scattering kernel of graphite based on the scattering law will be accurate sufficiently to evaluate the infinite multiplication factor of a graphite moderated reactor within an error of about 0.15% It is also emphasized from the two-dimensional S₄ calculations that the effect of reentrant hole perturbation should be so significant in the graphite bulk as to decrease the peak of the thermal spectra by 1012%.

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The critical supersaturation model (CSM) was examined by comparing its predictions with the experimental data of the forced evaporation of sodium reported in Part (I) of this series of papers. The results revealed that the CSM predicted a fairly lower Sher-wood number than that predicted in the experiment. This discrepancy may be due mainly to the oversimplified assumptions in the CSM.
A calculation of the fog movement in a boundary layer was also attempted by taking into account the force on fog particles by thermophoresis. The calculation showed that the particles were submerged deeply in the boundary layer and that they absorbed sodium vapor in accordance with their size. It was concluded that the fog movement in the boundary layer was essentially important for the exact estimation of the evaporation rate.

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Corrosion of Type 304 stainless steel by molten Cs₂O₃-CsO₂ has been investigated at 690 and 800°C. The Cs₂O₃-CsO₂ mixture was selected as corroding agent in order to clarify the corrosion behavior of stainless steel at a considerably high oxygen potential. At the initial stage a uniform Fe₃O₄ layer is formed and is then removed. After the removal of the oxide film intergranular penetration proceeds into the alloy substrate. Chromium-containing oxides are formed as corrosion products at the grain boundaries. After the grain boundary penetration has continued for a while, a Cr-depleted surface alloy layer is formed, which blocks further progressing of the intergranular penetration. Then, this Cr-depleted layer is detached, inducing the restart of the intergranular pene-tration. Compared to the reported intergranular penetration rates of stainless steel due to Cs₂O-Cs₂O₂, those due to Cs₂O₃-CsO₂ obtained in this study were generally lower, and changed in a more complicated fashion with time.

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This paper describes analysis of the fallout from the 19th Chinese nuclear explosion test. (1) The analysis identified the following 16 nuclides using the radioactive decay method : ⁹⁵Zr, ⁹⁵Nb, ⁹⁷Zr, ⁹⁷Nb, ⁹⁹Mo, ^99mTc, ¹³¹I, ¹³²Te, ¹³²I, ¹³³I, ¹³⁷Cs, ¹⁴⁰La, ¹⁴³Ce, ¹⁴⁷Nd, ²³⁷U and ²³⁹Np. (2) Assessment of a baby's thyroid dose by radioiodine based on this nuclear explosion test was carried out. Culculated dose is 4.5 mrem/yr which is nearly one-third of radioiodine release guideline for a light-water-cooled nuclear powerstation. (3) Nuclide concentration, (number of nuclides)/(nuclear fission yield), going back to predicted fission time was calculated. Assuming the fast fission of ²³⁹Pu, the con-centration curves of each nuclide crossed at approximately the same point. The reported fission time by ERDA of U.S.A. fell into the authors' speculated fission time region which was calculated from the time dependent nuclide concentration curves mentioned above. (4) The ²³⁷U was identified from the decay curves of ²³⁹Np photopeak (278 keV) and of multiplet of ²³⁹Np and ²³⁷U (207 keV). The estimated atomic ratio of ²³⁹Np: ²³⁷U at fission time was 28: 1.

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An analysis is made of locked rotor accidents in a molten salt breeder reactor (MSBR). The evaluation is performed using a point reactor model for the reactor power and a spatially lumped parameter model of primary system for fuel temperature.
In a reactor with circulating fuel such as an MSBR, the reduction or the stoppage of fuel flow caused by locked rotor of fuel pumps will result not only in adding positive reactivity due to the decrease of the loss of delayed neutron precursors out of the core, but also in loosing heat sink. In this report, locked rotor accidents of one, two, three and four pumps out of four fuel salt pumps are evaluated. It is shown that the transients of the reactor system will be within the safety range in virtue of the excellent nuclear and thermal characteristics of the MSBR.

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