The measured cross sections of 14 MeV (n, p) reaction for nuclei with mass number larger than 90 are analyzed in terms of the pre-equilibrium exciton model and an effective Q-value, that is derived from a semi-empirical mass formula whose parameters are smooth functions of mass number and are free from fluctuations near closed shells. The deviations from 1.0 of the ratios of experimental to theoretical cross sections calculated using the effective Q-values are markedly reduced as compared with the use of the true Q-values. The use of the effective Q-values also gives a better agreement between the experimental and calculated cross sections in the calculations based on the geometry-dependent hybrid model.

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A new method for obtaining three-dimensional neutron flux distribution in a reactor has been developed by taking into account the fact that the X-Y planar geometry is generally complex but the geometry along Z-axis is simple. In this method, the finite element method is applied to the X-Y plane calculation and the finite difference method to the Z-axis. For solving a three-dimensional neutron diffusion equation, these two methods are iterated suc-cessively until a consistency of the leakage coefficients is attained between the two. The present method is embodied as a computer program FEDM for FACOM M200 computer. With this program, a three-dimensional diffusion calculation was performed for comparing some numerical results with those by a conventional standard computer code ADC. The comparison has shown that they agree well with each other. Computing time required for this problem by the FEDM was shorter than that by the ADC for obtaining same accuracy on the eigenvalue. To indicate usefulness of this method, a demonstration calculation for a reactor with a complex geometry was performed, which was a difficult case to calculate with a conventional finite difference code.

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Comparisons are made between PALLAS calculated with meaured neutron and γ-ray doses above the ground in an air-ground medium for HENRE accelerator and BREN reactor, yielding good agreements except for a 8.23-m height of HENRE source, in which the cal-culation overestimates the neutron dose by a factor of 1.5 due to the use of a rough angular quadrature set. Disregard of the ground results in a decrease by a factor of 2 in both neutron and γ-ray doses compared with those for the presence of the ground, while for an infinite-air medium both these doses increase with distances from the source, which in-dicates that the ground should not be ignored in the neutron and secondary r-ray transport calculation. For assumed neutron skyshine calculations disregard of the ground results in a decrease in the neutron dose by a factor of 1.5 and 1.7 and also in the secondary γ-ray dose by a factor of 1.35 and 35 respectively for a 14-MeV source and a fission source. In addition to the importance of inclusion of the ground in neutron skyshine calculations, an additional essential factor is the secondary γ-ray production due to neutron inelastic scatter-ing interaction with nitrogen for the 14-MeV source, or the one due to neutron capture interactions in both ground and air for the fission source.

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A computer code is developed for analysis of dynamic behavior of a single cryogenic distillation column. A dynamic simulation study is performed for the lead column in a typical column cascade which consists of four columns and two catalytic equilibrators.
The atom fraction of protium in the bottom product and the reflux ratio are regarded as the controlled variable and the manipulated variable, respectively. Fluctuation or change of the feed composition is considered as the disturbance and the PI control scheme is in-troduced for a constant value control.
The criteria are derived, which can be used in setting the choice of the two PI con-troller parameters. Investigated are the effects of the controller parameters on the response of the controlled variable to a step change in the feed composition, and the validity of the criteria is verified. The parameter setting method proposed in the present study has two advantages : it accounts for the strong nonlinearity of the column and it predicts the unsta-ble region which must be avoided in the actual operation.

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The compatibility of Eu₂O₃ and (Eu, Gd)₂O₃ mixed oxides which contain 0, 1, 5, 10, 50 and 100 mo/0 of Gd₂O₃, with type 316 stainless steel was examined by out-of-pile heatings. The heating temperature ranged from 550 to 1, 000° and heating time from 500 h to up to 5, 000 h. Metallographic examinations of the stainless steel indicated that chemical reaction between Eu₂O₃ and stainless steel occurred at 650° and that grain boundary penetration extended up to 40 μm after heating at 1, 000° for 500 h. The penetration depth Δl was expressed as a function of heating temperature T as
Δl= 3.08 × 10₄ exp (-72 × 10₄/R T),
where R is the gas constant and the activation energy is given in cal/mol. Electron probe microanalysis and X-ray diffraction analysis indicated that main reaction product is europium silicate. When Gd, which is a decay product of Eu, is mixed with Eu₂O₃, the degree of reaction between (Eu, Gd)₂O₃ and stainless steel decreases as increase in concentration of Gd₂O₃. It was found that actually no grain boundary attack was observed even after heat-ing at 1, 000°C for 500 h when concentration of Gd₂O₃ in (Eu, Gd) ₂O₃ exceeded 10 mol/0. Discussion was made of reaction mechanism of Eu₂O₃ and (Eu, Gd)₂O₃ with stainless steel.

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In order to obtain fundamental perspectives on fuel cladding deformation behavior under changing temperature and pressure conditions in a hypothetical loss-of-coolant accident of PWR, Zircaloy-4 tube burst test was conducted in both air and 99.97, Ar atmospheres. The tubes were directly heated by ac-current and maintained at various temperatures, and pressurized gradually until rupture occurred. Rupture circumferential strains were generally larger in Ar gas than in air and attained a maximum around 1, 120 K in both atmospheres. Some tubes tested in air produced axially-extended long balloons, which proved net to be explained by such properties or ideas as effect of cooling on strain rate, superplasticity, geometrical plastic instability and stresses generated by surface oxide layer. A cause of the long balloon may be obtained in the anisotropy of the material structure. But even a qualitative analysis based on this property can not be made due to insufficient data of the anisotropy.

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A steady separate effects test on BWR spray cooling was performed at relatively high system pressures using the ROSA-III test vessel. These tests were conducted in order to promote a better understanding of the thermal-hydraulic phenomena in LOCA experiments and to obtain information necessary for improvement of analytical codes. The fraction of entrainment or overflow for various spray conditions was obtained and the data of CCFL at the upper tie-plate were compared with correlations. It was shown that the occurrence of CCFL significantly diminished core cooling effects and that rod quench by fall back water was quite irregular and unstable. Reflood core cooling was also studied.

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