Activation cross sections for the (n, 2n) reaction on Nd, Sm, Gd and Yb have been measured at 14.6 MeV by using a Ge(Li) r-ray detector. The following cross sections (mb) have been obtained : ¹⁴²Nd 1, 675±160, ¹⁴⁸Nd 1, 789±147, ¹⁵⁰Nd 1, 720±128, ¹⁵⁴Sm 2, 010±137, ¹⁶⁰Gd 2, 173±152, ¹⁷⁶Yb 2, 226±152. These (n, 2n) cross sections are compared with the theoretical calculations performed by a new model including pre-equilibrium and statistical models. A good agreement between the experimental and calculated cross sections is obtained.

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The pressure response obtained for a vertical column is identical to that resulting from the acoustic constraint model adopted by Cho et al. within the range of time required for the waves to traverse and retraverse the column (t<l/c), but beyond this point in time the present analysis yields responses that differ according to the history of the wave.
On the other hand, for spherical compression waves propagating symmetrically outwards in the coolant. the solution obtained is
where R denotes the initial radius of the FCI region and S(t) a unit step function. This time the pressure disturbance undergoes attenuation with the effect of both the factors exp(-ct/R) in time and (R/γ) in space, which renders it sensitive to differences in the effective interaction time of phase A. It is suggested that the predicted pressure should be reduced appreciably by adopting the rigorous solution of the spherical acoustic constraint model, combined with realistic values chosen for the interaction time.

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Incipient temperatures of sodium oxidation, sodium oxide aerosol release and sodium ignition were observed in relation with oxygen concentration in supplying gas by a thermobalance method. On this results, a burning rate and an aerosol release fraction were determined by burning about 0.5 g of sodium samples on a crucible in a burn tube under conditions ranging 400 to 600°C in sodium temperature, 0.1 to 1.0 N1/min in the supplying gas flow rate and 2.5 to 20v/o in the oxygen concentration.
Particle sizes of sodium aerosols released from the samples made a log-normal distribution, of which mass median diameter ranged from 0.6 to 2.0 μm. The burning rate increased with the increases of the sodium temperature, of the gas flow rate and of the oxygen concentration, and the aerosol release fraction also increased in proportion to the burning rate at fixed oxygen concentrations. It was found that the aerosol release rate defined as a product of the burning rate and the aerosol release fraction describes fairly well not only the present experimental data but also reported ones.

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Empirical studies of coherences between measurement variables from the operating data of a commercial nuclear power station of 460 MWe are applied to derive dynamical characteristics of the Boiling Water Reactor and to attempt to identify the noise sources of the neutron flux. Multivariate techniques with the partial coherence function and the multiple coherence function are introduced to eliminate correlated effects among measurement variables due to thermal hydraulic coupling and sophisticated reactivity feedbacks. From the results, the usual coherency (the ordinary coherence function) may not be adequate to estimate linear relations between measurement variables of the BWR. Furthermore, the noise sources of the neutron flux is discussed.

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The effect of neutron irradiation on the tensile deformation behavior of zirconium was examined at room temperature at various strain rates ranging of 2.2×10^-42.2×10^-2 sec^-1. The microstructure of the deformed specimens was observed by transmission electron microscopy. It was established that neutron irradiation diminishes the uniform elongation and the strain hardening rate, and hastens the onset of plastic instability. These phenomena are attributed to inhomogeneous deformation in the dislocation channels in the irradiated and deformed zirconium.
From the relation between strain rate and tensile properties (yield stress, ultimate tensile stress, uniform elongation and strain hardening rate), it was established that in unirradiated zirconium deformation is controlled by slip at strain rates below 6×10^-3 sec^-1, while above this threshold, twinning as well as slip contribute to deformation.
Neutron irradiation markedly inhibits deformation twinning in zirconium at room temperature. At 77K, on the other hand, deformation by twinning is more prominent in irradiated specimens. The mechanism of twinning inhibition due to neutron irradiation is discussed.

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Absorption process of gaseous methyl iodide by water or sodium hydroxide solutions was investigated using a semi-flow type experimental apparatus by measuring the concentration of all measurable chemical species in both the gas and the liquid phase.The experimental temperature ranged from 288 to 311 K and the gaseous methyl iodide and aqueous sodium hydroxide concentrations were approximately 0.6 × 10^-3 to 7 × 10^-3 and O to 0.2 mol/dm³, respectively. It is estimated that the dissolution of methyl iodide into the sodium hydroxide solution proceeds according to the following steps.
Step (1) Methyl iodide in air dissolves physically into the aqueous phase. Physical dissolution process obeys Henry's law.
Step (2) Methyl iodide dissolved into the aqueous phase is decomposed by a base catalytic hydrolysis and produces methyl alcohol and iodide ion.
The equilibrium constants of physical dissolution were obtained from the steady concentration in both the gas and the liquid phases in the semi-flow type experiment because the hydrolysis reaction rate of methyl iodide is very slow in comparison with the physical dissolution in this experimental conditions. The obtained value of the standard heat of solution of methyl iodide into water was 7.2 kcal/mol.
Salting-out effect was, observed when the concentration of sodium hydroxide in the absorbent was over 0.01 mol/dm³.

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The method of sequential cation-exchange separation of fission products proposed by Natsume et al. was applied to the preparation of fission-produced ⁹⁹Mo and ¹³²Te, with particular attention paid to increasing the recovery of ⁹⁹Mo and ¹³²Te, and to reducing contamination with ⁹⁵Zr-⁹⁵Nb and ¹⁰³Ru. The cation-exchange behavior of these nuclides was found to be influenced by the particle size of the target U₃O₈ powder, the method of dissolution, the standing time allowed between dissolution and separation, and the quantity of uranyl ion treated in one batch. In order to enhance the distribution of ¹³²Te in the Te fraction, and to reduce the contamination of the Mo and Te fractions with ⁹⁵Zr-⁹⁵Nb and ¹⁰³Ru, the ion-exchange separation should be applied immediately after dissolution of the U₃O₈ in nitric acid and upon treatment of the solution with concentrated HCI. Relatively coarse particles of U₃O₈ were found more suitable for the present purpose of preparing ¹³²Te. Batches of U₃O₈ smaller than about 0.5 g proved to result in better separation of ⁹⁹Mo and ¹³²Te, for a column bed volume of 25 ml.

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Tensile and low cycle fatigue tests were conducted on Hastelloy X in vacuum at several temperatures from room temperature to 900°C. The mid-range ductility minimum generally observed in nickel-base superalloys did not show itself in the material containing yttrium and which was solution heat treated at a higher temperature. The fatigue crack growth rate was calculated from the measured intervals of fatigue striation observed by scanning electron microscopy. The specimen that was fractured at 900°C did not present the typical fatigue surface, and instead the rupture was characterized by marked reduction in area and a large cavity in the center of the fracture.

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