A new method of exponential experiment was developed for a cylindrical subcritical assembly of hexagonal lattices. In this method, higher harmonics are excited by an eccentric point neutron source and are divided into 4 groups. Then, from the attenuation coefficients of the dominant modes in each group, the material buckling and the effective core radius (or the reflector saving) of the assembly are determined experimentally.
Experimental results show that this method is useful for cylindrical assemblies, and the bare homogeneous approximation is rather good even for a subcritical assembly with reflector.

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The diffusion parameters of ¹³³Xe in irradiated sintered pellets of several different uranium carbides were measured in postirradiation annealing experiment in the temperature range of 1, 000°1, 400°C.
A rapid increase of ¹³³Xe release was observed when the pellets reached 200°600°C while being heated to 1, 000°C. It was considered that this rapid release of ¹³³Xe could be explained, not by the diffusion model, but by the desorption phenomenon of ¹³³Xe evolved and adsorbed on the pellet surface during irradiation.
The apparent diffusion coefficient (D') obtained here appears to depend mainly on the actual surface area of the pellet and not on the fraction of its theoretical density. The values of D' obtained here for carbides at 1, 400°C were of the same order of magnitude as the values reported for sintered 97% dense UO₂ pellets.
The diffusion coefficients (D) of all samples were found to be in the range of 1×10^-191×10^-18cm²/sec at 1, 000°C and 1×10^-162×10^-15cm²/sec at 1, 400°C, having activation energies of 5078 kcal/mol.

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The study was carried out at 260° and 280°C, using an out-of pile stainless-steel water loop. Emphasis of the study was placed on the effect of dissolved oxygen on the formation of soluble corrosion product and insoluble crud in the water. The concentrations of both soluble corrosion product and insoluble crud increased with the dissolved oxygen concentration.
The particles of the insoluble crud caught in a 320-mesh filter in the loop purification system were blackish-brown platelets 50 to 100μ across. They were separated into magnetic and nonmagnetic fractions; through X-ray diffraction, the former was found to be mainly Fe₃O₄ and the latter ZrO₂.
It was observed that there was little relation between the composition of the crud and that of the main materials constituting the loop. The insoluble crud deposited more readily on 18-8 stainless-steel than on Zr alloy test specimens. The ionic forms of the elements in the soluble corrosion product were estimated from chemical analysis of the ion-exchange resin discarded from the loop water purification system.

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