Laboratory scale experiments have been carried out to obtain information on the sources of CH₃I, reported by various workers to have been detected under accidental conditions of fuels. Small pieces of slightly irradiated sintered UO₂ and U metal turnings were heated externally up to 1, 400°C in various carrier gases, and the carrier gases were analyzed for fission product iodine present in the form of CH₃I.
From the data obtained, it is concluded as follows: In the case of sintered UO₂, some amount of CH₃I appears to be released directly from the fuel below 600°C, whereas in case of U metal turnings, direct release does not apparently occur at any temperature. In oxidizing atmospheres, iodine released from either sintered UO₂ or U metal is considered to change into CH₃I only to a small extent, probably by gas phase formation.

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In order to determine the conditions under which core spray cooling can be effective after loss of coolant accident, spray cooling experiments have been conducted on a heater assembly at low heat fluxes corresponding to the decay heat following a reactor shut-down. A series of tests have been made at atmospheric pressure using two kinds of 36-rod heater assemblies (15 mm O.D. sheathed heaters arranged in 119 mm square channels, 1, 500 mm and 2, 500 mm heated length). The following results were obtained:
(1) The heaters are cooled either by water a film of water streaming down its surface or by fog-flow and radiation to surroundings.
(2) The rate of flow along any single rod did not generally deviate much from the value of the total channel flow rate multiplied by the ratio of cross sectional areas between single rod and total channel, but the smallest value was about 0.4 of this average.
(3) So long as the heat transfer surface is covered by water, the surface temperature is close to the saturation temperature. Once the covering film is dried up, the heat flux becomes related to the temperature of the wall above that of saturation by the equation
q"=1.5(Tw-T_sat)^3/2
(4) The dry-out is caused either by progressive evaporation of the falling film (applicable to the range of the channel flow rates up to 400 kg/hr at 20°C water) or by "choking" (or flooding) with the ascending flow of steam generated in the channel (range of the channel flow rates above 400 kg/hr at 20°C water).

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Neutron wave propagation is considered by multigroup diffusion theory in a heterogeneous multiplying system having periodic arrays of line fuel rods. The coupled equations are resolved into uncoupled equations by suitable linear transformation. By means of Green functions for a point or a line neutron source, the behavior of the neutron waves originating from a periodically varying neutron source are investigated in an infinite system.
In such a system, the neutron fluxes are represented by means of a Floquet solution relevant to the buckling Β which depends on the angular frequency ω of the external neutron source. Neutron waves propagate analogously to classic waves spreading in accordance with Hiiygens' & Fresnel's priciples.

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A new method of calculating the worth of cruciform control rods arranged in the D-lattice is presented. The lattice is divided into two regions: a transport region near the control rods, and a diffusion region removed from the rods. The neutron behavior in the former region is treated by collision probability method and in the latter by diffusion approximation. The prompt decay constants calculated by the present method are in very good agreement with ex-perimental data, which evidences the accuracy of the present method for evaluating cruciform control rod worth.

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A systematic study has been made on the effect of differences in conditions of applied vibration on the density obtained with a ternary grained powder of arc-fused and crushed UO₂ powder packed in a stainless steel cladding tube.
Comprehensive analysis is made of the relationships between densities obtained and vibration conditions, defined by combinations of two factors among four-i.e., frequency, displacement, velocity and acceleration. The highest density has been found to be obtained at the highest acceleration, provided that displacement is in the range of 1030 μm, and this range is found to be the optimum condition for all levels of acceleration.
The process of vibratory compaction is discussed on the basis of the combination of different factors conducive to the compaction, segregation and disintegration of the powder particles.

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