Internal stresses caused by non-uniform swelling of fissionable material

This paper examines a new cause of macro-stresses of the first kind in fuel elements-namely, nonuniform swelling of the fissionable material, caused by the fact that, owing to corrosion of the neutron flux, the amount of fission products formed is not uniform across-section of the fuel element. The authors give methods of calculating the magnitudes of the stresses. They note cases in which the stresses have an appreciable effect on the efficiency of the fuel element.Translated from Atomnaya Énergiya, Vol. 18, No. 5, pp. 483–487, May, 1965     

Method of estimating the critical parameters of a body of arbitrary shape made from fissionable material

In this paper we consider an approximation method for determining the critical parameters of a body of arbitrary shape (or a group of bodies) made from fissionable material. In contrast with the variational method, the method described here is extremely simple and gives an error which is favorable from the point of view of safety as applied to fissionable materials; hence it is useful for engineering calculations.The method has been applied to fast neutron systems where the single-velocity approximation gives good accuracy.We wish to express our gratitude to B. D. Stsiborskii and M. L Kuvshinov for calling our attention to the experiment with the two interacting spheres; we also wish to thank V. A. Davidenko, Yu. N. Babaev and N. A. Dmitriev for discussion of the present work and a number of valuable comments.     

On the question of the nature of radiation damage in fissionable materials

This article gives a survey of the theory of radiation damage in materials irradiated by fast particles. An attempt is made to describe the processes of phase transformations under neutron irradiation of fissionable materials with the aid of diffusion equations. In this way an expression for the coefficient of diffusion D is obtained. The possible result of the effect of thermal spikes on the structure of the eutectoid a + is investigated for an annealed uranium-molybdenum alloy.     

Calculation of neutron importance function in fissionable assemblies using Monte Carlo method

The purpose of the present work is to develop an efficient solution method for the calculation of neutron importance function in fissionable assemblies for all criticality conditions, based on Monte Carlo calculations.     

Parameters influencing the flow of packings of spheres and near spheres in cylindrical vessels

An experimental study has been made of some of the parameters governing the flow of pebbles in packed beds under the influence of gravity. The study centres on the flow of random packings of equal spheres in a cylindrical vessel with a conical hopper and a central outlet. The flow of regular concentric shell packings has also been investigated. Early experiments showed that flow patterns are unaffected by some of the parameters, including in particular the recirculation rate and interruptions of flow. This enabled greatly simplified and accelerated experiments to be performed. Of about 30 parameters relevant to a recirculating pebble bed reactor, 13 can have major effects on the flow pattern. The experiments indicate that most of the effects stem from the hopper. Those which are undesirable in a nuclear reactor core, such as dead zones and high residence time ratios, can be eliminated or minimized by selecting appropriate values of the parameters. Further improvements can be effected by the provision of multiple hoppers and outlets. A velocity discontinuity is observed in the cylindrical portion of all random packings, whether the vessel is fitted with a hopper or not. With regular concentric shell packings several velocity discontinuities are possible. They are explained by a flow mechanism whereby pebbles continually make and break contact with the cylindrical wall and with one another. This confirms that most of the major effects on the flow pattern must stem from the hopper.