Analysis of Granular Flow in a Pebble-Bed Nuclear Reactor

Pebble-bed nuclear reactor technology, which is currently being revived around the world, raises fundamental questions about dense granular flow in silos. A typical reactor core is composed of graphite fuel pebbles, which drain very slowly in a continuous refueling process. Pebble flow is poorly understood and not easily accessible to experiments, and yet it has a major impact on reactor physics. To address this problem, we perform full-scale, discrete-element simulations in realistic geometries, with up to 440,000 frictional, viscoelastic 6cm-diameter spheres draining in a cylindrical vessel of diameter 3.5m and height 10m with bottom funnels angled at 30 degrees or 60 degrees. We also simulate a bidisperse core with a dynamic central column of smaller graphite moderator pebbles and show that little mixing occurs down to a 1:2 diameter ratio. We analyze the mean velocity, diffusion and mixing, local ordering and porosity (from Voronoi volumes), the residence-time distribution, and the effects of wall friction and discuss implications for reactor design and the basic physics of granular flow.Comment: 18 pages, 21 figure

On Uniform Convergence of Sequences and Series of Fuzzy-Valued Functions

The class of membership functions is restricted to trapezoidal one, as it is general enough and widely used. In the present paper since the utilization of Zadeh’s extension principle is quite difficult in practice, we prefer the idea of level sets in order to construct for a fuzzy-valued function via related trapezoidal membership function. We derive uniform convergence of fuzzy-valued function sequences and series with some illustrated examples. Also we study Hukuhara differentiation and Henstock integration of a fuzzy-valued function with some necessary inclusions. Furthermore, we introduce the power series with fuzzy coefficients and define the radius of convergence of power series. Finally, by using the notions of H-differentiation and radius of convergence we examine the relationship between term by term H-differentiation and uniform convergence of fuzzy-valued function series

A new look at the classical sequence spaces by using multiplicative calculus

The important point to be noted on the non-Newtonian calculus is a self- contained system independent of any other system of calculus. Therefore, the reader may be surprised to learn that there is a uniform relationship between the corresponding operators of this calculus and the classical calculus. In the present paper, some fundamental theorems and notions of the classical calculus are in- Terpreted from the view point of multiplicative calculus and the analogies between them are given. We propose a concrete approach based on some topological prop- erties with respect to the multiplicative calculus. Finally, we give ?-completeness results on some sets of specific sequences

Effects of high degree deacetylated chitosan supplementation on yolk and blood immune status of laying hens

WOS: 000455051903002