Coarse-grained potential for interaction with a spherical colloidal particle and planar wall

An effective coarse-grained interaction potential between a point particle and a spherical colloidal particle with continuously distributed inverse power-law interaction sites is derived. The potential covers all ranges of spherical particle size, from a point particle up to an infinitely large particle forming a planar surface. In the small size limit, the point-to-point interaction is recovered, while in the limit of an infinitely large sphere the potential comes over to the known particle–wall potentials as, e.g., the 9–3 potential in the case of the Lennard–Jones interaction. Correctness and usefulness of the derived potential is exemplified by its application to SPC/E water at a graphite sphere and wall.

PBMR Fuel Kernel Model for the Prediction of Accurate Temperature Profiles

PBMR (Pebble Bed Modular Reactor) is a High-Temperature Gas-cooled Reactor (HTGR) utilizing spherical pebble like fuel elements. A pebble is a moulded graphite sphere about the size of a tennis ball that contains approximately 15000 homogeneously distributed, triso-coated low-enriched uranium dioxide (UO2) particles, about 1mm in diameter. In the case of fast reactivity transients the accurate time-dependent calculation of the uranium temperature is essential as the neutron balances in the nuclear reactor are strongly influenced by the actual fuel temperature. This paper presents a calculation model that calculates the temperature profile through a representative fuel kernel, its coating layers and the associated graphite moderator. The local nuclear fission heat is deposited directly in the fuel itself. Great care is taken with the definition of the boundary conditions and implementation thereof to ensure that the kernel temperature calculation model describes the physics as accurately as possible. This paper reports on this in detail. A sample calculation is included to illustrate the effect of and need for a more accurate model.