DLS, 2-D Diffusion with Line-of-Sight Method for Cavities

1 - Nature of physical problem solved: DLS is a two-dimensional diffusion program supplemented by the line-of-sight technique for the treatment of cavities. 2 - Method of solution: Within material-filled regions, diffusion theory is used, while cavities are treated using the line-of-sight method. The numerical solution of the diffusion equation is based upon balance formulae for all volume elements containing terms for source, absorption, and leakage. At the boundary of a cavity, the term for the entering currents used in the balance equation include the contributions of all other elements at the boundary of the cavity which can be seen from the element considered. These contributions are calculated with the aid of leakage factors and view factors. The leakage factors describe the ratio between the leaving current and the flux density. The program contains various options to calculate these leakage factors. The view factors describe the probability that a neutron leaving the cavity surface of an arbitrary volume element hits the considered volume element directly. The calculation of the factors proceeds upon the assumption that the neutrons emitted into the cavity will have a cosine shaped directional distribution. 3 - Restrictions on the complexity of the problem: The program is written for r-z geometry. Only cavities with strictly rectangular cross sections can be considered. For example, L-shaped cavities cannot be treated. Maximum number of: energy groups: 26; view factors: 20000; cavities: 5; materials: 15. The sum of radial and axial mesh intervals may not exceed 170. The total mesh number is restricted by machine size