Editing Boundary conditions (section)

== Radially infinite, axially finite 3D geometries ==

Three-dimensional model of a fuel assembly in an infinite lattice is an example of a geometry that is radially infinite and axially finite. The outer boundary of such geometry is formed by the surface at which the repeated boundary conditions are applied, and two axial planes that the define the bottom and top of the geometry model. The outside cells could then be defined, for example, as:

 <nowiki>
cell 997 0 outside  b1  b2 -b3
cell 998 0 outside -b2
cell 999 0 outside  b3</nowiki>

where surfaces b1, b2 and b3 are an infinite square prism and planes forming the bottom and the top of the geometry, respectively. It is important that the surface at which the boundary conditions are applied is listed first.

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Image:refl3Df.png|'''Reflective boundary conditions''' ("set&nbsp;bc&nbsp;2", yz-plot). See [[media:refl3Df.gif|animated particle tracks]].
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