Editing Automated depletion zone division (section)

=== Sub-division and geometry levels ===

In large complex geometries it may not be possible to handle every cell as a separate depletion zone. In such case the sep-entry can be used, for example, to sub-divide the fuel in a large LWR core into separate depletion zones on assembly-, instead of pin-basis. Another example is an HGTR geometry consisting of millions of individual fuel kernels. Instead of handling each kernel as a separate depletion zone, the division can be done based on compacts or pebbles.

The concept of a geometry level may be a bit difficult to understand, but basically it means that whenever there is a cell, lattice, or any other geometry structure filled with another universe, it adds a new level in the geometry. What makes things a bit more complicated is that regular structures, such as lattices, also form a new level. So in a typlical BWR assembly geometry, for example, the levels would be:

#Structures defining channel box wall, moderator channels, etc. and the outside world
#Lattice of fuel pins
#pin universes

The parameter ''LVL'' following the '''sep''' entry determines the number of levels counted <u>backwards</u> from the last one (''LVL'' = 1 being the last). 

Consider another example, consisting of 4 HTGR fuel pebbles, each filled with 50 TRISO particles. The geometry consits of 5 levels:

#Cube containing the pebbles, and the outside world
#Pebble distribution
#Pebble universes
#Particle distributions
#Particle universes

With 

 <nowiki>div fuel sep 1</nowiki>

the division is based on particle universes (level 5, last of the geometry levels), and each particle in each pebble is handled as a separate depletion zone, resulting in a total of 200 burnable materials. A geometry plot shows each fuel kernel in different color:

[[File:Divsep1_131224.png|500px]]

With 

 <nowiki>div fuel sep 3</nowiki>

the division is based on the pebble universe (level 2, the third universe counted backwards from the end), and the number of depletion zones is reduced to 4, one for each pebble:

[[File:Divsep3_131224.png|500px]]

When the number of pebbles and fuel kernels per pebble increases to several thousand, this makes a huge difference for the total number of depletion zones. 

The way the division works is not always very intuitive. In the example above, ''LVL'' = 2 results in the same division as ''LVL'' = 1, and ''LVL'' = 4 in the same divison as ''LVL'' = 3. Usually the best way is to try different values and look at the geometry plotter for the result (note that setting rgb values in the [[Input syntax manual#mat (material definition)|material cards]] fixes the color scheme and doesn't show the sub-division).