Automated depletion zone division

Serpent 2 has the capability to perform automated depletion zone division for materials in burnup calculation. There are two options:

• The number of radial regions in 2D pin-type objects can be entered directly in the material card ("Serpent 1" type division).
• The div card can be used to perform 3D depletion zone division.

Both approaches are discussed below. With automated depletion zone division it important to always check the volumes using the Monte Carlo based volume checker routine, and if necessary, define the volumes manually.

Division with divisor card

The div card can be used to separate each cell into its own depletion zone, and further sub-divide pin-type objects into axial-, radial and angular sub-zones.

the definition of material volumes

This capability existed already earlier for the pin-type structures, but the new method extends it to arbitrary 3D geometries. The division is invoked by a new input card:

div <mat> [sep <1/0>] [subz <nz> <zmin> <zmax>] [subr <nr> <rmin> <rmax>] [subs <ns> <s0>]

Parameter <mat> relates the division into the material that is divided. Optional parameter "sep" gets value 0 = no or 1 = yes, and it determines whether the material is divided into separate depletion zones. If the division is set, every cell containing material <mat> is handled separately in the burnup calculation. The division takes into account the universe-based geometry structure, so the same cell in two different univeses is treated as two separate cells. For fuel assembly geometries, for example, each pin is automatically treated as a separate material. If the assembly is put in a core lattice, the same pin in two different assembly positions are treated separately and so on. The method is really simple, but it easily results in a very large number of burnable materials. At the moment the division cannot account for symmetries, but I'm working on that...

The remaining parameters divide the materials into sub-regions. In the current update the sub-division is based on cylindrical objects. Parameter "subz" divides the material into <nz> axial regions between z = <zmin> and z = <zmax>. Parameter "subr" divides the region radially into <nr> rings between r = <rmin> and r = <rmax>. The last paramter "subs" divides the region into <ns> angular sectors, with the zero position given by angle <s0>.

Here's an example...

Imagine a BWR assembly geometry consisting of a 10 x 10 lattice of fuel pins with 13 different types:

Image

Defining a div-card for each fuel composition:

div fuel1 sep 1
div fuel2 sep 1
...
div fuel13 sep 1

divides identical compositions into different depletion zones:

Image

(some of the colors in the plot may be same or similar, but each regions now contains a different material)

Fuel types 9-13 contain gadolinium, so let's divide them into 10 rings:

div fuel9 sep 1 subr 10 0.0 4.38E-01
div fuel10 sep 1 subr 10 0.0 4.38E-01
div fuel11 sep 1 subr 10 0.0 4.38E-01
div fuel12 sep 1 subr 10 0.0 4.38E-01
div fuel13 sep 1 subr 10 0.0 4.38E-01

The division is made between 0 and 0.438 cm into 10 rings with equal cross-sectional area:

Image

Finally let's divide every pin into 4 angular sectors:

div fuel1 sep 1 subs 4 45.0
div fuel2 sep 1 subs 4 45.0
...
div fuel13 sep 1 subr 10 0.0 4.38E-01 subs 4 45.0

The angular segments are tilted by 45 degrees:

Image

Here's a closer view of 4 divided pins:

Image

The axial division works in a similar manner. The code should be able to calculate material volumes correctly for this type of geometries. The division can be used with any configuration, but if the volumes cannot be calculated for the original cells, they cannot be calculated for divisions either.