Crate wwgen

Weight window generation methods for MCNP

This crate contains methods for generating and manipulating weight windows from MCNP FMESH flux tallies.

There are many ways to do this. Currently the MAGIC method is implemented, with the option for first generating meshes from the Build-Up Density Exptrapolation (BUDE) method.

Mesh to Weight window

Basic use

A constant power factor and error tolerance are applied to all energy/time groups.

• powers - Softening factor used as ww=>ww^power
• max_errors - Errors above this are set to 0/analogue
• total_only - Only generate weights from Group::Total

Weights are calculated as (0.5 * (v.result / flux_ref)).powf(power). For example, applying a 0.7 de-tuning factor and setting voxels with errors below 10% to analogue:

// Read tally 104 from a meshtal file
let mesh = read_target("./data/meshes/fmesh_104.msht", 104).unwrap();
// Convert the mesh into a weight window set
let weight_window = mesh_to_ww(&mesh, 0.7, 0.10, false);

By default, this generates weight windows for all time and energy groups. To generate a simpler set of weight windows based only on the Group::Total, set the total_only boolean to true.

Advanced use

Mesh tally to global weight windows with fine de-tuning and errors

Same as mesh_to_ww but allows for individual de-tuning factors and error tolerances for each group. If powers or max_errors have a single entry this will be applied to all groups.

• powers - Softening factor used as ww=>ww^power
• max_errors - Errors above this are set to 0/analogue

A call to this may look like this, applying separate powers and errors to a mesh with 3 energy groups:

// Read tally 104 from a meshtal file
let mesh = read_target("./data/meshes/fmesh_104.msht", 104).unwrap();
// Convert the mesh into a set of weight windows, using different parameters per set
let ww = mesh_to_ww_advanced(&mesh,
                             &[0.7, 0.5, 0.85],
                             &[0.1, 0.1, 0.15]);

The lists should be ordered such that they match the following nested order:

for energy in energy_groups {
    for time in time_groups {
        calculate weights...
    }
}

For example, the following energy and time groups are related to the groups shown explicitly below.

Energy bin boundaries: 0.0 10.0 200.0
Time bin boundaries  : -1E+36 0.0 1E+16 1E+99
``

```text
0 -> Energy(10.0)   Time(0.0)       powers[0]   max_errors[0]
1 -> Energy(10.0)   Time(1E+16)     powers[1]   max_errors[1]
2 -> Energy(10.0)   Time(1E+99)     powers[2]   max_errors[2]
3 -> Energy(200.0)  Time(0.0)       powers[3]   max_errors[3]
4 -> Energy(200.0)  Time(1E+16)     powers[4]   max_errors[4]
5 -> Energy(200.0)  Time(1E+99)     powers[5]   max_errors[5]

Density extrapolation

Warning: Extremely WIP for testing

A very quick and naive implementation for the work in progress implemntation of the Build-Up Density Exptrapolation (BUDE) method.

This takes several meshes as arguments:

• void mesh (vd), run with voided materials
• uncollided (uc) flux mesh
• reduced density (rd) flux, with materials set to a fraction of their density

These are combined to build up an estimate of the flux that can be expected of a complete run with all materials in the geometry at their full density.

Enums

Error

The error type for the ntools-wwgen crate

Functions

extrapolate_density

Generate new mesh using the BUDE method

mesh_to_ww

Mesh tally to global weight windows with simple parameters

mesh_to_ww_advanced

Mesh tally to global weight windows with fine de-tuning and errors