Module reader

Parsers and logic for reading meshtal files

All functions are re-exported to the crate root for easy access.

Quickstart

The simplest methods for reading tallies from a meshtal file are the convenience functions:

// Extract all meshes from a file into a Vec<Mesh>
let mesh_list = read("/path/to/meshtal.msht").unwrap();

// Extract just one target mesh from a file into a single Mesh
let mesh = read_target("/path/to/meshtal.msht", 104).unwrap();

Under the hood these initialise the MeshtalReader. This is made public for fine control if absolutely needed, but the convenience functions are the preferred API for this module.

// Initialise the reader and set some options
let mut reader = MeshtalReader::new();
reader.disable_progress(); // disable the progress bar
reader.set_target_id(104); // choose a specific tally

// Parse the file
let path = Path::new("/path/to/meshtal.msht");
let mesh_list = reader.parse(path).unwrap();

Implementation overview

When read() is called, a MeshtalReader is initialised and the parse() method called on the provided file.

This proceeds in two stages:

• Pre-processing to check the tally numbers and formatting styles
• Extraction of each tally to a Mesh object

The meshtal files are parsed line-by-line using a buffered input stream so that, at most, a single line is held in memory. This reduces memory requirements significantly.

A lot of the mesh data are also derivable from the header information. For example, there is no need to store all of the voxel coordiante data explicitly. See Voxel for detalis, but this further reduces large meshes to ~24B per voxel.

Formatting notes

While not unique to CuV formats, it is certainly the biggest offender for a couple of formatting issues that break most other parsers.

Run-on numbers without whitespace are handled

For example, 1.00E+00-2.00E+00 is recognised and parsed as 1.00E+00 -2.00E+00 instead.

Broken exponential formatting is handled

For example, 1.00+002 is recognised and parsed as 1.00E+002 as though the missing exponent character is there.

Unphysical -ve results are handled

Only an issue for CuV, but it is possible to have -ve flux in the results for whatever reason. These are considered to be 0.0 in the voxel results.

Warnings are given for precision issues

Certainly a problem for Novel 1-Step calculations, but for whatever reason the MCNP developers decided that the mesh bounds were fine to have 3 significant figures.

This means that time and energy bins that are extremely large or close together are identical and can not be used when searching for groups.

It is therefore recommended that groups are found by index whenever this warning is raised.

Cell-Under-Voxel (CuV) notes

The UKAEA CuV modification for MCNP is a huge pain, but is fully supported though all the same interfaces.

Volume weighting

There are often multiple cells that correspond to a single voxel. The goal is to turn these into a single result.

Every cell contribution to the total flux in a voxel is weighted by the volume it occupies. i.e.

weight = cell volume / voxel volume

This is then applied as appropriate to the result and uncertainty.

Void records

To save space in the meshtal files the voidoff option can be specified in an MCNP run. This corresponds to the VoidRecord variants to be explicit.

• VoidRecord::On = Void cells are included in output data
• VoidRecord::Off = Void cells are excluded in output data

Both are completely handled in the background, but it is worth noting that any missing voxels for the VoidRecord::Off will be included in the Mesh.

These voxels with have a result and error of `0.0``, which is not accurate but it is necessary to fill the gaps.

Supplementary data

It is worth noting that all cell data on volumes, cells, etc… are parsed into CellData. However, these data are generally discarded to minimise memory requirements.

Future updates may store these data if it becomes useful to do so.

Structs

CellData

Additional information for CuV data parsing

MeshtalReader

A generalised reader for legacy meshtal files of any type

Enums

VoidRecord

Explicit states for the CuV ‘Voidoff=’ card

Functions

read

Read all meshes in a meshtal file

read_target

Read only the specified mesh from a meshtal file

read_target_pb

Read only the specified mesh, with progress bar