Group Constant File Generation With extractSerpent2GCs.py
Example problem: Two-region MSRE model
Here, group constants are taken from an example Serpent output using PyNE. These will be used to generate text-based group constant files using extractSerpent2GCs.py. The relevant files for this tutorial may be found in the MSRE_group_constants tutorial directory.
Moltres is not a spatially homogenized diffusion code. MOOSE is made for running big, intense problems, using modern HPC. Because there is no desire to homogenize spatially here, the materials that the user would like used in Moltres should each fill their own infinite universe. Then, this universe should have its group constants generated using the set gcu <material universe numbers> option in Serpent 2.
It's important that universe 0, the main universe, is not included. Serpent takes tallies for group constants in the first universe it identifies, so including 0 means that no further universes will be included in GC generation. (please double check this on the serpent forum).
Step 1: Generating Group Constants with Serpent 2
In this directory, we provide a Serpent input file for simulating ORNL's Molten Salt Reactor Experiment, documented largely on websites like this.
For group constant generation, Cole Gentry found that a 4 group structure with three thermal groups and one fast group works well in the graphite moderated FHR. There is also an available recommended 13-group structure commented out in the gentryGroups.serp file The PDF of these findings can be found here.
The "fuel" file contains "cards" (a relic term referring to the fortran-dominated reactor physics ages of yore) that will generate group constants at a few temperatures, and likewise for the "moder" file. Like a cooking show, we have prepared the important results for you in the fuel.coe and moder.coe files, which get parsed by serpentTools in the extractSerpent2GCs script. serpentTools is a suite of parsers designed by GATech for parsing SERPENT output files. More information can be found at here.
Step 2: Parsing Serpent 2 Output Files with extractSerpent2GCs.py
The command to run in order to generate the Moltres-compatible group constants is:
$MOLTRES/python/extractSerpent2GCs.py MSREProperties msre_gentry_4g tempMapping.txt secBranch.txt universeMapping.txt
where $MOLTRES is an environment variable leading to the install location of Moltres. An alternative would be to just add the $MOLTRES/python directory to your path.
The input syntax requires a directory name you'd like to create, a file base name that Moltres will look at, a file that maps primary branch names to temperatures, a file that lists the secondary branch names, and lastly a file that maps universe numbers from Serpent to material names. Group constants will be extracted for all materials listed in the last file.
The secBranch.txt file should be blank if no secondary branches were used, i.e. there is only one branch variation per burnup step.