Universe.volume variable and microscopic mgxs.MGXS instance computation

lbarone · March 14, 2024, 7:22am

Hi everyone,
I was trying to compute the microscopic fission cross section for Pu239. After the simulation and the MGXS.load_from_statepoint() the following error occur: “Volume information is needed to calculate microscopic cross sections for universe 1. This can be done by running a stochastic volume calculation via the openmc.VolumeCalculation object”. I set the volume with universe.volume but it did not work. Is there a possibility to use and already computed volume or the stochastic volume calculation is mandatory?
Thanks in advance!

Luigi Barone

Shimwell · March 14, 2024, 8:33am

You call alternatively set the material.volume to a numerical value. For instance if your material fills a sphere then you can easily find then set the volume without the stochastic volume calculation. Sometimes the volume of the cell that the material fills is not known so then the stochastic volume calculation is useful

Here is a stochastic volume example in case it is handy

github.com

fusion-energy/neutronics-workshop/blob/main/tasks/task_13_stochastic_volume_calculation/1_find_volume_of_cell.ipynb

{
 "cells": [
  {
   "attachments": {},
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "# Finding Volume of a Cell by sampling simulation.\n",
    "\n",
    "For the cell in this example we know the volume as it is a sphere.\n",
    "\n",
    "The method in this example can be adapted and then applied to a cell of unknown volume.\n",
    "\n",
    "We have a cell of known volume so that you can see how accurate the method is when the number of samples is increased.\n",
    "\n",
    "OpenMC samples within a provided bounding box and counts the samples that appear within the cell compared to those that appear outside the cell.\n",
    "\n",
    "By knowing the volume of the bounding box (which is a rectangle) one can determine the volume of the cell within that bounding box by looking at the ratio of volumes and samples in side the cell to outside the cell.\n",
    "\n",
    "The diagram shows the equations carried out by OpenMC in the background"

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lbarone · March 14, 2024, 10:56am

Thank you for the reply. However, it is not working yet. It looks like universe.volume = volume (or material.volume) does not correctly set the volume or does not store the information where needed.

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Universe.volume variable and microscopic mgxs.MGXS instance computation

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