Lesson 6 – Exercise: Simulating Radionuclide Decay Chains
In order to become more comfortable with using the ICRP database and simulating decay chains, in this Lesson we will work through a very simple example.
We will model all of the daughters of Ra-226 with half-lives greater than 1 year (as well as stable Pb).
100 Bq of Ra-226 is added to a Cell with 10 m3 of water and we will simulate the system for 10,000 years.
To create this model, you should start with a new model and follow these steps:
- Select “All species” from the Display field in the Species dialog.
- Press Include for Ra-226.
- Make sure that the range for Auto-include ICRP daughters is set from 1 year to 1e+12 years (this is the default).
- Select “Modeled species + Daughters” from the Display field in the Species dialog.
- Press Include for Pb.
- Select “Modeled species” from the Display field in the Species dialog to see the actual species that will be modeled.
- Delete the default species (Species1).
- Create a Cell and assign it a volume of water of 10 m3.
- Create a Data element (vector by species) called Initial Inventory defined as 100 Bq for Ra-226 (and 0 Bq of the other species).
- Convert the activity inventory to a mass inventory and add it to the Cell.
- Make sure you specify that the Time History of the mass in the Cell is saved.
- The Time Settings should be set to a Duration of 10,000 years with a 10-year timestep.
Stop now and try to build and run the model.
Once you are done with your model, save it to the “MyModels” subfolder of the “Contaminant Transport Course” folder on your desktop (call it ExerciseCT16.gsm). If, and only if, you get stuck, open and look at the worked out Exercise (ExerciseCT16_ICRP_Decay_Chains.gsm in the “Exercises” subfolder) to help you finish the model.
Let’s walk through this very simple model now.
The Species dialog should look like this:
The inventory should have been entered in a Data element that was defined as a vector of species:
This then should have been converted to a mass as follows:
The Cell should look like this:
If we run the model and plot the mass in the tank, the result looks like this:
Due to the large range of values, the Y-axis has been modified here to display a log scale.
Note: Your chart will not look like this (the line styles will be different). You can change the line styles for the items in the vector by selecting the Edit Properties button for the chart, and then pressing the Edit... button under Style in the list of Results.