Lesson 3 – Overview of the Source Element

Now that we have discussed conceptually what a Source element does, let’s start to explore what the Source element looks like and how its inputs are specified. The Source is a complex element, so our goal in this Lesson is to just to get an overview of the element and its various dialogs.  We will explore the details in later Lessons.

Let’s start by inserting a Source element in a new model now.  The Source properties dialog looks like this:

As noted in the previous Lesson, the mass in a Source is assumed to be present in discrete packages (e.g., 100 separate drums or perhaps a single concrete vault). For each individual package, zero, one or two layers of containment (barriers) can be explicitly considered to exist (these barriers must fail before the species can be released from the Source). The first two inputs (Number of Packages and Number of Barriers) are used to define the number of packages and the barriers in each package. We will start to discuss these inputs in some detail in the next Lesson.  Note that by default, there is a single package with no barriers.

The third input (# Packages failed by events) is an advanced feature that will be briefly discussed in Lesson 12.

For the purpose of exploring this dialog further, leave Number of Packages at 1 and from the Number of Barriers drop-list select “double”.  By doing so, you have specified that the Source consists of a single package (e.g., a concrete vault) with two barriers that must fail in order to release mass (e.g., the concrete wall and an inner liner). You will note that after you do so, the two buttons to the right (Outer Barrier… and Inner Barrier…) become active.  These buttons provide access to dialogs for describing the failure rates for these barriers. For example, press the Outer Barrier… button and the following dialog will be displayed:

This dialog allows you to define the failure rate for the barrier (by default it simply fails immediately).  We will start to explore this dialog in the next Lesson. For now close this dialog and return to the main Source dialog.

The next set of inputs (Source Inventory Settings) is used to provide the mass inventories for the Source.  Press the Edit... button now:

This is how we define the mass of the species in the Source.  A Source can have multiple inventories (you can add and delete inventories using the Add Inventory and Delete Inventory button, but there must always be at least one inventory). If you do define multiple inventories, you can move between them using the Previous and Next buttons.

For a given inventory, you first need to specify the Species Mass.  This must be a vector of species with dimensions of mass. It is the initial amount of species associated with this inventory (i.e., at the beginning of the simulation). You can also enter a Description, which is simply used for documenting the model. Note that the Species Mass is specified on a per package basis.  That is, it represents the mass in each package.  So if you had 100 packages, the total mass for this Inventory in the Source would be 100 times what you had specified here.

You then need to specify two properties for that Inventory: its Location, and whether it is contained in a Waste Matrix. Location is defined relative to the barriers, using a drop-list whose options depend on how many barriers you have specified.  If no barriers are specified, there is no option provided.  Similarly, if you have specified only a single barrier, the only option is “Outer” (the mass is located inside the single Outer barrier).  If you have specified a double barrier (as we have done), there are two options available: “Outer” and “Inner”.  “Inner” means that the mass is inside both barriers.  “Outer” means that the mass is inside the “Outer” barrier but outside the “Inner” barrier (i.e., it is located between the barriers).

The Waste Matrix input specifies whether the mass is bound in a matrix material that must degrade in order to release the mass.  By default it is not bound (“None”). The other three options in the drop-list are used to define that there is a matrix material that must degrade.  Each option uses a different algorithm for degrading the matrix. We will discuss this in detail in Lesson 5.

It should be clear from this brief discussion why a Source may have more than one Inventory.  It is because that in some cases, the mass may be distributed in different locations or may or may not be bound in a matrix material.  For example, some of the mass in the Source may be bound in grout, while other mass may not be.  This would require two specified Inventories.  In a more complex example (used nuclear fuel disposed in engineered waste packages), we might specify two barriers (the waste package itself and the cladding surrounding the fuel), and have three Inventories: 1) mass bound inside the uranium dioxide matrix (and inside both barriers); 2) mass inside both barriers but not bound in the matrix; and 3) mass present between the two barriers.

We are not actually going to enter an Inventory now as we are simply exploring the Source element in this Lesson.  We will create an Inventory in the next Lesson. So for now, close the Source Inventories dialog and return to the main Source dialog. 

The inputs we briefly introduced above allow you to define the mass initially present in the Source and the processes (containment failure and matrix degradation) that expose this mass.  But after the mass is exposed, where does it go and how do we specify the manner in which it is transported through and away from the Source?  In order to do this, GoldSim uses Cell pathways to represent these transport processes. In particular, one or more Cell pathways must be specified as being associated with the Source.  But where are these Cells?

If you close the Source element you will note that the Source has a blue triangle at the top-left corner of the icon, exactly as Container elements do:

This is because a Source element is actually a specialized type of Container. In fact, you will notice that Sources have Graphics and Information tabs that are associated with all Containers.  Source Containers can also be localized (discussed in Unit 9, Lesson 6 of the Basic Course).

If you look inside the Source Container, you will note that there is a single Cell (named Cell1) inside. This is referred to as an Associated Cell. 

You can insert any number of Associated Cells into a Source Container (but should not insert other types of pathways).  You can name these in any way that you want. The Associated Cells for a Source are intended to physically represent the interior of a single package within the source.  As we shall see in Lesson 8, they behave in a special way in order to represent a Source consisting of multiple packages. 

For the purpose of this example, create two new Associated Cells (named Cell2 and Cell3). Then exit the Source Container.

One or more of the Associated Cells must be designated as Inventory Cells. If you open the Source element again, you will note that at the bottom of the dialog you can specify the Inventory Cells:

Inventory Cells are the Cells into which mass will be placed once it is exposed.  Since the Associated Cells represent the inside of a package, the Inventory Cells represent that part of the interior of the package where the mass is initially physically located (and available for transport once it is exposed).  Note that not all Associated Cells need to receive mass directly from the Source (i.e., not all Associated Cells need be Inventory Cells). Once the exposed mass is available in the Inventory Cell(s), it can then be transported through the other Associated Cells and eventually out of the Source.

By definition, all Sources must have at least one Inventory Cell.  Therefore, by default, when you create a new Source, GoldSim automatically creates it with a new Associated Cell inside, and this Cell is automatically defined as an Inventory Cell. The Cell is assigned a default name (e.g., Cell1), which of course, you can subsequently change.

If you press the top button adjacent to the Inventory list (the green plus sign), a dialog for inserting a new Inventory Cell will be displayed.  It includes a list-box with all of the Cells in the Source that have not already been defined as Inventory Cells. For now, add both Cell2 and Cell3 as Inventory Cells.  The dialog should then look like this:

You can remove a Cell from the list of Inventory Cells by pressing the Remove button adjacent to the Inventory list (the red X).  Note that removing a Cell from the Inventory list does not delete the Associated Cell from the Container; it simply removes it from being an Inventory Cell.

Note that this Inventory list has three columns that you use to specify how the exposed mass is distributed among the Inventory Cells. The first column contains the names of the Cells (and cannot be directly edited). The second column (which is also not editable) shows the "balance", or the maximum fraction of exposed mass which could be assigned to that particular Inventory Cell. The third column represents the fraction of the balance of the exposed mass that you wish the Cell to receive.  Note that because it represents the fraction of the balance, this is a relative fraction, rather than an actual fraction.  The actual fraction received by each Inventory Cell is the product of column 2 and column 3. For example, in the screen shown below, Cell1 would receive 1 * 0.5 = 50% of the exposed mass, Cell2 would receive 0.4 * 0.5 = 20% of the exposed mass, and Cell3 would receive 0.3 * 1 = 30%.

Note the "fraction of balance" for the last Cell in the list cannot be edited (i.e., it is always 1).

Although this approach may seem a bit complex, specifying the fractions in this way ensures that the actual fractions always sum to 1 (even if they are defined probabilistically).

We will discuss associated Cells in detail in Lesson 6.

The bottom of the dialog (Save Results) provides options for which results are to be saved.  We will explore the various outputs of a Source element (and discuss these options) throughout the rest of the Unit.

The purpose of this Lesson was simply to provide an overview of the Source element.  As should be clear, it is a rather complex element (both in terms of the user interface and the calculations that it carries out). To really understand it, we need to start looking in more detail at each of the various inputs introduced above and running some models.  We will do that starting in the next Lesson with a very simple Example.