Lesson 1 - Unit 11 Overview

Source: A point, line or area at which mass or energy is added to a system, either instantaneously or continuously.

McGraw-Hill Dictionary of Scientific and Technical Terms

In Unit 1, Lesson 4 we noted that there are two different versions of the Contaminant Transport Module that can be licensed and added to GoldSim: the CT (Contaminant Transport) Module and the RT (Radionuclide Transport) Module.  Your copy of GoldSim will have neither, one or the other (but not both), depending on your license.

Through Unit 9 of the Course we discussed features that are common to both the CT Module and the RT Module. This is the second of two Units that discusses several features and topics that are specific to the RT Module.

In particular, this Unit describes a special element in the RT Module called a Source. 

In previous Units we described how you could introduce mass into a system by directly specifying an initial mass and/or a rate of addition to one or more pathways in the system.  For many kinds of systems, such an approach is all you will need.

Some systems, however, particularly those involving the simulation of proposed or existing waste disposal facilities, have as part of their design engineered packages or containers in which the waste is placed prior to disposal. The rate at which the disposed contaminant mass is released from such facilities can be very complex (and hence difficult to directly specify as a simple equation).  This is because in order to do so it is often necessary to directly model the mechanisms controlling these releases, such as failure of barriers surrounding the disposed waste and/or degradation of a matrix (e.g., grout) in which the contaminants are encapsulated. The Source element can be used to simulate these kind of complex release mechanisms. As we shall see, the Source element is rather complex, so it will require an entire Unit to describe it.

If you are not interested in this topic (or don’t have access to the RT Module), you can skip this Unit and proceed to Unit 12.

In this Unit, we will discuss the following:

• We will begin by describing conceptually the processes that can be simulated by a Source element (containment barriers, waste degradation, transport within and out of the Source), and discussing under what circumstances a Source element should be used.
• An overview of the Source element itself will then be provided.
• Sources can simulate containment barriers that must be breached before any contaminants can be released.  We will describe how loss of containment (failure of barriers) can be simulated.
• A Source can represent a single container or package (e.g., a large vault) or a collection of packages (e.g., a large number of drums).  We will discuss how both of these situations can be represented.
• Contaminant mass can be encapsulated within a matrix material (such as grout, glass or in the case of spent fuel, uranium dioxide) such that even after the barrier in which it is contained fails, no release may occur until this matrix material degrades. We will describe how the waste degradation process can be simulated.
• Once mass in a Source is exposed (i.e., accessible to the environment due to failure of barriers and/or degradation of matrix material), it must be transported out of and away from the Source.  We will describe how the Source element facilitates this calculation.
• Source barriers can fail according to very complex failure distributions, can fail by sudden (random) events, and/or can have multiple barriers (i.e., a package within a package).  We will briefly discuss these advanced features.

This Unit has a total of 13 Lessons (including this overview and a summary at the end), as well as several Exercises and Examples.