Gas-cooled Microreactor Assembly Model Description

The Gas-Cooled Microreactor (GC-MR) assembly model was developed at ANL as a modeling experiment that gathers several expected modeling challenges encountered by the U.S. industry. The GC-MR assembly uses a graphite structure, TRISO fuel blocks with 19.95 at% LEU fuel, YH2 moderator pins with FeCrAl envelope, and upper/lower BeO reflector regions. Additional modeling specificities were implemented in the GC-MR such as burnable poison blocks, helium coolant channels and a central control and shutdown rod. Figure 1 illustrates the GC-MR assembly model.

Figure 1: Description of the GC-MR assembly model

* Blocks contain both triangular and hexahedron elements*

The major technical parameters for the GC-MR assembly model are:

Both the TRISO and B4C poison particles are composed of concentric spherical regions. The particles are packed into graphite compacts. The TRISO particles have the following regions

The B4C poison particles have the following regions

The following thermal conductivities are used for modeling heat conduction. Certain materials have dedicated MOOSE (BISON) objects to represent their thermal properties as functions of temperature, while others can use a nominal value:

Either a specific value or a more detailed BISON model that computes thermal conductivity as a function of temperature is specified.

The GraphiteMatrixThermal also provides various models for homogenizing TRISO into graphite.

The helium coolant has the following properties