*2.2. Multi-Dimensional Modeling*

#### 2.2.1. Common Features for Consistent Modeling

The test section of interest was modeled by 36 subchannels as depicted in Figure 3. In total, 864 (6 × 6 × 24) hydraulic volumes were modeled for the heated section by using the multi-dimensional component of each system code. As with the one-dimensional model, instead of modeling the actual shape of the spacer grid, additional pressure loss was modeled for each specific location by giving the pressure loss coefficient provided by the specification [8]. In addition, the power condition in each subchannel was implemented by the heat structure components, which gave an equivalent heat condition according to the equivalent power fraction within the subchannel. With the connection to additional hydraulic volumes upstream and downstream, which were modeled by the multi-dimensional component, the test section of interest was connected to the common boundary conditions. Whole nodalization for each system code is depicted in Figure 4. The detailed description of the model of each system code is given in the following sections.

**Figure 3.** Cross-sectional view of nominal bundle test section.

**Figure 4.** Nodalization scheme of multi-dimensional model of each system code: (**a**) multi-dimensional model of MARS-KS; (**b**) multi-dimensional model of TRACE.
