## 3 Safety Evaluation of the DSM
### Thermal Analysis  
Thermal evaluation of the DSM was performed to confirm that the temperature of the DSM components and the SNF would be maintained within the limits under normal, off-normal, and accident conditions. It should be ensured that the temperature of the fuel cladding is maintained below the design limit during the storage period to prevent damage to the cladding. According to the requirements of NUREG-1567, with reference to ACI-349 [16], the local maximum temperature of cask concrete structures under normal and off-normal conditions should not exceed 93 \({}^{\circ}\)C, and is required to remain below 176 \({}^{\circ}\)C under accident conditions. NUREG-1536 requires the maximum temperature of the storage system's containment boundary components to be kept below the storage function maintenance temperature, and requires the fuel cladding pipe's maximum temperature to be kept below 400 \({}^{\circ}\)C under normal and off-normal conditions, and 570 \({}^{\circ}\)C under accident conditions. NUREG-1536 presents the temperature requirements of the storage system as follows:  
* The maximum temperature of the storage boundary components must be maintained below the storage function maintenance temperature. * Under all conditions, the maximum internal pressure must be maintained below the design pressure. At this time, the outdoor temperature of the dry storage system is the maximum annual average value of the operating area. In the thermal evaluation of the DSM, the analysis case considered normal conditions at an outside temperature of 40 \({}^{\circ}\)C, and off-normal and accident conditions with a 50% and 100% blocked air inlet, respectively. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Location**} & \multirow{2}{*}{**Neutron (mSv/h)**} & \multirow{2}{*}{**Gamma Ray (mSv/h)**} & \multicolumn{2}{c}{**Total Dose Rate**} \\  & & & & **(mSv/h)** \\ \hline \multirow{3}{*}{Inlet (lower)} & 1 & 3.293 \(\times\) 10\({}^{-6}\) & 1.297 \(\times\) 10\({}^{-6}\) & \\  & & (0.36) & (0.36) & 4.590\(\times\) 10\({}^{-6}\) \\ \multirow{3}{*}{\multirow{3}{*}{Outlet (upper)}} & 4.851 \(\times\) 10\({}^{-2}\) & 1.315 \(\times\) 10\({}^{-2}\) & \\  & & (0.42) & (0.22) & 6.166 \(\times\) 10\({}^{-2}\) \\ \multirow{3}{*}{Outlet (upper)} & 4.92 \(\times\) 10\({}^{-2}\) & 1.275 \(\times\) 10\({}^{-3}\) & \\  & & (0.30) & (0.46) & 5.048 \(\times\) 10\({}^{-2}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Dose rate as a function of inlet/outlet geometry. Figure 7: Dose rate as a function of concrete thickness. For thermal evaluation of the DSM, Fluent 19.2 [17]--a commercial computational fluid dynamics (CFD) program--was used. In addition, a conjugation heat-transfer model was used to evaluate the temperature of the airflow region, the concrete wall, and the canister. The heat transfer inside the DSM was evaluated using CFD tools, considering all of the conduction, convection, and radiation heat-transfer mechanisms. To study the effects of mesh resolution and near-wall treatment, three different computational meshes were constructed and evaluated, and a medium-sized mesh was selected. Foam glass insulation (thickness 50 mm) was used between the air layer and the concrete wall to prevent overheating of the concrete structure. The RNG k-epsilon turbulence model was used for the airflow region, and the density of air was set to change according to the temperature, to simulate natural convection. The interpolation scheme for pressure and velocity used a SIMPLE algorithm and upwind scheme. In this CFD calculation, the RMS residual levels for mass and momentum were considered to converge to \(1\times 10^{-4}\), while that for energy was considered to converge to \(1\times 10^{-6}\) or less. The inside of the canister was used to calculate the effective thermal conductivity. Figure 8 shows the calculation model used in the CFD analysis. For efficient CFD analysis, the flow analysis domain used a 1/4 model for normal conditions and a 1/2 model for off-normal and accident conditions.