## 5 Sensitivity Analysis  
The fuzzy-based structural/job risk assessment method developed in this study for the decommissioning process of nuclear power plants needs to be verified. Here, the sensitivity analysis was performed by changing each of the variables in turn to values that were \(\pm 100\%\) of those originally assigned. This will demonstrate that the model is relatively robust if the ranking is not reversed by changing the variables so dramatically. The results of this sensitivity analysis confirmed that the outcome values did not change significantly depending on the external environment, and that the evaluation method itself is therefore robust. The sensitivity analysis conducted for the risk assessment of cutting work carried out on the concrete structure of the nuclear power plant confirmed that the ranking of the risk assessment was not reversed despite the major change in the value of the input variables, as shown in Figure 5; Figure 6 shows that the ranking of risk assessment by risk type was also not reversed. The risk type designations used in these two figures is as shown in Table 14, which shows the results of the sensitivity analysis performed on the cutting work for the risk associated with each type of work. For example, as the data presented in Table 14 shows, the original risk result for A1 (wire saw transport-collapse) was 3.34, changing to 12.40 and 0.69 when two of the input variables, namely frequency and intensity, respectively, changed. Figure 4: Integrated risk graph by work type. Figure 5: Sensitivity analysis on structural/job risks by work-risk type. Based on the results of the sensitivity analysis, the method for assessing the risk of the decommissioning process proposed in this study is considered to be a robust method. When looking at the risk assessment results for the concrete structure cutting work, the structural/job risk was the highest for'remove residual concrete', followed by 'cutting using wire saw', 'wire saw installation' and 'wire saw transport'. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Type a**} & \multicolumn{4}{c}{**Structural/job Risk**} \\ \cline{2-5}  & \multicolumn{2}{c}{**Underestimated Risk**} & \multicolumn{2}{c}{**Original Risk**} & \multicolumn{2}{c}{**Overestimated Risk**} \\ \hline \multicolumn{5}{c}{Work-risk type} & - & - & - \\ A1 & Collapse & 0.69 & 3.34 & 12.40 \\ A2 & Drop & 0.53 & 3.23 & 12.69 \\ A5 & jam & 1.00 & 5.41 & 17.41 \\ B1 & Collapse & 2.07 & 10.33 & 30.10 \\ B2 & Drop & 1.56 & 7.94 & 24.79 \\ B5 & jam & 4.57 & 14.61 & 34.53 \\ B6 & Electric shock & 1.42 & 6.08 & 21.69 \\ C1 & Collapse & 8.57 & 29.22 & 60.56 \\ C2 & Drop & 9.35 & 29.75 & 60.56 \\ C3 & Eye attack & 1.95 & 9.74 & 30.81 \\ C5 & jam & 10.20 & 30.28 & 59.68 \\ C6 & Electric shock & 1.10 & 7.08 & 25.56 \\ D1 & Collapse & 19.17 & 47.32 & 83.11 \\ D3 & Eye attack & 25.50 & 66.75 & 103.89 \\ D4 & Fall & 22.24 & 58.08 & 99.88 \\ D5 & jam & 20.54 & 56.67 & 92.56 \\ D6 & Electric shock & 14.03 & 42.03 & 81.93 \\ \hline \multicolumn{5}{c}{Work type} & - & - & - \\ A & Wire saw transport & 0.74 & 3.99 & 14.17 \\ B & Wire saw installation & 2.41 & 9.74 & 27.78 \\ C & Cutting using wire saw & 6.23 & 21.21 & 47.64 \\ D & Remove residual concrete & 20.30 & 54.17 & 92.27 \\ \hline \multicolumn{5}{c}{Risk type} & - & - & - \\
1 & Collapse & 7.62 & 22.55 & 46.54 \\
2 & Drop & 3.82 & 13.64 & 32.68 \\
3 & Eye attack & 13.72 & 38.25 & 67.35 \\
4 & Fall & 22.24 & 58.08 & 99.88 \\
5 & Jam & 9.08 & 26.74 & 51.04 \\
6 & Electric shock & 5.51 & 18.40 & 43.40 \\ \hline \hline \end{tabular} a  
\end{table} 
Table 14: Results of sensitivity analysis on structural/job risks. Figure 6: Sensitivity analysis on structural/job risks by risk type. For each work phase, the risk was evaluated as high for the work types where the worker is expected to work on the decommissioning object at close range.