## 3 Development and Verification of the Inspection Device for Field Application  
Handling radiation in open spaces without fixed facilities has many risks. The proposed inspection device, which automatically rotates and can be mounted on pipes, requires safety verification for radiation leakage and public accessibility. Figure 3: Inspection flowchart using the orbital-rail-type automatic inspection device. Figure 2: Configuration of orbital-rail-type automatic inspection device using bendable digital detector array. To ensure radiation safety, we conducted an ALARA (as low as reasonably achievable) evaluation through simulation, after the design was completed, based on a theoretical framework [12; 13; 14; 15]. \[H_{irradiating}(^{H\mathcal{S}\
u}/_{h})=\Gamma\cdot B\cdot\frac{S}{D^{2}}e^{-ln2 \cdot\sum_{i}\frac{T_{i}}{HV_{i}}}\]  
Formula for calculating the theoretical radiation dose rate. \[\mathbf{D}_{general\ area}(m)=\sqrt{\frac{\Gamma}{1\mu Sv/h}\cdot B\cdot Se^{-ln2 \cdot\sum_{i}\frac{T_{i}}{HV_{i}}}}\]  
Formula for calculating \(1\ \mu Sv/h\). \[D_{general\ area}(m)=\sqrt{\frac{2030\frac{h^{50\cdot m^{2}}}{Ct\cdot h}}{\frac {1\mu Sv}{h}}\cdot 5\cdot 47 Ci\cdot e^{-ln2\cdot\frac{10}{10}}}=21.60\ \mathrm{m}\]  
Ambient dose equivalent formula. Table 5, which includes the equation for calculating the radiation dose rate from Se-75, can be interpreted as follows:  
(a) The equation calculates the radiation dose rate using the gamma constant (\(\Gamma\), rhm factor) and the source intensity (S) for Se-75 at a distance D (Distance) from the location of the dotted line source. This equation follows a negative exponential function (Exp) attenuated by the shielding material thickness (T) and the half-value layer (HVL) of the shielding material. The HVL value is provided in the Operating and Maintenance Manual from the manufacturer of the radiation source. (b) According to domestic law, the target dose rate is \(1\ \mu Sv/h\). This is the minimum dose rate requiring monitoring for the general public. (c) The verification of the radiation shielding performance of the inspection device developed in this study should include cross-validation through leakage radiation dose measurements by regulatory agencies [16]. Figure 4 presents the formula for determining the shield size based on the irradiation angle of the collimator. The source-to-detector distance (SDD) was 650 A (26 inches), the largest in actual piping applications, allowing shielding based on an outer diameter of 660 mm. Theoretical calculations determined that a tungsten collimator with a \(30^{\circ}\times 15^{\circ}\) angle required a minimum shield length of approximately 381 mm in the longitudinal direction of the weld line and 177 mm in the DDA width direction [17; 18; 19]. A shield measuring 400 mm \(\times\) 200 mm was used. This study modeled and simulated the current inspection and device geometry to evaluate radiation leakage, ensuring that the penetration area of the radiation source and the lead-plate shield arrangement were within acceptable limits. The verification of the radiation shielding performance of the developed inspection device should include cross-validation through leakage radiation dose measurements by regulatory agencies [16]. Figure 4 illustrates the formula for determining shield size based on the collimator's irradiation angle. The source-to-detector distance (SDD) in this study was 650 A (26 inches), suitable for shielding based on an outer diameter of 660 mm in actual piping applications. \begin{table}
\begin{tabular}{c c c c c} \hline
**HVL (mm)** & **Concrete** & **Lead** & **Tungsten** & **Steel** \\ \hline Se-75 & 30 & 1.0 & 0.8 & 8 \\ \hline \end{tabular}
\end{table} 
Table 5: Formula for predicting the half-value layer and theoretical radiation dose for each material using a Se-75 radiation source.