## 3 Application in the Reconstruction of the HWRR Decommissioning Model
### Point Cloud Data Acquisition for the HWRR Decommissioning Area  
According to the point cloud accuracy and model precision requirements of the HWRR, we have opted for the widely used large-space laser-scanning device, the FARO Laser Scanner Focus5 350, for acquiring point cloud data in the HWRR plant. This device has a maximum scanning speed of 976,000 pts/s, a measurement range of 0.6 m to 350 m,  
Figure 6: Layout diagram of control points (P points) in the HWRR plant. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**No.** & **Region** & **Building Area/m\({}^{2}\)** & **Number of Floors** \\ \hline
1 & Reactor main building & 8690 & 6 \\
2 & Ventilation center & 300 & 1 \\
3 & Low-level radioactive & & \\  & wastewater storage tank area & & \\
4 & Secondary water pump room & 489 & 1 \\ Total & & 11,562 & - \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The building areas for each region in the HWRR plant. and a longitudinal scanning angle \(\theta\) ranging from 0 to 300 degrees, coupled with a lateral scanning angle \(\alpha\) ranging from 0 to 360 degrees. Throughout the 3D laser-scanning process, a white target sphere with a diameter of 145 mm serves as the registration basis for data from two adjacent scanning stations, with a minimum of four staggered white target spheres placed around each scanning station. Given the complexity and specificity of the HWRR decommissioning area, particularly the large number of process rooms on the basement floor of the main building area and the confined spaces with numerous components such as equipment, pipes, and valves, the scanning task is challenging. Nevertheless, to ensure the integrity and accuracy of information, meticulous scanning of each decommissioning region is imperative, ensuring that the designated scanning stations are rational and effective. Initially, a reconnaissance is conducted on the scanning units in each HWRR region, determining the placement points for the scanner and the deployment points for the target spheres. The objective is to achieve maximum coverage with the minimum number of scanning stations, thereby reducing the number of point cloud stitching operations. While maintaining the point cloud acquisition rate, the effective point cloud overlap between adjacent scanning stations should not be less than 30%, and in challenging areas, it should not be less than 15%. After on-site installation of the FARO Laser Scanner Focus[5] 350, multiple target spheres are securely fixed in suitable positions within the scanning area. Considering the particularity of nuclear facilities, the target spheres are preferably positioned on the main structural elements of the buildings rather than on equipment or pipes within the buildings. Additionally, target spheres should be strategically placed to avoid obstructing critical scanning areas. The HWRR plant is then systematically scanned station by station, and the scanning approach is dynamically adjusted based on factors such as physical characteristics and on-site conditions. For instance, in areas with large equipment or compact spaces, additional stations are established to capture comprehensive point cloud data, thereby minimizing errors. Following the station-by-station and region-by-region scanning of each building and equipment in the HWRR plant, an on-site confirmation of the scanning results is conducted. If there are missing or abnormal point cloud data, supplementary scans are promptly carried out on-site. If the scanned point cloud data are complete and meet the requirements, they are promptly saved and imported into the corresponding point cloud processing software for subsequent data processing. When scanning the HWRR plant, the scanning resolution for the FARO Laser Scanner Focus[5] 350 was set to 1/4 in most scenes, and the scan quality was set to 3\(\times\).