## 3 Application in the Reconstruction of the HWRR Decommissioning Model
### On-Site Preparation for the HWRR Decommissioning Area  
The total area of the HWRR decommissioning area is approximately 13,550 m\({}^{2}\), with a total building area of around 11,562 m\({}^{2}\). Given the large size of the HWRR decommissioning area, and following on-site reconnaissance and data reviews, the entire plant area is categorized into four regions: the reactor main building, the secondary water pump room, the ventilation center, and the low-level radioactive wastewater storage tank area. The building areas for each region are detailed in Table 3. It is crucial to highlight that the current scope of work does not encompass the acquisition of point cloud data for internals within the HWRR core, which are scheduled to be dismantled in 2025. Currently, the reactor core is closed, and due to the high radiation dose, compact structure, and the fixation of certain internals inside the reactor core, conducting 3D laser scanning of the reactor's internals is not feasible at this stage. CAD modeling has been performed based on detailed drawings of the HWRR core. To update the existing CAD model, there is a consideration to conduct 3D laser scanning of the internals during the subsequent dismantling process of the reactor core. According to the high accuracy requirements for the input HWRR decommissioning model in the later decommissioning simulation process, it is necessary to divide the entire HWRR plant into four independent yet interconnected regions through controlled measurements. For the reactor main building, which consists of a multi-story structure with four aboveground floors and two underground floors, it is essential to partition the space on each floor into different units. Additionally, each floor space is further divided into numerous rooms serving different purposes: for example, the basement floor of the HWRR main building has more than 50 process rooms. To ensure modeling accuracy and \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**No.** & **Equipment** & **Brand** & **Specifications** & **Quantity** \\ \hline \multirow{4}{*}{1} & \multirow{4}{*}{3D laser scanner} & FARO Focus\({}^{\text{S}}\) 350 & Maximum measure speed: & \\  & & (FARO, Lake Mary, FL, USA) & 976,000 pts/s; & \\  & & (FARO, Lake Mary, FL, USA) & Angle accuracy: 0.00527\({}^{\circ}\); & \\  & & & & Distance accuracy: \(\pm\)1 mm; & \\  & & & & Angle accuracy: 0.00027\({}^{\circ}\); & \\
2 & Total station & TCRP 1201 (Leica, Wetzlar, Germany) & Distance accuracy: & 1 mm + 1.5 ppm; & 1 \\  & & & & Display resolution: 0.1 mm & \\  & & & & Effective pixels: & \\
3 & Camera & A7R2 (Sony, Tokyo, Japan) & 42.4 million; & \\  & & & & Maximum shutter speed: & 1 \\
4 & Target spheres & FARO (Lake Mary, FL, USA) & 1/8000 s & \\  & & & & 14.5 cm in diameter & 10 \\
5 & PC workstation & T-7920 (Dell, Austin, TX, USA) & Intel Xeon Gold 6248R CPU & \\  & & & & @ 3.00 GHz; & 4 \\  & & & TX, USA) & 128 G RAM & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Key equipment and specifications used in the laser-scanning 3D model reconstruction process. completeness, it is required to further subdivide the process rooms on each floor space into different groups. To accomplish coordinate transformation of the point cloud data for each decommissioning region, unit, and group within the HWRR, and to enhance the accuracy of the point cloud data stitching, it is crucial to deploy control points based on the field situation, establishing a regional coordinate control network in the HWRR plant. To ensure the control points are not oxidized over an extended period and exhibit excellent resistance to acid and alkali corrosion, the control points in the HWRR decommissioning area are fabricated using electro-galvamized cast iron and undergo surface heat treatment. A total of 20 control points are strategically placed within the HWRR plant, and a coordinate control network is established using the Leica TCRP 1201 high-precision total station (as indicated by the red spheres in Figure 6).