## 2 Evolutional Computational Methodology for Radiation Mapping  
### Available Historic NSC and SO Radiometric Datasets  
The dataset used in this study was obtained during the commissioning of the Main Cranes System (MCS) of the NSC. The MCS integrates two overhead bridge cranes with two 50 tonnes (55 US tons) trolley hoists that together work in tandem to handle loads up to 100 tonnes (110 US tons). Both the cranes and hoists are managed via a dedicated control system to allow their integrated usage within the NSC. The MCS bridges are each 96 m (315 feet) long and operate along a 150 m (492 foot) long runway track with six rails under the roof of the NSC building, above the shelter object at a height of 80 m. A third trolley suspends a Mobile Tool Platform (MTP) that is eventually to be equipped with a robotic arm system comprising various function-specific tools. It is here that the detector instrument was placed on the \"safe trolley\" of the MCS, with a slight offset from the center of its movement axis, on the north side of the trolley under its floor, at the level of the lower plane of the MCS movement, such that the detector is shielded from above by the MCS structural elements.  
The radiation detection system mounted onto the MCS comprises ruggedized ECOTEST(r) Group BDBG-09 \"Intelligent Detecting Unit of Gamma Radiation\" dual scintillator and Geiger-Muller devices combined with an ARM-based single board computer, with communication provided through a dedicated Wi-Fi interface [38; 39]. A BDBG-09 detector is capable of outputting gamma dose-rate (GDR) measurement across a dose-rate range of 0.05 uSv/h to 10 Sv/h, with a relative error of \(\pm\)17% [39]. With its environmentally sealed nature, wide dose range, broad thermal operating window, and low power consumption, it is widely used across the nuclear industry in Ukraine, France, Bulgaria, and Korea. The aforementioned single board ARM-based computer hosts the software developed for this application, providing an interface with the intelligent detector BDBG-09, processing primary information, and accumulating information in a local database (in case of a connection failure), as well as an interface with the existing NSC radiation monitoring system via a secure, encrypted Wi-Fi channel [38; 40].  
During the routine operation of the MCS, trolley movements and GDR measurements were continually obtained by the sensor, with values from 230 uSv/h to 28,490 uSv/h recorded by the NSC's Integrated Control System (ICS) and subsequently archived on the historical server. All measurements were obtained in the same horizontal plane. As a result, data on the GRD distribution (at the level of the MCS equipment above the SO) was obtained [38]. All of the gamma-ray point sources are, therefore, considered to be isotropic, with the detector uncollimated but omnidirectional. As a result, the subsequently detailed model does not consider the existing but poorly studied effect of gamma-ray re-reflection from the shell of the New Safe Confinement since the real detector is shielded from such radiation by the MCS.  
For each square meter in that plane under the MSC, the pair \((x,\,y)\) were assigned as coordinates, where \(x\) and \(y\) are integer numbers of meters from the beginning of the MCS coordinate system. If the MCS trolley visited a certain square with coordinates \((x,\,y)\), then all GDR measurement values for that location were recorded, and the arithmetic mean for all such records was calculated as value \(\gamma_{xy}\). Each \(\gamma_{xy}\) is linked as a value of <<virtual detector>> \(S_{j}\,(x,\,y)\) coordinates.