### Technology Application to the ChNPP  
Despite many developments in modern detection hardware and accompanying software, there still exists a significant number of scenarios where practical application is impossible owing to the high dose rates that would be encountered, combined with complex and intricate deployment environments. The SO is one example of such a high-hazard and challenging site, where safety restrictions do not permit the involvement of people to undertake routine measurements and inspections within the confines of the NSC. As has been shown following several earlier deployments, the significant gamma and neutron radiation levels under the NSC and inside the SO can rapidly disable the sensitive electronics of measurement equipment and control systems of robotic carriers, rendering them inoperable. In addition, the inability to deploy any form of radio communication infrastructure or provisioning of a wired communication network throughout the maze of rooms that comprised Chornobyl reactor Unit 4 (destroyed during the accident and now contained within the SO) also limits the use of robotic devices, alongside the basic installation and usage of a comprehensive sensor network inside the SO.  
These limitations are not trivial and, therefore, require the development and application of innovative approaches to properly understand the distribution of potentially lethal radiation levels under the NSC and to inform crucial future hazard-reduction and decommissioning operations. In the absence of a comprehensive detection/monitoring network within the SO that would accompany modern/current nuclear installations to provide operational and critical dosimetric information, the modern reprocessing of historical data provides the only practical solution. One such method of interpreting legacy data to derive a 3D representation of the present gamma radiation field surrounding the SO is presented in this work.  
This paper first provides a brief introduction to the tools used to collect input data for the reconstruction of the radiation map surrounding the SO collected during the commissioning of the NSC over the old sacrophagus. The subsequent section details a model used to reconstruct the radiation map of the SO alongside the assumptions and simplifications applied to this model. Next, the algorithm used to reconstruct the distribution of the gamma field directly on the roof of the SO is presented. The paper concludes by comparing and validating the outputs of this reconstruction algorithm with physical dose-rate measurements obtained on the SO roof by a group of reconnaissance scientists from the Institute of Safety Problems of NPPs of the National Academy of Sciences of Ukraine. It is shown that with an increase in the number of iterations of the processing algorithm, the reliability of the approximation and convergence onto the true scenario increases. This reliability underlines the potential for the technique to be used to reconstruct the extant radiation environment from historical data, therefore facilitating safe future on-site activities and, in the case of Chornobyl, efficient decommissioning and dismantling of both reactor Unit 4 and the surrounding SO within the NSC.