Research on Safety Evaluation and Visualization Technology of Small Pressurized Water Reactor Radiation Field

Abstract: Background
The compact structure of small reactors, combined with the complexity of the refueling process and the high radioactivity of spent fuel, makes radiation dose assessment during refueling particularly critical.For marine reactors, the refueling process is carried out at sea, and it is necessary to consider factors such as high wind and waves at sea, small operating space, and more prone to bumping, so the refueling process should be planned more carefully.
Purpose
In this study, after 1278 Effective Full Power Days (EFPDs) of operation, the KLT-40S (Korabl – Likhterovoz – Transportnii -40 MW Series，Ship-mounted Loop-type Turbine-driven 40 MW Serial/Upgraded Reactor) spent fuel assemblies underwent burnup and dose calculations.
Methods
The radiation dose safety assessment and scenario planning platform performs activity calculation on the spent fuel assemblies of KLT-40S by calling the ignition depletion calculation program ORIGEN2 to get the output file of the radiation source intensity of the spent fuel assemblies and the shielding materials, and then calls the Monte Carlo program Super MC3.3 to perform the radiation field calculation to get the text file of the results of the spatial radiation field distribution of the material exchange process, which serves as the text file for the visualization and rendering of radiation field in the virtual scenario. The text file of the radiation field distribution result is obtained, which is the input for the visualization and rendering of the radiation field in the virtual scene. Then, the path generation program generates the path walking scheme for the staff according to the spatial coordinate text data provided by the user. Finally, the platform is based on the Unity 3D engine to realize the dynamic change of radiation field during the KLT-40S reactor charging and discharging process, and the dynamic visualization of different radiation doses received by the staff when switching between scenes.Analyzing the radiation dose level to staff working in real time in a nuclear emergency scenario when radioactive noble gases fill the reactor compartment space due to the breakage of spent fuel assemblies during the lifting process of spent fuel assemblies using the spent fuel assembly breakage criterion analysis method and the ICRP human irradiation dose assessment model.
Results
The results indicate that when the spent fuel assembly is lifted within the shielding sleeve, the dose rate inside the assembly’s geometry peaks at 1.36×10⁴ μSv/h. At a distance of 3 meters from the center of the assembly, the spatial radiation dose rate is 6.02 μSv/h.In the event of spent fuel assembly breakage, based on the human radiation dose model, the permissible time for personnel to remain in the reactor compartment is approximately 14.60 to 38.46 hours.
Conclusions
Visualization technology provides a more intuitive representation of the spatial distribution of the radiation dose field.This study integrates dose assessment, simulation analysis, and visualization technology to support the design and analysis of the refueling process for small reactors.