Research On Modeling And Dose Assessment Methods For Decommissioning Nuclear Facilities Based On CAD

The decommissioning of nuclear facilities is an important stage in the process of nuclear energy application.The main task of the decommissioning operators of nuclear facilities in the radioactive plant is to complete the decontamination,dismantling and removal of nuclear facilities.In the nuclear decommissioning scene,the structure of nuclear equipment is complex,there are many types of nuclides,and the residual radioactivity is strong.The decommissioning construction of nuclear facilities will change the radiation environment,release a large amount of radionuclides,and increase the radiation risk of operators.China has a large number of nuclear facilities facing decommissioning.In order to reduce the overall cost of nuclear facility decommissioning and the radiation risk of on-site construction,CAD-based nuclear facility decommissioning simulation technology is gradually applied to decommissioning practice.Nuclear facility decommissioning simulation can simulate worker operations,evaluate scenario radiation,improve work efficiency,reduce decommissioning costs,and coordinate the decommissioning process.It plays an important role in the formulation and optimization of nuclear decommissioning operations.Based on CAD radiation modeling,the paper focuses on the internal and external exposure dose assessment needs of workers during the decommissioning of nuclear facilities,and conducts research on radiation calculation and dose assessment methods,including nuclear decommissioning environment modeling,gamma radiation calculation,airborne radionuclides diffusion assessment and worker dose assessment.The main research contents of the paper are as follows:(1)The CAD-based radiation modeling method of nuclear decommissioning environment is researched.In order to establish and process the CAD radiation model used in the decommissioning of nuclear facilities,the research uses the stylized processing method and the voxelized discrete method of the radiation model to realize the discrete processing of the radioactive item mode of arbitrary shape.According to the voxel model after the radioactive source is separated,the cutting method of the virtual nuclear facility is constructed to meet the cutting requirements of the nuclear facility.(2)The calculation method of gamma radiation under nuclear decommissioning environment is researched.In order to quickly calculate the dose distribution of gamma radiation in the nuclear decommissioning scene,the study considers the influence of the cutting and dismantling of radioactive items,decay,non-uniform activity distribution and self-shielding on the calculation of gamma radiation field,and the point-kernel method is used to realize the dynamic calculation of gamma radiation field.At the same time,in order to improve the calculation speed of the radiation field,a point kernel compression method and a non-uniform grid division method of the radiation field are proposed,which improve the calculation efficiency while ensuring the accuracy of the radiation field dose distribution.(3)The assessment method of airborne radionuclide diffusion in nuclear decommissioning plant is researched.In order to estimate the concentration distribution of airborne radionuclide during the decommissioning of nuclear facilities,the study considered the influence of plant space,nuclear facilities,exhaust ducts,and multiple leak points on airborne radionuclide diffusion in the real scene of nuclear decommissioning.The modified eddy diffusion model is used to dynamically calculate the concentration of airborne radionuclide,which provides data support for the calculation of internal exposure of workers.At the same time,based on the volume data of the radionuclide distribution in three-dimensional space,the concentration of airborne radionuclide is virtualized,which provides intuitive and fast airborne radionuclide diffusion information for radiation protection.(4)The dynamic evaluation method of internal and external radiation effective dose of decommissioned workers is researched.Focusing on the radiation protection requirements of the occupational exposure of nuclear facility decommissioning construction workers,the study takes into account the impact of radiation protective clothing on external exposure,adopts the method of organ monitoring points based on the human body stylized model,and evaluates the effective dose equivalent of external exposure.The real-time evaluation of the human external radiation dose with the dynamic change of the gamma radiation field is realized.The study also took into account the internal exposure caused by the inhalation of airborne radionuclide to workers without respiratory protection,and adopted the method of dose conversion coefficient to dynamically evaluate the effective dose of internal exposure caused by inhalation of the workers.The study provides an evaluation model for the radiation protection of operators during the decommissioning of nuclear facilities.Based on the above-mentioned research content,the paper focuses on the dynamic assessment of internal and external exposure doses of operators during nuclear decommissioning,and expands the radiation dose assessment system for nuclear facility decommissioning.The research results of this paper can provide technical support for nuclear facility accidents,maintenance,decommissioning and other radiation environment operations,simulate,evaluate and optimize the implementation of nuclear facility decommissioning,and provide low-cost training platform for workers in action trajectory,assistance operation and simulation monitoring.