Simulation Study On Radiation Dose Of RCV System During Nuclear Power Plant Overhaul

During the normal operation of nuclear power plant reactors,the materials of piping and equipment in the primary circuit system will be corroded.Then,the corrosion products are activated by the core to produce activated corrosion products.According to statistics,more than 90% of the collective dose,during the overhaul,is caused by the contact between the practitioners and the activated corrosion products on the pipe wall.Therefore,it is necessary to study the dose rate of radiation field,generated by the activation corrosion products in the main operation or the auxiliary system of the reactor.Thus,it provides support for the radiation protection work and strategy implementation of nuclear power overhaul,and then reduces the individual or collective dose rate of practitioners.In this paper,in order to study the dose rate distribution of the radiation field,generated by activation corrosion products in the RCV system,it mainly adopts the Monte Carlo method and point kernel integration method.The main research contents and results of this paper are as follows:(1)First of all,Geant4 is used for geometric modeling of piping equipment in different parts of the RCV system.In addition,a method,which equivalently simplified the pipeline of heat exchanger equipment,is proposed,and it greatly reduces the complexity of modeling.This simplification method greatly reduces the complexity of modeling.At the same time,according to different pipe types and source item distribution,a sampling of particles in the coolant and on the pipe wall is set up.In addition,combined with the measured data of nuclear power operation,a method of thinking based on Geant4 to inverse the dose rate to calculate the concentration of radionuclide substances in the pipeline is proposed.Furthermore,combined with the measured data of nuclear power operation,a method of thinking,based on Geant4 to inverse the dose rate to calculate the concentration of radionuclide substances in the pipeline,is proposed.Finally,through the distribution of γ-ray energy spectrum,the dose rate at the measurement points of the typical parts is simulated and calculated as the change of the main pump running time,and the dose rate at the measurement points of the typical parts shows a negative exponential growth law,which can provide a certain data reference for the radiation protection work of nuclear power overhaul.(2)Based on C++,a point-kernel integration algorithm is developed,which mainly includes algorithm modules such as grid division,distance between intersections,and accumulation factor calculation.First of all,the division of the point kernel mesh is realized by the function of Gmsh meshing,which divides the geometry into tetrahedral meshes and outputs the mesh information.Then,using the characteristics of tetrahedrons,we find the adjacent grid to each tetrahedral grid,which greatly improves the computational efficiency of the algorithm.In order to ensure the accuracy of the algorithm,different algorithm modules have been verified,and the verification results show that the algorithm is effective and accurate.Finally,through self-designed sample questions,we compared the calculation results of the point-kernel integration algorithm and Geant4,and the calculation deviation between the two is 1.67%.If both methods use single-threaded calculation,the calculation speed of the point-kernel integration algorithm is more than 200 times faster than Geant4 simulation calculation.If Geant4 uses 4 threads for simulation calculation,the single-threaded calculation speed of the point-kernel integration algorithm still has a greater advantage.Based on the excellent calculation performance of the point-kernel integration algorithm,it is very promising to apply it to the fast calculation of large and complex radiation fields.