Study On The Improved Gamma Scanning Detection Technology For Waste Drum In Nuclear Power Plant

Energy consumption increases to a certain scale as the rapid growth of social economy.Much radioactive waste will be produced with the growth of nuclear power plants,most of which is low and intermediate level radioactive waste?LILW?.LILW is the non-exempt waste whose specific activity is low than 4×10¹⁰Bq/kg or rate of heat release is low than 2kW/m³ that cannot be considered as ordinary waste.The waste radiation and its contamination level must be confirmed as well as the distribution of the radionuclide.The activity of LILW must be accurately measured before the final disposal to provide a scientific basis for its storage,transportation and final disposal.Due to the specificity of LILW,non-destructive assay?NDA?method is commonly used to measure the waste drums.The?-ray scanning technique for waste drums has gone through two stages:Segmented Gamma Scanning?SGS?and Tomographic Gamma Scanning?TGS?.Comparing those two gamma scanning technologies,The SGS measurement process is simple and fast,but with a large measurement error;TGS can obtain the distribution of the material and radionuclides in the waste drum accurately,but its complexity and time consumption of the measurement process make it hard to meet the requirements of large-scale detection.The research of several improved gamma scanning methods is carried out in this paper,aiming at the balance of rapid and accurate detection technique for LILW.?1?Further updating and redesigning are made for the LILW gamma scanning system based on the current system.Modularization and reconstruction are made for mechanical and controlling subsystem,and its designing criterions are summarized and elaborated.The whole structure is built up for the data accumulation and user interaction module and software design of the core part is finished.?2?Semi-tomographic gamma scanning?STGS?as an improved gamma scanning technology,combines the rules of SGS and TGS detection method and reconstruction principle.This method considers radioactive source in the rotating drum as ring source,and each segment is split into several ring voxels.Tomographic reconstruction method has been applied to the reconstruction of radioactivity distribution.The detection performance to 200L low density and 400L high density drums is discussed by both simulation and experiment.The maximum and average error of STGS is at most half of SGS in most cases and its detection time is 2-8 times of SGS.The perfect balance of accuracy and efficiency of STGS has been proven.?3?A new improved segmented gamma scanning method with two detectors is proposed and the equivalent radius is calculated through the compare of the two ray counts.The difference of the equivalent radius of the two counts is corrected and the radioactive nuclide of the whole drum is projected into one equivalent segment to avoid the amplification of the iteration residual during the image reconstruction.Performance of the method has been verified on 200L and 400L waste drum with high density.The maximal error of the improved method decreases several times and the mean error is reduced nearly in half compared with SGS.