Research On SGS Technique Of Source-less Efficiency Calibration For Drummed Radioactive Waste

Segmented gamma scanning?SGS?technique has been widely used in the field of the non-destructive assay of nuclear waste since 1970s,due to its fast detection speed and relatively accurate measurement results,SGS occupies the vast majority of the market in radioactive waste detection technique.However,considering the software hardware facilities,core technique method,the design of core component and other factors that causes a technological monopoly,the domestic market still relies mainly on foreign technical support.In this paper,to independently design a complete SGS process and an implementation plan for the measurement of drummed nuclear waste,research on construction method of efficiency matrix,optimization design method of the detector collimator and a reconstruction method of activity under different conditions have been conducted in SGS,which provides reference for key techniques in drummed radioactive waste measurements.The main conclusions of research in this paper are listed as follows:?1?The development and optimization of collimator in SGS systemConsidering the detection efficiency,wedge-disturbing and environmental noise,the Monte-Carlo method is used to optimize the detector collimator size in SGS system.The reference values of optimized collimator size under different stratification conditions?3¹8 layers?are given in this paper,and a complete design of detector collimator in SGS system is proposed.Based on the theoretical research,the size of collimator hole can be arbitrarily transformed between“1×1 cm”to“40×40 cm”.In this paper,the optimal parameter of the detector collimator is a rectangle with opening depth of 21.5 cm,width of 16.5 cm,and height of 6 cm.?2?The design of a rapid construction method for detection efficiency matrixIn this paper,the Monte-Carlo method is used to measure the effect of wedge-disturbing in SGS.The results show that:by using a detector collimator under optimized size,the wedge-disturbing is mainly from the upper and lower layers.Based on this,this paper proposes a method for rapid construction of detection efficiency matrix by using the efficiency function of body source,the corresponding function model and related parameters are also given in this paper.?3?The design of a uniformity characterization algorithm of sampleBased on the physical characteristics of sample and the whole SGS system,a uniformity characterization method which applied to drummed radioactive waste is proposed by using Matlab software to achieve the algorithm.Then the effect of sample uniformity on the accuracy of activity reconstruction can be studied.The results show that:under the same average density of sample,the distribution of radionuclides in the drum is relatively dispersed,the effect of sample uniformity on the activity estimation results can be ignored.The conclusion indicates that:besides the extreme distribution condition of radionuclides?single point source?,the efficiency calibration based on the hypothesis of the sample uniformity distribution is feasible and reasonable.?4?The experimental verification of activity reconstruction for the low density drummed radioactive wasteExperiments under different conditions including single-layer measurement?the density of sample was uniformly and non-uniformly distributed along the radial direction?and full-drum measurement?the density of sample was uniformly and non-uniformly distributed along the axial direction?are carried out for verification.The results show that:besides the extreme distribution?single point source?,when the sample density is lower than 0.98 g/cm³,the relative error of the activity reconstruction results for ¹³⁷Cs and ⁶⁰Co sources is less than±30%.The main technical innovations are as followed:?1?Monte-Carlo simulation is used to design a detector collimator with optimized size in SGS system?2?By using Monte-Carlo simulation and numerical fitting technique,a method for rapid reconstruction of detection efficiency matrix is proposed,and the corresponding function model and related parameters are given.?3?A uniformity characterization method of sample applied to drummed nuclear is proposed,and the algorithm is implemented by using Matlab software.