Study On The Helical Gamma Scanning Technology For Low And Medium Level Radioactive Waste Drum

As one of the strategic cores of national energy,nuclear power has been developing rapidly in recent years,and the problems of generation and accumulation of a large number of radioactive wastes need to be solved.The main radioactive waste produced by nuclear power plants is low and medium level radioactive waste which is contained in the drum.Before transportation and final disposal,it is necessary to detect the type and activity of radionuclides contained in the drum.Non-destructive assay(NDA)is widely used to detect low and medium level radioactive waste.Gamma scanning technology is widely used to detect low and medium level radioactive waste drum in nuclear power plants.Gamma scanning technology can be divided into segmented gamma scanning(SGS)and tomographic gamma scanning(TGS).SGS is only in the measurement of radioactive waste with low and medium density and homogeneous distribution of radionuclides and media,it shows good accuracy,because of the basic model itself limits.Although TGS is developed on the basis of SGS,which is suitable for the measurement of high density and inhomogeneous distribution of radionuclides and media,the measurement time of TGS is too long,which is not suitable for the detection of large quantities of radioactive waste,so TGS has not been widely applied.In order to solve the above problems,this paper aims to explore a kind of low and medium level radioactive waste drum detection technology that balances the measurement time and measurement accuracy.A new collimator is proposed.The new collimator can automatically adjust the flux of gamma ray into the sensitive volume of detector by controlling the size of collimator window.By studying the performance of the new collimator,it is found that the range of the gamma ray scanning device can be expanded by at least four times by using the new collimator.Helical gamma scanning(HGS)is proposed.HGS improves the traditional scanning mode of gamma ray scanning and adopts helical scanning mode to realize continuous measurement time.The measurement and reconstruction process of 400-lier low and medium density waste drum is simulated by Monte Carlo method.The results show that the measurement accuracy of HGS is better than SGS.Two-measurement position helical gamma scanning(THGS)is proposed.On the basis of HGS,THGS adds a helical scanning measurement at an eccentric position.The equivalent radius position of the radioactive source in the drum is determined by the ratio of the counting rate of the two positions,and the activity of the radioactive source can be accurately reconstructed.The measurement and reconstruction process of 400-liter high density waste drum is simulated by numerical calculation method.The results show that the measurement accuracy of THGS is better than HGS and SGS.