Direct Measurement Method and Verification of γ Nuclides in Boxed Waste

Abstract

According to the relevant provisions of the national radioactive waste management, radioactive waste is eventually sent to the waste disposal site storage, medium and low level waste must be packaged in standard packaging (steel drum or steel box, etc.), and the type and activity concentration of radionuclides should be marked in the packaging. At present, direct sampling is used to measure the radioactivity level of steel boxes, but it will damage the steel boxes and produce secondary waste. Currently, there is no method and system for direct measurement of radioactive solid waste steel boxes in China, which is a difficult problem to be solved urgently. Aiming at the problem of direct measurement of γ nuclides in FA-Ⅳ type radioactive solid waste steel tank, a set of non-destructive testing system was developed to measure radioactive solid waste. Based on the investigation results of the source term of the steel box, and taking into account the short detection time and the small error of the reconstruction results, the traditional CT principle and the discrete processing method were combined to establish the γ-ray spectrum measurement and analysis algorithm of the steel box of radioactive solid waste. In the process of analysis, the method of voxel measurement was adopted. The detection efficiency library was calculated and established to calculate the response of the detector under the actual measurement conditions, so as to establish the activity calculation equation. Monte Carlo method was used to simulate the actual steel box and source item data. Combined with algebraic reconstruction method, the detection efficiency correction model was established to realize the efficiency inversion correction of the physical coincidence part of the detected volume of voxels during the measurement process, and the direct measurement problem of γ nuclides in FA-Ⅳ steel boxes was solved, and the corresponding measurement system was established. In order to verify the reliability of the system, samples of the waste in the steel box were taken and sent to the laboratory for γ-ray spectrum measurement and analysis. The measurement results of the two methods were compared and analyzed, and the relative deviation of the two methods is less than 35%. And it is verified that the direct measurement method of the system can meet the requirements of measuring and analyzing the steel box of radioactive solid waste generated from reactor decommissioning and measuring error of waste receiving data in disposal site within 50%.

Keywords

• steel box
• γ-ray spectrum measurement and analysis
• monte carlo simulation
• algebraic reconstruction algorithm
• efficiency scale model