An Improved Gamma Scanning Assay Method for the 400-L Compacted Radioactive Waste Drum Based on the Segmented Equivalent Ring Source

An improved characterization assay algorithm for the 400-L low- and intermediate-level radioactive waste drum was developed based on the segmented equivalent ring source. The improved method (IM) was validated by experiments on a 200-L waste drum. The assay errors are smaller than that of segmented gamma scanning (SGS). Numerical measurements were performed on a 400-L waste drum with two densities of 1.5 and 2.5 g/cc. Three common nuclides, Ba-133, Cs-137, and Co-60, were selected. The results show that the source positions can be determined using two detectors through this method. The maximum error of the IM is several times smaller than that of SGS if the matrix is uniformly distributed in the waste drum. The mean errors are reduced by one third to half for all nuclides compared with SGS. If IM is applied in assaying the solidified wastes drum that contains one or two cylindrical iron products, the strong attenuation of gamma rays by irons and concretes will affect the determination of source positions. The assay accuracy decreases in this case, but it is overall better than that of SGS. The results indicate that IM is an accurate method for assaying the compacted waste drums with nonuniformly distributed radioactive sources.