Standard Test Method for Nondestructive Assay of Radioactive Material by Tomographic Gamma Scanning

Importancia y uso:

5.1 The TGS provides a nondestructive means of mapping the attenuation characteristics and the distribution of the radionuclide content of items on a voxel by voxel basis. Typically in a TGS analysis a vertical layer (or segment) of an item will be divided into a number of voxels. By comparison, a segmented gamma scanner (SGS) can determine matrix attenuation and radionuclide concentrations only on a segment by segment basis.

5.2 It has been successfully used to quantify  ²³⁸Pu, ²³⁹Pu, and ²³⁵U. SNM loadings from 0.5 g to 200 g of ²³⁹Pu (5, 6), from 1 g to 25 g of ²³⁵U (7), and from 0.1 to 1 g of ²³⁸Pu have been successfully measured. The TGS technique has also been applied to assaying radioactive waste generated by nuclear power plants (NPP). Radioactive waste from NPP is dominated by activation products (for example, ⁵⁴Mn, ⁵⁸Co, ⁶⁰Co,  ^110mAg) and fission products (for example, ¹³⁷Cs,  ¹³⁴Cs). The radionuclide activities measured in NPP waste is in the range from 3.7E+04 Bq to 1.0E+07 Bq. Some results of TGS application to non-SNM radionuclides can be found in the literature (8).

5.3 The TGS technique is well suited for assaying items that have heterogeneous matrices and that contain a non-uniform radionuclide distribution.

5.4 Since the analysis results are obtained on a voxel by voxel basis, the TGS technique can in many situations yield more accurate results when compared to other gamma ray techniques such as SGS.

5.5 In determining the radionuclide distribution inside an item, the TGS analysis explicitly takes into account the cross talk between various vertical layers of the item.

5.6 The TGS analysis technique uses a material basis set method that does not require the user to select a mass attenuation curve apriori, provided the transmission source has at least 2 gamma lines that span the energy range of interest.

5.7 A commercially available TGS system consists of building blocks that can easily be configured to operate the system in the SGS mode or in a far-field geometry.

5.8 The TGS provides 3-dimensional maps of gamma ray attenuation and radionuclide concentration within an item that can be used as a diagnostic tool.

5.9 Item preparation is limited to avoiding large quantities of heavily attenuating materials (such as lead shielding) in order to allow sufficient transmission through the container and the matrix.

Subcomité:

C26.10

Referida por:

C1490-14R23, C1592_C1592M-21, C1931-23

Volúmen:

12.01

Número ICS:

13.030.30 (Special wastes), 17.240 (Radiation measurements), 27.120.30 (Fissile materials and nuclear fuel technology)