Large-volume container waste generated from nuclear facility decommissioning exhibits extremely inhomogeneous nuclide distribution. Its activity measured using the traditional tomographic gamma scanning (TGS) technique shows errors of up to six orders of magnitude; this hinders its safe disposal.

This study aims to develop an improved tomographic gamma scanning (ITGS) technique based on the equivalent surface source method and establish a reconstruction algorithm.

Firstly, based on the count rate ratios of different γ-scan positions, the basic distribution of nuclides in the waste container was calculated, and the accurate activity reconstruction results were obtained by the combination of efficiency calibration. Then, γ-scan experiment was simulated for measuring various radioactive source distributions of Co-60 nuclides in large waste containers to verify the accuracy of this method, and the influence law for the nuclide distribution and measurement parameters on the reconstruction results was discovered.

Simulation results demonstrate that a deeper radioactive source location or larger medium density can increase the activity reconstruction error. However, based on the same measurement time, the ITGS measurement error can be controlled within an order of magnitude compared with the conventional TGS.

The proposed method achieves higher reconstruction accuracy under complex conditions such as multiple nuclide distributions and high medium density. Furthermore, it mitigates waste disposal safety hazards to humans and the environment by facilitating rational arrangements of the measurement system and activity reconstruction of radioactive waste containers.