Abstract: The effect of activity and density distribution of solid radioactive waste in barrels on the detection efficiency and uncertainty of two kinds of out-of-barrel activity measurement systems, integrated gamma-ray measurement System (IGS) and segmented gamma-ray measurement system (SGS), commonly used in nuclear power plants in China is described. Field tests and Monte Carlo simulations show that the out-of-barrel gamma measurement system basically meets the requirements for activity measurement of barrelled wastes in nuclear power plants, and the uncertainty of measurement results caused by the distribution of activity and density is within 17% and 20% respectively. At the same time, the position and function of this method should be correctly understood. In view of the existing problems, it is suggested that the relevant technical specifications should be prepared, the working environment of the equipment should ensured, and the personnel training should be strengthened.

Key words: Nuclear power plant, Solid radioactive waste, Out-of-barrel measurement, Factors