Abstract: After a radioactive leakage occurs in nuclear facilities, it is generally difficult to directly observe the release point of the source term. The location information of the source term could be obtained indirectly by using radiation monitoring data in the field and the inversion calculation of the diffusion model. Based on the quasi-reversible method, considering the aerosol particle gravity and Brownian diffusion, a direct inversion model for radioactive source terms in a closed space was carried out in this work. The k-epsilon turbulence equation and the convection-diffusion equation of particle pollutant diffusion were established by considering the typical aerosol dynamics parameters and combining the particle Eddy diffusion rate in the turbulent flow field. Then, by forcibly inverting the time step and replacing the second-order diffusion term with the fourth-order stable term, the numerical format of the equation is stabilized. Furthermore, a multi-sensor mode is adopted to reduce the impact of measurement errors, resulting in the inversion of quasi-reversible equations for multiple nominal sources. Finally, taking the “c-T” information of the sensor position as input, an appropriate stability coefficient for inversion was selected. The results show that this inversion model can accurately trace the location of the source term of particle pollutants in the convective diffusion environment within a closed space.

Key words: leakage accidents, identification of pollution sources, quasi-reversible method