Study On The Source Term Inversion Method Based On Containment Short-Range Detection Data

A new source term inversion method is presented to accurately estimate release rate of airborne radionuclides leaked into the environment,under the circumstance of nuclear power plant severe accidents.The method is based on containment short-range gamma-ray spectrometry data obtained by mobile detection points arranged near the containment.The key issues to study are listed below: i)which radionuclide should be selected to estimate source term;ii)how to determine the appropriate detection range and how to arrange effectively mobile detection points;iii)how to estimate accurately leak rate of a single radionuclide.In order to quantify radiation effect of source term released into the containment and source term released into the environment on detection point,flux of photon with specific energy is calculated.MCNP program is used to model the containment and simulate flux of photon induced by source term released into the containment;Gaussian plume diffusion model is used to calculate concentration distribution of airborne radionuclides near the containment.MCNP program is used to simulate flux of photon induced by source term released into the environment.An algorithm is proposed to estimate the release rate of a single radionuclide based on the difference between flux of photon induced by two kinds of source term versus distance from the containment.As verified by numerical experiments: i)Kr-88 could be selected as characteristic nuclide among all airborne radionuclides,due to its relatively high first characteristic gamma-ray energy and high leak rate;ii)the detection range is determined as within 100 meters from the containment;iii)the relation between gamma-ray spectrometry data and leak rate of characteristic radionuclide is established to obtain inversion result numerically accurately.