Comparison Between Different Source Reconstruction Methods of Atmospheric Leakages

Abstract

Abstract When a severe nuclear accident occurs, the diffusion and transportation of airborne radioactive materials can cause harmful effects on the public. An accurate source release rate assessment is necessary to evaluate the consequence of the accident. Provided the leakage source location is known, the source inversion method can inversely estimate the release rate by coupling environmental measurements and the atmospheric dispersion model. Since the Fukushima nuclear accident, source inversion has significantly progressed over the past decade. However, the recent accidental radionuclide leakages are characterized by unknown source locations, causing difficulties in source inversion. Consequently, source reconstruction that simultaneously localizes the atmospheric leakage source and retrieves the release rate has become a highly prevailing and challenging topic. In this study, we introduce and compare three source reconstruction schemes: the cost function method, the source-receptor sensitivity (SRS) statistical method, and the Bayes method. The benchmark SRS data are generated by the backward mode of the FLEXPART model. All methods are validated by the European Tracer Experiment-the first release (ETEX-I). The results indicate the respective advantages and disadvantages in source reconstruction, among which the Bayes method achieves the highest accuracy whereas the cost function method achieves the lowest computational cost. In addition, we compare the source reconstruction performance between the two Bayes methods with the assumption of constant release and time-varying release, respectively. The source release rates in all schemes (if needed) are estimated using the traditional Tikhonov regularization method. The results demonstrate that the Bayes method with constant release may contribute to the best source reconstruction performance. In summary, the above source reconstruction methods are suitable for different emergency response scenarios or stages, thus having the potential to be integrated into the nuclear emergency and response system.