Advanced Source Inversion Module of the JRODOS System

Abstract

The development of the source inversion algorithm is described which allows for estimation of the release rates of multiple nuclides and source height with the use of gamma dose rate (GDR) measurements. The method is applicable for the dispersion problems of different spatial scales: from ~1 to ~1000 km. The variational formulation of source inversion problem is used in which unknown release rates of different nuclides are adjusted to minimize the difference of calculated values and measurements. The sensitivities of calculated results with respect to release rates of different radionuclides are calculated with the aid of atmospheric transport model DIPCOT and the source receptor matrix (SRM) is thus constructed. The source inversion problem is regularized using prior (first guess) estimation of release rates. The method is proposed to account for the restrictions on the ratios of the release rates of different radionuclides in formulation of source inversion problem which allows for the assessment of the nuclide composition in radioactive release. The above restrictions are evaluated using the first guess source term. Parameterizations for the regularization parameters of source inversion problem which include root mean squared errors of measurents, first guess release rates, calculated values etc., are developed. The method was successfully tested using artificial measurements precalculated for the conditions of the ETEX experiment. Pilot implementation of the developed algorithm in the European nuclear emergency response system JRODOS is described.