RECASS SOURCE-TERM ESTIMATION SUBSYSTEM AND ITS APPLICATION FOR RECONSTRUCTION OF THE SOURCE RATE OF THE CHERNOBYL ACCIDENT

The work discusses the algorithm which is used in the RECASS For recon stnuction of the dynamics of a multiisotope source from outdoor measur ements. The algorithm is based on applying projective geometry to mini mise the objective. The contamination surface and/or space is divided into several domains of different area/volume and equal contamination. Squares of deviations of calculated and modelled contamination in the se domains are minimised. The algorithm allows the use of some linear restrictions (non-negativity of source rate, assumption of dynamics of the source, known relative concentrations of isotopes, direct measure ments in the source, etc). The algorithm also calculates the covarianc e matrix of the source rate. The way in which the software was applied to calculate the dynamics of the release of Cs-137, I-131, Ba-140, Zr -95, Ru-100 Ce-144 for the early period of the Chernobyl accident, bas ed on measurements of depositions, is discussed.