78 are calculated as a minimized weight summed for all paths µm(?0, . . . , ?i) from the initial box (?0) with discharge of radionuclides to the box i on the oriented graph G = (V, E) with a set V of nodes ?j correspondent to boxes and a set E of arcs ejk correspondent to the transfer possibility between the boxes j and k (graph elements as well as available paths are illustrated by Figure I-3). FIG.I-1. NRPA model structure. Reproduced courtesy of Elsevier [I-3].