[en] The Lawrence Livermore Laboratory is developing for the Nuclear Regulatory Commission a procedure to assess material control and accounting systems to prevent the possible theft of special nuclear materials (SNM). A computer code is described that evaluates the piping network within a plant and identifies all possible paths for removal of SNM from specified sources. As an example movement of plutonium nitrate solution from storage tanks to various exit points is described and simple approximate fluid-flow calculations are given for each path