VARIATIONAL NODAL TRANSPORT METHODS WITH HETEROGENEOUS NODES

The variational nodal transport method is generalized for the treatmen t of heterogeneous nodes while maintaining nodal balances. Adapting va riational methods to heterogeneous nodes requires the ability to integ rate over a node with discontinuous cross sections. Integrals are eval uated using composite Gaussian quadrature rules, which permit accurate integration while yielding acceptable computing times. Allowing struc ture within a nodal solution scheme avoids some of the necessity of cr oss-section homogenization and more accurately defines the intranodal flux shape. Ideally, any desired heterogeneity can be constructed with in the node, bur in reality, the finite set of basis functions limits the intranodal complexity that can be modeled. Comparison tests show t hat the heterogeneous variational nodal method provides accurate resul ts for moderate heterogeneities, even if some improvements are needed for very difficult configurations.