A RETRAN-03 computer code version has been developed to analyze reactor transients requiring three-dimensional reactor core neutronics models. The new code will enable the user to couple a complex RETRAN nuclear steam supply system model to a detailed multidimensional neutronics core model.

The neutronics model is based on a three-dimensional nodal model using the analytic nodal method that allows a detailed three-dimensional representation of the core but requires less computational effort than conventional fine-mesh finite difference methods. The model uses a full two-group diffusion equation implementation coupled to six delayed neutron groups.

Two representative analyses were used as evaluation cases. The work involved the first use of the RETRAN-03 advanced system analysis code using three-dimensional neutronics methods. The purpose of these studies was to gain experience in RETRAN-3D modeling methods and to compare the results with previous calculations as part of a code verification effort.

The work has led to a new capability for the RETRAN-03 code, enabling the user to examine the core behavior in more detail than in previous versions and to study transients that involve nonsymmetric core behavior.