Numerical Advisory Solutions
The RETRAN-3D computer program evolved from continued development of the RETRAN codes. It represents the latest in modeling capabilities and features which include the ability to reproduce RETRAN-02 results. Like its predecessor, RETRAN-02, RETRAN-3D was developed to perform licensing and best-estimate transient thermal-hydraulic analyses of light water reactors. It is maintained under a Quality Assurance program in compliance with 10CFR50 Appendix B. The RETRAN-3D code was developed for the United States Electric Power Industry under the sponsorship of EPRI. NAS operates the RETRAN User Group (RUG) for member organizations and performs RETRAN-3D and software development and maintenance for them.

RETRAN-3D is a well accepted transient thermal-hydraulic analysis code designed for use in best-estimate evaluation of light water reactor systems. It is based on the one-dimensional homogeneous equilibrium model (HEM). Two additional modeling options allow for increasing levels of improved modeling capability for two-phase flow conditions. One makes use of a slip model (dynamic or algebraic) to augment the HEM equations and eliminate the equal velocity assumption when two-phase conditions exist. The other uses both a slip model and the vapor continuity equation to augment the HEM balance equations. This eliminates the equal velocity and equal temperature assumptions of the HEM model. A gas continuity equation can be added to any of the three options described above to allow noncondensable gas flow to be modeled.

When using RETRAN-3D, heat generation in a nuclear reactor core can be modeled using three-dimensional, one-dimensional, or point reactor kinetic models. Component and auxiliary models allow for complete modeling capability for the nuclear steam supply system including controls. Many new models have been added to RETRAN-3D and many RETRAN-02 models have been revised to improve accuracy.

Both the steady-state and transient numerical solutions methods in RETRAN-3D have been revised to use implicit solution schemes where those in RETRAN-02 are a mixture of explicit and semi-implicit methods. This results in much improved steady-state initialization convergence for two-phase systems and a more stable transient solution, which can violate the material Courant limit for most slowly changing transients.

RETRAN-3D retains the analysis capabilities of RETRAN-02 in that it can be applied to: RETRAN-3D has much improved capabilities for the last two transient types and also has model extensions designed to provide analysis capabilities for: RETRAN-3D has been approved by the United States Nuclear Regulatory Commission for use in performing licensing calculations and is used by a large number of domestic and foreign electric utilities and research organizations. RETRAN-3D MOD005.0 is the current version, and is operational on PCs and Linux-based workstations.