The RETRAN-02 computer program 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-02 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-02 software development and maintenance for them.

RETRAN-02 is a versatile and reliable computer program for use in best-estimate transient thermal-hydraulic analysis of light water reactor systems. It is based on a one-dimensional homogeneous equilibrium mixture model with an optional phasic slip formulation based on either a drift flux model or a phasic velocity difference differential equation. RETRAN-02 contains both point reactor and one-dimensional kinetics models and component models for reactor control systems, pressurizers, and separators. It also has flexible heat conduction and heat transfer models that allow modeling of both reactor cores and steam generators. A unique capability of RETRAN-02 is its steady-state initialize feature, which aids users in establishing the desired initial state for transient simulations.

RETRAN-02 provides analysis capabilities for the following:

• BWR and PWR transients
• small break loss of coolant accidents
• Anticipated transients without scram

It is routinely used to support plant licensing, operational support, and training issues.

RETRAN-02 has been approved by the United States Nuclear Regulatory Commission for use in performing licensing calculations and is used by numerous electric utilities and national laboratories. RETRAN-02 MOD005.2 is the current version, and is operational on PCs and UNIX-based workstations.

Continued development of the RETRAN code source has lead to the RETRAN-3D code, which has improved capabilities and range of applications.