3. DESCRIPTION OF PROGRAM OR FUNCTION
ENTREE is a plant simulation code system that can be applicable to operational transients, coupled neturonic-thermal hydraulic instability and reactivity insertion accidents. The main objectives of ENTREE are development, verification and application of the three-dimensional plant simulation system TRAC/BF1-ENTREE-ACCORD-N for boiling water reactors (BWRs). The coupling phenomena considered in the BWR design field were reviewed in terms of their phenomenological natures. Basic specifications of existing three-dimensional plant simulation codes were compared with regard to modeling of neutron kinetic, two-phase flow dynamic and fuel heat conduction.
ENTREE is a three-dimensional neutron kinetic code based on the modern nodal methods. The assembly discontinuity factor (ADF) and the pin power reconstruction capabilities are also implemented for transient calculations, and they permit evaluation of detailed local pin power transition. The fully implicit scheme is implemented to deal with not only slow but also fast power transients based on the same formulations.
The modal analysis code ACCORD-N solves the two or three-dimensional higher neutron flux modes based on the two energy group diffusion equation. The higher neutron flux modes supply basic information for understanding space-dependent neutron kinetics. Specifically, they are fully utilized in regional instability evaluation as the shape function of external disturbance used for evaluating core stability. They are also useful in quantifying inter-modal interaction.
This ENTREE package includes the ENTREE and ACCORD-N codes; it does not include TRAC/BF1, which is proprietary code. TRAC/BF1 is a state-of-the-art plant simulation code based on the two-fluid model. Non-equilibrium two-phase fluid dynamics permits one to analyze not only slow, moderate transients but also fast transients without switching the basic governing equations.