nTRACER/COBRA-TF Coupling and Initial Assessment

The nTRACER direct whole core calculation code being developed at Seoul National University (SNU) has an internal T/H module to determine the temperature and density fields in the reactor. However, this module is based on a quite simplified model and considers only axial flow. The weakness of not-considering radial flow was overcome by coupling the MATRA (Multichannel Analysis for steady-state and Transient in Rod Array) code with nTRACER. MATRA can generate more realistic and detailed T/H field information for nTRACER, but it is a legacy code and does not have an efficient parallel computing capability. On the contrary, the COBRA-TF (Coolant-Boiling in Rod Arrays Two Fluids, CTF) subchannel code, which was developed for the T/H analysis of Light Water Reactor (LWR) vessels, has a good parallel computing capability based on the Message Passing Interface (MPI). The initial assessment of the coupled code demonstrates that more realistic coolant temperatures are obtainable by using CTF. The change in pin power distribution is noted with the realistic flow distribution even though the change is insignificant. The calculation utilizing the boron tracking model of CTF is noticeable. It makes possible for nTRACER to handle nonuniform boron distributions which can be encountered during some transients. Since further validation of the coupling is necessary, the coupling capabilities will be extended to transient applications where non-uniform distributions of inlet parameters such as boron concentration but also coolant temperature can occur