The coupled code TRAB-3D-SMABRE for 3D transient and accident analyses

The three-dimensional TRAB-3D core dynamics code is being internally coupled to the thermal hydraulics system code SMABRE. The codes have previously been coupled with a parallel coupling scheme. VTT's reactor dynamics codes have performed well in all the situations that they have originally been designed for. The most important limitation of the present code models is their inability to handle coolant flow reversal in the core channel, a phenomenon that can be encountered in e.g. BWR ATWS cases or VVER power excursions. The new coupling of the two codes is realized on the level of each node of each channel in the core, with each fuel bundle described with its own channel. Necessary interfaces have been created, an improved version of SMABRE's thermal hydraulics solution method developed, and a steady state procedure developed. A satisfactorily working steady state solution has been achieved. The next step in the development will be testing of the transient calculation. Besides solving the flow reversal limitation of the present dynamics models, a successful coupling will allow expanding into more realistic modelling of an open core.