Development of parallel coupling system between three-dimensional nodal kinetic code ENTREE and two-fluid plant simulator TRAC/BF1

The high-speed three-dimensional neutron kinetic code ENTREE: was developed based on the polynomial and semi-analytical nonlinear iterative nodal meth ods (PNLM and SANLM) with also introducing the discontinuity factor. In ord er to enhance the efficiency of transient calculation, the nonlinear correc tion-coupling coefficients are intermittently updated based on the changing rate of core state variables. By giving the analytical form for two-node p roblem matrix elements, the additional computing time in SANLM was minimize d. A fast algorithm was developed for the multi table macro-cross section r ebuilding process. The reactivity component model was implemented based on the variation of the neutron production and destruction terms. The code was coupled with the two-fluid thermal hydraulic plant simulator TRAC/BF1 thro ugh PVM or MPI protocols. Two codes are executed in parallel with exchangin g the feedback parameters explicitly. Based on the LMW PWR transient benchm ark, it was shown that bath PNLM and SANLM spend less than 20% excess compu ting time in comparison with the coarse mesh finite difference method (CFDM ). The implementation of the discontinuity factor was verified based on the DVP problem. Adequacy and parallel efficiency of the coupling system TRAC/ BF1-ENTREE was demonstrated based on the BWR cold water injection transient proposed by NEA/CRP.