Solution of Flow Equations in the USNRC Consolidated Code
John H. Mahaffy, Thomas J. Downar, Quan Wang · 2000
The USNRC consolidated reactor analysis code supports approximation of the time-dependent two-phase flow equations with both the semi-implicit and Stability Enhancing Two-Step (SETS) methods. Flow can be modeled in arbitrary networks of 1-D and 3-D regions. Regardless of the selected method, final solution always requires the solution of sparse systems of linear equations. The consolidated code has been structured to cleanly isolate the generation of these linear systems from their solution. Fortran 90 derived types are used to record the structure of the sparse matrices, and to store the nonzero coefficients. Two basic solution methods are provided in the code with automated selection for minimal run time based on the matrix configuration. The isolation of the solution subroutine permits developers to experiment with other solution methods, as technology or needs change. The consolidated code also supports an extended solution procedure that supports flows modeled with multiple processes, including use of other flow modeling programs as one or more of the other processes. This permits use of programs with special purpose flow models for components such as accumulators or core makeup tanks. It also opens the possibility for convenient use of 3-D CFD analysis of an area of special interest, while the consolidated code provides conditions in the balance of the system. 1.