Bond graph representation of nuclear reactor point kinetics and nearly incompressible thermal hydraulics

Abstract

This work presents a simplified 1D model for a pressurized water reactor core, suitable for very rapid transients like control rod ejection. The model is represented using the bond graph formalism, a technique for modeling engineering systems as combinations of connected elements. Bond graphs are a flexible way of presenting coupled physics problems by automating the computer science aspects of modeling and letting the modelers focus on the physics; they were introduced in earlier work. To help leverage the flexibility of bond graph representations of physical systems, a new bond graph processing code, BGSolver, is introduced. BGSolver has been developed by the authors over the past several years, and is now released as open source software. A rapid rod ejection benchmark is solved with both BGSolver and RELAP5-3D; BGSolver obtained full convergence with a 5 ms time step, while RELAP5-3D required a 1 ms time step, due to the fully coupled time integration that BGSolver employed, compared to an operator splitting-based time integrator of RELAP5-3D. BGSolver’s time integrator demonstrated 3rd-order convergence in time, a very desirable property. A single nonlinear solve was used to obtain the steady state with BGSolver.