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

• A simplified PWR core model is presented and represented with bond graphs.
• Third order accuracy in time obtained using a fully coupled time integrator.
• Superior convergence demonstrated for a fully coupled approach over operator split.
• BGSolver, a new open source bond graph processing code, is presented.

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.