Improvement of the one-dimensional dissolved-solute convection equation using the QUICKEST–ULTIMATE algorithm

The U.S.-NRC best-estimate system code TRACE adopts a finite volumes, first-order upwind discretization scheme to solve the dissolved-solute convection equation. Such a scheme is known to strongly suffer from numerical diffusion, which can be a significant drawback in analyzing certain safety relevant scenarios in nuclear power plants, e.g. with plugs of solute (or plugs of diluting water) traveling from the loops to the core and thus affecting the reactivity of the system. In such cases, high-order upwind convecting schemes are better suited to discretize and solve the solute convection equation. In particular, the explicit QUICKEST (Quadratic Upwind Interpolation for Convective Kinematics with Estimated Streaming Terms) scheme, together with the ULTIMATE (Universal Limiter for Transient Interpolation Modeling of the Advective Transport Equation) limiter, offers an attractive solution, thanks to the overall third-order accuracy, the intrinsic stability of the upwind scheme and the limited increase in computational costs. In order to demonstrate the feasibility and the advantages of the implementation of such a solution strategy in TRACE, the scheme has been implemented in the code and verified for simple geometries (e.g. straight pipes) and for a double T-junction loop, the latter in the context of using a CFD (Computational Fluid dynamics) code coupled with TRACE.

Research highlights▶ System code TRACE solute tracking equation improved with high-order upwind scheme. ▶ New scheme verified in straight pipe with plugs and steps of solute. ▶ New scheme validated with experimental data. ▶ Reduction of numerical diffusion improves accuracy. ▶ Neglecting numerical diffusion requires modeling of physical diffusion.