Space-time convergence analysis on BWR stability using TRACE/PARCS

Unstable behavior of Boiling Water Reactors (BWRs) is known to occur during operation at certain power and flow conditions. Even though BWR instability is not a severe safety concern, it could cause reactor scram and significantly decrease the economic performance of the plant. This paper aims to (a) quantify TRACE/PARCS space-time discretization error for simulation of BWR stability, (b) establish space (nodalization) and time discretization necessary for space-time converged model and (c) show that the space-time converged model gives more reliable results for both stable and unstable reactor. The space-time converged model is obtained when further refinement of numerical discretization parameters (nodalization and time step) has negligible effect on the solution. The study is significant because performing a space-time convergence analysis is a necessary step of qualification of the TRACE/PARCS model, and use of the space-time converged model increases confidence in the prediction of BWR stability.