PATHS: a Steady State Two-Phase Thermalhydraulic Solver for PARCS Depletion

Abstract

The PATHS code was developed to solve the steady state two-phase thermal-hydraulic equations for a Boiling Water Reactor (BWR) and to provide thermal-hydraulic feedback for BWR depletion calculations with the neutronics code PARCS. The PARCS code is coupled to RELAP5 and TRACE which are normally used to solve for the thermal hydraulic state for BWR applications. However, systems codes were developed primarily for transient analysis and it can be computationally expensive to perform null transients to achieve the steady-state for the many channel problems required for practical BWR depletion analysis. For steady state analysis of the reactor, it is much more efficient to use a lower order two phase solution methodology. The low order methodology improves the runtime without major compromises in the fluid density and temperature distributions that are important for depletion analysis. In the PATHS code, the drift flux model is used with the EPRI void model. PATHS results were compared to TRACE for fixed power computations at various powers and flow rates. Coupled PATHS/PARCS calculations were then validated using depletion data from cycles 1 and 2 of the Peach Bottom II BWR.