A Preliminary 3D Steam Flow Analysis for CET Behavior During LSTF SBLOCA Experiment Using FLUENT Code

Abstract

A 3D steam flow within simulated fuel bundle of Large Scale Test Facility (LSTF), a PWR system simulator, has been investigated by Computational Fluid Dynamics (CFD) analysis with Ansys Fluent code to clarify influences of the steam flow on Core Exit Temperature (CET) response. A LSTF SBLOCA experiment with 1.5% hot leg break as the OECD/NEA ROSA-2 Project Test 3 was simulated by the CFD code to clarify relation between CET and fuel rod surface temperature. A portion of the LSTF core above the mixture level up to around CET sensors was modeled by taking into account high, medium and low heat-zone heater rod bundle, including internal structures such as end-box and upper core plate (UCP). Simulation of steady-state condition at a certain time when mixture level lowered to a certain position at around half of the core height (post-5) was carried out by considering relevant boundary conditions which were developed based on the LSTF Test 3 results. The calculation results revealed that inner structures of the core such as core spacer, end box and UCP indeed affect the CET due to heat transfer from hot steam to these cool structures. 3D flow mixing may also contribute to the final CET values and the delayed increase in the CET relative to the Peak Cladding Temperature (PCT) in the core.