Thermal-Hydraulic Analysis of the Hottest Channel in the Core of TNRR Under Natural Convection Cooling Using ANSYS-Fluent

Abstract

A study of thermal-hydraulic behavior of the core of Tajoura Nuclear Research Reactor (TNRR) under natural convection cooling was performed. A narrow gap between two cylindrical elements in IRT-4 type fuel in the hottest fuel assembly was considered as the most critical. A two-dimensional CFD model of the narrow gap was developed using ANSYS Fluent code and to obtain admissible margins of core power and safe operation time before reaching the maximum allowable fuel cladding temperature of  102^∘ "C" . The effect of coolant mixing ratio in the pool was investigated for three different cases: 100% (complete mixing), 75% and 50% of total pool volume. Results from the study of transient cooling indicate that at 100% mixing in the pool, the hottest channel in the core can safely operate the reactor for about 42 hours at 100 kW, 10.5 hours at 400 kW, 8.3 hours at 500 kW and about 7 hours at 600 kW. Reducing the coolant pool mixing volume ratio to 75% or 50% greatly reduces the system’s thermal inertia, causing a rapid increase in temperature and greatly reducing safety time margins. This study establishes a basis for assessing the thermal capacity of the TNRR core under natural convection cooling and the limits of safe operation following a scram event or loss of flow of coolant.