THERMAL HYDRAULIC AND SAFETY ANALYSIS OF HEAT TRANSFER AND DISTRIBUTION IN THE GHANA RESEARCH REACTOR-1 (GHARR-1) CORE USING STAR-CCM+ CFD CODE

ABSTRACT Operational power of a nuclear reactor core is limited by thermal considerations. In principle, the allowable core power is restricted by the rate at which the heat can be transferred from the fuel to the coolant. Unlike in conventional combustion facilities where the heat is released in gas-flows, heat in the nuclear reactor core is mainly released in the structural material. If not properly removed the structural materials inevitably melt causing release of radioactive material. STAR-CCM+ CFD code was used to perform thermal hydraulic analysis of the Miniature Neutron Source reactor also known as the Ghana Research Reactor-1 (GHARR-1). The reactor has a Highly Enriched Uranium (HEU) core consisting 344 fuel pins arranged in 10 multi-concentric circle layers at a pitch distance of 10.95 mm. The present study however considered only the first two concentric rings with varying power of 15 to 30kW. The choice of the first two concentric rings was informed by the results of the computation of local power peaking factors based on power densities. The result indicates that the maximum radial peaking factor of 2.02 occurred at the mid-plane of the core while the maximum axial peaking factor of 1.57 was at the region of the second ring. The extent of the domain considered in this work was also limited by the computational resources available. Analysis of the temperature, pressure, mass flow rate and turbulent intensity in the first two concentric rings was performed to assess the steady state Thermal hydraulic behaviour of GHARR-1 core under natural convection cooling. Computational simulation was performed at 15 and 30 kW at a fixed mass flow rate of 0.11 kg/s. The mass flow rate was varied from 0.11 to 0.15 kg/s in steps of 0.02 kg/s at a fixed power of 30 KW.