keywords: Power calibration, thermal hydraulics, heat balance, calorimetric, NIRR-1
Accurate thermal power calibration is important to the safety and stability of the Nigeria Research Reactor (NIRR-1). The conversion of the NIRR-1 led to the increase in its maximum steady-state thermal power from 31 kW to 34 kW to ensure effective utilization for Neutron Activation Analysis (NAA). In this work, the impact of conversion on the thermal power calibration of the NIRR-1 was assessed using heat balance, calorimetric methods and flux-power relationship. For the calorimetric method, the total power dissipated was 2.3 kW with an uncertainty of ±26%. The total heat loss from the reactor was 1.1 kW. The average pool temperature was 22.70±0.12. For the heat balance method, the value of the average core flow rate, inlet and outlet temperature is 0.215 kg/s, 26.54±0.48 and 30.35±0.64oC, respectively while the total heat loss was 0.0065 kW. The reactor power dissipated was found to be 3.41506 kW, with uncertainty of ±8%. The uncertainty in power at a flux of 1.0×〖10〗^(11 ) n〖cm〗^(-2) s^(-1) which was ± 5% for the HEU core was found to have slightly increased to ± 8% using the heat balance method. Our results confirms that the heat balance method is more accurate in thermal power calibration of the reactor at low power for the LEU core compared to the calorimetric method and the flux-power-relationship is linear but reveals an increase in heat losses and uncertainty in thermal power and an increase in the factor for flux-power-relationship by 9.677%.