Conceptual Thermal Hydraulic Design of a 20MW Multipurpose Research Reactor

Abstract

The conceptual thermal hydraulic design analyses for a 20 MW reference AHR core have been jointly performed by KAERI and DNRI (VAEC). The preliminary core thermal hydraulic characteristics and the safety margins for the AHR core were studied for various core flow rates and fuel assembly powers. Statistical method and the MATRA_h subchannel code have been applied to evaluate the thermal hydraulic performances of the AHR core under the forced convection cooling mode during a nominal power operation and the natural circulation mode during a reactor shutdown condition. In addition, the safety margin evaluations were carried out for 2 typical accidents, a loss of flow accident by a primary pump seizure and a reactivity induced accident by a CAR rod withdrawal during a normal full power operation. Major design parameters for these analyses are a minimum critical heat flux ratio (MCHFR), an onset of a nucleate boiling (ONB) margin and a maximum fuel temperature. Results of the thermal hydraulic analyses show that the normal full power operation of the AHR could be ensured with a sufficient thermal margin for the onset of a nucleate boiling for a coolant velocity larger than 7.3 m/s. The AHR is also thought to have a sufficient natural circulation cooling capability up to at least 1.8MW to cool the core without the onset of a nucleate boiling in a channel after a normal reactor shutdown and during anticipated transients. It was also confirmed that the AHR core was sufficiently protected from the loss of a flow by a primary cooling pump seizure and the overpower transients by a CAR withdrawal from the MCHFR and fuel temperature points of view.