Analysis of oxide fuel element temperature of RSG-GAS by using experiment and calculation

Abstract

Multipurpose Reactor GA Siwabessy is a research reactor designed to have nominal power of 30 MWth, located in PUSPIPTEK area Serpong and operated by BATAN. RSG GAS utilizes LEU-MTR with enrichment 19.75% and uranium density of 2.96 g U/cm3, 40 fuel rods and 8 control rods, 4 irradiation position (IP) and 1 central irradiation position (CIP) in 2 × 2 lattice, and reactor core surrounded by beryllium reflector. Forced convection cooling mode is applied to remove heat of fission product at normal operation, while natural convection cooling mode is used for reactor physics experiment, or cooling after transient condition. Forced convection cooling mode does not employ primary cooling system, where power is limited to 1% of the nominal power, while natural convection cooling occurs after transient process due to loss of coolant. Heat transfer occurs because of difference in coolant flow density where coolant flows upward since natural circulation valve is opened. This research is aimed to analyze heat removal capability in natural convection cooling mode at the most severe condition following reactor scram. The experiment of cladding and coolant temperature measurement is carried out in fuel coolant channel using instrumented oxide fuel element. Capability of generating reactor power in natural convection cooling is calculated using NATCON code. The measurement result of the highest temperature of plate fuel element is 121°C. Meanwhile, the calculation results of NATCON show that the initial temperature of nucleate boiling TONB occurs at power 685.86 kW and cladding temperature is 126.35 °C. These experiment results indicate that nucleate boiling does not occur in natural convection cooling due to scram or in other words safety margin has been met.