Neutronic and thermal-hydraulic analysis for TRIGA Mark II in subcooled nucleate boiling condition

The TRIGA® (Training, Research, Isotopes production by General Atomics) 2000 research reactor in Bandung (TRIGA® 2000 Bandung) has undergone fuel reshuffling, and therefore there is a potential for subcooled nucleate boiling to occur in the reactor core, thus it is necessary to conduct a thorough investigation by calculation to explain whether the TRIGA® 2000 Bandung reactor can still operate below the operation safety limit. Herein, the optimization of the neutronic and thermal–hydraulic calculations using the MCNP® and COOLOD-N2 codes, respectively, has been carried out to reveal the main parameters to justify the operating safety limits, including superheat temperature and Departure from Nucleate Boiling Ratio (DNBR). The calculation results show that the predicted subcooled boiling condition occurs at a thermal power of 223 kW, while saturated nucleate boiling occurs at a reactor thermal power of 326 kW – 640 kW. The calculation results were also compared with the fuel temperature measured by Instrumented Fuel Element (IFE) at each power variation. Meanwhile, from the DNBR value perspective, the reactor still meets the operating safety limit if the reactor power is operated at 223 kW – 427 kW thermal power.