Phenomenological Analysis on 1,000°C Material Irradiation Testing in HANARO using the Instrumented-Capsule(15M-03K)

With the increasing demand for materials development for next-generation nuclear systems such as Molten Salt Reactors, Sodium-cooled Fast Reactors, and Very High-Temperature Reactors, high-temperature irradiation testing has become essential. This study aimed to establish irradiation technology capable of operating up to 1,000°C in the HANARO reactor. For this purpose, an instrumented capsule (15M-03K) with a double-layered thermal medium was designed, fabricated, and tested. Irradiation experiments were conducted in multiple reactor cycles between 2018 and 2024. The capsule achieved a maximum specimen temperature of 1,000°C, while stable operation was demonstrated at 800–900°C. A transient temperature drop observed at 1,000°C was promptly mitigated by helium injection, ensuring the safety of both the capsule and the reactor. Neutronic evaluations using MCNP confirmed the dominance of ~1 MeV neutrons in the specimens, with flux variations linked to control rod positions, and the accumulated fast neutron fluence was quantified for all cycles. These results demonstrate the feasibility of controlled high-temperature irradiation testing in HANARO and provide key data for material performance evaluation under advanced reactor conditions. The developed technology will contribute to future irradiation programs requiring longer durations, higher stability, and extended temperature ranges.