Thermo-siphon mock-up test for the cold neutron source of HANARO

Due to the national demand for a cold neutron beam utilization, a cold neutron research facility project has been carried out since July 2003 to install a cold neutron source (CNS) in HANARO. The CNS adopts a two-phase thermo-siphon of liquid hydrogen as a working fluid to remove a heat load. The CNS consists of an in-pool assembly (IPA) and other components including a hydrogen buffer tank. The liquid level in the moderator cell is measured by a gamma-ray densitometer under a normal cold operation, and the cool down time to fill the required liquid hydrogen into the moderator cell is numerically simulated and compared with the experimental data from a thermo-siphon mock-up test. The self-regulating characteristic of the two-phase thermo-siphon loop is also confirmed by a comparison of a model simulation's results, which use a thermodynamic model, with the experiment's results. From these results, the HANARO-CNS is found to maintain the required conditions for a stable cold neutron production against a heat load variation along with the reactor's power. Furthermore, the thermodynamic behavior in the IPA is observed to determine whether or not the integrity of the IPA is maintained under an abnormal condition of the helium refrigeration system.