The CNS (Cold Neutron Source) is a facility to moderate the thermal neutron flux into the cold neutron flux by passing the thermal neutron through the cold moderator in the nuclear reactor. The cold moderator contains a cryogenic fluid such as liquid hydrogen. A cryogenic thermosiphon is mainly used for the cold moderator. In order to obtain the stable cold neutron flux, the thermosiphon of cold moderator should properly run under the heat load change in the CNS.
In this thesis, an experimental study on the CNS mock-up thermosiphon is carried out by using argon as the working fluid to investigate the dynamic behavior of cryogenic thermosiphon. The mock-up thermosiphon is made of pyrex glass to observe the fluidic behavior of the cryogenic thermosiphon. To charge argon gas into the thermosiphon, a buffer tank is used and it is charged initially at 3.36 atm. The mock up thermosiphon is composed of three parts-evaporator, transfer tube, and condenser. The evaporator is an annular shape to enhance cold neutron efficiency. The transfer tube is designed to avoid flooding for the operation range. The condenser has fin and plate heat exchanger which is cooled by liquid nitrogen. Self-regulation characteristics can be performed by controlling the cooling capacity of the condenser. An electric heater, which is made of stainless steel shim, is attached to the fin to control the cooling capacity. When the heating power of the evaporator is increased or decreased compared to steady state operation value, the working temperature and the pressure of the thermosiphon is also elevated or reduced. The dynamic behavior of thermosiphon is observed for the various heating power at the evaporator and the experimental results are compared with the analysis. The void fraction of the evaporator is also determined by measuring the capacitance of the fluid and the results are compared with the simple bubble formation correlation.
