In two opposite sectors, cold neutrons are extracted to the experiments by neutron guides from a cold moderator of about 20 liters of liquid deuterium, at the very low temperature of 25 Kelvin. This "cold neutron source" is situated in a horizontal insert inside the moderator tank and near the target, where the thermal neutron flux has its maximum.
The heat generated by the irradiation of the cold moderator is removed by a thermosyphon cooling loop into a vertical insert, which contains at its top a heat exchanger. The heat exchanger liquefies and cools the rising two phase deuterium flow, which then flows back down to the cold moderator tank by gravity. On its secondary side, the heat exchanger is cooled by low temperature helium from a helium refrigerator. The helium is cooled by expansion in helium turbines.
The vertical and horizontal inserts of the cold neutron source are enclosed in vacuum for thermal insulation and in a protective gas enclosure for prevention of potentially explosive hydrogen-oxygen mixtures in case of a leak in the system. When the cold moderator is not operated and returns to ambient temperature, the liquid deuterium evaporates and its expanded volume is transfered into a storage tank or into a small volume, metal hydrid storage material.
