Abstract
The purpose of this report is to describe the system structure and thermal problems related to the design of a proposed cold neutron facility for a high flux reactor. The cryogenic system consisted of a helium refrigerator (60W at 20K), a condenser, and a liquid hydrogen moderator cell of 1l was constructed as a cold neutron facility in the KUR graphite thermal column. This system was tested outside of the reactor building for investigating the operation-characteristics at start-up, normal, transient and shut-down operations under a constant or periodic thermal load. The liquefaction capacity in the condenser was 25.3W at 21K and the ratio of this capacity to the designed value was about 50%. As a result, the facility has to be located in such a position where nuclear heating is smaller than 23W at 21K.
For the purpose of checking the response of the cryogenic system to the change of thermal load, a change of pressure in the reservoir tank was investigated by varying heat load which is supplied from electric heating coils wound around periphery of the moderator cell. From the Bode's diagram obtained by experiments, it was shown that such a cryogenic system has a characteristic of self regulation to the thermal disturbance smaller than 30% of the maximum heat absorption capacity.
