Cooling design and verification test for HANARO BNCT filter unit

The filter to shield fast neutron and gamma except thermal neutron is the key component in HANARO BNCT facility. The BNCT filter unit is made of the single crystals of silicon and bismuth in a cylindrical aluminum case. If the filter is cooled to the LN(liquid nitrogen) temperature, it is possible to in crease the thermal neutron by the factor of two. A thin vacuum gap and a liquid nitrogen gap were introduced into the outer region of the crystals to maintain the crystals at the LN temperature. In this paper, the basic design specifications were determined for the vacuum gap and the heat transfer characteristics were evaluated. Cooling tests using a mock-up filter unit were performed to verify the design concepts of the filter. In these tests, the variations of filter temperature, pressure in the vacuum gap and consumption rate of liquid nitrogen were measured. The verification test results will be useful to provide the functional data of BNCT filter unit which will be set up in the HANARO