Thermal hydraulic tests for developing two-phase thermo-siphon loop of CARR-CNS

The China Institute of Atomic Energy (CIAE) is now constructing the China Advanced Research Reactor (CARR: 60 MW), and designing the cold neutron source (CNS) with a two-phase hydrogen thermo-siphon loop consisting of a condenser, a single-moderator transfer tube and a cylindrical annulus moderator cell. The mockup tests reported here were carried out on a full-scale loop using Freon-113 as the working fluid in order to validate the self-regulating characteristics of the loop, with a void fraction less than 20% in the liquid of the moderator cell and requirements for establishing the condition under which the inner shell of the cell has only vapor and the outer shell liquid. During these mockup tests, the density ratio of liquid to vapor and the vapor volumetric evaporation rate due to heat load were kept the same as those in normal operation of the CARR-CNS. The results show that the loop has the required self-regulating characteristics and the inner shell of the moderator cell contains only vapor, the outer shell liquid. The local void fractions in the liquid increase with an increase in loop pressure under the condition of a constant vapor volumetric evaporation rate