Abstract: Natural circulation characteristics of an integrated natural circulation reactor were investigated theoretically and experimentally.Experiments were carried out on a test loop that had a symmetric two-circuit configuration.The inclination condition was achieved by a marine condition simulation platform.A series of data,such as the total flow rate,branch flow rates,inlet and outlet temperatures of electrical heater and heat exchangers,were obtained.Both experimental and analytical results showed that under inclination condition the total flow rate was reduced,whereas one branch flow rate was increased; meanwhile the temperature difference between hot leg and cold legs was increased.It is revealed that density difference existed between the up plenum and down plenum,which caused an additional driven force perpendicular to the original one and introduces an outer circulation.Under the co-action of inner and outer circulation,one branch circulation was enhanced and the other was depressed.This unbalance between branch circulations can be alleviated by shortening the distance between heat exchangers and enlarging the distance between the heat exchanger and heating section.