Research On Graphite Dust Behavior In 10MW High Temperature Gas-cooled Reactor

The behavior of the graphite dust is the unique feature of the pebble bed High Temperature Gas-cooled Reactors (HTGRs) and might intensively influence the reactor operation and maintenance. A study on the graphite dust behavior was comprehensively done in the project basing on 10MW High Temperature Gas-cooled Test Reactor (HTR-10), which is the first trail in the field. The behavior of the graphite dust covers dust production, coagulation and aggregation, deposition and its radioactive effects on the environment. In order to get the better understanding of the graphite dust behavior of HTR-10, the following research topics were done and the corresponding results were achieved. ⑴The friction properties of the graphite IG-11 used in HTR-10 were experimentally studied by SRV standard friction and wear tester and its dependences on sliding distance, sliding velocity, load, ambient atmosphere, temperature and surface roughness were revealed. Theoretical explanations for the test results were also made. ⑵The effects of temperature, load and ambient atmosphere on the wear properties of graphite IG-11 by SRV standard friction and wear tester were experimentally tested and theoretically explained. The graphite particles size distribution during wear process were acquired through Scanning Electronic Microscope (SEM) imaging and the particle size analyzing by the software. The graphite particle size frequency density distributions were also given. ⑶For the structural arrangement and reactor operation condition of HTR-10, the graphite dust producing rate of HTR-10 was estimated as 2.74 kg/year. The produced graphite dust size distributions were also predicted. ⑷The size frequency density distribution of the graphite dust were acquired through the coagulating calculation of the dust in the helium atmosphere according to the particle kinetics. The result shows that the graphite dust coagulation in HTR-10 is not serious. ⑸The particle depositions were theoretically analyzed in a laminar pipe flow, a turbulent pipe flow and a laminar flow over a vertical plate surface with variable temperature. A method to calculate the deposition ratio was given and verified by the existing test results. Based on these studies, the graphite dust deposition to the hot gas duct of HTR-10 was predicted and the results show that the deposition ratio at HTR-10 hot gas duct has a very small value of 0.00017. ⑹The radioactive species bounded in graphite dust of HTR-10 were analyzed. The radioactive activity of the releasing graphite dust to the environment at the loss-of-coolant accident was also estimated.