The design of test platform for study on abrasion of graphite spheres in the fuel handling system of pebble-bed high temperature gas-cooled reactors

The high temperature gas cooled reactor (HTR) is characterized by a graphite core structure, helium gas coolant and ceramic fuel elements. With inherent safety feature, the HTR is considered to be one of the generation IV nuclear reactors. The pebble bed design has been used for HTR-10 and HTR-PM in China, so that allows a continuous fuel loading and discharging operation. However, the pebble's movement through the fuelling system and the core produces graphite dust. It has been estimated that abrasion due to pebble's circulation contributes the major part of the graphite dust production. In the process of circulation the pebbles are lifted pneumatically from the exit at the bottom of the core to the top and re-inserted into the core. The pebbles make multiple collisions with the stainless steel lifting pipe, thereby causing abrasion of the graphite pebbles. Abrasion due to pebble to steel contact is more severe than pebble to pebble contact and pebble to graphite core wall contact, so that a test platform was designed to investigate the abrasion behavior in the lifting pipes in this study. A stainless steel pipe with a height of c.a. 9 m and inner diameter of 62 mm is used to simulate the lifting pipe; graphite pebble with diameter of 60 mm is lifted pneumatically in the pipe. The control of mean lifting velocity was evaluated and the effect of lifting speed on the abrasion behavior of graphite pebble was investigated. The results obtained in this study will help the understanding of graphite dust generation in HTR-10 and HTR-PM. (author)