Measurement on effective thermal diffusivity and conductivity of pebble bed under vacuum condition in High Temperature Gas-cooled Reactor

A full-radius-scale heat test facility has been developed by the Institute of Nuclear and New Energy Technology (INET) of Tsinghua University in China to measure the effective thermal diffusivity and conductivity of pebble bed in High Temperature Gas-cooled Reactor (HTGR). In present test, a separate-effect transient experiment under vacuum condition is conducted successfully up to 1200 °C. Through inverse method and experimental temperature data, this paper presents the process of determining these thermal parameters and compares the results with previous researches, which reveals that the results are comparable in low-temperature region and valid in high-temperature region. In addition, it also studies the experimental errors and the results' uncertainties in this test. The correct knowledge on effective thermal diffusivity and conductivity of pebble bed inside the reactor core is significant to ensure the valid design and inherent safety, which will give a better balance between safety and economic competitiveness.