The direct measurement of HTR-10 in-core neutron flux

Abstract

The direct measurement of neutron flux in reactor core is of great significance for accurately understanding the physical characteristics of reactors, verifying the correctness of core simulation calculations, and developing and improving physical analysis models. The high-temperature gas-cooled reactor HTGR is a pebble-bed type modular reactor which is developed by the Institute of Nuclear and New Energy Technology (INET) in Tsinghua University. Large number of spherical fuel elements are piled up in the reactor core. During operation, the fuel elements flow downward slowly under the actions of gravity. As a consequence, the in-core neutron flux cannot be measured directly in the reactor core for it is impossible to arrange measurement points in the pebble bed. In a recent study, we took advantage of the neutron activation features of the temperature-measuring graphite pebbles (monitors) which were put into the core during the temperature measurement experiment period, and measured the in-core neutron flux of HTR-10. The cobalt element in the monitors was activated during the reactor’s operation period and was utilized to reflect the level of neutron flux. The experimental data including the peak value and radial distribution of in-core neutron flux was obtained. The results show that the neutron flux in the radial direction presents a distribution law with higher value in center and lower value in periphery, with an overall uniform distribution. In addition, the experimental and theoretical calculation data are compared, and consistent results have been shown. The study of in-core neutron flux measurement provides an important experimental evidence for verifying the physical analysis model of HTGRs, and develops an effective method for direct measurement of neutron flux of pebble bed type reactors.