Study on on-line temperature measurement technology for core of pebble bed high temperature gas-cooled reactor

The core of the pebble bed high temperature gas-cooled reactor HTR is filled with a large number of spherical elements, which flow downward from the top of the core while the reactor is in operation. Because of the mixing ratio of spherical elements and the uncertainty of pebble flow, some (hot spots) possibly appear as a result of fuel pebble aggregation in local parts of the core. At present, the analyzation of this issue is not sufficient precise in theory, therefore on-line temperature measurement is of great significance to the improvement of HTR core thermal analysis model. In this paper, a technical scheme for online measurement of HTR core temperature is presented. The temperature monitors, with built-in metal fuse wires and the same shape as normal graphite pebble, are employed to participate in the circulation of pebbles in core. The core temperature is measured and recorded when the monitors flow through the hot spots. Based on the proposed core temperature measurement technique, the temperature and distribution in HTR-10 core were actually measured effectively and the technique was verified by practical application.