Fuel temperature measurement as an alternative in-core power measuring technique

Fuel temperature measurement is described as an alternative to neutron flux measurement. Thermocouples are incorporated into the fuel rod with minimal disturbance to the lattice. One of the major problems associated with the technique is handling of connector cables along with the fuel element. Fuel temperature measurement has been tested in the Otto Hahn reactor where the first core, FDR-1, was instrumented with 18 sensors in two fuel elements. The second core, FDR-2, had 9 thermocouples installed, of which 3 remained operational at time of reporting. Static measurements were performed at various steady power conditions and output compared to conventional in-core flux detectors. Dynamic fuel temperature measurements also compared favourably with neutron flux measurement. The thermocouple time constant was found to be smaller than that of the fuel pin, giving sufficiently rapid indication of the fuel pin's state. (O.T.)