Fuel centerline temperature response of LWR fuel rods on reactor scram.

Using four kinds of fuel rods, i.e. one 8×8 standard type fuel rod, two kinds of high performance fuel rods (with Cu-barrier and with Zr-liner) and one fuel rod filled with He/Xe mixed gas, the fuel centerline ternperatures measurements were conducted at reactor scram of the Japan Materials Testing Reactor (JMTR) by thermocouples instrumented to each fuel rod.From the temperature response of these thermocouples at reactor scram, we estimated the thermal time-constants of the fuel rods and investigated whether the fuel centerline temperature responses of LWR fuel rods with different designs are different.It was concluded that the thermal resistance of the fuel rod with the Zr-liner is higher than that of the fuel rod with the Cu-barrier where the inside surface roughness of the cladding with the Zr-liner is 6.6μm, because the thermal time-constant of the fuel rod with the Zr-liner is greater than that of the fuel rod with the Cu-barrier.