Design of an instrumented microwave multimode cavity for sintering of nuclear ceramics

Abstract This paper describes the development of an innovative instrumented and automated 2.45GHz multimode microwave cavity for sintering of uranium oxide based nuclear fuels (UO2, (U,Pu)O2, (U,Am)O2 …). The cavity and the sintering cell were designed using Finite Element simulation and the expertise acquired over years on microwave heating. This original setup allows for hybrid and homogeneous heating of nuclear fuels. Reliable in situ monitoring of the samples' shrinkage and temperature is performed with an optical dilatometer and infrared pyrometers calibrated with a specific protocol. A dedicated software including a Proportional-Integral-Derivative (PID) controller was developed to precisely control the sintering cycles like under conventional heating. The setup is also designed for operating in a glovebox under reducing sintering atmosphere. A stable and homogeneous heating with controlled sintering cycles is reached to successfully sinter UO2 crack free pellets to high density. This is a key point of innovation compared to previous studies in the literature on microwave sintering of nuclear ceramics. The pellets' final densities are equivalent to those obtained under conventional sintering, but with a significant decrease in the total duration of the sintering cycle.