Development of microwave sensor for measuring moisture in granulation process

Nakayama, Shigeru*; Kawaguchi, Koichi  ; Segawa, Tomoomi ; Yamada, Yoshikazu 

In the nuclear fuel fabrication process, moisture content is very important parameter because of criticality safety control. Considering future commercial nuclear fuel fabrication plant, rapid and durable moisture sensor is required. We have developed an open-ended semi-coaxial microwave sensor to measure moisture involved in a substance. This sensor has no semiconductor tips, so it can be used in strong radiation field. In this paper, we carry out a preliminary experiment for measuring moisture of MOX(UO+PuO) in granulation process, in which water is added as a binder. In our preliminary experiment, to simulate granulated MOX powder, granulated tungsten trioxide powder, which has similar dielectric constant to MOX and has voids to hold water inside, was used. The principle of microwave measurement of moisture is as follows. When the tungsten trioxide contained in a pyrex beaker is placed at the open end of the cavity, the resonant frequency is shifted by a variation in the end of capacitance which results from the difference in the dielectric constant of tungsten trioxide from that of air. Furthermore, the peak value of the resonance curve is attenuated by the absorption of microwave in the tungsten trioxide. Therefore, the moisture content of tungsten trioxide can be estimated by measuring either the frequency shift or attenuation. They are measured using a tracking generator and a spectrum analyzer. In our presentation, we will show the experimental results in detail.