Applicability of the Electrochemical Oxygen Sensor for In-Situ Evaluation of MgO Solubility in the MgF2–LiF Molten Salt Electrolysis System

The measurement and evaluation of MgO solubility in the molten fluoride system is of significant importance in the recently proposed magnesium electrolysis reduction process. In the present study, an in-situ quantitative method of evaluating the concentration of dissolved MgO in molten fluoride is proposed. The MgO solubility in the 32.8MgF2–67.2LiF system was measured at 1083 and 1123 K using a combustion analyzer. MgO saturation was achieved in under 2 h, and higher solubilities were observed as the temperature increased. Thermodynamic assessment was carried out in order to ascertain the applicability of the electrochemical oxygen sensor, which indicated that the logarithm of oxygen concentration in molten fluoride has a linear relationship with the measured electromotive force (EMF) potential. The EMF potential of the controlled MgO concentration was measured, and a straight calibration line was obtained, describing the relationship between the measured EMF and the logarithm of MgO concentration. From the obtained calibration line, MgO concentration in the 0.4 wt% MgO was calculated. The calculated value was 0.44 wt% that was in excellent accordance with the controlled MgO concentration of 0.4 wt%, verifying the practical applicability of electrochemical oxygen for the in-situ monitoring and evaluation of MgO solubility in the electrolysis magnesium reduction process.

Temperature Profile Measurement in Simulated Fuel Assembly Structure with Wire-Mesh Technology

When light water reactor (LWR) is subject to a cold shutdown, it needs to be cooled with pure water or seawater to prevent the core melting. To precisely evaluate the cooling characteristics in the fuel assembly, a measurement method capable of installing to the fuel assembly structure and determining the temperature distribution with high temporal resolution, high spatial resolution, and in multidimension is required. Furthermore, it is more practical if applicable to a pressure range up to the rated pressure 16 MPa of a pressurized water reactor (PWR). In this study, we applied the principle of the wire-mesh sensor technology used in the void fraction measurement to the temperature measurement and developed a simulated fuel assembly (bundle) test loop with installing the temperature profile sensors. To investigate the measurement performance in the bundle test section, it was confirmed that a predetermined temperature calibration line with respect to time-average impedance was calculated and became a function of temperature. To evaluate the followability of measurement in a transient temperature change process, we fabricated a 16 × 16 wire-mesh sensor device and measured the hot-water jet-mixing process into the cold-water pool in real time and calculated the temperature profile from the temperature calibration line obtained in advance from each measurement point. In addition, the sensors applied to three-dimensional temperature distribution measurement of a complex flow field in the bundle structure. The axial and cross-sectional profiles of temperature were quantified in the forced flow field with nonboiling when the 5×5 bundle was heated by energization.

Using Capacitance Sensors for the Continuous Measurement of the Water Content in the Litter Layer of Forest Soil

Little is known about the wetting and drying processes of the litter layer (Llayer), likely because of technical difficulties inherent in nondestructive water content (WC) monitoring. We developed a method for continuously measuring the WC of leaf litter (the “LWC method”)in situusing capacitance sensors. To test variants of this approach, five (for the LWC_5) or ten (for the LWC_10 method)Quercus serrataleaves were attached around capacitance sensors. The output voltage used for each LWC method was linearly correlated with the gravimetric WC (LWC_5:R2=0.940; LWC_10:R2=0.942), producing different slopes for each calibration line. Forin situcontinuous measurements of WC in theLlayer, two sensors were used, one placed on top of theLlayer and the other at the boundary between theLand mineral layers. The average continuous WC of theLlayer was then calculated from the output voltage of the two sensors and the calibration function, and this value was linearly correlated with the gravimetric WC(R2=0.697). However, because theLlayer characteristics (e.g., thickness, water-holding capacity, and species composition) may differ among study sites, appropriate approaches for measuring this layer’s moisture properties may be needed.