Development of measurement techniques for density and liquid level of molten salt to assess an inventory in equipment of pyro-processing.

For realizing reprocessing facilities involving pyrochemical processes, account measures of nuclear materials in process equipments are required. The electro-refiner is one of the main process equipment in pyro-processing and stores a large amount of molten salt containing approximately 10wt% of actinide elements. The electro-refiner therefore has the largest inventory of nuclear materials in the process equipment. The electro-refining process is characterized by simultaneous reactions of dissolution of a spent metal fuel on anode and deposition of actinide elements on cathode, which results in fluctuation of the concentrations of nuclear materials in the salt. Hence it is required to determine the concentration of nuclear materials with rapidity and to assay an inventory in electro-refiner. To meet the requirement, we developed a density measurement equipment and a liquid level measurement equipment and evaluated their accuracies by use of simulated materials. For density measurement, the Archimedean method was applied and reveals the accuracy to be ±0.2% against published data. Impedance measurement method was applied for liquid level measurement. Its accuracy was achieved to be ±0.5mm against theoretical value. From these results, it is concluded that a volume of molten salt in an assumed large electro-refiner can be measured with an error of ±0.6%. For measuring concentration of actinides, electro-chemical method was tested the applicability for measuring the concentration in molten salt by use neodymium. It was confirmed that the concentration and measured electric current were in the proportional correlation, which indicates that it is possible to apply the electro-chemical method for in-situ measurement of the elements in the salt.