Review of Candidate Techniques for Material Accountancy Measurements in Electrochemical Separations Facilities

Electrochemical reprocessing (also commonly known as pyroprocessing) of used nuclear fuel is an alternative to aqueous reprocessing that confers a number of advantages, including the ability to process more recently discharged fuel, smaller resultant waste volumes, and the lack of isolation of plutonium in the product stream. While electrochemical reprocessing systems have seen a significant research and development effort, nuclear safeguards and the security of these systems remain underdeveloped, particularly given the significant differences in operating environment and process flow sheet compared with established aqueous methods. In this paper we present an overview of the current state of the art for several of the most promising candidate techniques for material accountancy and process monitoring measurements for electrochemical separations facilities for used nuclear fuel, specifically passive radiation signatures (gamma spectroscopy, neutron spectroscopy, alpha spectrometry, calorimetry, and microcalorimetry), active radiation signatures (X-ray interrogation and its derivatives, high-resolution X-ray, k-edge densitometry, and hybrid k-edge densitometry; laser-induced breakdown spectroscopy; active neutron interrogation and neutron coincidence counting; inductively coupled plasma mass spectrometry; and optical measurements such as ultraviolet visible spectroscopy, near-infrared spectroscopy, and Raman spectroscopy), and control and process state variable monitoring (cyclic voltammetry and bulk measurements such as level and density, load cell forces, and off-gas monitors). This assessment includes an evaluation of each measurement’s respective modality (i.e., whether the measurement relates to elemental, isotopic, or other properties), published best estimates of measurement precision, measurement latency, and an overall evaluation of each technique’s level of technical maturity. Additionally, this study assesses the most likely locations within the pyroprocessing flow sheet where measurements may be deployed, the physical information required to properly capture the behavior of such measurements, and potential modeling strategies for such measurements. This latter component thus serves to inform future development of process monitoring models in existing and proposed electrochemical separations simulation models.