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During normal operations, the only deposition on a spent nuclear fuel electrorefiner cathode consists of uranium. A computer model, ERAD, was used to simulate conditions under which the electrorefiner salt was progressively contaminated from spent nuclear fuel processing without operator intervention. The model was adjusted to reflect three scenarios: one in which salt removed with every cathode deposit was returned but the UCl 3 concentration was never adjusted, one in which the salt was not removed and UCl 3 concentration was never adjusted, and one in which the Pu/U ratio in the salt was allowed to reach a value of one before starting the first scenario. Under the base conditions simulated, uranium initially deposits alone but eventually plutonium begins to co-deposit along with uranium. Up to 350 g of plutonium was calculated to deposit along with 8.3–9.5 kg of uranium. While precise tracking of changes in the salt composition may not be possible, the model was able to identify markers for plutonium deposition by tracking changes in electrode potential. This type of marker should ultimately provide inspectors with more options for situations when they have limited access to electrorefiner data. [ABSTRACT FROM AUTHOR]

In this paper, we apply an advanced safeguards approach and associated methods for process monitoring to a hypothetical nuclear material processing system. The assessment regarding the state of the processing facility is conducted at a system-centric level formulated in a hybrid framework. This utilizes architecture for integrating both time- and event-driven data and analysis for decision making. While the time-driven layers of the proposed architecture encompass more traditional process monitoring methods based on time series data and analysis, the event-driven layers encompass operation monitoring methods based on discrete event data and analysis. By integrating process- and operation-related information and methodologies within a unified framework, the task of anomaly detection is greatly improved. This is because decision-making can benefit from not only known time-series relationships among measured signals but also from known event sequence relationships among generated events. This available knowledge at both time series and discrete event layers can then be effectively used to synthesize observation solutions that optimally balance sensor and data processing requirements. The application of the proposed approach is then implemented on an illustrative monitored system based on pyroprocessing and results are discussed. [ABSTRACT FROM AUTHOR]

Several countries have shown interest in developing the electrochemical treatment of used nuclear fuel (UNF), commonly termed pyroprocessing. From a proliferation perspective, an advantage of pyroprocessing is its inability to isolate pure plutonium. However, because plutonium is present in the process, it needs to be effectively safeguarded to protect against diversion of plutonium-containing materials that could be post-processed elsewhere. The most complicated unit to safeguard in the process is the electrorefiner where UNF is chemically separated into several material entities. Molten LiCl–KCl serves as the electrolyte into which actinides (including uranium and plutonium), rare earths, and other active metals from the fuel are partitioned after being oxidized to chloride salts. Various voltammetric methods are being developed to measure the concentration of actinides in the molten salt in near-real-time. However, these methods have mostly been applied to molten salt mixtures containing a single actinide. Unfortunately, the presence of multiple actinides will create interferences in the electrochemical responses which could make traditional analysis of voltammetric data inaccurate for determining individual species concentrations. It is proposed to use multivariate techniques to more accurately predict concentrations of multiple actinides from voltammetric data. Two techniques, principal component analysis and partial least squares, are demonstrated on experimental and simulated data for molten salt mixtures containing uranium and plutonium. These techniques consistently yielded more accurate predictions of uranium and plutonium concentrations than simply using peak height. Possible methods of employing multivariate techniques in safeguarding an electrorefiner are also demonstrated. [ABSTRACT FROM AUTHOR]