Advanced Process Monitoring Safeguards Technologies at Pacific Northwest National Laboratory

Abstract

There is a renewed interest worldwide to promote the use of nuclear power and close the nuclear fuel cycle. The long term successful use of nuclear power is critically dependent upon adequate and safe processing and disposition of the spent nuclear fuel. Liquid-liquid extraction is a separation technique commonly employed for the processing of the dissolved spent nuclear fuel. The instrumentation used to monitor these processes must be robust, require little or no maintenance, and be able to withstand harsh environments such as high radiation fields and aggressive chemical matrices. In addition, the ability for continuous on-line monitoring allows for numerous benefits. Researchers from Pacific Northwest National Laboratory (PNNL) are developing three non-destructive assay technologies designed to meet safeguards needs at reprocessing facilities in the future, providing the ability to monitor these activities autonomously, continuously, and in near-real-time (NRT). Raman and spectrophotometric techniques are being evaluated for on-line real-time monitoring of the U(VI)/nitrate ion/nitric acid and Pu(IV)/Np(V)/Nd(III), respectively. Both techniques demonstrated robust performance in the repetitive batch measurements of each analyte in a wide concentration range. Static spectroscopic measurements serve as training sets for the multivariate data analysis to obtain partial least squares predictive models. These models have been validated using on-line centrifugal contactor extraction tests. Another technology being developed is the Multi-Isotope Process (MIP) Monitor, which relies on the collection and NRT multivariate analysis of gamma spectra taken at discrete locations within a recycling facility. Using PCA (principal components analysis) or another multivariate technique, it is possible to automatically compare spectral patterns from the gamma-emitting constituents in process streams for statistically relevant signs of changes in the process chemistry or dissolved fuel characteristics in NRT. The MIP monitor is designed to identify small changes in the gamma ray spectra over time emanating from process streams that may indicate an unplanned change in process conditions. These “off-normal” conditions may be caused by incidental upsets within the system or may indicate something more serious, such as an intentional effort to divert special nuclear material for the system by altering process conditions. Initial simulations and experiments have illustrated the MIP monitor's ability to detect and identify changes in process streams through gamma spectra.