Isotope Enrichment Detection by Laser Ablation - Dual Tunable Diode Laser Absorption Spectrometry

摘要

The global expansion of nuclear power is motivating the development of new safeguardstechnology to mitigate proliferation risks arising from the growing uranium enrichment industry.Current enrichment monitoring instruments are subject to information barriers that provide onlyyeso detection of highly enriched uranium (HEU) production. More accurate accountancymeasurements are restricted to gamma and weight measurements taken in the cylinder storage yard.The in-facility instruments, such as Continuous Enrichment Monitoring system (CEMO) andCascade Header Enrichment Monitor (CHEM), face a host of significant challenges in practicaloperation and are not uniformly used in all facilities under safeguards. Offsite analysis ofenvironmental and cylinder content samples have much higher effectiveness, but this approachrequires onsite sampling, shipping, and time-consuming laboratory analysis and reporting.Moreover, access to the cascade hall for environmental sample collection is limited via the LimitedFrequency Unannounced Access (LFUA) inspection modality for the purpose of protectingsensitive nuclear technology information. Given that large modern centrifuge cascades can quicklyproduce a significant quantity (SQ) of HEU in various misuse scenarios, these limitations inverification raise questions regarding timely detection of facility misuse.The Pacific Northwest National Laboratory (PNNL) is developing an unattended safeguardsinstrument concept, combining continuous aerosol particulate collection with uranium isotopeassay, to provide timely analysis of enrichment levels within low enriched uranium (LEU) facilities.This approach is based on laser vaporization of aerosol particulate samples, followed by wavelengthtuned laser diode spectroscopy, to characterize the uranium isotopic ratio by subtle differences inatomic absorption wavelengths. Environmental sampling media from an integrated aerosol collectoris automatically introduced into a small, reduced pressure chamber, where a focused pulsed laservaporizes a 10 to 20-onm sample diameter. The ejected plasma forms a plume of atomic vapor.Tunable diode lasers are directed through the plume and each isotope is detected by monitoringabsorbance signals on a shot-to-shot basis. The media is translated by a micron resolution scanningsystem to fully characterize the sample surface. Single-shot detection sensitivity approaching thefemtogram range and relative isotope ratio uncertainty better than 10% has been demonstrated withsurrogate materials. In this paper we present measurement results on samples containingbackground materials (e.g., dust, minerals, soils) laced with micron-sized target particles havingisotopic ratios ranging from 1 to 50%.