Year
2009
Abstract
The global expansion of nuclear power is motivating the development of new safeguards technology to mitigate proliferation risks arising from the growing uranium enrichment industry. Current enrichment monitoring instruments are subject to information barriers that provide only yes/no detection of highly enriched uranium (HEU) production. More accurate accountancy measurements are restricted to gamma and weight measurements taken in the cylinder storage yard. The in-facility instruments, such as Continuous Enrichment Monitoring system (CEMO) and Cascade Header Enrichment Monitor (CHEM), face a host of significant challenges in practical operation and are not uniformly used in all facilities under safeguards. Offsite analysis of environmental and cylinder content samples have much higher effectiveness, but this approach requires onsite sampling, shipping, and time-consuming laboratory analysis and reporting. Moreover, access to the cascade hall for environmental sample collection is limited via the Limited Frequency Unannounced Access (LFUA) inspection modality for the purpose of protecting sensitive nuclear technology information. Given that large modern centrifuge cascades can quickly produce a significant quantity (SQ) of HEU in various misuse scenarios, these limitations in verification raise questions regarding timely detection of facility misuse. The Pacific Northwest National Laboratory (PNNL) is developing an unattended safeguards instrument concept, combining continuous aerosol particulate collection with uranium isotope assay, 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 wavelength tuned laser diode spectroscopy, to characterize the uranium isotopic ratio by subtle differences in atomic absorption wavelengths. Environmental sampling media from an integrated aerosol collector is automatically introduced into a small, reduced pressure chamber, where a focused pulsed laser vaporizes a 10 to 20-m 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 monitoring absorbance signals on a shot-to-shot basis. The media is translated by a micron resolution scanning system to fully characterize the sample surface. Single-shot detection sensitivity approaching the femtogram range and relative isotope ratio uncertainty better than 10% has been demonstrated with surrogate materials. In this paper we present measurement results on samples containing background materials (e.g., dust, minerals, soils) laced with micron-sized target particles having isotopic ratios ranging from 1 to 50%.