Safeguards Verification Measurements Using Laser Ablation, Absorbance Ratio Spectrometry in Gaseous Centrifuge Enrichment Plants

Laser Ablation, Absorbance Ratio Spectrometry (LAARS) is a newverification measurement technology under development at theU.S. Department of Energy’s (DOE) Pacific Northwest NationalLaboratory (PNNL). LAARS uses three lasers to ablate and thenmeasure the relative isotopic abundance of uranium compounds.An ablation laser is tightly focused on uranium-bearing solids,producing a small plasma plume containing uranium atoms. Twocollinear wavelength-tuned spectrometry lasers transit throughthe plume and the absorbance of U-235 and U-238 isotopes aremeasured to determine U-235 enrichment. The measurementhas high relative precision and detection limits approaching thefemtogram range for uranium. It is independent of chemicalform and degree of dilution with nuisance dust and other materials.High speed sample scanning and pinpoint characterization allowmeasurement rates approaching one million particles/hour todetect and analyze the enrichment of trace uranium in samples.The spectrometer is assembled using commercially available componentsand features a compact and low-power design. Futuredesigns can be engineered for reliable, autonomous deploymentwithin an industrial plant environment.Two specific applications of the spectrometer are underdevelopment: 1) automated unattended aerosol samplingand analysis and 2) on-site small sample destructive assaymeasurement. The two applications propose game-changingtechnological advances in gaseous centrifuge enrichment plant(GCEP) safeguards verification. The aerosol measurementinstrument, LAARS-environmental sampling (ES), collectsaerosol particles from the plant environment in a purpose-builtrotating drum impactor and then uses LAARS-ES to quicklyscan the surface of the impactor to measure the enrichmentsof the captured particles. The current approach to plant misusedetection involves swipe sampling and offsite analysis. Thoughthis offsite analysis approach is very robust, it generally requiresseveral months to obtain results from a given sample collection.The destructive assay instrument, LAARS-destructive assay (DA),uses a simple purpose-built fixture with a sampling planchet tocollect adsorbed UF6 gas from a cylinder valve or from a processline tap or pigtail. A portable LAARS-DA instrument scans themicrogram quantity of uranium collected on the planchet andthe assay of the uranium is measured to ~0.16 percent relativeprecision. Currently, destructive assay samples for bias defectmeasurements are collected in small sample cylinders for offsitemass spectrometry measurement.