New horizons in microparticle forensics: Actinide imaging and detection of 238Pu and 242mAm in hot particles.

Micrometer-sized pollutant particles are of highest concern in environmental and life sciences, cosmochemistry, and forensics. From their composition, detailed information on origin and potential risks to human health or environment is obtained. We combine secondary ion mass spectrometry with resonant laser ionization to selectively examine elemental and isotopic composition of individual particles at submicrometer spatial resolution. Avoiding any chemical sample preparation, isobaric interferences are suppressed by five orders of magnitude. In contrast to most mass spectrometric techniques, only negligible mass is consumed, leaving the particle intact for further studies. Identification of actinide elements and their isotopes on a Chernobyl hot particle, including 242mAm at ultratrace levels, proved the performance. Beyond that, the technique is applicable to almost all elements and opens up previously unexplored scientific applications.

Cesium and Strontium Contamination of Nuclear Plant Stainless Steel: Implications for Decommissioning and Waste Minimization.

Stainless steels can become contaminated with radionuclides at nuclear sites. Their disposal as radioactive waste would be costly. If the nature of steel contamination could be understood, effective decontamination strategies could be designed and implemented during nuclear site decommissioning in an effort to release the steels from regulatory control. Here, batch uptake experiments have been used to understand Sr and Cs (fission product radionuclides) uptake onto AISI Type 304 stainless steel under conditions representative of spent nuclear fuel storage (alkaline ponds) and PUREX nuclear fuel reprocessing (HNO3). Solution (ICP-MS) and surface measurements (GD-OES depth profiling, TOF-SIMS, and XPS) and kinetic modeling of Sr and Cs removal from solution were used to characterize their uptake onto the steel and define the chemical composition and structure of the passive layer formed on the steel surfaces. Under passivating conditions (when the steel was exposed to solutions representative of alkaline ponds and 3 and 6 M HNO3), Sr and Cs were maintained at the steel surface by sorption/selective incorporation into the Cr-rich passive film. In 12 M HNO3, corrosion and severe intergranular attack led to Sr diffusion into the passive layer and steel bulk. In HNO3, Sr and Cs accumulation was also commensurate with corrosion product (Fe and Cr) readsorption, and in the 12 M HNO3 system, XPS documented the presence of Sr and Cs chromates.

Analysis of contaminated nuclear plant steel by laser-induced breakdown spectroscopy.

Laser Induced Breakdown Spectroscopy (LIBS) has the potential to allow direct, standoff measurement of contaminants on nuclear plant. Here, LIBS is evaluated as an analytical tool for measurement of Sr and Cs contamination on type 304 stainless steel surfaces. Samples were reacted in model acidic (PUREX reprocessing) and alkaline (spent fuel ponds) Sr and Cs bearing liquors, with LIBS multi-pulse ablation also explored to measure contaminant penetration. The Sr II (407.77nm) and Cs I (894.35nm) emission lines could be separated from the bulk emission spectra, though only Sr could be reliably detected at surface loadings >0.5mgcm-2. Depth profiling showed decay of the Sr signal with time, but importantly, elemental analysis indicated that material expelled from LIBS craters is redistributed and may interfere in later laser shot analyses.