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.
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. 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.
We report on the characterization of our newly developed resonant laser–SNMS system dedicated for spatially resolved ultra-trace analysis of radionuclides in environmental samples including first analytical results.
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