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.
In this work, a robust stand-off alpha detection method using the secondary effects of alpha radiation has been sought. Alpha particles ionise the surrounding atmosphere as they travel. Fluorescence photons produced as a consequence of this can be used to detect the source of the alpha emissions. This paper details experiments carried out to detect this fluorescence, with the focus on photons in the ultraviolet C (UVC) wavelength range (180–280 nm). A detector, UVTron R9533 (Hamamatsu, 325-6, Sunayama-cho, Naka-ku, Hamamatsu City, Shizuoka Pref., 430-8587, Japan), designed to detect the UVC emissions from flames for fire alarm purposes, was tested in various gas atmospheres with a 210Po alpha source to determine if this could provide an avenue for stand-off alpha detection. The results of the experiments show that this detector is capable of detecting alpha-induced air fluorescence in normal indoor lighting conditions, as the interference from daylight and artificial lighting is less influential on this detection system which operates below the UVA and UVB wavelength ranges (280–315 nm and 315–380 nm respectively). Assuming a standard true1r2 drop off in signal, the limit of detection in this configuration can be calculated to be approximately 240 mm, well beyond the range of alpha-particles in air, which indicates that this approach could have potential for stand-off alpha detection. The gas atmospheres tested produced an increase in the detector count, with xenon having the greatest effect with a measured 52% increase in the detector response in comparison to the detector response in an air atmosphere. This type of alpha detection system could be operated at a distance, where it would potentially provide a more cost effective, safer, and faster solution in comparison with traditional alpha detection methods to detect and characterise alpha contamination in nuclear decommissioning and security applications.
The United Kingdom (UK) has a significant legacy of nuclear installations to be decommissioned over the next 100 years and a thorough characterisation is required prior to the development of a detailed decommissioning plan. Alpha radiation detection is notoriously time consuming and difficult to carry out due to the short range of alpha particles in air. Long-range detection of alpha particles is therefore highly desirable and this has been attempted through the detection of secondary effects from alpha radiation, most notably the air-radioluminescence caused by ionisation. This paper evaluates alpha induced air radioluminescence detectors developed to date and looks at their potential to develop a stand-off, alpha radiation detector which can be used in the nuclear decommissioning field in daylight conditions to detect alpha contaminated materials.
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