Characterization of U(VI)-phases in corroded cement products by micro(µ)-spectroscopic methods

Cementation is an industrial scale conditioning method applied to fix and solidify liquid low and intermediate level radioactive wastes (LLW/ILW) prior to underground disposal in geological formations.To assist prognosis of the long-term safety of cemented waste, alteration of uranium doped cement productswas studied in chloride-rich solutions relevant for final LLW/ILW disposal in rock salt. After long-time exposure of the full-scale LLW/ILW simulates to concentrated NaCl and MgCl2 brines, solid samples were retrieved for chemical and mineralogical analysis with an emphasis on uranium speciation in the corroded cement matrix.Bulk and recent spatially resolved micro(μ) U L3-XAFS measurements point to the occurrence of a diuranate type U(VI) phase forming throughout the corroded cement monoliths. U-enriched hot spots with dimensions up to several tens of μm turn out to be generally X-ray amorphou

Embryonic buoyancy control as a mechanism of ultraviolet radiation avoidance

Pelagic fish have long been presumed to produce buoyant embryos which float and hatch at or near surface waters. Due to their transparency and rapid development, mahi embryos are thought to be especially vulnerable to stressors occurring in surface waters, such as ultraviolet radiation (UVR) and increased temperatures. In the present study, we suggest a possibly critical mechanism of UVR avoidance by pelagic fish embryos. Specifically, we provide evidence that mahi embryos are able to sense UVR and may alter buoyancy as a means of reducing exposure to the most harmful stressors occurring in the upper layers of the water column. Further, once the UVR exposure was terminated, embryos displayed fast recovery of positive buoyancy indicating this response is rapidly dynamic and not pathological. The mechanism behind buoyancy control is not known, but evidence from the current study suggests that ammonia sequestration, as seen in multiple other fish species, is not the primary control mechanism employed by embryonic mahi. Finally, expression of antioxidant and UV repair enzymes were investigated to elucidate possible involvement in observed buoyancy changes and to explore alternative methods of repairing UVR damage. [Display omitted] •Mahi embryos display early onset of negative buoyancy when exposed to UVR.•Recovery of positive buoyancy observed once UVR exposure was terminated.•Rapid upregulation of photolyase suggests efficient UV-repair mechanism in mahi.•Ammonia sequestration/excretion unlikely mechanism of buoyancy control