Nuclear environmental forensics using radiocesium isotopes

• Applicant: Professor Dr. Georg Steinhauser
• Subject Area: Analytical Chemistry
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 419819104

Nuclear forensics is the interdisciplinary science of the determination of the provenance, age or legal background of nuclear/radioactive materials. In the present proposal, this approach shall be expanded to environmental research questions. Whenever an environmental sample is contaminated with radionuclides (in particular radiocesium) from more than one source, it has been very difficult to establish the sources of each contamination and to determine the provenance of the contaminations. This challenge is exemplified by the Fukushima nuclear accident that caused releases of radioactive substances from 3 or 4 reactors, i.e. up to 4 different sources. Presently, it has proven to be very difficult to tell which source(s) contaminated an environmental sample with radiocesium, because typical radioanalytical methods as well as mass spectrometric methods (after acidic digestion) only reveal the integral contamination contained in the entire environmental sample. The sample hence may no longer exhibited a distinct signature (isotopic fingerprint) of one source if it has been contaminated by more than one source. Herein we propose nuclear forensics for the releases from Fukushima on a µm-scale to solve this long-existing problem. A significant amount of the radioactive releases occurred in the form of glassy, amorphous microspheres that may represent an archive of fission products from the molten nuclear fuel. These granules are chemically inert and virtually insoluble in water and are assumed to preserve their content for a long time. We propose the use of laser ablation triple-quadrupole inductively-coupled plasma mass spectrometry (LA-ICP-QQQ) to identify the isotopic radiocesium composition of single microspheres and reveal the provenance of each particle via the highly specific 135Cs/137Cs isotopic fingerprint that is clearly distinct for each of the sources. It is assumed that the microspheres have been "loaded" with their content inside the reactors and hence exhibit only minute concentrations of ubiquitous, interfering barium isotopes (135Ba and 137Ba, respectively) from the environment. ICP-QQQ is capable of suppressing this interference instrumentally via reaction gases. This method makes one of the most challenging radionuclide in environmental analysis finally measurable. An inter-method comparison between ICP-QQQ and instrumental neutron activation analysis is planned.In this project, an analytical protocol based on current questions around the Fukushima nuclear accident shall be developed, which shall then be available for environmental forensic research questions in Germany. This includes research related to the search for a nuclear waste repository, accident preparedness, or the decommissioning of nuclear facilities (identification of the source of a contamination).

• DFG Programme: Research Grants