Quantification of C-14 in artificially activated reactor graphite via AMS
Mr Raphael Margreiter1, Dr. Matthias Dewald2, Ms. Martina Gwozdz3, Dr. Stefan Heinze3, Prof. Dr. Alfred Dewald3, Prof. Dr. Klaus Eberhardt4, PD Dr. Erik Strub1
1Division For Nuclear Chemistry, University Of Cologne, Cologne, Germany, 2Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) gGmbH, Cologne, Germany, 3Institute of Nuclear Physics, University of Cologne, Cologne, Germany, 4Institute for Nuclear Chemistry, Johannes Gutenberg University, Mainz, Germany
There are currently 250.000 Mg activated reactor graphite around the globe without a well-defined disposal path . A relevant subgroup of this material is the roughly 1000 Mg reactor graphite in Germany, largely from the prototype reactors AVR (Jülich) and THTR-300 (Hamm-Uentrop). The disposal of this material is as of now still an unresolved challenge. The still ongoing research presented here tries to address some of the difficulties and to open a possible path toward an orderly disposal procedure, mainly by investigating the possible application of the CologneAMS system for precise quantification of C-14 in reactor graphite.
The main challenge of measuring activated graphite samples with AMS are the relatively high C-14 concentrations compared to the routine measurements for carbon dating. In the ongoing project, this is addressed by the development of a dedicated gas system, consisting of a conventional elemental analyzer and a gas dilution system, which is directly coupled to the AMS ion source . To obtain accurate results with this system, it must be extensively tested using samples with elevated C-14 concentration. This work describes the production, the preparation, and the measurement of the corresponding samples.
We chose three materials to obtain defined C-14 concentrations by irradiating with thermal neutrons. Two of the three materials chosen for our studies are graphite blocks originally intended for uses within the AVR prototype reactor itself, namely as reflector material (sample K) and thermic shielding (sample S). The third graphite sample was part of the shielding material for a low-level measuring station in the nuclear chemistry division at the university of cologne (sample G).
Each of the three samples underwent neutron activation at the TRIGA II research reactor in Mainz, Germany, 3 hours, 10 minutes, and 1 minute respectively. This resulted in a variety of samples with C-14/C-12 ratios ranging from 10-13 up to 3*10-10. The samples were also analyzed by means of γ-measurements for the detection of trace amounts of short- and long-lived impurities in the material.
Results and Discussion
First measurements of the samples with the AMS gas system were performed using solid dilutions of the materials. This showed that this technique opens a way to measure samples with elevated C-14 covering at least 4 orders of magnitude. The main challenge is to avoid not only contaminations of the AMS system but also reservoir effects in different part of the gas system, possibly leading to cross-interferences when measuring samples with different C-14 concentrations. In the next step, the irradiated samples will be used to demonstrate the equivalency of the solid dissolution and gas dilution and for the development of a procedure to enable fast routine measurements of irradiated reactor graphite.
 Vulpius, D., et al., Thermal Treatment of neutron-irradiated nuclear Graphite Nuclear Engineering and Design, Bd. 265, S. 294–309 2013
 Gwozdz, M., et al., Characterisation of Reactor Graphite with Ion Beam Techniques, AMS 15 Sydney Contribution
Supported by the German Federal Ministry of Education and Research, funding code: 15S9410B.
Raphael Margreiter is currently a Ph.D. student at the Nuclear Chemistry Division of the University of Cologne, working on questions regarding the decommissioning of nuclear facilities.