Analytical Sciences, Short talk
AS-027

Technetium-99 - A new tracer for nuclear forensics

M. Hofstetter1,2, D. Buckingham3, K. Iten3, C. Pomaro3, S. Röllin2, P. Steinegger1,4*
1Department of Chemistry and Applied Biosciences, ETH Zürich, 8093 Zürich, Switzerland, 2Spiez Laboratory, Austrasse, 3700 Spiez, Switzerland, 3NBC Defense Battalion 20/3, Swiss Armed Forces, Switzerland , 4Paul Scherrer Institut, 5232 Villigen PSI, Switzerland

Technetium-99 (99Tc) is a radioisotope of mainly anthropogenic origin formed by nuclear fission1. In reprocessed uranium fuel an industrial threshold of 10’000 Bq 99Tc per kg uranium (U) is recommended2. Chemically, the element Tc shows similar properties as the actinides U and plutonium, which allows it to bypass the separation steps during reprocessing, fluorination and enrichment3. This leads to varying 99Tc contamination in U material and allows the differentiation between material of natural origin, as well as mixed and reprocessed material. Our studies cover 32 samples of the most relevant U materials within the U fuel cycle, including natural uranium ore concentrate (Yellow Cake), UO2 powder, different forms of U fuel, and waste samples from enrichment. Our investigations revealed 99Tc concentrations from 0.1080 ± 0.0345 to 1463 ± 239 Bq per kg U and demonstrate that the careful analysis of 99Tc can give valuable insights of the materials origin. More specifically, if the material originates from a natural feed stock (Yellow Cake) or if it has been already irradiated and reprocessed. Therefore, the method is a powerful signature to classify otherwise chemically identical U materials.

Figure 1: Reactor-grade UO2 can be obtained from natural uranium ore concentrate (Yellow Cake) or from uranium that has been previously irradiated and reprocessed. The compounds of Tc show similar chemical and physical properties as the corresponding U compounds, thus its separation from U during reprocessing and enrichment is challenging. This renders it as a valuable forensic tracer for previously irradiated U material.

References:

1K. Yoshihara, Technetium and Rhenium their Chemistry and its Applications, Springer Berlin Heidelberg, Berlin, Heidelberg, 1996, Ch. Technetium in the environment, pp. 17–35.
2Nuclear Fuel Cycle and Materials Section, Management of Reprocessed Uranium (TECDOC-1529), International Atomic Energy Agency, 2007.
3E. B. Munday, Preconceptual design of the gas-phase decontamination demonstration cart (K/TCD-1076), Tech. rep., Oak Ridge K-25 Site, Oak Ridge, Tennessee 37831-7387 (1993).