Electrochemical Isotope Enrichment for Radionuclide Recycling

The disposal of liquid organic waste containing carbon-14 (¹⁴C) remains to some extent an unresolved problem. Permanent disposal is not possible, and at the same time there continues to be substantial demand for the isotope ¹⁴C in research and industry, resulting in a sharp rise in prices due to the shortage on the global market.

Pilot-scale facility

Building on their experience in the electrochemical treatment of such waste streams, researchers at Fraunhofer IKTS have developed a pilot-scale facility (Fig. 1) that enables recovery of the isotope ¹⁴C from ¹⁴C-enriched gas fractions while simultaneously decontaminating the liquid waste. This process involves the electrochemical conversion of organic compounds into CO₂, whereby ¹⁴C-CO₂ is released and subsequently converted into inorganic salts suitable for permanent disposal. This can drastically reduce disposal costs, which otherwise typically range from 250,000 to 450,000 euros per cubic meter.

Process combination for ¹⁴C enrichment

In order to move closer to this ambitious objective, extensive investigations were first carried out into the kinetics of gas and radioactivity release from various organic compounds. Here, clear maxima in ¹⁴C release were observed over the course of the reaction. During these phases, ¹⁴C is present at particularly high activity levels in the anodic gas (Fig. 2). This effect can be exploited to separately collect ¹⁴C-enriched gas fractions (Fig. 3) deand set them apart from fractions containing only low ¹⁴C levels that nevertheless enter radioactive waste streams. This opens up the possibility of subjecting waste streams with sufficiently high ¹⁴C activity to an electrolysis step (electrochemical total oxidation), followed by further enrichment using the Clusius–Dickel process (thermal diffusion). The facility is able to separate ¹⁴C-rich gas fractions from those with lower ¹⁴C content by means of automated valve control. Additional opportunities for control are offered by process management.

Radionuclide recycling and cost potential

The aim is to use this newly developed process to treat radioactive waste at state collection facilities and at companies in the pharmaceutical industry, crop protection research and nuclear waste management. In addition to enrichment of ¹⁴C with simultaneous decontamination of the liquid waste, the process also enables recycling of ¹⁴C. One kilogram of ¹⁴C currently costs more than 10 million euros, while disposal of one cubic meter of such waste costs approximately 400,000 euros. Further investigations are already focusing on the recovery of other isotopes such as tritium.