Tritium, a radioactive hydrogen isotope, is essential for nuclear fusion and promises infinite clean energy. For more than 30 years, the Tritium Institute in Karlsruhe has been a pioneer in the safe handling and fuel cycle research of tritium.
Proton, deuterium, and tritium are the three isotopes of hydrogen. While proton and deuterium are stable and abundant on Earth, tritium stands out as a beta-ray emitter with a half-life of about 12.3 years.
Tritium is only naturally produced in the upper atmosphere, so its procurement relies heavily on technological means. Tritium is produced in nuclear reactions and is a valuable by-product of nuclear fission reactors. Most importantly, tritium has emerged as an essential element in the pursuit of commercial fusion power. The deuterium-tritium fusion reaction stands out as the most advanced and most feasible route to achieving the goal of unlimited clean energy.
Development of safe and efficient fuel cycles for fusion reactors
In today's rapidly evolving field of nuclear fusion, an astonishing variety of confinement types are being investigated through numerous public and private experimental initiatives. However, the choice between magnetic and inertial confinement does not largely affect the technical requirements and challenges associated with the tritium fuel cycle.
In any case, tritium must be stored and injected into the reaction site, and the exhaust gases, which are a complex mixture of unburned fuel, helium “ash”, other by-products and many secondary impurities, must be efficiently treated. In addition, an external loop must be established in which the tritium produced by the reaction of fusion-generated neutrons with lithium is purified and prepared for reinjection. In a DEMO-like reactor with a thermal power of about 3 GW, several hundred grams of tritium are consumed in the reactor and produced from lithium every day. This process requires the disposal of several kilograms of tritium that circulate continuously through the treatment loop.
© Christian Grupe, Karlsruhe Institute of Technology
More than 30 years of tritium handling and research at the Tritium Institute in Karlsruhe
Due to its radioactive nature, safe and efficient handling of large quantities of tritium poses challenges and requires dedicated technological advances covering all aspects of the tritium cycle, including tritium production, safe storage, accurate detection and efficient processing.
In the early 1990s, the Karlsruhe Institute for Tritium Research (TLK) was founded with the mission to develop a deuterium-tritium fuel cycle for nuclear fusion. Today, TLK holds a license to handle 40g of tritium and currently has a large stock of around 30g. This, plus extensive infrastructure systems and experimental equipment, makes TLK a large-scale research facility unlike any other in the world. Early pioneering R&D efforts at TLK targeted the internal fuel cycle of ITER, resulting in the delivery of an integrated design. What was once simply an experimental system has now evolved into the robust backbone of TLK's closed tritium cycle. These advanced systems enable a large number of advanced experiments with high-purity tritium. The 1,600m² area contains more than 20 dedicated glove boxes, where many experiments are run in parallel and where setup and teardown take place. This is crucial in a fast-developing environment, such as research with and on tritium. TLK is host to the Karlsruhe Tritium Neutrino Experiment (KATRIN), which has attracted worldwide attention due to its recent success in the direct mass measurement of neutrinos, performed since 2018. By June 2024, more than 1,000 days of tritium circulation have been achieved with an unprecedented total throughput of 31 kg tritium (98.5% purity).
In addition to its research on KATRIN and the fusion fuel cycle, TLK also conducts research in the areas of tritium astroparticle physics and fundamental properties of the tritium molecule. Additionally, TLK develops technologies and components to overcome the challenges of handling and processing tritium on an industrial scale. TLK is leading the development and application of tritium analytics integrated into these processes.
Addressing current technical challenges of tritium
To address the challenges of tritium in future reactors, tritium research at TLK is organized around four strategic thrusts:
Tritium properties and material interactions
Instead of studying tritium, hydrogen and deuterium can be used as proxies for its physical and chemical properties. However, due to its complex radiochemistry, the use of tritium is unavoidable. Ultimately, there is no substitute for experimentation with tritium. Tritium data allows scientists and engineers to model and design tritium processes and components up to the system level. Ongoing research into the fundamental properties of tritium includes understanding tritium's viscosity as well as its solubility in materials. Understanding the latter is paramount for any comprehensive concept and design.
© Andrea Fabry, Karlsruhe Institute of Technology Analysis and accounting of tritium and hydrogen
Tritium research and processing requires dedicated analytical methods. TLK is leading the development and field testing of tritium specific technologies (e.g. Raman, IR and beta-induced X-ray spectroscopy systems) for robust applications in accurate process monitoring. In addition, TLK aims to develop comprehensive metrology strategies specifically designed for the high throughput tritium loops of fusion reactors. These are required to ensure reliable tracking and management of tritium inventories as mandated by regulatory agencies. Many ongoing tasks are focused on devising tritium assays and analytical concepts tailored for ITER, the largest current experimental endeavor on the road to fusion power. The nature of TLK's closed tritium loop allows both new and commercially available detectors to be characterized for tritium service under relevant process conditions.
© Andrea Fabry, Karlsruhe Institute of Technology Tritium qualification of the process and scale-up of the system to technical scale
TLK bridges the gap between small-scale experimental studies and plant-scale process systems. It provides public and private research activities with numerous experimental equipment for complete tritium qualification of processes, components and entire systems. Current examples include the development of permeation barrier concepts to reduce tritium migration and the implementation of existing and new isotope separation systems to increase the recycle factor of tritium plants. The main research thrust is to address the pressing problem of tritium extraction from blanket purge gases.
Tritium decontamination, safety and waste management
Finally, TLK is developing end-of-life solutions for tritium-facing components to reduce contaminant waste. We currently have established UV/ozone cleaning methods to remove a wide range of surface contamination, allowing for in-situ decontamination, and are further investigating decontamination through advanced vacuum furnace processing.
To achieve a safe, efficient and economical tritium fuel cycle, these fundamental unsolved problems need to be addressed and a wide range of tritium technologies needs to be developed and established. We need to not only drive technology research forward, but also start building the training and knowledge of the future workforce and current tritium experts. Based in Germany and funded by the Helmholtz Association, TLK is a major player in tritium research in Europe. Our team is not only ready but also enthusiastic about the transition from fundamental research to commercial fusion applications.
This article will also be published in Issue 19 of our quarterly magazine.
