Tritium Impact and Transfer in Advanced Nuclear reactorS

Tritium (3H), the radioactive isotope of hydrogen, has an extremely low natural occurrence due to its 12.32 years half-life; it is a low-abundance by-product in normal operations of today nuclear reactors, but future GEN IV fission and fusion reactors are expected to generate and transport significantly higher levels of tritium. Moreover, due to high temperature operation conditions, tritium could permeate through the confinement materials: indeed, as all hydrogen isotopes, it is highly mobile in materials such as metals. As a part of the international effort as Europe transitions to low-carbon energy sources, technological solutions to prevent release into the environment and characterization tool to monitor tritium levels are needed, with key implications on safety and social acceptability. Consequences of accidental exposure, whether through dispersion in the environment and integration to the food chain, or directly to the workers or population, are to be understood to be able to propose suitable strategies, for instance developing permeation barrier to minimize tritium permeation at source.
TITANS (Tritium Impact and Transfer in Advanced Nuclear reactorS) is a transdisciplinary project carried out by 21 partners from material sciences, process engineering, biology, dosimetry, environmental sciences and modelling, within the framework of Horizon Europe Euratom research and innovation programme. TITANS aims at contributing to research and innovation on cross-cutting activities required to improve knowledge on tritium management with a multidisciplinary approach at each step of the tritium life cycle: develop tritium release mitigation strategies, improve waste management and refine knowledge in the field of radiotoxicity, radiobiology and dosimetry. Three scientific work packages address these issues:
- WP1: Proposals for enhancement of barriers against tritium permeation and tritiated waste management
- WP2: Tritium inventory management and modelling
- WP3: Dosimetry, risk assessment and radiation protection following accidental exposure to tritiated dust
Communication and dissemination of the work is of key importance, with a dedicated work-package to spread the knowledge gained to the various scientific communities and train young or new researchers and engineers to the specificities of tritium via webinars or organization of a Tritium School in Hybrid mode.

The work carried out on enhancement of barriers against tritium permeation and tritiated waste management on the second half of the project has tackled several tasks, amongst them:
- The APRIL facility upgrade successfully provided the first direct experimental data on deuterium permeation through Eurofer97 in EU DEMO WCLL relevant conditions;
- T release from contaminated filters in case of a fire event were assessed via the Total Combustion Facility;
- Significant progress was obtained on coatings for liquid-metal environments, with new material tested and their impact for D and T retention and permeation evaluated, highting the promising behavior or SiC coating for Eurofer corrosion barrier.

Related “Tritium inventory management and modelling”, a few highlights of the first half of the project are:
- The capacity of NMR to probe hydrogen isotope incorporation at the molecular scale was confirmed, thereby offering a powerful characterization methodology for sequestration materials.
- The benchmark study between KUTIM, and mHIT EcosimPro was implemented on data from the Superfennec liquid sodium loop at CEA as the fission validation scenario.

On characterizing the impact of exposure to tritium, reference datas from H particle exposure were compared to the tritiated ones study:
- Particles exposure in mussels’ population showed specific bioaccumulation in the digestive gland, with oxidative DNA damage in digestive gland cells for acute and mid-term chronic exposure.
- The T biokinetics by the skin route study displayed minimal tritium permeation for intact skin, confirming the protective role of the stratum corneum. A significant absorption increase is observed for damaged and abraded skin, highlighting a concrete occupational risk in nuclear decommissioning contexts.
Inhalation exposure route was also addressed: both steel and cement particles significantly increased loss of chromosomes and chromosomal breakage in macrophages cells for all concentrations, but no dose-dependent effect was observed. Interestingly, chromosomal damage occurred after exposure to both hydrogenated and tritiated particles.
- A dosimetric assessment software was developed for reproduction with radiation transport codes, integrating the obtained data on internalization of particles by cells and their position with respect to the nucleus.

In addition to permeation barrier, nuclear operators currently rely on trapping systems to minimize release, and most of the tritium is then accumulated as a waste in the form of tritiated water. Developping a tritiated water-processing route to allow the recycling of tritium both minimizes nuclear waste and increases tritium avalaibilty by reusing it, which is highly valuable as it is scarce and potential fuel to nuclear fusion power plants. Another type of nuclear waste is particularly delicate to handle: tritiated metallic dust produced during fusion operation and fusion/fission plant dismantling: adequate conditioning must be conceived to prevent any safety and biological concern during handling and storage.
Decommissioning of nuclear facilities is known to generate fine airborne dust, namely steel and cement aerosols. The presence of tritium in such materials will therefore generate tritiated particles, possibly dispersed in the environment, yet very little studies exist on induced consequences for human/animals/environment contamination.

Periodic Reporting for period 2 - TITANS (Tritium Impact and Transfer in Advanced Nuclear reactorS)

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