Study of high-energy radiation-induced processes in advanced tritium breeding ceramics

Current state of research:

In the International Thermonuclear Experimental Reactor (ITER), which is under construction in Cadarache (France), several concepts of Test Blanket Modules (TBMs) will be tested to develop a closed tritium breeding cycle for future burning plasma machines, such as DEMO (Demonstration fusion power plant). Presently lithium orthosilicate (Li₄SiO₄) and lithium metatitanate (Li₂TiO₃) in the form of ceramic pebbles are the most promising candidates for tritium breeding in the EU’s solid breeder TBM concept. Li₄SiO₄ has a higher lithium density and a slightly better tritium release behaviour at lower temperatures, while Li₂TiO₃ has superior mechanical properties.

Advanced Li₄SiO₄ pebbles with additions of Li₂TiO₃ as a secondary phase are under development as an alternative candidate for the tritium breeding in nuclear fusion reactors in order to combine the advantages of both phases within one single tritium breeding ceramic. However, to develop and evaluate a new two-phase composition for the tritium breeding ceramic, it is crucial to understand high-energy radiation-induced processes in the Li₄SiO₄ pebbles with various contents of Li₂TiO₃. The formed radiation-induced defects and radiolysis products in the Li₄SiO₄ pebbles can induce changes of thermal and mechanical properties, swelling and degradation of mechanical integrity, and can also affect the diffusion and release processes of generated tritium.

Aims of the project:

(1) Investigate and describe the formation, accumulation and annihilation of radiation-induced defects and radiolysis products in the Li₄SiO₄ pebbles with various contents of Li₂TiO₃ under the simultaneous action of 5 MeV accelerated electrons and high temperature. The irradiation experiments with neutrons are expensive and require careful planning and preparation due to the formation of radioactive isotopes and restrictions imposed by law. Therefore, the flux of 5 MeV accelerated electron beam will be used in this project instead of neutrons to introduce radiation-induced defects and radiolysis products by ionising radiation in the Li₄SiO₄ pebbles, while avoiding nuclear reactions and thereby the formation of radioactive isotopes.

(2) Ensure long-term cooperation, sharing of knowledge and strengthening of the partnership between the UL, ICP (Latvia) and the KIT, IAM (Germany).

(3) Further training of the bachelor and PhD students taking part in the project.

1. KIT, IAM (Germany), February-March 2019:

The fabrication and thermal treatment of the Li₄SiO₄ pebbles with various contents of Li₂TiO₃. Systematic study of unirradiated pebbles including:

(1) microstructure of surface and cross-section by scanning electron microscopy (SEM);

(2) chemical composition by inductively coupled plasma – optical emission spectrometry (ICP-OES);

(3) phase composition by powder X-ray diffractometry (p-XRD);

(4) open porosity by mercury porosimetry and closed porosity by helium pycnometry.

2. UL, ICP (Latvia), April-May 2019:

The irradiation of the Li₄SiO₄ pebbles with various contents of Li₂TiO₃ under the simultaneous action of 5 MeV accelerated electrons and high temperature. Systematic study of the unirradiated and irradiated pebbles including:

(1) accumulated paramagnetic radiation-induced defects and radiolysis products by electron spin resonance (ESR) spectrometry (in cooperation with the Latvian Institute of Organic Synthesis);

(2) accumulated optically active radiation-induced defects and radiolysis products (also known as colour centres) by absorption spectrometry (in cooperation with the Institute of Solid State Physics, University of Latvia);

(3) recombination processes of the accumulated radiation-induced defects and radiolysis products by thermally stimulated luminescence (TSL) technique;

(4) phase composition changes by attenuated total reflection Fourier transformation infrared (ATR-FTIR) spectrometry;

(5) phase composition changes by Raman spectrometry (in cooperation with the Daugavpils University).

3. KIT, IAM (Germany), end of May 2019 (possible date of mid-term meeting: 27.05.2019):

Mid-term meeting to discuss project development and research stay to perform analyses of the irradiated Li₄SiO₄ pebbles with various contents of Li₂TiO₃ including:

(1) microstructure of the surface and cross-section changes by SEM;

(2) phase composition changes by p-XRD;

(3) open porosity by mercury porosimetry and closed porosity by helium pycnometry.

4. UL, ICP (Latvia), June-September 2019:

Processing of the obtained results and preparation of the manuscript for the publication in an international peer reviewed scientific journal (e.g. Fusion Engineering and Design or Journal of Nuclear Materials).

5. KIT (Germany), beginning of September 2019:

(possible dates of summer school: 01.09.2019-14.09.2019):

Further education of at least one PhD student in the Karlsruhe International School on Fusion Technologies 2019.

6. UL, ICP (Latvia), end of October 2019 (possible date of closing meeting: 30.10.2019):

Closing meeting to discuss the obtained results of the project and further research and collaboration opportunities.

Direct: The direct target group of this project will make all necessary experiments and measurements to achieve the set aims of this project. In addition, the direct target group will present the obtained results in the local and international scientific conferences. The obtained results of this project will be published in an international peer reviewed scientific journal (e.g. Fusion Engineering and Design or Journal of Nuclear Materials). In this project, it is planned to prepare at least one publication and participate in at least three scientific conferences. The direct target group will consist of 10 persons.

Indirect: The indirect target group of this project will be those who will receive information about the obtained results of this project. The international scientific nuclear fusion research community is measurable in thousands. The results of this project are useful and necessary for the organization “Fusion for Energy (F4E)”, the EUROfusion consortium and for all partners of the ITER organization, who are working on the development of tritium breeding ceramics for future nuclear fusion reactors (EU, Japan, China, South Korea and India).

Mid-term meeting at the KIT, IAM (Germany).

Possible date: 27.05.2019

Participants: at least 5 persons

Dr. chem. Artūrs Zariņš, BSc. phys. Jānis Čipa, Dr. rer. nat. Regina Knitter, Dr. rer. nat. Julia Heuser, MEng. chem. Oliver Leys and other colleagues from the KIT, IAM.

Closing meeting at the UL, ICP (Latvia).

Possible date: 30.10.2019

Participants: at least 10 persons

Dr. chem. Artūrs Zariņš, BSc. phys. Jānis Čipa, Dr. chem. Gunta Kizane, Dr. chem. Larisa Baumane, MSc. chem. Mihails Halitovs, MSc. chem. Liga Avotina, MSc. chem. Andris Leščinskis, Dr. rer. nat. Regina Knitter, Dr. rer. nat. Julia Heuser, MEng. chem. Oliver Leys and other colleagues from the UL, ICP.

Public events in the frames of the project will be open to all interested persons.