To create a gradient structure in which the graphite and SiC are less likely to peel off even under neutron irradiation, the material composition was changed in 5 times with additively manufacturing of 10 µm thick per a layer.

JAEA is carrying out R&Ds on practical technologies that will enable the production of various ceramic nuclear fuels for next-generation innovative reactors, such as sodium fast reactors (SFRs) and high-temperature gas-cooled reactors (HTGRs), by applying three-dimensional additive manufacturing (3D printing) technology.

SFRs can annihilate minor actinides (MA), which have high radioactivity over the long term. The 3D printing technology will enable safe production of fuel pellets with MA particles dispersed in mixed oxide (MOX). For HTGR, the technology can fabricate an oxidizing accident resistant fuel (ATF), in which TRISO-coated fuel particles^* are regularly dispersed in graphite matrix as a neutron moderator, the fuel operating temperature is reduced to approach to the reactor core outlet temperature (950 ºC), and the graphite matrix outer surface is coated with silicon carbide (SiC) to provide an excellent oxidation resistance at high temperatures.

We have now succeeded in using a 3D printer to create a functionally-gradient material in which the composition ratio of graphite, whose dimension is changed under neutron irradiation, and SiC, whose dimension is stable, was gradually changed (Fig. 1). The result demonstrated the possibility of this being a new manufacturing method to add the high-temperature oxidation resistance of SiC to a graphite body.

This 3D printing technology has the potential to create innovative nuclear fuels with added new functionality and is expected to be a key common technology for manufacturing high-performance fuels for both innovative reactor types.

 

^* TRISO-coated fuel particle: A granular HTGR fuel with a diameter of about 1 mm, made of a spherical nuclear fuel kernel such as uranium dioxide (UO₂), coated with four thin isotropic ceramic layers acting as a triple-structural container (TRISO stands for Tri-structural Isotropic) and a buffer to retain fission products.

Ueta, S. et al., Experimental Additive Manufacturing of Green Body of SiC/Graphite Functionally Graded Materials by Stereolithography, International Journal of Applied Ceramic Technology, vol.20, issue 1, 2023, p.261–265.

Paper URL: https://doi.org/10.1111/ijac.14190

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