European steel for Test Blanket Modules arrives in Korea

The extreme conditions inside a fusion reactor are not suitable for just any kind of material. Only a selected few are resistant enough to be part of the plasma-facing components, exposed to super-hot temperatures and high-energy neutron irradiation. This is why a lot of research has gone into developing materials fit for future fusion devices.

One of the materials best placed is EUROFER97, from the family of Reduced Activation Ferritic/Martensitic (RAFM) steels. This high-performance alloy was designated as the European reference material for the first wall and blanket of DEMO, the reactor that will follow ITER. However, EUROFER97 will already be trialled in ITER, forming the structure of Europe's Test Blanket Modules (TBM).

Plugged in two equatorial ports of the ITER device, the TBMs will stand out from the rest of the "tiles" in the wall of the vessel. Essentially, ITER will be the test environment for these prototypes that will be used as DEMO's breeding blanket. Thanks to them, experts will learn more about the physics of tritium breeding and extraction, which hold the key for the fuel self-sufficiency of future reactors. In a nutshell, the neutrons released in the fusion reaction will bounce on the lithium inside the blanket producing tritium, the atom that fuses with deuterium.

Four types of TBMs designed by different parties will be studied in ITER. Europe is working on two concepts: a water-cooled lithium (WCLL) led by F4E, and a helium-cooled ceramic pebbles (HCCP), co-developed with Korea.

All TBMs will be boxed in a 0.5 m³ protective metallic frame, with each party trialling a different steel alloy. Europe is championing EUROFER97 as a structural material. "This steel is our best candidate for the TBMs. It was developed by European steelmakers in the early 2000s and tailored for fusion reactors. Researchers have proved that it can withstand the heat fluxes, corrosion and radiation environment, while producing lower radioactive waste than other steels used in the fission nuclear industry," explains Milan Zmitko, F4E's Technical Project Officer for the TBMs fabrication.

In 2015, F4E signed the contract for the production of 27 tonnes of EUROFER97, forged in the form of plates and bars by German contractor Saarschmiede and Austrian sub-contractor Boehler Bleche. The steel has been used for Europe's TBMs fabrication development activities, managed by F4E in collaboration with French partners Framatome and CEA, with the spare material stored in Poland.

Following the signature of the Europe-Korea partnership in 2023, the parties decided to also go with EUROFER97 as a first structure for the joint TBM. F4E is providing 40% of the in-kind contributions for the project, including the procurement of the steel, with Korea putting in 60%.

EUROFER97 steel will form the structure supporting the breeding materials of the TBMs. ©Saarschmiede

This May, a batch of 5,8 tonnes left Poland for the Port of Busan, Korea, where the TBM teams at the Korea Institute of Fusion Energy signed off the shipment some weeks later. It was an encouraging moment for the teams: seeing the first delivery of hardware for the fabrication development activities, more hands-on work can now commence within the collaboration.

"The arrival of the steel plates in Busan is another tangible step giving shape to the joint activities with ITER KOREA. However, using a first-of-a-kind material in the frame of a partnership comes with some challenges, as the EUROFER-97 properties and design rules have still to be developed and integrated in the nuclear code. This will run in parallel with the design and fabrication development activities split between the two teams," stated Joelle Vallory, Deputy Project Leader of the F4E-ITER KOREA team.

The preliminary design phase of the TBM project is expected to run until 2026 including all the fabrication development activities. The preliminary design review will then lead to the last adjustments before the teams give the green light for fabrication.

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