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Non-destructive testing

Making the invisible visible

23 Feb 2026 - Jeremy Mercer

The X-ray inspection underway on sector #1 is part of a wider set of tools used to verify critical welds.

Thomas Antonini of Momentum, a consortium supporting ITER construction, inspects the placement of the lead bags that will shield against X-rays during the inspection of sector #1.

Since 2024, teams at ITER have been repairing the critical “bevel joints” where the vacuum vessel sectors will be joined in the tokamak pit. Once their geometry is restored to nominal by filling the “valleys” or shaving off the “hills,” another task awaits: radiographic testing to ensure the uniformity of the welding and the compliance of the repairs.

“We use X-rays to check right down to the heart of these thick metal shells to make sure that the repair is compliant,” says Miguel Dapena-Febrer, ITER’s Radiation Safety Coordinator who oversees the radiographic testing to ensure it is being done in secure conditions in terms of radio protection. “This is a very important process that requires powerful X-ray generators and it needs to be done in very specific conditions.”  

Radiographic testing on the vacuum vessel sectors is part of the broader non-destructive testing program to verify welding and other mechanical interventions. The radiographic testing program began in 2016 on the cryostat base and today there are multiple radiographic teams doing as many as 60 radiographic tests a week.

Miguel Dapena-Febrer, ITER’s Radiation Safety Coordinator, shows the passive dosimeter (left) and active dosimeter (right) that people involved in radiographic testing wear for safety purposes. The data captured by the passive device can be read afterwards while the active device gives a live reading of the radiation in the environment.

Vacuum vessel sector #1 is the fifth sector to undergo radiographic testing. It is a rigorous process that checks the quality of the welding to depths in the tens of millimetres. More than 20 passes can be made over an area that is being tested to ensure the quality of the welding. Two sets of radiographic tests conducted on accessible areas of sector #1 have confirmed the repairs. With the sector positioned vertically in tooling, the final bevel regions are now accessible for testing.

To prepare for the tests, protective measures against the ionizing radiation are taken. Radiographic testing is done on nights or weekends to limit the number of people in the vicinity, a vast number of lead-filled bags weighing between 17 and 24 kilograms are draped around the sector to form a protective curtain, and the team doing the testing wears dosimeters to ensure they are not exposed to doses above regulatory limits.

Thomas Antonini, the Momentum Construction Manager managing the process, said the positioning of the X-ray generator and the films used to capture the images were an essential part of the process.

“All preparations went smoothly and the testing has started successfully,” says Thomas Antonini. “With lessons learned over time on similar operations, we have been able to secure the process, which is good for our assembly schedule.”

Just behind the vacuum vessel sector, lead bags weighing between 17 and 24 kilograms (yellow) have been placed on the scaffolding to form a shielding curtain against the X-rays.

When radiographic testing on vacuum vessel sectors began, a gammagraph was used and it took about four hours for a film. Now, using an X-ray generator, the process can be completed in one hour. When the welding of the sector modules begins in the tokamak pit, a linear accelerator will be used and the time may be reduced to as little as 10 minutes per film. As a result, radiation protection provisions will have to be strengthened accordingly.

Radiographic testing on vacuum vessel sector #1 is scheduled to be concluded by the first week of March.

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