Workshop Construction for Largest Components of ITER Fusion Reactor Begins

At the vast construction site of the world's largest experimental fusion reactor ITER in Southern France--which will be one of the largest and most complex machines ever built--another facility will now be built for the on site fabrication of huge components that are too large for transport since they weight up to 1250 tonnes. It was now reported that ground breaking is set for May for a temporary workshop where the four main sections of the cryostat, the outer shell of the complex machinery of the tokamak, will be assembled from 54 smaller segments manufactured by India.

Like the largest superconducting poloidal magnetic field coils, which are also assembled on-site in a large hall, the size and weight of the main cryostat segments makes travel along the already reinforce roads connecting the ITER site to a port impossible. The cryostat base section—1250 tons—is in fact the single largest load of ITER Tokamak assembly; the other three cryostat sections (lower cylinder, upper cylinder and top lid) weigh in the range of 600-800 tons each.

Within the on-site Cryostat Workshop, assembly activities will take place on two huge steel platforms built to support the weight of the components, jigs and fixtures.

"The 30 x 30 metre assembly platforms will also act as transporters," said Bharat Doshi, Leader of the Cryostat Section, in a release. "The Cryostat Workshop will be linked by rail to the Assembly cleaning facility and building. Once completed, the cryostat sections can be moved on their assembly platforms by rails/rollers to the Assembly cleaning facility and from there transported to the Tokamak Pit by main bridge crane."

Planned along the fence on the northeast corner of the ITER platform, the football field-size (50 x 100 m) Cryostat Workshop will be approximately 100 metres from the Assembly Building. It will be equipped with equipment for machining, welding and testing, and a large "goliath" crane capable of travelling the facility's full length. "Assembling the four main sections, each 30 metres in diameter, will require several kilometres of joint welding in total," specifies Bharat.

As a high vacuum component, the cryostat is subject to strict quality requirements. Two types of testing will be carried out in the Workshop: an examination of each weld through non-destructive means (ultrasonics or radiography) and the vacuum leak testing of each joint (helium mass spectrometer leak detection). Dimensions and tolerance control will be achieved using sophisticated alignment and metrology equipment. Approximately 50 people are expected to manage the machining, alignment, welding and testing operations during assembly of the cryostat segments.

"The ITER cryostat will have the privilege of beginning and ending the assembly of the ITER Tokamak," says Bharat. "The base section of the cryostat will be the first large component installed in the Tokamak Pit and the top lid of the cryostat will be the last large component, set into place after the installation of the vacuum vessel, magnets, thermal shielding and central solenoid."

As soon as the Tokamak and Assembly buildings (and their heavy-lift crane) are available, the cryostat base must be ready ... and the lower cryostat cylinder soon after that.

The contract for the design, fabrication and assembly of the cryostat was awarded in August 2012 by the Indian Domestic Agency to Larsen & Toubro Ltd—this contract also includes the set-up of the Cryostat Workshop, workshop assembly activities, and in-pit assembly (integration of cryostat main sections, welding, etc.).