Cryostat lower cylinder now on stage

10 Jul 2017 - R.A.

The Cryostat Workshop, in the northeast corner of the ITER worksite, has become a crowded and busy place. There are now two 30-metre assembly platforms supporting assembly and welding work on the cryostat base and the cryostat lower cylinder.

A steel ring pierced with dozens of openings, some perfectly circular, some rectangular with rounded angles, a few as high and wide as a cathedral door—tier one of the cryostat lower cylinder is in the early stages of assembly in the on-site Cryostat Workshop.

At one end of the 110-metre long building, workers are busy finalizing the welds underneath the first tier of the cryostat base—a perfectly circular plate that is 30 metres in diameter.

At the other, workers are positioning the first elements of cryostat lower cylinder on a specially constructed assembly platform that will support the five-metre-tall elements as they are aligned and welded.

The space between the two work areas is almost fully occupied by large steel elements, as yet unwrapped and waiting to be assembled.

Whereas the massive presence of the base section conveys the exceptional size of the ITER cryostat (30 metres high and 30 metres in diameter once completed), the early stages of lower cylinder assembly reveal its complexity.

The three segments of the lower cylinder that are already positioned on the assembly frame help us to visualize what the completed cryostat will look like: a huge cylindrical steel vessel pierced with dozens of openings. Some are perfectly circular, some are the size of an average window with rounded angles, and a few are as high and wide as a cathedral door.

Workers from MAN Diesel and Turbo, the Larsen & Toubro Ltd. subcontractor responsible for assembly and welding, carefully manoeuvre one of the six 60-tonne lower cylinder segments into position on the assembly frame. The second-tier segments will come later, creating a 10-metre-tall component.

And we're only seeing half of the lower cylinder. Six tier-two segments, also five metres tall, are expected to arrive at ITER in late July from their manufacturing location in India. Once completely assembled, the full lower cylinder section will measure 10.4 metres in height and weigh 375 tonnes.

In the weeks and months to come, work will progress in parallel on the two lower sections of the cryostat.

The bottom plates of the cryostat base (tier one) should be fully welded by the end of this month. At that point, the six curved rim elements of tier two will be installed to be welded to tier one.

On the other side of the shop, the three remaining tier-one segments of the lower cylinder will join the three already on the assembly platform to form a full ring.

Before our eyes in the Cryostat Workshop, one of the most spectacular and strategic components of the ITER machine is taking shape. Once completed, it will be the second largest and by far the most complex vacuum-tight container ever built.

A massive vacuum-tight container

Procured by India, the ITER cryostat is made of four sections: base, lower and upper cylinder and top lid. Weighing 1,250 tonnes, the base section is the single largest load of ITER Tokamak assembly. The cryostat acts as a "thermos" to insulate the ultra-cold environment of the superconducting magnetic system.

Tolerance control in the assembly of the 60-tonne segments is achieved using sophisticated laser alignment and metrology equipment ... and also a standard spirit level.

A crowded place

Cryostat base section at one end, lower cylinder at the other, and storage in between. The 110-metre-long Cryostat Workshop is a crowded and busy place with work progressing in parallel on two main cryostat sections.

Relative to the size of the segment, the 50-millimetre thick stainless steel plate appears rather thin. Under the openings in this photo is a an access door that will be used for inspection and maintenance inside the cryostat before the beginning of nuclear operations.

ITER cryostat engineer Guillaume Vitupier (left) and Eric Scherer, of the German contractor MAN Diesel and Turbo in charge of assembling and welding operations. Manufactured in India by Larsen & Toubro Ltd, the ITER cryostat is part of India's contribution to the project.

The fourth 60-degree segment of lower cylinder tier one is now positioned into the frame; two others remain wrapped in their protective transport cover. On top of the tier one segments, the tier two segments will one day be installed—forming the 10.4-metre-tall lower cylinder.

Crane, slings, spreader beam, and more slings

The lifting system for the lower cylinder consists of a gantry crane onto which a spreader beam is attached by way of powerful slings; another set of slings attach the lower cylinder segments to the beam. The system allows for the very precise positioning of the segments on the assembly frame.

A tall steel ring pierced with dozens of openings—some perfectly circular, some rectangular with rounded angles, a few as high and wide as a cathedral door. This is tier one of the cryostat lower cylinder.