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Energy: Building the plasma cage

Provence in southern France is well known to us Brits as a warm, pleasant land. But part of it will soon get hotter - 10 times hotter than the sun in fact. Mark Hansford reports from Cadarache, where engineers are currently pushing more than a few boundaries in building the world’s largest experimental nuclear fusion reactor.

Within seconds of alighting from the minibus at the ITER thermonuclear fusion research site in Cadarache in southern France, you know that something not quite of this world is being developed there.

Your eyes are immediately drawn across the vast 1km long, 500m wide site to the deep pit that is currently being shored up with around 35,000m3 of heavily reinforced concrete.

The immediate impression is that it is a space being prepared for something quite out of the ordinary. And it is: the world’s first commercially-sized nuclear fusion reactor, no less. Known as a tokamac, it is a 24,000t beast that needs some serious caging.

Largest temperature gradient in the universe

“It is the largest temperature gradient in the universe that we are trying to create here,” says Atkins energy director and ITER project director Christophe Junillon. Atkins is part of the Engage consortium that won the €150M (£123M) contract to act as the project’s designer and engineer. Other members of Engage are Spain’s Empresarios Agrupados and France’s Assystem and Iosis.

“The gas in the tokamac will be heated to 150M°C,” he says. On the sun the reaction happens at 15M°C. “Yet 10m away, some cooling elements will be at just 4°C above absolute zero.”

Clearly, this is no ordinary project. It is actually the realisation of a decades-old vision set in motion in November 1985 when then Soviet leader Mikhail Gorbachev proposed to United States president Ronald Reagan that an international project be set up to develop fusion energy “for the benefit of all mankind”.

Nuclear fusion is the real golden goose of the energy industry. It works by setting up an energy producing reaction contained within a magnetic field at very high temperatures (see box).

The amount of energy produced is - in theory - 10 times that needed to create the high temperature fusion conditions. The amount of fuel needed (water and lithium) is also small and no CO2 is produced in the process.

There is no meltdown risk either because the reaction ceases naturally in case of power outage; and the minute amount of nuclear waste produced has a very short half-life.

It must be good: after all, it’s what powers the sun. It is just difficult to recreate on Earth because of the high temperatures needed.

But ITER aims to prove that producing energy from nuclear fusion is possible, and to that end work to create a building tough enough to house the 29m tall, 28m wide tokamac is now in full flow.

At the same time, work to build the raft of ancillary buildings and infrastructure needed to service the reactor is also underway.

These other buildings are projects in themselves, but all eyes are on the tokamac.

“The tokamac building is the guts of it,” says Atkins chief engineer Peter Sedgwick. “Everything else feeds into it.”

Right now Vinci subsidiary GTM Sud is nearing the end of its £16.4M contract to create the 17.85m deep pit in which the tokamac will sit.

Since May 2010, work has involved excavation of around 235,000m3 of limestone, construction of a ground support structure consisting of around 35,000m3 of reinforced concrete, construction of the 1.5m thick, 11,000m2 reinforced concrete base mat, and installation of 493 reinforced concrete plinths topped with anti-seismic elastomeric bearings.

“It is the largest temperature gradient in the universe that we are trying to create here”

Christophe Junillon, Atkins

All this has been done to the exacting standards set down by the Engage consortium, appointed by client Fusion for Energy (F4E) to act as architect engineer for ITER’s buildings and civil infrastructure works.

It is a traditional-style contract which sees Engage carry out all design work, support the client in selecting contractors and then fully represent the client in construction supervision and for the final acceptance of the works.

There is little scope for early contractor involvement here as it is an experimental nuclear facility being built to a compliant design.

As a result, Engage’s workload is immense. It will put in around 1.7M hours of work over eight years of design and construction, with most done from F4E’s English-speaking project offices in Cadarache, 60km north east of Marseilles. And it’s been all action since day one, says Sedgwick.

“We arrived here in April 2010 and by September we had to produce the preliminary design for the tokamac building.

“That’s just five months to build a team, pulling guys from three countries,” he says. “We felt everybody had to be here, so they get to know the project, and get to know the client. It is, after all, a hugely complicated project.

“Getting confinement through concrete is a real skill. A structural crack provides no resistance to a radioactive gas”

Peter Sedgwick, Atkins

“By September we were producing 800 drawings and 200-plus reports with 230 engineers,” says Sedgwick. “And all while we had a contractor digging a hole and wanting a construction design.”

Last year was all about detailed design and Atkins’ big achievement there was persuading the regulator - first up - that the structure could be built without any form of steel containment structure. “Getting confinement through concrete is a real skill,” says Sedgwick. “A structural crack provides no resistance to a radioactive gas.”

Radioactive gas particles are typically 3 microns to 10 microns wide. A 200 micron wide crack, though tiny, is huge compared to the gas particle.

Proving that a concrete structure can be built, and then stand up to any form of use or abuse, with no cracks was a real test. “It’s not codified in France as all nuclear vessels have steel confinement. It’s not standard,” he says.

Approval risk

“So we brought our UK nuclear experience to show how confinement through just concrete would work. There was a huge risk that [the approval process] could have delayed things, and [if ultimately rejected] still ended up with a stainless steel containment structure,” explains Sedgwick.

“We analysed it thoroughly and while we modified the reinforcement in places, we have not changed the concrete mix design,” says Sedgwick.

The key was in positioning the reinforcement to minimise the areas that are in tension.

“We don’t rely on the tensile strength of the concrete at all,” he says.

Incredibly, a standard C32/40 concrete is specified where containment is needed, with even more standard C25/C30 everywhere else.

“It’s only 40 cube concrete. We demonstrated that with good construction we can meet the confinement requirements,” he says.

The resulting cost saving run to tens of millions of pounds, given the size and thickness of the steel containment structure that would have been needed. “It was a good one to win,” says Sedgwick.

His team also managed to find time to value engineer the 493 concrete plinths that the tokamac building will sit on, taking the original concept of 21 different types and standardising them. That significantly sped up GTM’s work, allowing it to place up to six a day.

“It is only 40 cube concrete. We demonstrated that with good construction, we can meet the confinement requirements”

Peter Sedgwick, Atkins

Effort is now focused on construction design, and with that the number of engineers needed has now settled down at around 80. But the workload is not letting up for those that remain.

“We are designing process buildings that are stuffed with equipment that is still only at the preliminary design stage,” says Sedgwick. “There are 2,500 engineers around the world working on this project and everything they do could affect the constructability of it.

“We run the risk of not knowing where we are going to attach all the equipment, or even if it all fits.”

The potential for clashes, of course, is huge. The project uses a 3D Catia model, which is spoken about with reverence in the office.

“It is just essential. You just wouldn’t be able to do this without it,” says Sedgwick. Yet even with that, the number of clashes present even today are enormous.

“A clash report would be a blizzard,” says Sedgwick.

Mechanical and electrical team

A team of 10 mechanical and electrical engineers has been brought in to form a link between the civils designers and the process engineers. Work to eliminate the clashes thrown up by resulting changes will keep them occupied until construction of the tokamac building starts in anger.

“To start with, the process drives everything,” says Junillon. “But once we start pouring concrete, the structure has to drive the process.”

“It is inevitable that we are going to have to do some post construction fixing, but it is good to have it as an aspiration that there will be none,” adds Sedgwick.

All in all, it’s quite a task. “It is one of the biggest architect/engineer contracts in Europe,” notes F4E project leader Laurent Schmeider, who will soon be calling further on Engage’s time to help him pick the contracting consortium which will build the structure that will house the tokamac itself.

Known as TB03 it is the most important civils contract on the project and F4E has set a maximum price of £208M.

Four consortiums - three Spanish-led and one French-led - have been shortlisted and F4E is going to use competitive dialogue to pick the winner, with the award expected in early 2013.

“There are 2,500 engineers around the world working on this project and everything they do could affect its constructability”

Laurent Schmeider, F4E

“We are using competitive dialogue because this is a nuclear operation and is very important to get feedback on what is difficult to build. If we don’t use competitive dialogue European Union procurement rules do not allow us to change the specification should we need to,” explains Schmeider. “Also, we need to be able to consider whetherthe relationship would be right.”

It also comes down to price, and current bids from the shortlisted four are slightly above budget.

“We need to get a compliant offer; the candidates are very close to the maximum price but there is some work to do,” says Schmeider.

“This is a nuclear facility and we are pricing a compliant design that contractors cannot change. To get within the price we need to be able to discuss the allocation of risk.

“But TB03 will be signed in 2012 - or very early 2013 - if I want to stay here,” he notes wryly.

The make-up of the consortiums will be key, he adds.

“TB03 needs firms with strong skills in nuclear.They need to be well aware of the rules of nuclear regulators and it would be an advantage if they had experience of working with the French regulator. The consortiums also tend to have one company with concrete expertise, one with steel expertise, etcetera.”

But that make-up does not stretch to UK contractors. “Personally, I have tried to involve UK companies, but so far I have failed,” says Schmeider.

Which is a shame. If ITER works more than one or two fusion reactors will be built around the world. Spain or France’s finest are about to get quite a head start.

 

Fusion and ITER

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Fusion can only take place within plasma, a hot, electrically charged gas. Creating plasma requires huge amounts of energy, but the fusion reaction can potentially release even more and scientists believe that if the technology can be developed it has the potential to become an extremely efficient method of producing energy.

On the sun, gas below the surface is put under immense pressure forcing temperatures to 15M˚C, the temperature at which gas becomes plasma.

Plasma can be described as a hot electrically-charged gas in which the negatively charged electrons in atoms are completely separated from the positively charged atomic nuclei (or ions).

The challenge for engineers and scientists is to replicate these conditions on earth. This is not easy, because the high pressures below the sun’s surface cannot be matched. So gases have to be heated to the mind-bogglingly high temperature of about 150M˚C, ten times hotter than those encountered on the sun.

The fusion reaction that is easiest to accomplish is the reaction between deuterium, which is extracted from water, and tritium which is made from Lithium. The reaction takes place in the plasma state and when deuterium and tritium nuclei fuse, helium is created and energy bearing neutrons are released.
Energy from the neutrons can then be used to generate electricity.

Scientists have built devices able to produce temperatures more than ten times higher than those in the sun. To reach these temperatures there must first be powerful heating. Thermal loss must be minimised by keeping the hot fuel particles away from the container walls. This is achieved by creating a magnetic “cage” made by strong magnetic fields which contain the hot plasma.

In a tokamak, the plasma is held in a doughnut-shaped vessel. Using special coils, a magnetic field causes the plasma particles to circulate in spirals, without touching the wall of the chamber.

The tokamak is the most highly developed configuration at present. The word is a Russian term for a torus shaped magnetic chamber. In such chambers, megawatts of power have been produced, but only for a few seconds. In Europe, this was achieved in 1991 in the Joint European Torus (JET), the world’s largest fusion device, which currently holds the world record for fusion power.

Thermonuclear fusion research body ITER, which means “the way” in Latin, aims to prove that this reaction can be sustained on a commercial scale.

It is developing a tokamak capable of generating 500MW of fusion power continuously for up to 10 minutes. With a plasma capacity of 840m3 it will be 30 times more powerful than JET, and close to the size of future commercial reactors.

Within the tokamak, some components will have to withstand heat loads comparable to those one would encounter close to the surface of the sun. Other components, less than 10m away, will operate at -269˚C, just 4.15˚C above absolute zero, to cool the powerful electromagnets which control the plasma.

The first plasma is expected to be created in 2020, 13 years after work on site began and almost 35 years after the idea was first mooted at the Geneva Superpower Summit.

Then, it began as a collaboration between the former Soviet Union, the United States, the European Union and Japan under the auspices of the International Atomic Energy Agency (IAEA). Today, its members are China, the European Union, India, Japan, South Korea, the Russian Federation and the US.

The project is being funded through in-kind contributions from the seven members of the consortium, with responsibility for manufacturing and delivering components shared equally.

On this basis, China, India, Japan, Korea, Russian and the US are each contributing approximately 9% of the total project cost. This is currently estimated at around £12bn. As host to ITER - and therefore with more to gain - Europe’s share of the cost and workload represents 45% of the total project cost. That contribution is currently estimated at £5.4bn and is being managed by Fusion for Energy (F4E).

If the ITER project succeeds, learning will move to Japan. In 2020 design of a demonstration project that would actually produce usable energy starts. The dream is alive.

 

 

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