You are hereOur visit to the Culham Centre for Fusion Energy

Our visit to the Culham Centre for Fusion Energy

By Kim - Posted on 01 November 2012

A visit to the Culham Centre for Fusion Energy (CCFE) has been on the ‘hit list’ for a while. When we did get around to inquiring, way back in January, we were told that it was such a popular tour that there was a waiting list. The 12th September was the first slot available. We took it therefore, reserving twenty places. We didn’t think we’d fill twenty places mind you.

In the event, with accretion over the months, there were 18 of us on the list on the day. These were not all members of course, as we made no secret of the fact that anyone was welcome. As some members are also members of Bedford Climate Change Forum (BCCF), they were able to recruit a few attendees from that organisation. Some people on the mailing list came also, and there were some relations, partners and friends too. We invited Watford and Milton Keynes Humanists, and two people from the later group accepted. Of course, some people fell into more than one of these categories.

As agreed we released the unused two places back to CCFE, who said that they would have no trouble getting attendees from their waiting list.

Being conscious of our climate change responsibilities we packed cars as much as possible. I took two guests who met me at work quite early, as we were keen to miss the traffic, which we knew could be bad. Of course, as a result we arrived an hour and a half early because there was no traffic. I guess we achieved our objective therefore. We took refuge in ‘The Wagon and Horses’ in Culham village, a nice traditional pub with half a dozen ales on tap.

Come starting time, we were efficiently booked in and given our passes, although the internal car park was rather casually pointed out, with the result that we overshot and explored the furthest reaches of the site. As CCFE is built on an old airfield you will appreciate that it is quite large.

There were beverages and biscuits in reception, and we had the opportunity to take away brochures, leaflets and DVDs. There were probably 100 visitors present.

So what’s it all about? This was all nicely explained in a presentation at the start of the visit. This was non-technical and aimed at people with a basic grasp of high-school science. Nuclear fusion has for years been tipped as the power source of the future. It is not to be confused with nuclear fission, which all existing nuclear power stations use.

In fission, a heavy, unstable, atom, usually of Uranium, is smashed by bombarding it with neutrons, a neutron being one of the particles that make up the nucleus of an atom. The result is that the atom splits into two lighter atoms, with more neutrons flying off which can be used to smash more uranium atoms, the famous chain reaction. Oh, and there is a lot of energy released too, which is the point of the exercise. The energy is ultimately used to heat water, which is turned to steam and is used in a steam turbine to generate electricity in exactly the same manner as in a fossil fuelled power station.

The advantage of fission is that it is relatively easy to do. The main disadvantage is that lots of radioactive waste results, some of which is dangerous for hundreds of years. The structure of the reactor is also made radioactive by the process. There are subsidiary disadvantages, as a string of high profile accidents has proved.

Fusion on the other hand takes the opposite approach. Two light atoms are forced together, and what results is a stable atom of Helium. Of the two atoms to be forced together, one is abundant in the sea and is not radioactive. The other is radioactive, but it can be made during the fusion process. The waste product of the reaction is not radioactive at all. The structure of the machine is made slightly radioactive by prolonged use, but there is far less waste than with fission. There is no long-lived nuclear waste, as there is with fission.

Energetic neutrons are produced in the reaction. These are absorbed by a lithium blanket around the machine, which heats up and allows water to be boiled. Once again electricity is generated in exactly the same way as with a fission reactor or a fossil fuelled power station, using steam turbines.

So why don’t we use fusion? Well, basically because it is so difficult to do it. The temperatures required are in the order of millions of degrees Celsius, so hot that the fuel becomes a plasma, a fourth state of matter. At these temperatures, the atoms of the fuel have tremendous energy and they would damage anything they came into contact with, namely the fusion reactor itself. These factors make the process technically very difficult. The usual approach is to use powerful electromagnets to suspend the hot fuel in the centre of a ring shaped reaction vessel. The nuclear physics is well understood, but the engineering required for achieving a sustained reaction is not.

Ironically the difficulty of achieving a fusion reaction is the very factor that makes it safe. Unlike a fission reactor, which contains a lot of fuel, a fusion reactor contains very little fuel; typically one hundredth of a gram of fuel is present in the machine at any one time. Further, should anything go wrong, the reaction stops. It is so difficult to get it to start in the first place that it simply cannot run away out of control.

No fusion reactor is currently a net producer of power. All machines worldwide currently consume more power than they produce. One machine at Culham consumes 1% of the UK’s generating capacity when it runs. They are forbidden to operate it at times of peak demand, such as when a popular TV show ends. People then put kettles on, or flush their toilets. All of those toilets need water supplied by electric pumps.
Culham opened as an experimental facility in the early 1960s. Since then a secession of experimental machines have been used to study how a commercial power plant could be constructed. The current two machines at the lab are known as MAST and JET.

After the lecture we were divided into groups of about a dozen people each to tour the site. Our party was divided into two, forming Group 3 and Group 4. The groups set off, each with a tour leader. The groups were carefully choreographed around the site to ensure we saw everything. We stopped along the way for talks with the scientists and engineers who worked on the machines. Occasionally we’d pass other groups visiting the scientists in a different order. The place was a warren of corridors and fire doors.

My group visited MAST first. MAST is a small experimental machine funded entirely by the UK taxpayer. MAST stands for Mega Amp Spherical Tokomak. It is 3 metres in diameter, 5 metres high, and runs at 15 million degrees Celsius. Its purpose is to investigate smaller fusion machines as well as to look at the use of new materials. The choice of materials used inside a fusion reactor is crucial for efficiency and durability and a lot of work is being done on this. A MAST fusion pulse lasts for approximately half a second – after which the machine requires 15 minutes to cool down.

Despite MAST being funded by the UK taxpayer, fusion research is an international collaboration with all findings being shared. This has been a feature of the field since the start. Even at the height of the Cold War Europe and Russia were exchanging knowledge and fusion experts were visiting facilities across borders. Fusion power has no military applications.

The second experimental machine, JET, exemplifies this international collaboration. JET stands for Joint European Torus, and this one is a European project, built with components sourced from across the continent. JET is the largest fusion reactor in the world.

JET achieves a fusion pulse of around 30 seconds, and operates at a temperature of 200 million degrees Celsius. The centre of the Sun, for comparison, is 15 million degrees Celsius. During maximum output trials JET achieved an output equivalent to 70% of the energy put into it. That sounds a bit impractical, but remember this is a research machine, it was never intended to be a power station.

As an aside, JET uses flywheels to store energy from the national grid, and this can quickly be reconverted into electrical power for each experiment. There are two flywheels, each weighing 775 Tonnes and spinning at 225 rpm. One wag has calculated that if one were to escape, at full speed, it would reach Newbury before it stopped.

Luckily for us, JET was undergoing maintenance, and this meant that we could get right up to the machine. Normally, when operating, it sits behind three metre thick concrete walls. Those free neutrons may generate heat but they are also lethal to humans. Of course, with the machine switched off, there were no neurons and no residual radiation.

Jet costs £1 million a week to run. The engineer with us at that time said that people spend more than that on mobile phone ringtones, so it is cheap as these projects go. (I have not bothered to check this claim.)

We were shown the engineering mock-up, which is currently being used to test and improve remote maintenance techniques, to avoid having to send humans into the reactor vessel. We also saw the rather impressive remote handing facility, where 3D computer models were being used to plan how to carry out those remote maintenance operations.

The staff at Culham came over as genuinely enthusiastic and committed to their jobs. They were aware that this was a world-leading establishment and they were proud to work there and to show it off. The JET engineer mentioned previously said that showing people around was one of the best parts of his job; he didn’t actually get paid to do it.

The next stage on the road towards commercial fusion reactors is another international collaboration called ITER, the International Thermonuclear Experimental Reactor. This will be built in France, at Cadarache in Provence. The European Union will put up 45% of the 14 billion Euro cost, the other partners contributing 9% each. The other partners are Russia, China, Japan, South Korea, India and the United States. A lot of the work being done at Culham now is specifically designed to feed in to ITER.

ITER will be the stepping-stone from the experimental machines to a full-scale commercial reactor. Twice the size of JET, it will be the first machine to produce more energy than it consumes, with the aim of producing ten times the input energy eventually. It will come on-stream in 2020.

One of our party was extremely cynical about the potential of fusion power. Even if it works, it would not be possible to construct machines fast enough to cater for the demand. The staff members were appreciative of this viewpoint, and conceded that fusion reactors would initially take their place as a part of the mix of generating stations.

One engineer said that it might not be possible to get it to work. But then again it might be possible. And if we didn’t try it certainly wouldn’t work.

We left later than planned, at 21:45 and it was after 23:00 when we got home. I was in bed after midnight, and with no real dinner. Still, it was worth it.



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