Nuclear fusion comes step closer as reactor design complete

Engineers planning the world’s largest nuclear fusion reactor have completed designs for the system’s most technically challenging component, known as the ‘blanket’.

The team at ITER based in southern France are hoping to build the first experimental nuclear fusion reactor to generate more energy than it consumes, with the aim of creating a power source that doesn’t produce carbon dioxide or large amounts of long-term radioactive waste.

The proposed blanket system that will line the inside of ITER’s doughnut-shaped 500MW tokamak reactor chamber overcomes the major challenge of how to absorb some of the 150 million °C heat that will be generated by the fusion reaction while containing the radiation produced.

ITER’s engineers say the blanket is the last major component to be designed and completion will allow the project to move to the main manufacturing stage, with procurement due to start later this year and eventual assembly of the blanket scheduled to begin in May 2021.

‘The blanket modules have to be designed to withstand electromagnetic loads on top of the already quite heavy thermal loads,’ ITER’s head of internal components, Mario Merola, told The Engineer. ‘This makes the design of the blanket system one of the most challenging of the whole ITER machine.’

The reactor will mirror the process that generates energy in the Sun: two isotopes of hydrogen are heated to extreme temperatures so they become ions (plasma) and then collided and fused together, releasing a fast-travelling neutron that transfers energy as heat.

The blanket is what will capture this energy. It will consist of 440 four-tonne modules covering a total surface of 600m², each comprising a beryllium ‘first wall’ containing a water-cooling system to contain the plasma and absorb the heat, and a water and steel shield block to absorb the neutrons themselves.

Each first wall panel will be made from a number of ‘fingers’ attached to a central backbone through which the pressurised cooling water will flow, passing over an array of cooling fins and reaching temperatures of up to 150°C.

‘[This means] if during the manufacturing something goes wrong, at worst we reject the finger and not the whole part, which would be quite valuable,’ said Merola.

Six additional modules will be located in ports around the middle of the chamber that will test ways of releasing or ‘breeding’ tritium, one of the hydrogen isotopes used in the fusion reactor, by reacting the plasma with lithium.

Test ideas include breeding tritium from lithium held in ceramic material or from a liquid lithium lead compound. Future commercial-scale reactors would likely include tritium breeding on each of the blanket’s modules.

Previous designs for the ITER blanket featured two dedicated components for limiting the plasma but the engineers decided this would not provide enough flexibility and so redesigned the system so the entire blanket would act as a physical boundary to the plasma.

This meant each module had to be shaped to produce a curved surface so if there were any manufacturing misalignment the edges would not protrude with a sharp leading edge into the plasma and risk damage.

This issue also led the engineers to separate the shield block from the first wall so the more vulnerable, plasma-facing element could be replaced if needed without removing the entire module. Each panel is expected to be replaced at least once in ITER’s lifetime.

The first wall panels will need to absorb both the radiative heat on the surface at an intensity of up to 5MW/m² – around 5,000 times more than that felt on a summer’s day outside in the south of France – and the volumetric heat transferred by the neutrons, which carry around 80 per cent of the energy produced by the fusion reaction.

The blanket also needs to cope with electromagnetic loads, forces exerted by magnetic fields interacting with the currents induced when the reactor shuts down abruptly.

Once the first wall has captured the neutrons’ heat, hydrogen and iron atoms contained, respectively, in the shield block’s optimal combination of water and steel will absorb the neutrons themselves.

This article originally appeared on The Engineer.

Space harpoon could tackle satellite debris problem

UK engineers have developed a space harpoon that could help tackle the growing problem of space debris orbiting the Earth.

The team from satellite firm Astrium wanted to create a relatively simple and therefore reliable way to capture some of the larger pieces of junk from among the thousands currently in orbit, which pose a serious risk to functioning satellites.

A craft carrying a pneumatic launcher would fire a harpoon into its target and use a tether to drag it out of orbit and down into the atmosphere where it would burn up, in order to prevent it from colliding with other objects.

It makes sense to target bigger objects, said Jaime Reed, project leader and specialist mission systems engineer at Astrium, because they have a higher chance of causing collisions and any impacts would produce a large increase in the number of smaller fragments.

‘It’s more cost effective to go for the big objects unless you can come up with a way of sweeping up lots of small ones,’ he told The Engineer.

He added that NASA studies suggested that around 10 to 15 large objects of over one tonne in mass needed to be removed from orbit in the next five to 10 years otherwise collisions would cause the number of small fragments to increase exponentially, making the problem much harder to deal with.

The idea of the harpoon came from the mechanism that will be used by the Rosetta space probe that is currently en route to intercept and attach itself to a comet between Earth and Mars.

The point of the spear is under 10cm in length to prevent it from travelling through whatever item it is fired at and piercing a fuel tank or damaging internal mechanisms that could create more debris.

There are around 22,000 trackable objects larger than 10cm in diameter in orbit, 94 per cent of which are debris: disused rocket stages, old satellites and fragments of collisions between these items.

Authorities also estimate there are around 700,000 objects larger than 1cm and 170 million objects larger than 1mm, all of which can cause damage to working satellites and spacecraft.

Numerous ideas for tackling the space debris problem have been put forward in recent years, including robotic arms, nets and sweepers, and scientists are due to meet next week at ESA’s space debris conference in Germany to discuss different options.

But Astrium missions systems engineer Andrew Ratcliffe pointed out that the cost of developing overly complicated solutions could be higher than the cost of doing nothing.

‘The problem with nets is that the gauze could create smaller particles and break bits off,’ he said. ‘One of the big requirements is not creating more debris than you remove.’

The space debris issue has received growing publicity in the last few years and space authorities have introduced guidelines limiting the time that satellites can remain in orbit, forcing manufacturers to devise ways to pull them down after 25 years.

Government satellites and spacecraft are routinely moved out of the path of suspected incoming debris but the space agencies have yet to firmly schedule any cleanup missions to remove existing objects, although ESA has announced intentions for a Space Cleanup initiative to start in 2015.

This article originally appeared on The Engineer.

We can't wait for a magic solution to climate change

Spending money on low-carbon technology today isn’t a waste - it’s what will make future breakthroughs possible.

Judging the true environmental cost of any technology is incredibly difficult. Materials, manufacturing, distribution, lifetime usage ­– all these things add up. So it’s fair to question whether items that claim to be environmentally friendly really make a direct contribution to attempts to cut greenhouse gas emissions.

That’s the latest approach being taken by controversial Danish writer Bjørn Lomborg in an attempt to challenge mainstream thinking on climate change. Lomborg, who has a PhD in political science, has spent much of the last 15 years arguing with climate scientists on the extent to which global temperatures are likely to rise due to greenhouse gas emissions, most notably in his book The Skeptical Environmentalist.

His more recent ideas have focused around our responses to the problem of man-made global warming (which he agrees exists), and he has argued against spending vast sums of money on technologies that are not yet effective or cheap enough to have a substantial impact, most recently taking on the topic of electric vehicles.

Some of his basic points are hard to argue with: current mitigation efforts in the West are costly and ineffective; most future emissions will come from the developing world; wind turbines and solar panels are still too expensive; and electric cars still have too great an impact on the environment.

The Engineer would also, unsurprisingly, be in favour of increasing research into new technologies, as Lomborg suggests. But none of these points add up to a convincing argument that we shouldn’t be buying environmental technology now. The idea that we can or should just wait for scientists to invent better ways of producing clean energy or powering vehicles misunderstands the way technology is developed, rolled out and taken up (and ignores much of the role of engineers).

Technology doesn’t go straight from a lab to our homes, roads or power stations. It must be optimised, scaled up, manufactured and, crucially, paid for. We can’t wait for a university spin-out firm to suddenly start mass-producing the ideal electric vehicle. We need the existing automotive supply chain to bring their considerable expertise to the problem of manufacturing every component in the most efficient and cost-effective way. People must see owning an EV as a practical solution for their needs, which requires both education and a decent charging infrastructure. And none of this will happen unless at least some people start buying electric cars now.

Solar panels have already seen a dramatic fall in price in recent years, not because a scientist suddenly came up with a new design for solar energy collection but because Chinese firms in particular developed better manufacturing methods. And it’s hard to see how or why they would have done it without subsidies to encourage the creation of a market for solar in the first place.

Lomborg is right that renewable energy won’t really become widespread until it is cost competitive with fossil fuels. Yet the hydrocarbon industry has received heavy subsidies for years, which have helped it to become a source of cheap power. So why shouldn’t renewables receive government support if we agree that they need to be part of the solution to cutting emissions?

There’s almost always an argument for making subsidies better targeted and more effective, and it’s easy for governments to make a mess of them, as the recent debacle over UK solar feed-in tariffs shows. But technological breakthroughs on their own are unlikely to be be enough to displace established marketplaces.

There’s another underlying point in all this. Lomborg says it won’t matter if the West spends lots of money on reducing its emissions if developing countries increase theirs. Indeed, if the UK scrapped its carbon cutting efforts all together it would probably make very little direct impact on global temperatures.

However, as the countries who have benefited the most from fossil fuel-powered industrialisation – and the one’s who hold most of the world’s wealth – developed nations have a responsibility to create the solutions to prevent runaway climate change. If we don’t do it, then how can we ask the rest of the world to act on our behalf?

This article originally appeared on The Engineer.