Project investigates net power from nuclear fusion

In an EPSRC-funded project, researchers based at Queen Mary University will focus on harnessing power from a tokamak design where reacting plasma is confined by powerful magnets.

The International Thermonuclear Experimental Reactor (ITER) consortium is currently building a tokamak in France that it hopes will generate around 10 times the power put into it. However, while ITER will merely dissipate thermal power, its planned successor, DEMO (DEMOnstration Power Plant), is to be the first fusion reactor to generate electrical power, hopefully by 2033.

’I think it’s a reasonable bet that we will have a tokamak that produces net power for a sustained period — the question then is how to best get it away and turn it into electricity,’ said Prof Chris Lawn of Queen Mary who will oversee the project.

A tokamak comprises a hollowed-out, doughnut-shaped reactor vessel (or toroid) that compresses and holds a ribbon of plasma gas using powerful magnets. Therefore, power has to be generated by extracting heat from the blanket of material surrounding the toroid core.

It is possible that DEMO will use some form of pressurised water reactor (PWR) configuration to generate electricity (a method currently used in fission) where water would be simply passed though the blanket to then raise steam in a secondary circuit.

However, Lawn said that other options have not been properly considered yet and PWR in its current guise may not actually be the most efficient.

’You’ve got some very exceptional circumstances in fusion — very high heat fluxes on this blanket and a very high volumetric heat generation rate — which may mean that strategy is very difficult, because you’ve got to prevent nucleate boiling,’ he said, refering to bubble formation at the liquid-solid interface.

The team will consider different approaches that might employ a different medium of extraction, including helium, liquid metal, steam or gas.

’Our project may uncover options, although not entirely novel, whose optimal deployment might not have been considered properly,’ Lawn said.

The team will use a top-down approach, looking at whole designs, as well as more specifically at the technology used for cooling turbine blades, for example.

The project is supported by a CASE award from the Culham Centre for Fusion Energy in Oxfordshire.