Victoria University of Wellington's Dr Joseph V Minervini and Dr Nick Long take a close look at nuclear fusion and what it might have to do with New Zealand 

Production of power by nuclear fusion has been an alluring dream since the process was first investigated in the 1950s. It often appears as the prevalent power source in science fiction and futuristic novels and movies. But is it truly clean and limitless? Why is it taking so long to commercialise? And does New Zealand have any role to play in this technology?

Fusion is the process creating energy in the sun and the stars. In nuclear fusion, two light nuclei combine while releasing enormous amounts of energy. It is the opposite to the widely understood process of nuclear fission, where an unstable heavy nucleus is broken apart to release energy. The most common fusion reaction being pursued in experimental devices uses deuterium and tritium, which are isotopes of hydrogen, the most abundant element in the universe.

Deuterium, also called heavy hydrogen, is naturally abundant in the ocean. Tritium, unfortunately, is only present naturally in trace amounts. However, the fusion process itself can generate its own tritium fuel by a reaction with lithium, which is abundant on earth.

In the fusion reaction, the hydrogen isotopes are heated to about 100 million °C. At this temperature, they are stripped of their electrons and form a gas of positively charged particles called a plasma. The charged particles of the plasma can be controlled using magnetic fields. By shaping the magnetic fields appropriately, we can confine their motion and contain them in, essentially, a magnetic bottle. So far, the most successful bottle shape is that of a torus, leading to a design known as the tokamak.

When the plasma is heated in the tokamak by radiofrequency waves, the deuterium and tritium fuse to form a helium atom and an energetic neutron. It is the neutron’s energy we are after. The neutron and its energy are absorbed in a ‘blanket’, comprised mostly of lithium. In this process, heat is released and tritium is created along with helium. Ultimately, this heat will convert water to steam and run a turbine generator to produce electricity as in a usual power plant. The tritium that is generated is captured and separated from the helium and recycled to fuel the plasma again.

From a safety and environmental standpoint, fusion avoids all major problems associated with fission reactors. There are no long-lasting radioactive waste products to be stored for centuries. Nor can the process be diverted to weapons production and dangerous nuclear proliferation. At the end of the useful life of the machine, there will be lightly radioactive components that can be safely stored and will eventually decay to a harmless state. Also, there is no comparable release of radioactive material if the plasma chamber is breached. The fusion reaction is difficult to start and maintain and will cease instantly should a major disturbance or breach occur. There is no ‘chain reaction’ that can run out of control.

The fusion process is therefore arguably the most clean and limitless form of energy we have. So what are we waiting for? One reason fusion has been taking so long to develop is the complexity of the large magnets needed to create and maintain the strong magnetic fields around the plasma. Such magnets cannot be made using copper coils but use special conductors called superconductors operating only a few degrees above absolute zero. Until recently, the superconductors available limited the magnitude of magnetic field in such a way that a tokamak had to be huge (think of fitting snugly in the Beehive) to generate net power.

Over the past few decades, a new type of superconducting wire has been developed that can operate at much higher fields. Fusion power density increases rapidly with magnetic field. So, for example, doubling the magnetic field at the plasma can increase fusion power by a factor of 10 or more. It is this property which has inspired fusion researchers to develop ‘compact fusion’. Now a tokamak can be the size of an office in the Beehive.

Small is good. Not only to get more power from a compact device, but the smaller scale leads to faster construction and lower cost. Until now, fusion has been funded mostly by government agencies. But today there are two privately funded companies that will use the new superconductors to put fusion power on the grid. Commonwealth Fusion Systems is partnering with the Massachusetts Institute of Technology in the United States to design and build a 100 MW test reactor. The goal is to build a fusion device using the D-T fuel to generate net power within 10 years. Tokamak Energy in Abingdon, England, will develop a similar small-scale device, but use slightly different plasma physics to achieve the same goal.

Given New Zealand has ample renewable resources in hydro, wind and geothermal energy, it is reasonable to ask whether fusion energy will ever play a role here. If New Zealand is to decarbonise its transport and industrial energy needs, it will need a lot more electricity generation. The hydro resources are close to their economic and environmental limits and have the disadvantage that hydro power is most available in summer (from the snow melt) while energy demand peaks in winter. Wind is intermittent and also suffers from seasonal variation. Geothermal is perhaps the best base load source but there is the inconvenient fact that it is not entirely carbon neutral, releasing greenhouse gases from the geothermal fluids. Fusion has none of these limitations.

A fusion future should not be ruled out for New Zealand. With a deep expertise in the superconductors used in compact fusion, New Zealand researchers and companies are already playing a small role in this next generation of fusion development, providing conductor characterisation and instrumentation systems. In terms of success, fusion is high-risk technology development, but not reckless. We know fusion works, as we have the stars as evidence. Bringing that power to earth is in the best traditions of pioneering scientists and engineers who dreamed big and then did the hard work to make something real.