Q: What is nuclear fusion? How is it different from fission?

A: Fusion and fission are two different processes which occur at the atomic scale.

In fusion, the atoms in light elements, like hydrogen, are joined together, releasing energy in the process. Fusion reactions occur naturally in our sun, and power every star in the galaxy.

In fission, the atoms in heavier elements like uranium are broken apart. Energy is also released during this process. Fission is the process which is used in conventional nuclear power plants.

The only by-product of fusion reactions is helium, a harmless gas which has no significant impact on the environment.

Unlike fission which splits heavy atoms and creates toxic waste, fusion creates helium from hydrogen inside a specially shaped reaction chamber that uses powerful magnetic fields to control the reaction.

STEP proposes to harness the potential of fusion reactions to deliver clean, reliable, carbon-free power to homes, businesses, and infrastructure

Q: How safe is the technology and process?

A:Unlike conventional nuclear fission reactors, fusion machines, often known as ‘tokamaks’, produce no potentially harmful waste during their reactions – instead, their only product aside from power is helium, a harmless inert gas.

The kinds of uncontrollable runaway reactions, sometimes called meltdowns, that have sometimes occurred in fission reactors are simply not possible in a fusion reactor.

That is because the process of fusion cannot occur naturally on Earth, as it does in the sun and stars. In order for the fusion reaction to be sustained, the special conditions created in the interior of the tokamak must be perfectly maintained at all times: if interrupted the reaction will stop instantly.

STEP will use deuterium and tritium as fuels for the fusion process. Both deuterium and tritium are isotopes of hydrogen, and both will be consumed completely during the process of fusion.

Deuterium is a common isotope, abundant in seawater. Tritium is much rarer, making up only trace elements of the Earth’s atmosphere.

While tritium is radioactive, it is commonly used in medicine as a tracer for diagnostic procedures. It has a half-life of just 12 years, vastly shorter than that of the heavy radioactive elements used in fission reactors, which can be tens of thousands of years.

Inside the STEP reactor, the fusion of deuterium and tritium will produce energetic neutrons and helium. The neutrons will be captured in a liquid metal blanket around the machine, which will also generate more tritium fuel.

The neutrons heat the blanket, and that heat is used to drive a conventional steam turbine to generate electricity.

These neutrons pose no environmental threat, since they are entirely contained within the tokamak building.

Q: Can you clarify this what levels of radioactive waste are produced?

A: There is no radioactive waste produced. The only waste product from the fusion reaction itself is helium.

However, the vessel, called a tokamak, used in the process will become irradiated during the process. The level of radioactivity is similar to that arising from radioisotope production for medicine. Affected material can be stored on-site and the aim is to recycle as much as possible back into use at the facility.

The Regulatory Horizons Council Report on Fusion Energy Regulation notes that no high-level waste (such as spent fuel rods in fission power stations) will be generated by fusion, and that the waste hazard posed by fusion will be ‘orders of magnitude lower than fission’. Fusion reactors ‘are considered inherently safe’.

Q: Why do we need fusion when we have wind, solar, tidal energy etc; and hydrogen is being developed?

A: Fusion is one part of the energy mix that is needed to ensure we can develop sustainable low carbon energy provision – it shouldn’t be thought of as an either / or option. We need a variety of sources and a secure energy generation method that is not weather dependent, to serve the baseline requirement. Since coal and gas are not viable, and nuclear fission, which currently provides at least 20% of our power in Scotland alone, is retiring, we need to fill the gap.

Solar, wind and tidal generation are all valuable sources of renewable power for national energy grids. However, their ability to generate electricity can fluctuate with the availability of the natural resources which power them.

STEP will provide a constant baseline flow of electricity to the grid, helping to ensure that power needs are met as the UK and nations around the world transition to low-carbon generation processes.

Q: How does STEP compare to other fusion projects around the world?

A: There are a number of exciting fusion energy projects currently underway around the world, including ITER in France and JET and MAST in the UK, each of which have already made major contributions to our understanding of generating power through fusion.

STEP is aiming to build on those achievements by building a prototype plant which can demonstrate the ability to generate net electricity from fusion and deliver it to the National Grid. STEP will be a fully integrated power plant, not just a fusion machine, and its plan to connect to national infrastructure is part of what sets it apart from other fusion reactor projects.

Other useful sources of information are:

International Atomic Energy Authority (IAEA) Frequently Asked Questions

Culham Centre for Fusion Energy (CCFE) Frequently Asked Questions

Eurofusion Frequently Asked Questions